diff --git a/packages/builtin-tools/src/tools/AgentTool/__tests__/filterIncompleteToolCalls.test.ts b/packages/builtin-tools/src/tools/AgentTool/__tests__/filterIncompleteToolCalls.test.ts
new file mode 100644
index 000000000..5429c6ce8
--- /dev/null
+++ b/packages/builtin-tools/src/tools/AgentTool/__tests__/filterIncompleteToolCalls.test.ts
@@ -0,0 +1,180 @@
+import { describe, expect, test } from 'bun:test'
+import type { Message } from 'src/types/message.js'
+import { filterIncompleteToolCalls } from '../filterIncompleteToolCalls.js'
+
+describe('filterIncompleteToolCalls', () => {
+  test('drops assistant tool uses that do not have matching results', () => {
+    const messages = [
+      {
+        type: 'assistant',
+        uuid: 'a1',
+        message: {
+          role: 'assistant',
+          content: [{ type: 'tool_use', id: 'missing', name: 'Read' }],
+        },
+      },
+      {
+        type: 'user',
+        uuid: 'u1',
+        message: { role: 'user', content: 'continue' },
+      },
+    ] as unknown as Message[]
+
+    expect(
+      filterIncompleteToolCalls(messages).map(message => String(message.uuid)),
+    ).toEqual(['u1'])
+  })
+
+  test('preserves assistant text when dropping orphan tool uses', () => {
+    const messages = [
+      {
+        type: 'assistant',
+        uuid: 'a1',
+        message: {
+          role: 'assistant',
+          content: [
+            { type: 'text', text: 'I will read the file.' },
+            { type: 'tool_use', id: 'missing', name: 'Read' },
+          ],
+        },
+      },
+    ] as unknown as Message[]
+
+    const filtered = filterIncompleteToolCalls(messages)
+    expect(filtered).toHaveLength(1)
+    const first = filtered[0]!
+    const content = first.message!.content
+    expect(
+      Array.isArray(content) ? content.map(block => block.type) : [],
+    ).toEqual(['text'])
+  })
+
+  test('keeps completed parallel tool calls when dropping an orphan', () => {
+    const messages = [
+      {
+        type: 'assistant',
+        uuid: 'a1',
+        message: {
+          role: 'assistant',
+          content: [
+            { type: 'tool_use', id: 'done', name: 'Read' },
+            { type: 'tool_use', id: 'missing', name: 'Grep' },
+          ],
+        },
+      },
+      {
+        type: 'user',
+        uuid: 'u1',
+        message: {
+          role: 'user',
+          content: [{ type: 'tool_result', tool_use_id: 'done', content: 'ok' }],
+        },
+      },
+    ] as unknown as Message[]
+
+    const filtered = filterIncompleteToolCalls(messages)
+    expect(filtered.map(message => String(message.uuid))).toEqual(['a1', 'u1'])
+    const first = filtered[0]!
+    const content = first.message!.content
+    expect(
+      Array.isArray(content)
+        ? content.map(block =>
+            block.type === 'tool_use' ? block.id : block.type,
+          )
+        : [],
+    ).toEqual(['done'])
+  })
+
+  test('keeps assistant tool uses that have matching results', () => {
+    const messages = [
+      {
+        type: 'assistant',
+        uuid: 'a1',
+        message: {
+          role: 'assistant',
+          content: [{ type: 'tool_use', id: 'done', name: 'Read' }],
+        },
+      },
+      {
+        type: 'user',
+        uuid: 'u1',
+        message: {
+          role: 'user',
+          content: [{ type: 'tool_result', tool_use_id: 'done', content: 'ok' }],
+        },
+      },
+    ] as unknown as Message[]
+
+    expect(
+      filterIncompleteToolCalls(messages).map(message => String(message.uuid)),
+    ).toEqual(['a1', 'u1'])
+  })
+
+  test('drops orphan tool results when their tool use was removed', () => {
+    const messages = [
+      {
+        type: 'user',
+        uuid: 'u1',
+        message: {
+          role: 'user',
+          content: [
+            { type: 'tool_result', tool_use_id: 'missing', content: 'late' },
+          ],
+        },
+      },
+    ] as unknown as Message[]
+
+    expect(filterIncompleteToolCalls(messages)).toEqual([])
+  })
+
+  test('keeps user text while dropping orphan tool results', () => {
+    const messages = [
+      {
+        type: 'assistant',
+        uuid: 'a1',
+        message: { role: 'assistant', content: 'done' },
+      },
+      {
+        type: 'user',
+        uuid: 'u1',
+        message: {
+          role: 'user',
+          content: [
+            { type: 'text', text: 'keep this' },
+            { type: 'tool_result', tool_use_id: 'missing', content: 'late' },
+          ],
+        },
+      },
+    ] as unknown as Message[]
+
+    const filtered = filterIncompleteToolCalls(messages)
+    expect(filtered.map(message => String(message.uuid))).toEqual(['a1', 'u1'])
+    const content = filtered[1]!.message!.content
+    expect(Array.isArray(content) ? content : []).toEqual([
+      { type: 'text', text: 'keep this' },
+    ])
+  })
+
+  test('drops malformed tool blocks without ids', () => {
+    const messages = [
+      {
+        type: 'assistant',
+        uuid: 'a1',
+        message: {
+          role: 'assistant',
+          content: [{ type: 'tool_use', name: 'Read' }],
+        },
+      },
+      {
+        type: 'user',
+        uuid: 'u1',
+        message: {
+          role: 'user',
+          content: [{ type: 'tool_result', content: 'late' }],
+        },
+      },
+    ] as unknown as Message[]
+
+    expect(filterIncompleteToolCalls(messages)).toEqual([])
+  })
+})
diff --git a/packages/builtin-tools/src/tools/AgentTool/filterIncompleteToolCalls.ts b/packages/builtin-tools/src/tools/AgentTool/filterIncompleteToolCalls.ts
new file mode 100644
index 000000000..7e30754ee
--- /dev/null
+++ b/packages/builtin-tools/src/tools/AgentTool/filterIncompleteToolCalls.ts
@@ -0,0 +1,110 @@
+import type {
+  AssistantMessage,
+  Message,
+  UserMessage,
+} from 'src/types/message.js'
+
+/**
+ * Removes invalid or orphaned tool_use/tool_result blocks while preserving
+ * completed tool-call pairs. This is intentionally block-level, not
+ * message-level, so completed parallel tool calls stay paired with results.
+ */
+export function filterIncompleteToolCalls(messages: Message[]): Message[] {
+  const toolUseIdsWithResults = new Set<string>()
+
+  for (const message of messages) {
+    if (message?.type === 'user') {
+      const userMessage = message as UserMessage
+      const content = userMessage.message.content
+      if (Array.isArray(content)) {
+        for (const block of content) {
+          if (block.type === 'tool_result' && block.tool_use_id) {
+            toolUseIdsWithResults.add(block.tool_use_id)
+          }
+        }
+      }
+    }
+  }
+
+  const retainedToolUseIds = new Set<string>()
+  const withoutOrphanToolUses: Message[] = []
+
+  for (const message of messages) {
+    if (message?.type === 'assistant') {
+      const assistantMessage = message as AssistantMessage
+      const content = assistantMessage.message.content
+      if (Array.isArray(content)) {
+        let changed = false
+        const filteredContent = content.filter(block => {
+          if (block.type !== 'tool_use') return true
+          if (!block.id) {
+            changed = true
+            return false
+          }
+          if (toolUseIdsWithResults.has(block.id)) {
+            retainedToolUseIds.add(block.id)
+            return true
+          }
+          changed = true
+          return false
+        })
+
+        if (!changed) {
+          withoutOrphanToolUses.push(message)
+          continue
+        }
+        if (filteredContent.length > 0) {
+          withoutOrphanToolUses.push({
+            ...assistantMessage,
+            message: {
+              ...assistantMessage.message,
+              content: filteredContent,
+            },
+          })
+        }
+        continue
+      }
+    }
+    withoutOrphanToolUses.push(message)
+  }
+
+  const filteredMessages: Message[] = []
+  for (const message of withoutOrphanToolUses) {
+    if (message?.type !== 'user') {
+      filteredMessages.push(message)
+      continue
+    }
+    const userMessage = message as UserMessage
+    const content = userMessage.message.content
+    if (!Array.isArray(content)) {
+      filteredMessages.push(message)
+      continue
+    }
+    let changed = false
+    const filteredContent = content.filter(block => {
+      if (block.type !== 'tool_result') return true
+      if (!block.tool_use_id) {
+        changed = true
+        return false
+      }
+      if (retainedToolUseIds.has(block.tool_use_id)) return true
+      changed = true
+      return false
+    })
+    if (!changed) {
+      filteredMessages.push(message)
+      continue
+    }
+    if (filteredContent.length > 0) {
+      filteredMessages.push({
+        ...userMessage,
+        message: {
+          ...userMessage.message,
+          content: filteredContent,
+        },
+      })
+    }
+  }
+
+  return filteredMessages
+}
diff --git a/packages/builtin-tools/src/tools/AgentTool/runAgent.ts b/packages/builtin-tools/src/tools/AgentTool/runAgent.ts
index baeed9022..de55b53f8 100644
--- a/packages/builtin-tools/src/tools/AgentTool/runAgent.ts
+++ b/packages/builtin-tools/src/tools/AgentTool/runAgent.ts
@@ -86,8 +86,11 @@ import {
 import type { ContentReplacementState } from 'src/utils/toolResultStorage.js'
 import { createAgentId } from 'src/utils/uuid.js'
 import { resolveAgentTools } from './agentToolUtils.js'
+import { filterIncompleteToolCalls } from './filterIncompleteToolCalls.js'
 import { type AgentDefinition, isBuiltInAgent } from './loadAgentsDir.js'
 
+export { filterIncompleteToolCalls } from './filterIncompleteToolCalls.js'
+
 /**
  * Initialize agent-specific MCP servers
  * Agents can define their own MCP servers in their frontmatter that are additive
@@ -886,50 +889,6 @@ export async function* runAgent({
   }
 }
 
-/**
- * Filters out assistant messages with incomplete tool calls (tool uses without results).
- * This prevents API errors when sending messages with orphaned tool calls.
- */
-export function filterIncompleteToolCalls(messages: Message[]): Message[] {
-  // Build a set of tool use IDs that have results
-  const toolUseIdsWithResults = new Set<string>()
-
-  for (const message of messages) {
-    if (message?.type === 'user') {
-      const userMessage = message as UserMessage
-      const content = userMessage.message.content
-      if (Array.isArray(content)) {
-        for (const block of content) {
-          if (block.type === 'tool_result' && block.tool_use_id) {
-            toolUseIdsWithResults.add(block.tool_use_id)
-          }
-        }
-      }
-    }
-  }
-
-  // Filter out assistant messages that contain tool calls without results
-  return messages.filter(message => {
-    if (message?.type === 'assistant') {
-      const assistantMessage = message as AssistantMessage
-      const content = assistantMessage.message.content
-      if (Array.isArray(content)) {
-        // Check if this assistant message has any tool uses without results
-        const hasIncompleteToolCall = content.some(
-          block =>
-            block.type === 'tool_use' &&
-            block.id &&
-            !toolUseIdsWithResults.has(block.id),
-        )
-        // Exclude messages with incomplete tool calls
-        return !hasIncompleteToolCall
-      }
-    }
-    // Keep all non-assistant messages and assistant messages without tool calls
-    return true
-  })
-}
-
 async function getAgentSystemPrompt(
   agentDefinition: AgentDefinition,
   toolUseContext: Pick<ToolUseContext, 'options'>,
diff --git a/packages/builtin-tools/src/tools/ListPeersTool/ListPeersTool.ts b/packages/builtin-tools/src/tools/ListPeersTool/ListPeersTool.ts
index e520243a5..f6c52ea80 100644
--- a/packages/builtin-tools/src/tools/ListPeersTool/ListPeersTool.ts
+++ b/packages/builtin-tools/src/tools/ListPeersTool/ListPeersTool.ts
@@ -84,22 +84,48 @@ Use this tool to discover messaging targets before sending cross-session message
     // UDS socket directory. The implementation scans for live sockets
     // and optionally includes Remote Control bridge peers.
     const peers: PeerInfo[] = []
+    const seen = new Set<string>()
+    const addPeer = (peer: PeerInfo): void => {
+      if (seen.has(peer.address)) return
+      seen.add(peer.address)
+      peers.push(peer)
+    }
+
+    /* eslint-disable @typescript-eslint/no-require-imports */
+    const udsMessaging =
+      require('src/utils/udsMessaging.js') as typeof import('src/utils/udsMessaging.js')
+    const udsClient =
+      require('src/utils/udsClient.js') as typeof import('src/utils/udsClient.js')
+    const bridgePeers =
+      require('src/bridge/peerSessions.js') as typeof import('src/bridge/peerSessions.js')
+    /* eslint-enable @typescript-eslint/no-require-imports */
 
-    // Discovery is handled by the UDS messaging subsystem initialized in setup.ts.
-    // Return discovered peers from the app state.
-    const appState = context.getAppState()
-    const messagingSocketPath = (appState as Record<string, unknown>).messagingSocketPath as string | undefined
+    const messagingSocketPath = udsMessaging.getUdsMessagingSocketPath()
     if (messagingSocketPath) {
       // Self entry for reference
       if (_input.include_self) {
-        peers.push({
-          address: `uds:${messagingSocketPath}`,
+        addPeer({
+          address: udsMessaging.formatUdsAddress(messagingSocketPath),
           name: 'self',
           pid: process.pid,
         })
       }
     }
 
+    for (const peer of await udsClient.listPeers()) {
+      if (!peer.messagingSocketPath) continue
+      addPeer({
+        address: udsMessaging.formatUdsAddress(peer.messagingSocketPath),
+        name: peer.name ?? peer.kind,
+        cwd: peer.cwd,
+        pid: peer.pid,
+      })
+    }
+
+    for (const peer of await bridgePeers.listBridgePeers()) {
+      addPeer(peer)
+    }
+
     return {
       data: { peers },
     }
diff --git a/packages/builtin-tools/src/tools/SendMessageTool/SendMessageTool.ts b/packages/builtin-tools/src/tools/SendMessageTool/SendMessageTool.ts
index 4e9737051..cab0a03c5 100644
--- a/packages/builtin-tools/src/tools/SendMessageTool/SendMessageTool.ts
+++ b/packages/builtin-tools/src/tools/SendMessageTool/SendMessageTool.ts
@@ -130,6 +130,41 @@ export type SendMessageToolOutput =
   | RequestOutput
   | ResponseOutput
 
+const UDS_INLINE_TOKEN_MARKER = '#token='
+
+function stripInlineUdsToken(target: string): string {
+  const markerIndex = target.indexOf(UDS_INLINE_TOKEN_MARKER)
+  return markerIndex === -1 ? target : target.slice(0, markerIndex)
+}
+
+function hasInlineUdsToken(to: string): boolean {
+  const addr = parseAddress(to)
+  // Empty-token markers are still inline-token attempts. Observable input
+  // redaction preserves "#token=" so cloned inputs remain rejected.
+  return (
+    addr.scheme === 'uds' && addr.target.includes(UDS_INLINE_TOKEN_MARKER)
+  )
+}
+
+function recipientForDisplay(to: string): string {
+  const addr = parseAddress(to)
+  if (addr.scheme !== 'uds') return to
+  return `uds:${stripInlineUdsToken(addr.target)}`
+}
+
+function redactInlineUdsTokenForRejection(to: string): string {
+  const addr = parseAddress(to)
+  if (addr.scheme !== 'uds') return to
+  const markerIndex = addr.target.indexOf(UDS_INLINE_TOKEN_MARKER)
+  if (markerIndex === -1) return to
+  return `uds:${addr.target.slice(0, markerIndex)}${UDS_INLINE_TOKEN_MARKER}`
+}
+
+function redactObservableInlineUdsToken(input: { to: string }): void {
+  if (!hasInlineUdsToken(input.to)) return
+  input.to = redactInlineUdsTokenForRejection(input.to)
+}
+
 function findTeammateColor(
   appState: {
     teamContext?: { teammates: { [id: string]: { color?: string } } }
@@ -541,15 +576,17 @@ export const SendMessageTool: Tool<InputSchema, SendMessageToolOutput> =
     },
 
     backfillObservableInput(input) {
-      if ('type' in input) return
       if (typeof input.to !== 'string') return
 
+      redactObservableInlineUdsToken(input as { to: string })
+      if ('type' in input) return
+
       if (input.to === '*') {
         input.type = 'broadcast'
         if (typeof input.message === 'string') input.content = input.message
       } else if (typeof input.message === 'string') {
         input.type = 'message'
-        input.recipient = input.to
+        input.recipient = recipientForDisplay(input.to)
         input.content = input.message
       } else if (typeof input.message === 'object' && input.message !== null) {
         const msg = input.message as {
@@ -560,7 +597,7 @@ export const SendMessageTool: Tool<InputSchema, SendMessageToolOutput> =
           feedback?: string
         }
         input.type = msg.type
-        input.recipient = input.to
+        input.recipient = recipientForDisplay(input.to)
         if (msg.request_id !== undefined) input.request_id = msg.request_id
         if (msg.approve !== undefined) input.approve = msg.approve
         const content = msg.reason ?? msg.feedback
@@ -569,16 +606,17 @@ export const SendMessageTool: Tool<InputSchema, SendMessageToolOutput> =
     },
 
     toAutoClassifierInput(input) {
+      const recipient = recipientForDisplay(input.to)
       if (typeof input.message === 'string') {
-        return `to ${input.to}: ${input.message}`
+        return `to ${recipient}: ${input.message}`
       }
       switch (input.message.type) {
         case 'shutdown_request':
-          return `shutdown_request to ${input.to}`
+          return `shutdown_request to ${recipient}`
         case 'shutdown_response':
           return `shutdown_response ${input.message.approve ? 'approve' : 'reject'} ${input.message.request_id}`
         case 'plan_approval_response':
-          return `plan_approval ${input.message.approve ? 'approve' : 'reject'} to ${input.to}`
+          return `plan_approval ${input.message.approve ? 'approve' : 'reject'} to ${recipient}`
       }
     },
 
@@ -630,6 +668,17 @@ export const SendMessageTool: Tool<InputSchema, SendMessageToolOutput> =
           errorCode: 9,
         }
       }
+      if (
+        addr.scheme === 'uds' &&
+        hasInlineUdsToken(input.to)
+      ) {
+        return {
+          result: false,
+          message:
+            'uds addresses must not include inline auth tokens; use the ListPeers address',
+          errorCode: 9,
+        }
+      }
       if (input.to.includes('@')) {
         return {
           result: false,
@@ -753,6 +802,19 @@ export const SendMessageTool: Tool<InputSchema, SendMessageToolOutput> =
     },
 
     async call(input, context, canUseTool, assistantMessage) {
+      if (typeof input.message === 'string') {
+        const addr = parseAddress(input.to)
+        if (addr.scheme === 'uds' && hasInlineUdsToken(input.to)) {
+          return {
+            data: {
+              success: false,
+              message:
+                'uds addresses must not include inline auth tokens; use the ListPeers address',
+            },
+          }
+        }
+      }
+
       if (feature('UDS_INBOX') && typeof input.message === 'string') {
         const addr = parseAddress(input.to)
         if (addr.scheme === 'bridge') {
@@ -772,10 +834,10 @@ export const SendMessageTool: Tool<InputSchema, SendMessageToolOutput> =
           const { postInterClaudeMessage } =
             require('src/bridge/peerSessions.js') as typeof import('src/bridge/peerSessions.js')
           /* eslint-enable @typescript-eslint/no-require-imports */
-          const result = await postInterClaudeMessage(
+          const result = (await postInterClaudeMessage(
             addr.target,
             input.message,
-          ) as { ok: boolean; error?: string }
+          )) as { ok: boolean; error?: string }
           const preview = input.summary || truncate(input.message, 50)
           return {
             data: {
@@ -787,6 +849,7 @@ export const SendMessageTool: Tool<InputSchema, SendMessageToolOutput> =
           }
         }
         if (addr.scheme === 'uds') {
+          const recipient = recipientForDisplay(input.to)
           /* eslint-disable @typescript-eslint/no-require-imports */
           const { sendToUdsSocket } =
             require('src/utils/udsClient.js') as typeof import('src/utils/udsClient.js')
@@ -797,14 +860,14 @@ export const SendMessageTool: Tool<InputSchema, SendMessageToolOutput> =
             return {
               data: {
                 success: true,
-                message: `”${preview}” → ${input.to}`,
+                message: `”${preview}” → ${recipient}`,
               },
             }
           } catch (e) {
             return {
               data: {
                 success: false,
-                message: `Failed to send to ${input.to}: ${errorMessage(e)}`,
+                message: `Failed to send to ${recipient}: ${errorMessage(e)}`,
               },
             }
           }
diff --git a/packages/builtin-tools/src/tools/SendMessageTool/__tests__/udsRecipientSanitization.test.ts b/packages/builtin-tools/src/tools/SendMessageTool/__tests__/udsRecipientSanitization.test.ts
new file mode 100644
index 000000000..e0ce1a823
--- /dev/null
+++ b/packages/builtin-tools/src/tools/SendMessageTool/__tests__/udsRecipientSanitization.test.ts
@@ -0,0 +1,181 @@
+import { describe, expect, test } from 'bun:test'
+import { SendMessageTool } from '../SendMessageTool.js'
+
+describe('SendMessageTool UDS recipient handling', () => {
+  test('redacts inline UDS tokens before classifier and observable paths', async () => {
+    const tokenAddress = 'uds:/tmp/peer.sock#token=secret-token'
+
+    const observableInput = {
+      to: tokenAddress,
+      message: 'hello',
+    } as Record<string, unknown>
+    SendMessageTool.backfillObservableInput!(observableInput)
+
+    expect(observableInput.recipient).toBe('uds:/tmp/peer.sock')
+    expect(observableInput.to).toBe('uds:/tmp/peer.sock#token=')
+    expect(JSON.stringify(observableInput)).not.toContain('secret-token')
+    expect(
+      SendMessageTool.toAutoClassifierInput({
+        to: tokenAddress,
+        message: 'hello',
+      }),
+    ).toBe('to uds:/tmp/peer.sock: hello')
+  })
+
+  test('keeps redacted UDS token rejection through observable backfill', async () => {
+    const observableInput = {
+      to: 'uds:/tmp/peer.sock#token=secret-token',
+      message: {
+        type: 'plan_approval_response',
+        request_id: 'req-1',
+        approve: false,
+        reason: 'needs tests',
+      },
+    } as Record<string, unknown>
+
+    SendMessageTool.backfillObservableInput!(observableInput)
+
+    expect(observableInput.to).toBe('uds:/tmp/peer.sock#token=')
+    expect(observableInput.recipient).toBe('uds:/tmp/peer.sock')
+    expect(observableInput.type).toBe('plan_approval_response')
+    expect(observableInput.request_id).toBe('req-1')
+    expect(observableInput.approve).toBe(false)
+    expect(observableInput.content).toBe('needs tests')
+    expect(JSON.stringify(observableInput)).not.toContain('secret-token')
+
+    const result = await SendMessageTool.validateInput!(
+      observableInput as never,
+      {} as never,
+    )
+
+    expect(result.result).toBe(false)
+    if (result.result !== false) {
+      throw new Error('expected validation to reject redacted inline UDS token')
+    }
+    expect(result.message).toContain('inline auth tokens')
+  })
+
+  test('keeps inline-token rejection when observable input is cloned', async () => {
+    const observableInput = {
+      to: 'uds:/tmp/peer.sock#token=secret-token',
+      message: 'hello',
+    } as Record<string, unknown>
+
+    SendMessageTool.backfillObservableInput!(observableInput)
+    const clonedInput = {
+      to: observableInput.to,
+      message: observableInput.message,
+      summary: 'hello peer',
+    }
+
+    const validation = await SendMessageTool.validateInput!(
+      clonedInput as never,
+      {} as never,
+    )
+    const result = await SendMessageTool.call(
+      clonedInput as never,
+      {} as never,
+      undefined as never,
+      undefined as never,
+    )
+
+    expect(validation.result).toBe(false)
+    expect(result.data.success).toBe(false)
+    expect(JSON.stringify(clonedInput)).not.toContain('secret-token')
+    expect(JSON.stringify(result)).not.toContain('secret-token')
+  })
+
+  test('redacts UDS tokens in structured classifier text', async () => {
+    const to = 'uds:/tmp/peer.sock#token=secret-token'
+
+    expect(
+      SendMessageTool.toAutoClassifierInput({
+        to,
+        message: { type: 'shutdown_request' },
+      }),
+    ).toBe('shutdown_request to uds:/tmp/peer.sock')
+    expect(
+      SendMessageTool.toAutoClassifierInput({
+        to,
+        message: {
+          type: 'plan_approval_response',
+          request_id: 'req-1',
+          approve: true,
+        },
+      }),
+    ).toBe('plan_approval approve to uds:/tmp/peer.sock')
+    expect(
+      SendMessageTool.toAutoClassifierInput({
+        to,
+        message: {
+          type: 'plan_approval_response',
+          request_id: 'req-2',
+          approve: false,
+        },
+      }),
+    ).toBe('plan_approval reject to uds:/tmp/peer.sock')
+    expect(
+      SendMessageTool.toAutoClassifierInput({
+        to,
+        message: {
+          type: 'shutdown_response',
+          request_id: 'shutdown-1',
+          approve: false,
+        },
+      }),
+    ).toBe('shutdown_response reject shutdown-1')
+  })
+
+  test('redacts from the first inline UDS token marker', async () => {
+    const tokenAddress = 'uds:/tmp/peer.sock#token=first#token=second'
+
+    const observableInput = {
+      to: tokenAddress,
+      message: 'hello',
+    } as Record<string, unknown>
+    SendMessageTool.backfillObservableInput!(observableInput)
+
+    expect(observableInput.to).toBe('uds:/tmp/peer.sock#token=')
+    expect(observableInput.recipient).toBe('uds:/tmp/peer.sock')
+    expect(JSON.stringify(observableInput)).not.toContain('first')
+    expect(JSON.stringify(observableInput)).not.toContain('second')
+    expect(
+      SendMessageTool.toAutoClassifierInput({
+        to: tokenAddress,
+        message: 'hello',
+      }),
+    ).toBe('to uds:/tmp/peer.sock: hello')
+  })
+
+  test('rejects inline UDS tokens during validation', async () => {
+    const result = await SendMessageTool.validateInput!(
+      {
+        to: 'uds:/tmp/peer.sock#token=secret-token',
+        message: 'hello',
+      },
+      {} as never,
+    )
+
+    expect(result.result).toBe(false)
+    if (result.result !== false) {
+      throw new Error('expected validation to reject inline UDS token')
+    }
+    expect(result.message).toContain('inline auth tokens')
+    expect(JSON.stringify(result)).not.toContain('secret-token')
+  })
+
+  test('rejects inline UDS tokens during execution without leaking them', async () => {
+    const result = await SendMessageTool.call(
+      {
+        to: 'uds:/tmp/peer.sock#token=secret-token',
+        message: 'hello',
+      },
+      {} as never,
+      undefined as never,
+      undefined as never,
+    )
+
+    expect(result.data.success).toBe(false)
+    expect(JSON.stringify(result)).not.toContain('secret-token')
+  })
+})
diff --git a/src/bridge/peerSessions.ts b/src/bridge/peerSessions.ts
index c194c9b62..716c879de 100644
--- a/src/bridge/peerSessions.ts
+++ b/src/bridge/peerSessions.ts
@@ -6,6 +6,38 @@ import { getBridgeAccessToken } from './bridgeConfig.js'
 import { getReplBridgeHandle } from './replBridgeHandle.js'
 import { toCompatSessionId } from './sessionIdCompat.js'
 
+export type BridgePeerSession = {
+  address: string
+  name?: string
+  cwd?: string
+  pid?: number
+}
+
+/**
+ * List locally registered sessions that have published a Remote Control
+ * session ID. The PID registry is the local source of truth for bridge peers
+ * already known to this machine; SendMessage can use these bridge:<id>
+ * addresses when the current process has an active bridge handle.
+ */
+export async function listBridgePeers(): Promise<BridgePeerSession[]> {
+  const { listAllLiveSessions } = await import('../utils/udsClient.js')
+  const sessions = await listAllLiveSessions()
+  const peers: BridgePeerSession[] = []
+
+  for (const session of sessions) {
+    if (session.pid === process.pid || !session.bridgeSessionId) continue
+    const compatId = toCompatSessionId(session.bridgeSessionId)
+    peers.push({
+      address: `bridge:${compatId}`,
+      name: session.name ?? session.kind,
+      cwd: session.cwd,
+      pid: session.pid,
+    })
+  }
+
+  return peers
+}
+
 /**
  * Send a plain-text message to another Claude session via the bridge API.
  *
diff --git a/src/cli/print.ts b/src/cli/print.ts
index eb2b543f8..c4e8c4569 100644
--- a/src/cli/print.ts
+++ b/src/cli/print.ts
@@ -2763,13 +2763,37 @@ function runHeadlessStreaming(
   // when a message arrives via the UDS socket in headless mode.
   if (feature('UDS_INBOX')) {
     /* eslint-disable @typescript-eslint/no-require-imports */
-    const { setOnEnqueue } = require('../utils/udsMessaging.js')
+    const { drainInbox, setOnEnqueue } =
+      require('../utils/udsMessaging.js') as typeof import('../utils/udsMessaging.js')
     /* eslint-enable @typescript-eslint/no-require-imports */
+
+    const enqueueUdsInboxMessages = (): boolean => {
+      const entries = drainInbox()
+      for (const entry of entries) {
+        const value =
+          typeof entry.message.data === 'string'
+            ? entry.message.data
+            : jsonStringify(entry.message.data)
+        enqueue({
+          mode: 'prompt',
+          value,
+          uuid: randomUUID(),
+        })
+      }
+      return entries.length > 0
+    }
+
     setOnEnqueue(() => {
       if (!inputClosed) {
-        void run()
+        if (enqueueUdsInboxMessages()) {
+          void run()
+        }
       }
     })
+
+    if (enqueueUdsInboxMessages()) {
+      void run()
+    }
   }
 
   // Cron scheduler: runs scheduled_tasks.json tasks in SDK/-p mode.
diff --git a/src/commands/peers/peers.ts b/src/commands/peers/peers.ts
index aed37d327..fcb7e17a7 100644
--- a/src/commands/peers/peers.ts
+++ b/src/commands/peers/peers.ts
@@ -1,6 +1,9 @@
 import type { LocalCommandCall } from '../../types/command.js'
 import { listPeers, isPeerAlive } from '../../utils/udsClient.js'
-import { getUdsMessagingSocketPath } from '../../utils/udsMessaging.js'
+import {
+  formatUdsAddress,
+  getUdsMessagingSocketPath,
+} from '../../utils/udsMessaging.js'
 
 export const call: LocalCommandCall = async (_args, _context) => {
   const mySocket = getUdsMessagingSocketPath()
@@ -29,11 +32,11 @@ export const call: LocalCommandCall = async (_args, _context) => {
         ? `  started: ${formatAge(peer.startedAt)}`
         : ''
 
-      lines.push(
-        `  [${status}] PID ${peer.pid} (${label})${cwd}${age}`,
-      )
+      lines.push(`  [${status}] PID ${peer.pid} (${label})${cwd}${age}`)
       if (peer.messagingSocketPath) {
-        lines.push(`           socket: ${peer.messagingSocketPath}`)
+        lines.push(
+          `           socket: ${formatUdsAddress(peer.messagingSocketPath)}`,
+        )
       }
       if (peer.sessionId) {
         lines.push(`           session: ${peer.sessionId}`)
@@ -43,7 +46,7 @@ export const call: LocalCommandCall = async (_args, _context) => {
 
   lines.push('')
   lines.push(
-    'To message a peer: use SendMessage with to="uds:<socket-path>"',
+    'To message a peer: use SendMessage with the shown uds:<socket-path> address',
   )
 
   return { type: 'text', value: lines.join('\n') }
diff --git a/src/commands/poor/__tests__/poorMode.test.ts b/src/commands/poor/__tests__/poorMode.test.ts
index c2a80f3cf..539c804e1 100644
--- a/src/commands/poor/__tests__/poorMode.test.ts
+++ b/src/commands/poor/__tests__/poorMode.test.ts
@@ -5,7 +5,8 @@
  * After the fix, it reads from / writes to settings.json via
  * getInitialSettings() and updateSettingsForSource().
  */
-import { describe, expect, test, beforeEach, mock } from 'bun:test'
+import { afterAll, describe, expect, test, beforeEach, mock } from 'bun:test'
+import * as settingsModule from '../../../utils/settings/settings.js'
 
 // ── Mocks must be declared before the module under test is imported ──────────
 
@@ -13,24 +14,48 @@ let mockSettings: Record<string, unknown> = {}
 let lastUpdate: { source: string; patch: Record<string, unknown> } | null = null
 
 mock.module('src/utils/settings/settings.js', () => ({
+  loadManagedFileSettings: () => ({ settings: null, errors: [] }),
+  getManagedFileSettingsPresence: () => ({
+    hasBase: false,
+    hasDropIns: false,
+  }),
+  parseSettingsFile: () => ({ settings: null, errors: [] }),
+  getSettingsRootPathForSource: () => '',
+  getSettingsFilePathForSource: () => undefined,
+  getRelativeSettingsFilePathForSource: () => '',
   getInitialSettings: () => mockSettings,
+  getSettingsForSource: () => mockSettings,
+  getPolicySettingsOrigin: () => null,
+  getSettingsWithErrors: () => ({ settings: mockSettings, errors: [] }),
+  getSettingsWithSources: () => ({ effective: mockSettings, sources: [] }),
+  getSettings_DEPRECATED: () => mockSettings,
+  settingsMergeCustomizer: () => undefined,
+  getManagedSettingsKeysForLogging: () => [],
+  // Keep unrelated exports aligned with the real settings module so this
+  // full-surface mock cannot change later test files if Bun keeps it alive.
+  hasAutoModeOptIn: () => true,
+  hasSkipDangerousModePermissionPrompt: () => false,
+  getAutoModeConfig: () => undefined,
+  getUseAutoModeDuringPlan: () => true,
+  rawSettingsContainsKey: (key: string) => key in mockSettings,
   updateSettingsForSource: (source: string, patch: Record<string, unknown>) => {
     lastUpdate = { source, patch }
     mockSettings = { ...mockSettings, ...patch }
   },
 }))
 
-// Import AFTER mocks are registered
-const { isPoorModeActive, setPoorMode } = await import('../poorMode.js')
-
-// ── Helpers ──────────────────────────────────────────────────────────────────
+afterAll(() => {
+  mock.restore()
+  mock.module('src/utils/settings/settings.js', () => settingsModule)
+})
 
-/** Reset module-level singleton between tests by re-importing a fresh copy. */
-async function freshModule() {
-  // Bun caches modules; we manipulate the exported functions directly since
-  // the singleton `poorModeActive` is reset to null only on first import.
-  // Instead we test the observable behaviour through set/get pairs.
-}
+// Import AFTER mocks are registered. The query suffix gives this file its own
+// module instance so cross-file poorMode.js mocks cannot replace the subject
+// under test during Bun's shared coverage run.
+const poorModeModulePath = '../poorMode.js?poorModeTest'
+const { isPoorModeActive, setPoorMode } = (await import(
+  poorModeModulePath
+)) as typeof import('../poorMode.js')
 
 // ── Tests ────────────────────────────────────────────────────────────────────
 
diff --git a/src/services/AgentSummary/__tests__/agentSummary.test.ts b/src/services/AgentSummary/__tests__/agentSummary.test.ts
new file mode 100644
index 000000000..368671f03
--- /dev/null
+++ b/src/services/AgentSummary/__tests__/agentSummary.test.ts
@@ -0,0 +1,152 @@
+import { beforeEach, describe, expect, test } from 'bun:test'
+import { asAgentId } from '../../../types/ids.js'
+import type { Message } from '../../../types/message.js'
+import type {
+  CacheSafeParams,
+  ForkedAgentResult,
+} from '../../../utils/forkedAgent.js'
+import { startAgentSummarization } from '../agentSummary.js'
+
+const transcriptMessages = [
+  { type: 'user', message: { content: 'start' }, uuid: 'u1' },
+  {
+    type: 'assistant',
+    message: { content: [{ type: 'text', text: 'working' }] },
+    uuid: 'a1',
+  },
+  { type: 'user', message: { content: 'continue' }, uuid: 'u2' },
+] as unknown as Message[]
+
+type ForkCall = {
+  cacheSafeParams: CacheSafeParams
+}
+
+describe('startAgentSummarization', () => {
+  let scheduled: (() => void | Promise<void>) | undefined
+  let handle: { stop: () => void } | undefined
+  let forkCalls: ForkCall[]
+  let updateCalls: Array<{ taskId: string; summary: string }>
+  let transcriptMessagesForTest: Message[]
+
+  beforeEach(() => {
+    forkCalls = []
+    updateCalls = []
+    scheduled = undefined
+    handle = undefined
+    transcriptMessagesForTest = transcriptMessages
+  })
+
+  test('summarizes bounded transcript once and skips unchanged fingerprints', async () => {
+    handle = startAgentSummarization(
+      'task-1',
+      asAgentId('a0000000000000000'),
+      {
+        forkContextMessages: [
+          { type: 'user', message: { content: 'stale' }, uuid: 'old' },
+        ],
+        model: 'claude-test',
+      } as unknown as CacheSafeParams,
+      () => undefined,
+      {
+        clearTimeout: () => undefined,
+        getAgentTranscript: async () => ({
+          messages: transcriptMessagesForTest,
+          contentReplacements: [],
+        }),
+        isPoorModeActive: () => false,
+        logError: () => undefined,
+        logForDebugging: () => undefined,
+        runForkedAgent: async (args: ForkCall) => {
+          forkCalls.push(args)
+          return {
+            messages: [
+              {
+                type: 'assistant',
+                message: {
+                  content: [{ type: 'text', text: 'Reading udsClient.ts' }],
+                },
+              },
+            ],
+          } as unknown as ForkedAgentResult
+        },
+        setTimeout: ((callback: TimerHandler) => {
+          if (typeof callback !== 'function') {
+            throw new Error('Expected timer callback')
+          }
+          scheduled = callback as () => void | Promise<void>
+          return 1 as unknown as ReturnType<typeof setTimeout>
+        }) as unknown as typeof setTimeout,
+        updateAgentSummary: (taskId: string, summary: string) => {
+          updateCalls.push({ taskId, summary })
+        },
+      },
+    )
+
+    expect(typeof scheduled).toBe('function')
+    await scheduled!()
+
+    expect(forkCalls).toHaveLength(1)
+    expect(updateCalls).toEqual([
+      { taskId: 'task-1', summary: 'Reading udsClient.ts' },
+    ])
+
+    const forkContext = forkCalls[0].cacheSafeParams.forkContextMessages ?? []
+    expect(forkContext.map(message => String(message.uuid))).toEqual([
+      'u1',
+      'a1',
+      'u2',
+    ])
+    expect(forkContext.some(message => String(message.uuid) === 'old')).toBe(
+      false,
+    )
+
+    await scheduled!()
+
+    expect(forkCalls).toHaveLength(1)
+    expect(updateCalls).toHaveLength(1)
+  })
+
+  test('skips summarization when bounded context is too small', async () => {
+    transcriptMessagesForTest = transcriptMessages.slice(0, 2)
+
+    handle = startAgentSummarization(
+      'task-1',
+      asAgentId('a0000000000000000'),
+      {
+        forkContextMessages: transcriptMessages,
+        model: 'claude-test',
+      } as unknown as CacheSafeParams,
+      () => undefined,
+      {
+        clearTimeout: () => undefined,
+        getAgentTranscript: async () => ({
+          messages: transcriptMessagesForTest,
+          contentReplacements: [],
+        }),
+        isPoorModeActive: () => false,
+        logError: () => undefined,
+        logForDebugging: () => undefined,
+        runForkedAgent: async (args: ForkCall) => {
+          forkCalls.push(args)
+          return { messages: [] } as unknown as ForkedAgentResult
+        },
+        setTimeout: ((callback: TimerHandler) => {
+          if (typeof callback !== 'function') {
+            throw new Error('Expected timer callback')
+          }
+          scheduled = callback as () => void | Promise<void>
+          return 1 as unknown as ReturnType<typeof setTimeout>
+        }) as unknown as typeof setTimeout,
+        updateAgentSummary: (taskId: string, summary: string) => {
+          updateCalls.push({ taskId, summary })
+        },
+      },
+    )
+
+    expect(typeof scheduled).toBe('function')
+    await scheduled!()
+
+    expect(forkCalls).toEqual([])
+    expect(updateCalls).toEqual([])
+  })
+})
diff --git a/src/services/AgentSummary/__tests__/summaryContext.test.ts b/src/services/AgentSummary/__tests__/summaryContext.test.ts
new file mode 100644
index 000000000..fe0eb3057
--- /dev/null
+++ b/src/services/AgentSummary/__tests__/summaryContext.test.ts
@@ -0,0 +1,261 @@
+import { describe, expect, test } from 'bun:test'
+import type { Message } from '../../../types/message.js'
+import {
+  buildSummaryContext,
+  estimateMessageChars,
+  getSummaryContextFingerprint,
+  MAX_SUMMARY_CONTEXT_CHARS,
+  selectSummaryContextMessages,
+} from '../summaryContext.js'
+
+function makeMessage(
+  type: 'user' | 'assistant',
+  uuid: string,
+  content: string,
+): Message {
+  return {
+    type,
+    uuid,
+    message: {
+      role: type,
+      content,
+    },
+  } as unknown as Message
+}
+
+describe('selectSummaryContextMessages', () => {
+  test('keeps a bounded recent suffix that starts with a user message', () => {
+    const messages = [
+      makeMessage('assistant', 'a0', 'older assistant'),
+      makeMessage('user', 'u1', 'first prompt'),
+      makeMessage('assistant', 'a1', 'first response'),
+      makeMessage('user', 'u2', 'second prompt'),
+      makeMessage('assistant', 'a2', 'second response'),
+    ]
+
+    const selected = selectSummaryContextMessages(messages, {
+      maxMessages: 3,
+      maxChars: 1_000,
+    })
+
+    expect(selected.map(message => String(message.uuid))).toEqual(['u2', 'a2'])
+  })
+
+  test('returns no context when the newest message exceeds the byte budget', () => {
+    const messages = [
+      makeMessage('user', 'u1', 'first prompt'),
+      makeMessage('assistant', 'a1', 'x'.repeat(100)),
+    ]
+
+    const selected = selectSummaryContextMessages(messages, {
+      maxMessages: 10,
+      maxChars: 10,
+    })
+
+    expect(selected).toEqual([])
+  })
+
+  test('uses serialized message size for nested content budgets', () => {
+    const messages = [
+      makeMessage('user', 'u1', 'first prompt'),
+      {
+        ...makeMessage('assistant', 'a1', 'short'),
+        nested: {
+          payload: Array.from({ length: 50 }, (_value, index) => ({
+            index,
+            text: 'x'.repeat(20),
+          })),
+        },
+      } as unknown as Message,
+    ]
+
+    const selected = selectSummaryContextMessages(messages, {
+      maxMessages: 10,
+      maxChars: 200,
+    })
+
+    expect(selected).toEqual([])
+  })
+
+  test('stops at an older oversized message after keeping the recent suffix', () => {
+    const messages = [
+      makeMessage('user', 'u1', 'x'.repeat(5_000)),
+      makeMessage('user', 'u2', 'small prompt'),
+      makeMessage('assistant', 'a2', 'small answer'),
+    ]
+
+    const selected = selectSummaryContextMessages(messages, {
+      maxMessages: 10,
+      maxChars: 1_000,
+    })
+
+    expect(selected.map(message => String(message.uuid))).toEqual(['u2', 'a2'])
+  })
+
+  test('drops leading orphan tool results after bounding', () => {
+    const messages = [
+      makeMessage('assistant', 'a0', 'older assistant'),
+      {
+        type: 'user',
+        uuid: 'u1',
+        message: {
+          role: 'user',
+          content: [
+            { type: 'tool_result', tool_use_id: 'tool-1', content: 'ok' },
+          ],
+        },
+      } as unknown as Message,
+      makeMessage('assistant', 'a1', 'after orphan'),
+      makeMessage('user', 'u2', 'next prompt'),
+    ]
+
+    const selected = selectSummaryContextMessages(messages, {
+      maxMessages: 3,
+      maxChars: 1_000,
+    })
+
+    expect(selected.map(message => String(message.uuid))).toEqual(['u2'])
+  })
+})
+
+describe('getSummaryContextFingerprint', () => {
+  test('estimates circular messages as unbounded', () => {
+    const circular = makeMessage('assistant', 'a1', 'cycle') as Message & {
+      self?: unknown
+    }
+    circular.self = circular
+
+    expect(estimateMessageChars(circular)).toBe(Number.POSITIVE_INFINITY)
+  })
+
+  test('ignores non-json primitive fields in size estimates', () => {
+    const message = makeMessage('assistant', 'a1', 'metadata') as Message & {
+      skipUndefined?: undefined
+      skipFunction?: () => void
+      skipSymbol?: symbol
+    }
+    message.skipUndefined = undefined
+    message.skipFunction = () => undefined
+    message.skipSymbol = Symbol('ignored')
+
+    expect(estimateMessageChars(message)).toBeGreaterThan(0)
+  })
+
+  test('returns null for an empty transcript', () => {
+    expect(getSummaryContextFingerprint([])).toBeNull()
+  })
+
+  test('changes when the transcript grows', () => {
+    const messages = [
+      makeMessage('user', 'u1', 'first prompt'),
+      makeMessage('assistant', 'a1', 'first response'),
+    ]
+
+    const first = getSummaryContextFingerprint(messages)
+    const second = getSummaryContextFingerprint([
+      ...messages,
+      makeMessage('user', 'u2', 'next prompt'),
+    ])
+    expect(first?.startsWith('2:a1:')).toBe(true)
+    expect(second?.startsWith('3:u2:')).toBe(true)
+    expect(first).not.toBe(second)
+  })
+
+  test('changes when message content changes under the same uuid', () => {
+    const first = getSummaryContextFingerprint([
+      makeMessage('user', 'u1', 'first prompt'),
+      makeMessage('assistant', 'a1', 'first response'),
+    ])
+    const second = getSummaryContextFingerprint([
+      makeMessage('user', 'u1', 'first prompt'),
+      makeMessage('assistant', 'a1', 'updated response'),
+    ])
+
+    expect(first).not.toBe(second)
+  })
+
+  test('includes a truncation marker for oversized primitive values', () => {
+    const prefix = 'x'.repeat(MAX_SUMMARY_CONTEXT_CHARS + 100)
+    const first = getSummaryContextFingerprint([
+      makeMessage('assistant', 'a1', `${prefix}a`),
+    ])
+    const second = getSummaryContextFingerprint([
+      makeMessage('assistant', 'a1', `${prefix}b`),
+    ])
+
+    expect(first).not.toBe(second)
+  })
+
+  test('fingerprints circular message references without recursing forever', () => {
+    const circular = makeMessage('assistant', 'a1', 'cycle') as Message & {
+      self?: unknown
+    }
+    circular.self = circular
+
+    expect(getSummaryContextFingerprint([circular])).toContain(':a1:')
+  })
+})
+
+describe('buildSummaryContext', () => {
+  test('returns bounded messages and fingerprint for summarizable context', () => {
+    const messages = [
+      { type: 'user', uuid: 'u1', message: { content: 'start' } },
+      {
+        type: 'assistant',
+        uuid: 'a1',
+        message: { content: [{ type: 'text', text: 'working' }] },
+      },
+      { type: 'user', uuid: 'u2', message: { content: 'continue' } },
+    ] as unknown as Message[]
+
+    const result = buildSummaryContext(messages, null)
+
+    expect(result.skipReason).toBeUndefined()
+    expect(result.messages.map(message => String(message.uuid))).toEqual([
+      'u1',
+      'a1',
+      'u2',
+    ])
+    expect(result.fingerprint).toContain('3:u2:')
+  })
+
+  test('reports unchanged contexts by fingerprint', () => {
+    const messages = [
+      { type: 'user', uuid: 'u1', message: { content: 'start' } },
+      {
+        type: 'assistant',
+        uuid: 'a1',
+        message: { content: [{ type: 'text', text: 'working' }] },
+      },
+      { type: 'user', uuid: 'u2', message: { content: 'continue' } },
+    ] as unknown as Message[]
+    const first = buildSummaryContext(messages, null)
+
+    const second = buildSummaryContext(messages, first.fingerprint)
+
+    expect(second.skipReason).toBe('unchanged')
+    expect(second.fingerprint).toBe(first.fingerprint)
+  })
+
+  test('filters incomplete tool calls before deciding context is too small', () => {
+    const messages = [
+      { type: 'user', uuid: 'u1', message: { content: 'start' } },
+      {
+        type: 'assistant',
+        uuid: 'a1',
+        message: {
+          content: [{ type: 'tool_use', id: 'missing', name: 'Read' }],
+        },
+      },
+      { type: 'user', uuid: 'u2', message: { content: 'continue' } },
+    ] as unknown as Message[]
+
+    const result = buildSummaryContext(messages, null)
+
+    expect(result.skipReason).toBe('too_small')
+    expect(result.messages.map(message => String(message.uuid))).toEqual([
+      'u1',
+      'u2',
+    ])
+  })
+})
diff --git a/src/services/AgentSummary/__tests__/summaryPrompt.test.ts b/src/services/AgentSummary/__tests__/summaryPrompt.test.ts
new file mode 100644
index 000000000..9e8f03cac
--- /dev/null
+++ b/src/services/AgentSummary/__tests__/summaryPrompt.test.ts
@@ -0,0 +1,34 @@
+import { describe, expect, test } from 'bun:test'
+import {
+  buildSummaryPrompt,
+  createSummaryPromptMessage,
+} from '../summaryPrompt.js'
+
+describe('buildSummaryPrompt', () => {
+  test('builds the first summary prompt without previous-summary pressure', () => {
+    const prompt = buildSummaryPrompt(null)
+
+    expect(prompt).toContain('Describe your most recent action')
+    expect(prompt).toContain('Good: "Reading runAgent.ts"')
+    expect(prompt).not.toContain('Previous:')
+  })
+
+  test('asks for a new summary when a previous one exists', () => {
+    const prompt = buildSummaryPrompt('Reading udsMessaging.ts')
+
+    expect(prompt).toContain('Previous: "Reading udsMessaging.ts"')
+    expect(prompt).toContain('say something NEW')
+  })
+})
+
+describe('createSummaryPromptMessage', () => {
+  test('creates the minimal user message shape used by forked summaries', () => {
+    const message = createSummaryPromptMessage('Summarize progress')
+
+    expect(message.type).toBe('user')
+    expect(message.message.role).toBe('user')
+    expect(message.message.content).toBe('Summarize progress')
+    expect(message.uuid).toBeString()
+    expect(message.timestamp).toBeString()
+  })
+})
diff --git a/src/services/AgentSummary/agentSummary.ts b/src/services/AgentSummary/agentSummary.ts
index 50146b3c7..d212a5c72 100644
--- a/src/services/AgentSummary/agentSummary.ts
+++ b/src/services/AgentSummary/agentSummary.ts
@@ -13,7 +13,6 @@
 import type { TaskContext } from '../../Task.js'
 import { isPoorModeActive } from '../../commands/poor/poorMode.js'
 import { updateAgentSummary } from '../../tasks/LocalAgentTask/LocalAgentTask.js'
-import { filterIncompleteToolCalls } from '@claude-code-best/builtin-tools/tools/AgentTool/runAgent.js'
 import type { AgentId } from '../../types/ids.js'
 import { logForDebugging } from '../../utils/debug.js'
 import {
@@ -21,34 +20,32 @@ import {
   runForkedAgent,
 } from '../../utils/forkedAgent.js'
 import { logError } from '../../utils/log.js'
-import { createUserMessage } from '../../utils/messages.js'
 import { getAgentTranscript } from '../../utils/sessionStorage.js'
+import { buildSummaryContext } from './summaryContext.js'
+import {
+  buildSummaryPrompt,
+  createSummaryPromptMessage,
+} from './summaryPrompt.js'
 
 const SUMMARY_INTERVAL_MS = 30_000
 
-function buildSummaryPrompt(previousSummary: string | null): string {
-  const prevLine = previousSummary
-    ? `\nPrevious: "${previousSummary}" — say something NEW.\n`
-    : ''
-
-  return `Describe your most recent action in 3-5 words using present tense (-ing). Name the file or function, not the branch. Do not use tools.
-${prevLine}
-Good: "Reading runAgent.ts"
-Good: "Fixing null check in validate.ts"
-Good: "Running auth module tests"
-Good: "Adding retry logic to fetchUser"
-
-Bad (past tense): "Analyzed the branch diff"
-Bad (too vague): "Investigating the issue"
-Bad (too long): "Reviewing full branch diff and AgentTool.tsx integration"
-Bad (branch name): "Analyzed adam/background-summary branch diff"`
-}
+export type AgentSummaryDependencies = Partial<{
+  clearTimeout: typeof clearTimeout
+  getAgentTranscript: typeof getAgentTranscript
+  isPoorModeActive: typeof isPoorModeActive
+  logError: typeof logError
+  logForDebugging: typeof logForDebugging
+  runForkedAgent: typeof runForkedAgent
+  setTimeout: typeof setTimeout
+  updateAgentSummary: typeof updateAgentSummary
+}>
 
 export function startAgentSummarization(
   taskId: string,
   agentId: AgentId,
   cacheSafeParams: CacheSafeParams,
   setAppState: TaskContext['setAppState'],
+  dependencies: AgentSummaryDependencies = {},
 ): { stop: () => void } {
   // Drop forkContextMessages from the closure — runSummary rebuilds it each
   // tick from getAgentTranscript(). Without this, the original fork messages
@@ -58,39 +55,67 @@ export function startAgentSummarization(
   let timeoutId: ReturnType<typeof setTimeout> | null = null
   let stopped = false
   let previousSummary: string | null = null
+  let lastHandledTranscriptFingerprint: string | null = null
+  const clearTimeoutImpl = dependencies.clearTimeout ?? clearTimeout
+  const getAgentTranscriptImpl =
+    dependencies.getAgentTranscript ?? getAgentTranscript
+  const isPoorModeActiveImpl =
+    dependencies.isPoorModeActive ?? isPoorModeActive
+  const logErrorImpl = dependencies.logError ?? logError
+  const logForDebuggingImpl =
+    dependencies.logForDebugging ?? logForDebugging
+  const runForkedAgentImpl = dependencies.runForkedAgent ?? runForkedAgent
+  const setTimeoutImpl = dependencies.setTimeout ?? setTimeout
+  const updateAgentSummaryImpl =
+    dependencies.updateAgentSummary ?? updateAgentSummary
 
   async function runSummary(): Promise<void> {
     if (stopped) return
-    if (isPoorModeActive()) {
-      logForDebugging('[AgentSummary] Skipping summary — poor mode active')
+    if (isPoorModeActiveImpl()) {
+      logForDebuggingImpl('[AgentSummary] Skipping summary — poor mode active')
       scheduleNext()
       return
     }
 
-    logForDebugging(`[AgentSummary] Timer fired for agent ${agentId}`)
+    logForDebuggingImpl(`[AgentSummary] Timer fired for agent ${agentId}`)
 
     try {
       // Read current messages from transcript
-      const transcript = await getAgentTranscript(agentId)
+      const transcript = await getAgentTranscriptImpl(agentId)
       if (!transcript || transcript.messages.length < 3) {
         // Not enough context yet — finally block will schedule next attempt
-        logForDebugging(
+        logForDebuggingImpl(
           `[AgentSummary] Skipping summary for ${taskId}: not enough messages (${transcript?.messages.length ?? 0})`,
         )
         return
       }
 
-      // Filter to clean message state
-      const cleanMessages = filterIncompleteToolCalls(transcript.messages)
+      const summaryContext = buildSummaryContext(
+        transcript.messages,
+        lastHandledTranscriptFingerprint,
+      )
+      if (summaryContext.skipReason === 'unchanged') {
+        logForDebuggingImpl(
+          `[AgentSummary] Skipping summary for ${taskId}: transcript unchanged`,
+        )
+        return
+      }
+
+      if (summaryContext.skipReason === 'too_small') {
+        logForDebuggingImpl(
+          `[AgentSummary] Skipping summary for ${taskId}: no bounded context available`,
+        )
+        return
+      }
 
       // Build fork params with current messages
       const forkParams: CacheSafeParams = {
         ...baseParams,
-        forkContextMessages: cleanMessages,
+        forkContextMessages: summaryContext.messages,
       }
 
-      logForDebugging(
-        `[AgentSummary] Forking for summary, ${cleanMessages.length} messages in context`,
+      logForDebuggingImpl(
+        `[AgentSummary] Forking for summary, ${summaryContext.messages.length} messages in context`,
       )
 
       // Create abort controller for this summary
@@ -112,9 +137,9 @@ export function startAgentSummarization(
       // ContentReplacementState is cloned by default in createSubagentContext
       // from forkParams.toolUseContext (the subagent's LIVE state captured at
       // onCacheSafeParams time). No explicit override needed.
-      const result = await runForkedAgent({
+      const result = await runForkedAgentImpl({
         promptMessages: [
-          createUserMessage({ content: buildSummaryPrompt(previousSummary) }),
+          createSummaryPromptMessage(buildSummaryPrompt(previousSummary)),
         ],
         cacheSafeParams: forkParams,
         canUseTool,
@@ -136,21 +161,24 @@ export function startAgentSummarization(
           )
           continue
         }
-        const contentArr = Array.isArray(msg.message!.content) ? msg.message!.content : []
+        const contentArr = Array.isArray(msg.message!.content)
+          ? msg.message!.content
+          : []
         const textBlock = contentArr.find(b => b.type === 'text')
         if (textBlock?.type === 'text' && textBlock.text.trim()) {
           const summaryText = textBlock.text.trim()
-          logForDebugging(
+          logForDebuggingImpl(
             `[AgentSummary] Summary result for ${taskId}: ${summaryText}`,
           )
+          lastHandledTranscriptFingerprint = summaryContext.fingerprint
           previousSummary = summaryText
-          updateAgentSummary(taskId, summaryText, setAppState)
+          updateAgentSummaryImpl(taskId, summaryText, setAppState)
           break
         }
       }
     } catch (e) {
       if (!stopped && e instanceof Error) {
-        logError(e)
+        logErrorImpl(e)
       }
     } finally {
       summaryAbortController = null
@@ -163,14 +191,14 @@ export function startAgentSummarization(
 
   function scheduleNext(): void {
     if (stopped) return
-    timeoutId = setTimeout(runSummary, SUMMARY_INTERVAL_MS)
+    timeoutId = setTimeoutImpl(runSummary, SUMMARY_INTERVAL_MS)
   }
 
   function stop(): void {
-    logForDebugging(`[AgentSummary] Stopping summarization for ${taskId}`)
+    logForDebuggingImpl(`[AgentSummary] Stopping summarization for ${taskId}`)
     stopped = true
     if (timeoutId) {
-      clearTimeout(timeoutId)
+      clearTimeoutImpl(timeoutId)
       timeoutId = null
     }
     if (summaryAbortController) {
diff --git a/src/services/AgentSummary/summaryContext.ts b/src/services/AgentSummary/summaryContext.ts
new file mode 100644
index 000000000..d4c00e1d4
--- /dev/null
+++ b/src/services/AgentSummary/summaryContext.ts
@@ -0,0 +1,219 @@
+import { createHash } from 'node:crypto'
+import { filterIncompleteToolCalls } from '@claude-code-best/builtin-tools/tools/AgentTool/filterIncompleteToolCalls.js'
+import type { Message } from '../../types/message.js'
+
+export const MAX_SUMMARY_CONTEXT_MESSAGES = 120
+export const MAX_SUMMARY_CONTEXT_CHARS = 200_000
+
+function estimateJsonChars(
+  value: unknown,
+  limit: number,
+  seen = new Set<object>(),
+): number {
+  if (value === null) return 4
+  switch (typeof value) {
+    case 'string':
+      return value.length + 2
+    case 'number':
+    case 'boolean':
+      return String(value).length
+    case 'undefined':
+    case 'function':
+    case 'symbol':
+      return 0
+    case 'object': {
+      if (seen.has(value)) return Number.POSITIVE_INFINITY
+      seen.add(value)
+      let total = 2
+      if (Array.isArray(value)) {
+        for (let index = 0; index < value.length; index++) {
+          total += String(index).length + 3
+          total += estimateJsonChars(value[index], limit - total, seen)
+          if (total > limit) return total
+        }
+      } else {
+        const record = value as Record<string, unknown>
+        for (const key in record) {
+          if (!Object.hasOwn(record, key)) continue
+          total += key.length + 3
+          total += estimateJsonChars(record[key], limit - total, seen)
+          if (total > limit) return total
+        }
+      }
+      seen.delete(value)
+      return total
+    }
+  }
+  return 0
+}
+
+function updateFingerprintHash(
+  hash: ReturnType<typeof createHash>,
+  value: unknown,
+  limit: { remaining: number },
+  seen = new Set<object>(),
+): void {
+  if (limit.remaining <= 0) return
+  if (value === null || typeof value !== 'object') {
+    const text = String(value)
+    const consumed = Math.min(text.length, limit.remaining)
+    if (consumed <= 0) return
+    hash.update(typeof value)
+    hash.update(':')
+    hash.update(text.slice(0, consumed))
+    if (consumed < text.length) {
+      hash.update(`#truncated:${text.length}:${text.slice(-64)}`)
+    }
+    limit.remaining -= consumed
+    return
+  }
+  if (seen.has(value)) {
+    hash.update('[Circular]')
+    return
+  }
+  seen.add(value)
+  if (Array.isArray(value)) {
+    for (let index = 0; index < value.length; index++) {
+      if (limit.remaining <= 0) break
+      const key = String(index)
+      hash.update(key)
+      limit.remaining -= key.length
+      updateFingerprintHash(hash, value[index], limit, seen)
+    }
+  } else {
+    const record = value as Record<string, unknown>
+    for (const key in record) {
+      if (limit.remaining <= 0) break
+      if (!Object.hasOwn(record, key)) continue
+      hash.update(key)
+      limit.remaining -= key.length
+      updateFingerprintHash(hash, record[key], limit, seen)
+    }
+  }
+  seen.delete(value)
+}
+
+export function estimateMessageChars(
+  message: Message,
+  limit = Number.POSITIVE_INFINITY,
+): number {
+  const estimated = estimateJsonChars(message, limit)
+  if (!Number.isFinite(estimated)) {
+    return Number.POSITIVE_INFINITY
+  }
+  return estimated
+}
+
+function hasToolResultBlock(message: Message): boolean {
+  if (message.type !== 'user') return false
+  const content = message.message?.content
+  return (
+    Array.isArray(content) &&
+    content.some(block => {
+      return Boolean(
+        block &&
+          typeof block === 'object' &&
+          'type' in block &&
+          block.type === 'tool_result',
+      )
+    })
+  )
+}
+
+export function getSummaryContextFingerprint(
+  messages: Message[],
+): string | null {
+  const lastMessage = messages.at(-1)
+  if (!lastMessage) return null
+  const hash = createHash('sha256')
+  updateFingerprintHash(hash, messages, {
+    remaining: MAX_SUMMARY_CONTEXT_CHARS,
+  })
+  return `${messages.length}:${lastMessage.uuid}:${hash.digest('hex').slice(0, 16)}`
+}
+
+export function selectSummaryContextMessages(
+  messages: Message[],
+  limits: {
+    maxMessages?: number
+    maxChars?: number
+  } = {},
+): Message[] {
+  const maxMessages = limits.maxMessages ?? MAX_SUMMARY_CONTEXT_MESSAGES
+  const maxChars = limits.maxChars ?? MAX_SUMMARY_CONTEXT_CHARS
+  if (maxMessages <= 0 || maxChars <= 0) return []
+
+  const selected: Message[] = []
+  let selectedChars = 0
+
+  for (let i = messages.length - 1; i >= 0; i--) {
+    const message = messages[i]
+    if (!message) continue
+
+    const messageChars = estimateMessageChars(message, maxChars - selectedChars)
+    if (messageChars > maxChars) {
+      if (selected.length === 0) return []
+      break
+    }
+
+    if (
+      selected.length >= maxMessages ||
+      selectedChars + messageChars > maxChars
+    ) {
+      break
+    }
+
+    selected.unshift(message)
+    selectedChars += messageChars
+  }
+
+  while (selected.length > 0) {
+    const first = selected[0]
+    if (!first) break
+    if (first.type !== 'user' || hasToolResultBlock(first)) {
+      selected.shift()
+      continue
+    }
+    break
+  }
+
+  return selected
+}
+
+export type SummaryContextBuildResult = {
+  messages: Message[]
+  fingerprint: string | null
+  skipReason?: 'too_small' | 'unchanged'
+}
+
+export function buildSummaryContext(
+  messages: Message[],
+  previousFingerprint: string | null,
+): SummaryContextBuildResult {
+  const cleanMessages = filterIncompleteToolCalls(messages)
+  const boundedMessages = filterIncompleteToolCalls(
+    selectSummaryContextMessages(cleanMessages),
+  )
+  const fingerprint = getSummaryContextFingerprint(boundedMessages)
+
+  if (fingerprint && fingerprint === previousFingerprint) {
+    return {
+      messages: boundedMessages,
+      fingerprint,
+      skipReason: 'unchanged',
+    }
+  }
+
+  if (boundedMessages.length < 3) {
+    return {
+      messages: boundedMessages,
+      fingerprint,
+      skipReason: 'too_small',
+    }
+  }
+
+  return {
+    messages: boundedMessages,
+    fingerprint,
+  }
+}
diff --git a/src/services/AgentSummary/summaryPrompt.ts b/src/services/AgentSummary/summaryPrompt.ts
new file mode 100644
index 000000000..ce3138f2a
--- /dev/null
+++ b/src/services/AgentSummary/summaryPrompt.ts
@@ -0,0 +1,32 @@
+import { randomUUID, type UUID } from 'node:crypto'
+import type { UserMessage } from '../../types/message.js'
+
+export function buildSummaryPrompt(previousSummary: string | null): string {
+  const prevLine = previousSummary
+    ? `\nPrevious: "${previousSummary}" — say something NEW.\n`
+    : ''
+
+  return `Describe your most recent action in 3-5 words using present tense (-ing). Name the file or function, not the branch. Do not use tools.
+${prevLine}
+Good: "Reading runAgent.ts"
+Good: "Fixing null check in validate.ts"
+Good: "Running auth module tests"
+Good: "Adding retry logic to fetchUser"
+
+Bad (past tense): "Analyzed the branch diff"
+Bad (too vague): "Investigating the issue"
+Bad (too long): "Reviewing full branch diff and AgentTool.tsx integration"
+Bad (branch name): "Analyzed adam/background-summary branch diff"`
+}
+
+export function createSummaryPromptMessage(content: string): UserMessage {
+  return {
+    type: 'user',
+    message: {
+      role: 'user',
+      content,
+    },
+    uuid: randomUUID() as UUID,
+    timestamp: new Date().toISOString(),
+  }
+}
diff --git a/src/utils/__tests__/ndjsonFramer.test.ts b/src/utils/__tests__/ndjsonFramer.test.ts
new file mode 100644
index 000000000..344c1e58c
--- /dev/null
+++ b/src/utils/__tests__/ndjsonFramer.test.ts
@@ -0,0 +1,153 @@
+import { EventEmitter } from 'node:events'
+import type { Socket } from 'node:net'
+import { describe, expect, test } from 'bun:test'
+import { attachNdjsonFramer } from '../ndjsonFramer.js'
+
+type TestSocket = Socket & {
+  destroyed: boolean
+  emitData: (chunk: Buffer) => void
+}
+
+function createTestSocket(): TestSocket {
+  const emitter = new EventEmitter() as TestSocket
+  emitter.destroyed = false
+  emitter.destroy = ((_error?: Error) => {
+    emitter.destroyed = true
+    emitter.emit('close')
+    return emitter
+  }) as TestSocket['destroy']
+  emitter.emitData = (chunk: Buffer) => {
+    emitter.emit('data', chunk)
+  }
+  return emitter
+}
+
+describe('attachNdjsonFramer', () => {
+  test('accepts a complete frame at the configured byte limit', () => {
+    const socket = createTestSocket()
+    const messages: unknown[] = []
+    const errors: Error[] = []
+
+    attachNdjsonFramer(
+      socket,
+      msg => messages.push(msg),
+      text => JSON.parse(text) as unknown,
+      {
+        maxFrameBytes: Buffer.byteLength('{"a":1}', 'utf8'),
+        onFrameError: error => errors.push(error),
+      },
+    )
+
+    socket.emitData(Buffer.from('{"a":1}\n'))
+
+    expect(messages).toEqual([{ a: 1 }])
+    expect(errors).toEqual([])
+    expect(socket.destroyed).toBe(false)
+  })
+
+  test('destroys a complete frame over the configured byte limit', () => {
+    const socket = createTestSocket()
+    const messages: unknown[] = []
+    const errors: Error[] = []
+
+    attachNdjsonFramer(
+      socket,
+      msg => messages.push(msg),
+      text => JSON.parse(text) as unknown,
+      {
+        maxFrameBytes: 8,
+        onFrameError: error => errors.push(error),
+      },
+    )
+
+    socket.emitData(Buffer.from('{"long":true}\n'))
+
+    expect(messages).toEqual([])
+    expect(errors[0]?.message).toContain('NDJSON frame exceeded')
+    expect(socket.destroyed).toBe(true)
+  })
+
+  test('destroys oversized no-newline input before a frame can form', () => {
+    const socket = createTestSocket()
+    const messages: unknown[] = []
+    const errors: Error[] = []
+
+    attachNdjsonFramer(
+      socket,
+      msg => messages.push(msg),
+      text => JSON.parse(text) as unknown,
+      {
+        maxFrameBytes: 8,
+        onFrameError: error => errors.push(error),
+      },
+    )
+
+    socket.emitData(Buffer.from('x'.repeat(9)))
+
+    expect(messages).toEqual([])
+    expect(errors[0]?.message).toContain('NDJSON frame exceeded')
+    expect(socket.destroyed).toBe(true)
+  })
+
+  test('lets callers own oversized-frame shutdown when configured', () => {
+    const socket = createTestSocket()
+    const errors: Error[] = []
+
+    attachNdjsonFramer(
+      socket,
+      () => undefined,
+      text => JSON.parse(text) as unknown,
+      {
+        maxFrameBytes: 8,
+        onFrameError: error => errors.push(error),
+        destroyOnFrameError: false,
+      },
+    )
+
+    socket.emitData(Buffer.from('{"long":true}\n'))
+
+    expect(errors[0]?.message).toContain('NDJSON frame exceeded')
+    expect(socket.destroyed).toBe(false)
+  })
+
+  test('reports malformed non-empty frames without changing default compatibility', () => {
+    const socket = createTestSocket()
+    const messages: unknown[] = []
+    const errors: Error[] = []
+
+    attachNdjsonFramer(
+      socket,
+      msg => messages.push(msg),
+      text => JSON.parse(text) as unknown,
+      {
+        onInvalidFrame: error => errors.push(error),
+      },
+    )
+
+    socket.emitData(Buffer.from('{not-json\n'))
+
+    expect(messages).toEqual([])
+    expect(errors).toHaveLength(1)
+    expect(socket.destroyed).toBe(false)
+  })
+
+  test('destroys malformed frames when configured by the caller', () => {
+    const socket = createTestSocket()
+    const errors: Error[] = []
+
+    attachNdjsonFramer(
+      socket,
+      () => undefined,
+      text => JSON.parse(text) as unknown,
+      {
+        destroyOnInvalidFrame: true,
+        onInvalidFrame: error => errors.push(error),
+      },
+    )
+
+    socket.emitData(Buffer.from('{not-json\n'))
+
+    expect(errors).toHaveLength(1)
+    expect(socket.destroyed).toBe(true)
+  })
+})
diff --git a/src/utils/__tests__/teammateMailbox.test.ts b/src/utils/__tests__/teammateMailbox.test.ts
new file mode 100644
index 000000000..f6279dab7
--- /dev/null
+++ b/src/utils/__tests__/teammateMailbox.test.ts
@@ -0,0 +1,462 @@
+import { afterEach, beforeEach, describe, expect, test } from 'bun:test'
+import { mkdir, readFile, rm, writeFile } from 'node:fs/promises'
+import { mkdtempSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { dirname, join } from 'node:path'
+import type { Message } from 'src/types/message.js'
+import {
+  compactMailboxMessages,
+  getLastPeerDmSummary,
+  getInboxPath,
+  markMessageAsReadByIndex,
+  markMessageAsReadByIdentity,
+  markMessagesAsRead,
+  markMessagesAsReadByPredicate,
+  MAX_MAILBOX_MESSAGE_TEXT_BYTES,
+  MAX_MAILBOX_FILE_BYTES,
+  MAX_MAILBOX_MESSAGES,
+  MAX_READ_MAILBOX_MESSAGES,
+  MAX_UNREAD_PROTOCOL_MAILBOX_MESSAGES,
+  readMailbox,
+  type TeammateMessage,
+  writeToMailbox,
+} from 'src/utils/teammateMailbox.js'
+
+let tempHome = ''
+let previousConfigDir: string | undefined
+
+function message(
+  text: string,
+  read: boolean,
+  timestamp = new Date(0).toISOString(),
+): TeammateMessage {
+  return {
+    from: 'team-lead',
+    text,
+    timestamp,
+    read,
+  }
+}
+
+async function seedMailbox(
+  agentName: string,
+  teamName: string,
+  messages: TeammateMessage[],
+): Promise<void> {
+  const inboxPath = getInboxPath(agentName, teamName)
+  await mkdir(dirname(inboxPath), { recursive: true })
+  await writeFile(inboxPath, JSON.stringify(messages, null, 2), 'utf-8')
+}
+
+async function readRawMailbox(
+  agentName: string,
+  teamName: string,
+): Promise<TeammateMessage[]> {
+  const content = await readFile(getInboxPath(agentName, teamName), 'utf-8')
+  return JSON.parse(content) as TeammateMessage[]
+}
+
+describe('compactMailboxMessages', () => {
+  test('prioritizes unread messages and keeps only recent read history', () => {
+    const compacted = compactMailboxMessages(
+      [
+        message('read-1', true),
+        message('read-2', true),
+        message('unread-1', false),
+        message('read-3', true),
+        message('unread-2', false),
+        message('read-4', true),
+        message('read-5', true),
+        message('unread-3', false),
+      ],
+      { maxMessages: 5, maxReadMessages: 2 },
+    )
+
+    expect(compacted.map(m => m.text)).toEqual([
+      'unread-1',
+      'unread-2',
+      'read-4',
+      'read-5',
+      'unread-3',
+    ])
+  })
+
+  test('retains unread protocol messages separately from regular cap', () => {
+    const protocol = message(
+      JSON.stringify({ type: 'permission_response', request_id: 'req-1' }),
+      false,
+    )
+    const compacted = compactMailboxMessages(
+      [
+        protocol,
+        ...Array.from({ length: 5 }, (_value, index) =>
+          message(`regular-${index}`, false),
+        ),
+      ],
+      {
+        maxMessages: 2,
+        maxReadMessages: 0,
+        maxUnreadProtocolMessages: 1,
+      },
+    )
+
+    expect(compacted.map(m => m.text)).toEqual([
+      protocol.text,
+      'regular-3',
+      'regular-4',
+    ])
+  })
+
+  test('does not prioritize malformed JSON-like unread messages as protocol', () => {
+    const compacted = compactMailboxMessages(
+      [
+        message('{not-json', false),
+        message('regular-1', false),
+        message('regular-2', false),
+      ],
+      {
+        maxMessages: 1,
+        maxReadMessages: 0,
+        maxUnreadProtocolMessages: 10,
+      },
+    )
+
+    expect(compacted.map(m => m.text)).toEqual(['regular-2'])
+  })
+
+  test('caps unread protocol messages with an independent bound', () => {
+    const compacted = compactMailboxMessages(
+      Array.from(
+        { length: MAX_UNREAD_PROTOCOL_MAILBOX_MESSAGES + 1 },
+        (_value, index) =>
+          message(
+            JSON.stringify({
+              type: 'permission_response',
+              request_id: `req-${index}`,
+            }),
+            false,
+          ),
+      ),
+    )
+
+    expect(compacted).toHaveLength(MAX_UNREAD_PROTOCOL_MAILBOX_MESSAGES)
+    expect(compacted[0]?.text).toContain('req-1')
+  })
+
+  test('keeps retained mailbox bytes under an explicit budget', () => {
+    const compacted = compactMailboxMessages(
+      Array.from({ length: 20 }, (_value, index) =>
+        message(`msg-${index}-${'x'.repeat(200)}`, false),
+      ),
+      {
+        maxMessages: 20,
+        maxReadMessages: 0,
+        maxRetainedBytes: 1_000,
+      },
+    )
+
+    expect(
+      Buffer.byteLength(JSON.stringify(compacted), 'utf8'),
+    ).toBeLessThanOrEqual(1_000)
+    expect(compacted.length).toBeLessThan(20)
+    expect(compacted.at(-1)?.text).toContain('msg-19')
+  })
+
+  test('returns an empty mailbox when even one message exceeds retained budget', () => {
+    const compacted = compactMailboxMessages([message('too-large', false)], {
+      maxMessages: 10,
+      maxReadMessages: 0,
+      maxRetainedBytes: 1,
+    })
+
+    expect(compacted).toEqual([])
+  })
+})
+
+describe('teammate mailbox retention', () => {
+  beforeEach(() => {
+    previousConfigDir = process.env.CLAUDE_CONFIG_DIR
+    tempHome = mkdtempSync(join(tmpdir(), 'teammate-mailbox-'))
+    process.env.CLAUDE_CONFIG_DIR = tempHome
+  })
+
+  afterEach(async () => {
+    if (previousConfigDir === undefined) {
+      delete process.env.CLAUDE_CONFIG_DIR
+    } else {
+      process.env.CLAUDE_CONFIG_DIR = previousConfigDir
+    }
+    await rm(tempHome, { recursive: true, force: true })
+    tempHome = ''
+  })
+
+  test('writeToMailbox compacts oversized unread inbox files', async () => {
+    const existing = Array.from(
+      { length: MAX_MAILBOX_MESSAGES + 20 },
+      (_value, index) => message(`old-${index}`, false),
+    )
+    await seedMailbox('worker', 'alpha', existing)
+
+    await writeToMailbox(
+      'worker',
+      {
+        from: 'team-lead',
+        text: 'newest',
+        timestamp: new Date(1).toISOString(),
+      },
+      'alpha',
+    )
+
+    const after = await readMailbox('worker', 'alpha')
+    expect(after).toHaveLength(MAX_MAILBOX_MESSAGES)
+    expect(after[0]?.text).toBe('old-21')
+    expect(after.at(-1)?.text).toBe('newest')
+  })
+
+  test('markMessagesAsRead compacts read history after consumption', async () => {
+    const existing = Array.from(
+      { length: MAX_MAILBOX_MESSAGES + 20 },
+      (_value, index) => message(`msg-${index}`, false),
+    )
+    await seedMailbox('worker', 'alpha', existing)
+
+    await markMessagesAsRead('worker', 'alpha')
+
+    const after = await readRawMailbox('worker', 'alpha')
+    expect(after).toHaveLength(MAX_READ_MAILBOX_MESSAGES)
+    expect(after.every(m => m.read)).toBe(true)
+    expect(after[0]?.text).toBe(
+      `msg-${MAX_MAILBOX_MESSAGES + 20 - MAX_READ_MAILBOX_MESSAGES}`,
+    )
+  })
+
+  test('markMessagesAsReadByPredicate leaves structured messages unread', async () => {
+    await seedMailbox('worker', 'alpha', [
+      message('plain', false),
+      message(JSON.stringify({ type: 'permission_request' }), false),
+    ])
+
+    await markMessagesAsReadByPredicate(
+      'worker',
+      m => !m.text.includes('permission_request'),
+      'alpha',
+    )
+
+    const after = await readRawMailbox('worker', 'alpha')
+    expect(after.map(m => m.read)).toEqual([true, false])
+  })
+
+  test('markMessageAsReadByIdentity survives compaction shifting indexes', async () => {
+    const permissionResponse = message(
+      JSON.stringify({ type: 'permission_response', request_id: 'req-1' }),
+      false,
+    )
+    await seedMailbox('worker', 'alpha', [
+      permissionResponse,
+      ...Array.from({ length: MAX_MAILBOX_MESSAGES + 20 }, (_value, index) =>
+        message(`regular-${index}`, false),
+      ),
+    ])
+
+    await writeToMailbox(
+      'worker',
+      {
+        from: 'team-lead',
+        text: 'newest',
+        timestamp: new Date(2).toISOString(),
+      },
+      'alpha',
+    )
+    const marked = await markMessageAsReadByIdentity(
+      'worker',
+      'alpha',
+      permissionResponse,
+    )
+
+    const after = await readRawMailbox('worker', 'alpha')
+    expect(marked).toBe(true)
+    expect(after.some(m => m.text === permissionResponse.text && !m.read)).toBe(
+      false,
+    )
+  })
+
+  test('markMessageAsReadByIndex also compacts through the compatibility path', async () => {
+    const existing = Array.from(
+      { length: MAX_MAILBOX_MESSAGES + 10 },
+      (_value, index) => message(`msg-${index}`, false),
+    )
+    await seedMailbox('worker', 'alpha', existing)
+
+    await markMessageAsReadByIndex('worker', 'alpha', existing.length - 1)
+
+    const after = await readRawMailbox('worker', 'alpha')
+    expect(after).toHaveLength(MAX_MAILBOX_MESSAGES)
+    expect(after.some(m => m.text === `msg-${existing.length - 1}`)).toBe(false)
+    expect(after.at(-1)?.text).toBe(`msg-${existing.length - 2}`)
+  })
+
+  test('writeToMailbox rejects oversized message text instead of storing it', async () => {
+    await expect(
+      writeToMailbox(
+        'worker',
+        {
+          from: 'team-lead',
+          text: 'x'.repeat(MAX_MAILBOX_MESSAGE_TEXT_BYTES + 1),
+          timestamp: new Date(3).toISOString(),
+        },
+        'alpha',
+      ),
+    ).rejects.toThrow('Mailbox message text exceeds')
+
+    expect(await readRawMailbox('worker', 'alpha')).toEqual([])
+  })
+
+  test('writeToMailbox fails closed when an existing mailbox is corrupt', async () => {
+    const inboxPath = getInboxPath('worker', 'alpha')
+    await mkdir(dirname(inboxPath), { recursive: true })
+    await writeFile(inboxPath, '{not-json', 'utf-8')
+
+    await expect(
+      writeToMailbox(
+        'worker',
+        {
+          from: 'team-lead',
+          text: 'new',
+          timestamp: new Date(4).toISOString(),
+        },
+        'alpha',
+      ),
+    ).rejects.toThrow()
+
+    expect(await readFile(inboxPath, 'utf-8')).toBe('{not-json')
+  })
+
+  test('readMailbox fails closed on corrupt mailbox content', async () => {
+    const inboxPath = getInboxPath('worker', 'alpha')
+    await mkdir(dirname(inboxPath), { recursive: true })
+    await writeFile(inboxPath, '{not-json', 'utf-8')
+
+    await expect(readMailbox('worker', 'alpha')).rejects.toThrow()
+  })
+
+  test('readMailbox rejects non-array mailbox files', async () => {
+    const inboxPath = getInboxPath('worker', 'alpha')
+    await mkdir(dirname(inboxPath), { recursive: true })
+    await writeFile(inboxPath, JSON.stringify({ text: 'not an array' }), 'utf-8')
+
+    await expect(readMailbox('worker', 'alpha')).rejects.toThrow(
+      'expected message array',
+    )
+  })
+
+  test('readMailbox rejects malformed stored message shapes', async () => {
+    const inboxPath = getInboxPath('worker', 'alpha')
+    await mkdir(dirname(inboxPath), { recursive: true })
+    await writeFile(
+      inboxPath,
+      JSON.stringify([{ from: 'lead', text: 'missing timestamp' }]),
+      'utf-8',
+    )
+
+    await expect(readMailbox('worker', 'alpha')).rejects.toThrow(
+      'Invalid mailbox message shape',
+    )
+  })
+
+  test('readMailbox rejects non-object stored messages', async () => {
+    const inboxPath = getInboxPath('worker', 'alpha')
+    await mkdir(dirname(inboxPath), { recursive: true })
+    await writeFile(inboxPath, JSON.stringify(['not an object']), 'utf-8')
+
+    await expect(readMailbox('worker', 'alpha')).rejects.toThrow(
+      'expected object',
+    )
+  })
+
+  test('readMailbox rejects oversized mailbox files before parsing', async () => {
+    const inboxPath = getInboxPath('worker', 'alpha')
+    await mkdir(dirname(inboxPath), { recursive: true })
+    await writeFile(inboxPath, `[${' '.repeat(MAX_MAILBOX_FILE_BYTES)}]`, 'utf-8')
+
+    await expect(readMailbox('worker', 'alpha')).rejects.toThrow(
+      'Mailbox file exceeds',
+    )
+  })
+
+  test('markMessageAsReadByIdentity returns false for missing mailbox files', async () => {
+    await expect(
+      markMessageAsReadByIdentity('worker', 'alpha', message('absent', false)),
+    ).resolves.toBe(false)
+  })
+
+  test('markMessageAsReadByIdentity returns false when the expected message moved out', async () => {
+    await seedMailbox('worker', 'alpha', [message('other', false)])
+
+    await expect(
+      markMessageAsReadByIdentity('worker', 'alpha', message('missing', false)),
+    ).resolves.toBe(false)
+
+    expect((await readRawMailbox('worker', 'alpha'))[0]?.read).toBe(false)
+  })
+
+  test('markMessageAsReadByIdentity returns false on corrupt mailbox content', async () => {
+    const inboxPath = getInboxPath('worker', 'alpha')
+    await mkdir(dirname(inboxPath), { recursive: true })
+    await writeFile(inboxPath, '{not-json', 'utf-8')
+
+    await expect(
+      markMessageAsReadByIdentity('worker', 'alpha', message('missing', false)),
+    ).resolves.toBe(false)
+  })
+})
+
+describe('getLastPeerDmSummary', () => {
+  test('extracts the final peer direct-message summary from assistant tool use', () => {
+    const messages = [
+      { type: 'user', message: { content: 'wake up' } },
+      {
+        type: 'assistant',
+        message: {
+          content: [
+            {
+              type: 'tool_use',
+              name: 'SendMessage',
+              input: {
+                to: 'worker-1',
+                message: 'please check the UDS bounds',
+                summary: 'Checking UDS bounds',
+              },
+            },
+          ],
+        },
+      },
+    ] as unknown as Message[]
+
+    expect(getLastPeerDmSummary(messages)).toBe(
+      '[to worker-1] Checking UDS bounds',
+    )
+  })
+
+  test('stops peer direct-message summary search at the wake-up boundary', () => {
+    const messages = [
+      {
+        type: 'assistant',
+        message: {
+          content: [
+            {
+              type: 'tool_use',
+              name: 'SendMessage',
+              input: {
+                to: 'worker-1',
+                message: 'old message',
+              },
+            },
+          ],
+        },
+      },
+      { type: 'user', message: { content: 'new prompt' } },
+    ] as unknown as Message[]
+
+    expect(getLastPeerDmSummary(messages)).toBeUndefined()
+  })
+})
diff --git a/src/utils/__tests__/udsMessaging.test.ts b/src/utils/__tests__/udsMessaging.test.ts
new file mode 100644
index 000000000..392daa1ac
--- /dev/null
+++ b/src/utils/__tests__/udsMessaging.test.ts
@@ -0,0 +1,614 @@
+import { afterEach, beforeEach, describe, expect, test } from 'bun:test'
+import {
+  chmod,
+  mkdir,
+  mkdtemp,
+  readdir,
+  rm,
+  stat,
+  symlink,
+  unlink,
+  writeFile,
+} from 'node:fs/promises'
+import { createHash } from 'node:crypto'
+import { createConnection, createServer } from 'node:net'
+import { dirname, join } from 'node:path'
+import { tmpdir } from 'node:os'
+import {
+  drainInbox,
+  getDefaultUdsSocketPath,
+  MAX_UDS_INBOX_ENTRIES,
+  MAX_UDS_INBOX_BYTES,
+  MAX_UDS_FRAME_BYTES,
+  MAX_UDS_CLIENTS,
+  formatUdsAddress,
+  parseUdsTarget,
+  sendUdsMessage,
+  setOnEnqueue,
+  startUdsMessaging,
+  stopUdsMessaging,
+  UDS_AUTH_TIMEOUT_MS,
+} from '../udsMessaging.js'
+
+let previousConfigDir: string | undefined
+let tempConfigDir = ''
+
+function socketPath(label: string): string {
+  const suffix = `${process.pid}-${Date.now()}-${Math.random().toString(16).slice(2)}-${label}`
+  if (process.platform === 'win32') {
+    return `\\\\.\\pipe\\claude-code-test-${suffix}`
+  }
+  return join(tmpdir(), 'claude-code-test', `${suffix}.sock`)
+}
+
+function sleep(ms: number): Promise<void> {
+  return new Promise(resolve => setTimeout(resolve, ms))
+}
+
+async function waitForEnqueues(
+  expected: number,
+  sendMessages: () => Promise<void>,
+): Promise<void> {
+  let count = 0
+  let resolveDone: (() => void) | undefined
+  const done = new Promise<void>(resolve => {
+    resolveDone = resolve
+  })
+
+  setOnEnqueue(() => {
+    count++
+    if (count >= expected) resolveDone?.()
+  })
+
+  await sendMessages()
+  await Promise.race([
+    done,
+    sleep(5_000).then(() => {
+      throw new Error(`Timed out waiting for ${expected} UDS enqueues`)
+    }),
+  ])
+  setOnEnqueue(null)
+}
+
+beforeEach(async () => {
+  previousConfigDir = process.env.CLAUDE_CONFIG_DIR
+  tempConfigDir = await mkdtemp(join(tmpdir(), 'uds-messaging-home-'))
+  process.env.CLAUDE_CONFIG_DIR = tempConfigDir
+})
+
+afterEach(async () => {
+  setOnEnqueue(null)
+  drainInbox()
+  await stopUdsMessaging()
+  if (previousConfigDir === undefined) {
+    delete process.env.CLAUDE_CONFIG_DIR
+  } else {
+    process.env.CLAUDE_CONFIG_DIR = previousConfigDir
+  }
+  if (tempConfigDir) {
+    await rm(tempConfigDir, { recursive: true, force: true })
+    tempConfigDir = ''
+  }
+})
+
+async function closeServer(server: ReturnType<typeof createServer>): Promise<void> {
+  await new Promise<void>(resolve => {
+    server.close(() => resolve())
+  })
+}
+
+describe('UDS inbox retention', () => {
+  test('drainInbox returns each pending socket message once', async () => {
+    const path = socketPath('drain')
+    await startUdsMessaging(path, { isExplicit: true })
+    expect(process.env.CLAUDE_CODE_MESSAGING_TOKEN).toBeUndefined()
+
+    await waitForEnqueues(2, async () => {
+      await sendUdsMessage(path, { type: 'text', data: 'one' })
+      await sendUdsMessage(path, { type: 'text', data: 'two' })
+    })
+
+    const drained = drainInbox()
+    expect(drained.map(entry => entry.message.data)).toEqual(['one', 'two'])
+    expect(drained.every(entry => entry.status === 'processed')).toBe(true)
+    expect(drainInbox()).toEqual([])
+  })
+
+  test('inbox is capped when messages arrive faster than they are drained', async () => {
+    const path = socketPath('cap')
+    await startUdsMessaging(path, { isExplicit: true })
+
+    await waitForEnqueues(MAX_UDS_INBOX_ENTRIES, async () => {
+      for (let i = 0; i < MAX_UDS_INBOX_ENTRIES; i++) {
+        await sendUdsMessage(path, { type: 'text', data: String(i) })
+      }
+    })
+    await expect(
+      sendUdsMessage(path, { type: 'text', data: 'overflow' }),
+    ).rejects.toThrow('inbox full')
+
+    const drained = drainInbox()
+    expect(drained).toHaveLength(MAX_UDS_INBOX_ENTRIES)
+    expect(drained[0]?.message.data).toBe('0')
+    expect(drained.at(-1)?.message.data).toBe(String(MAX_UDS_INBOX_ENTRIES - 1))
+  })
+
+  test('inbox is capped by retained bytes before entry count', async () => {
+    const path = socketPath('byte-cap')
+    await startUdsMessaging(path, { isExplicit: true })
+
+    const payload = 'x'.repeat(32 * 1024)
+    let accepted = 0
+    for (;;) {
+      try {
+        await sendUdsMessage(path, { type: 'text', data: payload })
+        accepted++
+        if (accepted > MAX_UDS_INBOX_BYTES / payload.length + 20) {
+          throw new Error('byte cap was not enforced')
+        }
+      } catch (error) {
+        expect(error).toBeInstanceOf(Error)
+        expect((error as Error).message).toContain('inbox full')
+        break
+      }
+    }
+
+    const drained = drainInbox()
+    expect(drained.length).toBe(accepted)
+    expect(drained.length).toBeLessThan(MAX_UDS_INBOX_ENTRIES)
+  })
+
+  test('ping replies with pong without enqueueing inbox work', async () => {
+    const path = socketPath('ping')
+    await startUdsMessaging(path, { isExplicit: true })
+
+    await sendUdsMessage(path, { type: 'ping' })
+    expect(drainInbox()).toEqual([])
+  })
+
+  test('udsClient helpers authenticate through the capability file', async () => {
+    const path = socketPath('uds-client')
+    await startUdsMessaging(path, { isExplicit: true })
+    const { isPeerAlive, sendToUdsSocket } = await import('../udsClient.js')
+
+    expect(await isPeerAlive(path)).toBe(true)
+    await waitForEnqueues(1, async () => {
+      await sendToUdsSocket(path, 'hello from client')
+    })
+
+    const drained = drainInbox()
+    expect(drained).toHaveLength(1)
+    expect(drained[0]?.message.data).toBe('hello from client')
+    expect(drained[0]?.message.meta).toBeUndefined()
+  })
+
+  test('udsClient peer probe fails closed on oversized pong frames', async () => {
+    const path = socketPath('uds-client-oversized-pong')
+    if (process.platform !== 'win32') {
+      await mkdir(dirname(path), { recursive: true })
+    }
+    const receiver = createServer(socket => {
+      socket.on('data', () => {
+        socket.write('x'.repeat(MAX_UDS_FRAME_BYTES + 1))
+      })
+    })
+    await new Promise<void>((resolve, reject) => {
+      receiver.on('error', reject)
+      receiver.listen(path, () => resolve())
+    })
+
+    try {
+      const { isPeerAlive } = await import('../udsClient.js')
+      expect(await isPeerAlive(path, 3_000, 'test-token')).toBe(false)
+    } finally {
+      await closeServer(receiver)
+      if (process.platform !== 'win32') {
+        await unlink(path).catch(() => undefined)
+      }
+    }
+  })
+
+  test('udsClient send fails closed when no capability token exists', async () => {
+    const path = socketPath('uds-client-no-token')
+    const { sendToUdsSocket } = await import('../udsClient.js')
+
+    await expect(sendToUdsSocket(path, 'hello')).rejects.toThrow(
+      'No auth token found',
+    )
+  })
+
+  test('sendUdsMessage fails closed before connecting without an auth token', async () => {
+    await expect(
+      sendUdsMessage(socketPath('no-auth-token'), { type: 'text', data: 'x' }),
+    ).rejects.toThrow('without auth token')
+  })
+
+  test('drained entries never expose the UDS auth token', async () => {
+    const path = socketPath('strip-token')
+    await startUdsMessaging(path, { isExplicit: true })
+
+    await waitForEnqueues(1, async () => {
+      await sendUdsMessage(path, {
+        type: 'notification',
+        meta: { keep: 'visible' },
+      })
+    })
+
+    const drained = drainInbox()
+    expect(drained).toHaveLength(1)
+    expect(drained[0]?.message.meta).toEqual({ keep: 'visible' })
+    expect(drained[0]?.message.meta).not.toHaveProperty('authToken')
+  })
+
+  test('rejects unauthenticated socket messages', async () => {
+    const path = socketPath('auth')
+    await startUdsMessaging(path, { isExplicit: true })
+
+    const response = await new Promise<string>((resolve, reject) => {
+      let responseText = ''
+      const conn = createConnection(path, () => {
+        conn.write(`${JSON.stringify({ type: 'text', data: 'bad' })}\n`)
+      })
+      conn.setTimeout(5_000, () => {
+        conn.destroy()
+        reject(new Error('Timed out waiting for auth rejection'))
+      })
+      conn.on('data', chunk => {
+        const text = chunk.toString('utf-8')
+        if (text.includes('\n')) {
+          responseText = text
+        }
+      })
+      conn.on('close', () => resolve(responseText))
+      conn.on('error', reject)
+    })
+
+    expect(JSON.parse(response).type).toBe('error')
+    expect(drainInbox()).toEqual([])
+  })
+
+  test('disconnects malformed JSON clients without enqueueing inbox work', async () => {
+    const path = socketPath('malformed-client')
+    await startUdsMessaging(path, { isExplicit: true })
+
+    const response = await new Promise<string>((resolve, reject) => {
+      let responseText = ''
+      const conn = createConnection(path, () => {
+        conn.write('{not-json\n')
+      })
+      conn.setTimeout(5_000, () => {
+        conn.destroy()
+        reject(new Error('Timed out waiting for malformed frame close'))
+      })
+      conn.on('data', chunk => {
+        responseText += chunk.toString('utf-8')
+      })
+      conn.on('close', () => resolve(responseText))
+      conn.on('error', reject)
+    })
+
+    const parsed = JSON.parse(response)
+    expect(parsed.type).toBe('error')
+    expect(parsed.data).toBe('invalid frame')
+    expect(drainInbox()).toEqual([])
+  })
+
+  test('disconnects idle unauthenticated clients', async () => {
+    const path = socketPath('idle-client')
+    await startUdsMessaging(path, { isExplicit: true })
+
+    const response = await new Promise<string>((resolve, reject) => {
+      let responseText = ''
+      const conn = createConnection(path)
+      conn.setTimeout(UDS_AUTH_TIMEOUT_MS + 2_000, () => {
+        conn.destroy()
+        reject(new Error('Timed out waiting for auth timeout close'))
+      })
+      conn.on('data', chunk => {
+        responseText += chunk.toString('utf-8')
+      })
+      conn.on('close', () => resolve(responseText))
+      conn.on('error', reject)
+    })
+
+    const parsed = JSON.parse(response)
+    expect(parsed.type).toBe('error')
+    expect(parsed.data).toBe('authentication timeout')
+    expect(drainInbox()).toEqual([])
+  })
+
+  test('destroys oversized frames before enqueueing inbox work', async () => {
+    const path = socketPath('oversized')
+    await startUdsMessaging(path, { isExplicit: true })
+
+    await new Promise<void>((resolve, reject) => {
+      const conn = createConnection(path, () => {
+        conn.write('x'.repeat(MAX_UDS_FRAME_BYTES + 1))
+      })
+      conn.setTimeout(5_000, () => {
+        conn.destroy()
+        reject(new Error('Timed out waiting for oversized frame close'))
+      })
+      conn.on('close', () => resolve())
+      conn.on('error', () => resolve())
+    })
+
+    expect(drainInbox()).toEqual([])
+  })
+
+  test('default socket path is regenerated after stop', async () => {
+    const firstPath = getDefaultUdsSocketPath()
+    await startUdsMessaging(firstPath)
+    await stopUdsMessaging()
+
+    expect(getDefaultUdsSocketPath()).not.toBe(firstPath)
+  })
+
+  test('rejects oversized receiver responses before retaining them', async () => {
+    const path = socketPath('oversized-response')
+    if (process.platform !== 'win32') {
+      await mkdir(dirname(path), { recursive: true })
+    }
+    const receiver = createServer(socket => {
+      socket.on('data', () => {
+        socket.write('x'.repeat(MAX_UDS_FRAME_BYTES + 1))
+      })
+    })
+    await new Promise<void>((resolve, reject) => {
+      receiver.on('error', reject)
+      receiver.listen(path, () => resolve())
+    })
+
+    try {
+      await expect(
+        sendUdsMessage(
+          path,
+          { type: 'text', data: 'hello' },
+          { authToken: 'test-token' },
+        ),
+      ).rejects.toThrow('UDS response frame exceeded size limit')
+    } finally {
+      await closeServer(receiver)
+      if (process.platform !== 'win32') {
+        await unlink(path).catch(() => undefined)
+      }
+    }
+  })
+
+  test('rejects closed receiver responses without waiting for timeout', async () => {
+    const path = socketPath('closed-response')
+    if (process.platform !== 'win32') {
+      await mkdir(dirname(path), { recursive: true })
+    }
+    const receiver = createServer(socket => {
+      socket.end()
+    })
+    await new Promise<void>((resolve, reject) => {
+      receiver.on('error', reject)
+      receiver.listen(path, () => resolve())
+    })
+
+    try {
+      await expect(
+        sendUdsMessage(
+          path,
+          { type: 'text', data: 'hello' },
+          { authToken: 'test-token' },
+        ),
+      ).rejects.toThrow('before response')
+    } finally {
+      await closeServer(receiver)
+      if (process.platform !== 'win32') {
+        await unlink(path).catch(() => undefined)
+      }
+    }
+  })
+
+  test('rejects malformed receiver responses without waiting for timeout', async () => {
+    const path = socketPath('malformed-response')
+    if (process.platform !== 'win32') {
+      await mkdir(dirname(path), { recursive: true })
+    }
+    const receiver = createServer(socket => {
+      socket.on('data', () => {
+        socket.write('{not-json\n')
+      })
+    })
+    await new Promise<void>((resolve, reject) => {
+      receiver.on('error', reject)
+      receiver.listen(path, () => resolve())
+    })
+
+    try {
+      await expect(
+        sendUdsMessage(
+          path,
+          { type: 'text', data: 'hello' },
+          { authToken: 'test-token' },
+        ),
+      ).rejects.toThrow('Invalid UDS response frame')
+    } finally {
+      await closeServer(receiver)
+      if (process.platform !== 'win32') {
+        await unlink(path).catch(() => undefined)
+      }
+    }
+  })
+
+  test('rejects inline auth token UDS targets instead of parsing them', async () => {
+    const path = socketPath('inline-token')
+
+    expect(formatUdsAddress(path)).toBe(`uds:${path}`)
+
+    const targetWithToken = `${path}#token=secret`
+    expect(() => parseUdsTarget(targetWithToken)).toThrow('inline auth token')
+    try {
+      parseUdsTarget(targetWithToken)
+    } catch (error) {
+      expect((error as Error).message).not.toContain('secret')
+    }
+
+    const { sendToUdsSocket } = await import('../udsClient.js')
+    await expect(sendToUdsSocket(targetWithToken, 'hello')).rejects.toThrow(
+      'inline auth token',
+    )
+  })
+
+  test('fails closed and cleans temp files when capability target is occupied', async () => {
+    const path = socketPath('capability-target-dir')
+    const capabilityDir = join(tempConfigDir, 'messaging-capabilities')
+    const capabilityName = `${createHash('sha256').update(path).digest('hex')}.json`
+    await mkdir(join(capabilityDir, capabilityName), {
+      recursive: true,
+      mode: 0o700,
+    })
+
+    await expect(
+      startUdsMessaging(path, { isExplicit: true }),
+    ).rejects.toThrow()
+
+    expect(process.env.CLAUDE_CODE_MESSAGING_SOCKET).toBeUndefined()
+    expect(await readdir(capabilityDir)).toEqual([capabilityName])
+  })
+
+  if (process.platform !== 'win32') {
+    test('creates the listening socket with owner-only permissions', async () => {
+      const path = socketPath('socket-mode')
+      await startUdsMessaging(path, { isExplicit: true })
+
+      const mode = (await stat(path)).mode & 0o777
+      expect(mode).toBe(0o600)
+    })
+
+    test('fails closed when the capability directory is not private', async () => {
+      const previousConfigDir = process.env.CLAUDE_CONFIG_DIR
+      const tempHome = join(
+        tmpdir(),
+        `uds-capability-${process.pid}-${Date.now()}-${Math.random().toString(16).slice(2)}`,
+      )
+      process.env.CLAUDE_CONFIG_DIR = tempHome
+      const capabilityDir = join(tempHome, 'messaging-capabilities')
+      await mkdir(capabilityDir, { recursive: true, mode: 0o755 })
+      await chmod(capabilityDir, 0o755)
+
+      try {
+        const path = socketPath('broad-capdir')
+        await expect(
+          startUdsMessaging(path, { isExplicit: true }),
+        ).rejects.toThrow('permissions are too broad')
+        await expect(stat(path)).rejects.toThrow()
+      } finally {
+        if (previousConfigDir === undefined) {
+          delete process.env.CLAUDE_CONFIG_DIR
+        } else {
+          process.env.CLAUDE_CONFIG_DIR = previousConfigDir
+        }
+        await rm(tempHome, { recursive: true, force: true })
+      }
+    })
+
+    test('fails closed when the capability directory is a symlink', async () => {
+      const previousConfigDir = process.env.CLAUDE_CONFIG_DIR
+      const tempHome = join(
+        tmpdir(),
+        `uds-capability-link-${process.pid}-${Date.now()}-${Math.random().toString(16).slice(2)}`,
+      )
+      const target = join(tempHome, 'target')
+      process.env.CLAUDE_CONFIG_DIR = tempHome
+      await mkdir(target, { recursive: true, mode: 0o700 })
+      await symlink(target, join(tempHome, 'messaging-capabilities'), 'dir')
+
+      try {
+        await expect(
+          startUdsMessaging(socketPath('symlink-capdir'), { isExplicit: true }),
+        ).rejects.toThrow('not a private directory')
+      } finally {
+        if (previousConfigDir === undefined) {
+          delete process.env.CLAUDE_CONFIG_DIR
+        } else {
+          process.env.CLAUDE_CONFIG_DIR = previousConfigDir
+        }
+        await rm(tempHome, { recursive: true, force: true })
+      }
+    })
+
+    test('fails closed when an explicit socket parent is not private', async () => {
+      const parent = join(
+        tmpdir(),
+        `uds-socket-parent-${process.pid}-${Date.now()}-${Math.random().toString(16).slice(2)}`,
+      )
+      await mkdir(parent, { recursive: true, mode: 0o755 })
+      await chmod(parent, 0o755)
+
+      try {
+        await expect(
+          startUdsMessaging(join(parent, 'messaging.sock'), {
+            isExplicit: true,
+          }),
+        ).rejects.toThrow('socket parent permissions are too broad')
+      } finally {
+        await rm(parent, { recursive: true, force: true })
+      }
+    })
+
+    test('fails closed when an explicit socket parent is a file', async () => {
+      const parentFile = join(
+        tmpdir(),
+        `uds-socket-parent-file-${process.pid}-${Date.now()}-${Math.random().toString(16).slice(2)}`,
+      )
+      await writeFile(parentFile, 'not a directory', 'utf-8')
+
+      try {
+        await expect(
+          startUdsMessaging(join(parentFile, 'messaging.sock'), {
+            isExplicit: true,
+          }),
+        ).rejects.toThrow('socket parent is not a directory')
+      } finally {
+        await rm(parentFile, { force: true })
+      }
+    })
+
+    test('stop tolerates an already removed socket path', async () => {
+      const path = socketPath('already-removed')
+      await startUdsMessaging(path, { isExplicit: true })
+      await unlink(path)
+
+      await stopUdsMessaging()
+
+      expect(process.env.CLAUDE_CODE_MESSAGING_SOCKET).toBeUndefined()
+    })
+
+    test('rejects clients over the configured connection cap', async () => {
+      const path = socketPath('client-cap')
+      await startUdsMessaging(path, { isExplicit: true })
+      const sockets: ReturnType<typeof createConnection>[] = []
+
+      try {
+        for (let i = 0; i < MAX_UDS_CLIENTS; i++) {
+          const socket = await new Promise<ReturnType<typeof createConnection>>(
+            (resolve, reject) => {
+              const conn = createConnection(path, () => resolve(conn))
+              conn.on('error', reject)
+            },
+          )
+          sockets.push(socket)
+        }
+
+        await new Promise<void>((resolve, reject) => {
+          const extra = createConnection(path)
+          extra.on('close', () => resolve())
+          extra.on('error', reject)
+          extra.setTimeout(5_000, () => {
+            extra.destroy()
+            reject(new Error('Timed out waiting for client cap close'))
+          })
+        })
+      } finally {
+        for (const socket of sockets) {
+          socket.destroy()
+        }
+      }
+    })
+  }
+})
diff --git a/src/utils/__tests__/udsResponseReader.test.ts b/src/utils/__tests__/udsResponseReader.test.ts
new file mode 100644
index 000000000..71203da62
--- /dev/null
+++ b/src/utils/__tests__/udsResponseReader.test.ts
@@ -0,0 +1,171 @@
+import { describe, expect, test } from 'bun:test'
+import { EventEmitter } from 'node:events'
+import type { Socket } from 'node:net'
+import { attachUdsResponseReader } from '../udsResponseReader.js'
+
+class FakeSocket extends EventEmitter {
+  destroyed = false
+  ended = false
+
+  destroy(): this {
+    this.destroyed = true
+    this.emit('close', true)
+    return this
+  }
+
+  end(): this {
+    this.ended = true
+    this.emit('close', false)
+    return this
+  }
+
+  emitData(chunk: Buffer): void {
+    this.emit('data', chunk)
+  }
+}
+
+function asSocket(socket: FakeSocket): Socket {
+  return socket as unknown as Socket
+}
+
+describe('attachUdsResponseReader', () => {
+  test('tracks byte limits across split multibyte response chunks', () => {
+    const socket = new FakeSocket()
+    let settled = false
+    let settledError: Error | undefined
+
+    attachUdsResponseReader(asSocket(socket), {
+      maxFrameBytes: 128,
+      onSettled: error => {
+        settled = true
+        settledError = error
+      },
+    })
+
+    const multibyte = String.fromCodePoint(0x20ac)
+    const frame = Buffer.from(
+      JSON.stringify({ type: 'response', data: `ok ${multibyte}` }) + '\n',
+      'utf8',
+    )
+    const multibyteStart = frame.indexOf(Buffer.from(multibyte, 'utf8')[0])
+
+    socket.emitData(frame.subarray(0, multibyteStart + 1))
+    expect(settled).toBe(false)
+
+    socket.emitData(frame.subarray(multibyteStart + 1))
+    expect(settled).toBe(true)
+    expect(settledError).toBeUndefined()
+    expect(socket.ended).toBe(true)
+  })
+
+  test('rejects malformed response frames immediately', () => {
+    const socket = new FakeSocket()
+    let settledError: Error | undefined
+
+    attachUdsResponseReader(asSocket(socket), {
+      maxFrameBytes: 128,
+      onSettled: error => {
+        settledError = error
+      },
+    })
+
+    socket.emitData(Buffer.from('{bad-json}\n'))
+
+    expect(settledError?.message).toBe('Invalid UDS response frame')
+    expect(socket.destroyed).toBe(true)
+  })
+
+  test('skips blank frames before a valid response', () => {
+    const socket = new FakeSocket()
+    let settled = false
+    let settledError: Error | undefined
+
+    attachUdsResponseReader(asSocket(socket), {
+      maxFrameBytes: 128,
+      onSettled: error => {
+        settled = true
+        settledError = error
+      },
+    })
+
+    socket.emitData(Buffer.from('\n \n'))
+    expect(settled).toBe(false)
+
+    socket.emitData(Buffer.from(`${JSON.stringify({ type: 'response' })}\n`))
+    expect(settled).toBe(true)
+    expect(settledError).toBeUndefined()
+    expect(socket.ended).toBe(true)
+  })
+
+  test('rejects receiver error frames', () => {
+    const socket = new FakeSocket()
+    let settledError: Error | undefined
+
+    attachUdsResponseReader(asSocket(socket), {
+      maxFrameBytes: 128,
+      onSettled: error => {
+        settledError = error
+      },
+    })
+
+    socket.emitData(
+      Buffer.from(`${JSON.stringify({ type: 'error', data: 'denied' })}\n`),
+    )
+
+    expect(settledError?.message).toBe('denied')
+    expect(socket.destroyed).toBe(true)
+  })
+
+  test('uses custom socket error formatting', () => {
+    const socket = new FakeSocket()
+    let settledError: Error | undefined
+
+    attachUdsResponseReader(asSocket(socket), {
+      maxFrameBytes: 128,
+      onSettled: error => {
+        settledError = error
+      },
+      formatSocketError: error =>
+        new Error(`wrapped:${(error as Error).message}`),
+    })
+
+    socket.emit('error', new Error('connect failed'))
+
+    expect(settledError?.message).toBe('wrapped:connect failed')
+    expect(socket.destroyed).toBe(true)
+  })
+
+  test('rejects socket end before response', () => {
+    const socket = new FakeSocket()
+    let settledError: Error | undefined
+
+    attachUdsResponseReader(asSocket(socket), {
+      maxFrameBytes: 128,
+      onSettled: error => {
+        settledError = error
+      },
+    })
+
+    socket.emit('end')
+
+    expect(settledError?.message).toBe('UDS socket ended before response')
+    expect(socket.destroyed).toBe(true)
+  })
+
+  test('rejects clean socket close before response', () => {
+    const socket = new FakeSocket()
+    let settledError: Error | undefined
+
+    attachUdsResponseReader(asSocket(socket), {
+      maxFrameBytes: 128,
+      onSettled: error => {
+        settledError = error
+      },
+    })
+
+    socket.emit('close', false)
+
+    expect(settledError?.message).toBe('UDS socket closed before response')
+    expect(socket.destroyed).toBe(true)
+  })
+})
diff --git a/src/utils/ndjsonFramer.ts b/src/utils/ndjsonFramer.ts
index 968ee5217..69717fc11 100644
--- a/src/utils/ndjsonFramer.ts
+++ b/src/utils/ndjsonFramer.ts
@@ -7,9 +7,18 @@
  */
 import type { Socket } from 'net'
 
+export type NdjsonFramerOptions = {
+  maxFrameBytes?: number
+  onFrameError?: (error: Error) => void
+  destroyOnFrameError?: boolean
+  onInvalidFrame?: (error: Error) => void
+  destroyOnInvalidFrame?: boolean
+}
+
 /**
  * Attach an NDJSON framer to a socket. Calls `onMessage` for each
- * complete JSON line received. Malformed lines are silently skipped.
+ * complete JSON line received. Malformed lines are skipped by default;
+ * callers may opt into error callbacks or socket destruction.
  *
  * @param parse - Optional custom JSON parser (defaults to JSON.parse).
  *                Useful when the caller uses a wrapped parser like jsonParse
@@ -19,21 +28,73 @@ export function attachNdjsonFramer<T = unknown>(
   socket: Socket,
   onMessage: (msg: T) => void,
   parse: (text: string) => T = text => JSON.parse(text) as T,
+  options: NdjsonFramerOptions = {},
 ): void {
   let buffer = ''
+  let bufferBytes = 0
+  const maxFrameBytes = options.maxFrameBytes ?? Number.POSITIVE_INFINITY
+
+  const rejectOversizedFrame = (bytes: number): void => {
+    const error = new Error(
+      `NDJSON frame exceeded ${maxFrameBytes} bytes (${bytes})`,
+    )
+    options.onFrameError?.(error)
+    if (options.destroyOnFrameError ?? true) {
+      socket.destroy(error)
+    }
+  }
+
+  const rejectInvalidFrame = (error: unknown): void => {
+    const frameError =
+      error instanceof Error ? error : new Error('Invalid NDJSON frame')
+    options.onInvalidFrame?.(frameError)
+    if (options.destroyOnInvalidFrame ?? false) {
+      socket.destroy(frameError)
+    }
+  }
+
+  const emitLine = (line: string): void => {
+    if (!line.trim()) return
+    try {
+      onMessage(parse(line))
+    } catch (error) {
+      rejectInvalidFrame(error)
+    }
+  }
 
   socket.on('data', (chunk: Buffer) => {
-    buffer += chunk.toString()
-    const lines = buffer.split('\n')
-    buffer = lines.pop() ?? ''
-
-    for (const line of lines) {
-      if (!line.trim()) continue
-      try {
-        onMessage(parse(line))
-      } catch {
-        // Malformed JSON — skip
+    let start = 0
+    for (let index = 0; index < chunk.length; index++) {
+      if (chunk[index] !== 0x0a) continue
+
+      const segmentBytes = index - start
+      if (
+        Number.isFinite(maxFrameBytes) &&
+        bufferBytes + segmentBytes > maxFrameBytes
+      ) {
+        rejectOversizedFrame(bufferBytes + segmentBytes)
+        return
       }
+
+      buffer += chunk.subarray(start, index).toString('utf8')
+      emitLine(buffer)
+      buffer = ''
+      bufferBytes = 0
+      start = index + 1
+    }
+
+    const tailBytes = chunk.length - start
+    if (
+      Number.isFinite(maxFrameBytes) &&
+      bufferBytes + tailBytes > maxFrameBytes
+    ) {
+      rejectOversizedFrame(bufferBytes + tailBytes)
+      return
+    }
+
+    if (tailBytes > 0) {
+      buffer += chunk.subarray(start).toString('utf8')
+      bufferBytes += tailBytes
     }
   })
 }
diff --git a/src/utils/swarm/inProcessRunner.ts b/src/utils/swarm/inProcessRunner.ts
index 1735500b4..06fde705a 100644
--- a/src/utils/swarm/inProcessRunner.ts
+++ b/src/utils/swarm/inProcessRunner.ts
@@ -97,7 +97,7 @@ import {
   getLastPeerDmSummary,
   isPermissionResponse,
   isShutdownRequest,
-  markMessageAsReadByIndex,
+  markMessageAsReadByIdentity,
   readMailbox,
   writeToMailbox,
 } from '../teammateMailbox.js'
@@ -405,10 +405,10 @@ function createInProcessCanUseTool(
             if (msg && !msg.read) {
               const parsed = isPermissionResponse(msg.text)
               if (parsed && parsed.request_id === request.id) {
-                await markMessageAsReadByIndex(
+                await markMessageAsReadByIdentity(
                   identity.agentName,
                   identity.teamName,
-                  i,
+                  msg,
                 )
                 if (parsed.subtype === 'success') {
                   processMailboxPermissionResponse({
@@ -801,10 +801,10 @@ async function waitForNextPromptOrShutdown(
         logForDebugging(
           `[inProcessRunner] ${identity.agentName} received shutdown request from ${shutdownParsed?.from} (prioritized over ${skippedUnread} unread messages)`,
         )
-        await markMessageAsReadByIndex(
+        await markMessageAsReadByIdentity(
           identity.agentName,
           identity.teamName,
-          shutdownIndex,
+          msg,
         )
         return {
           type: 'shutdown_request',
@@ -839,10 +839,10 @@ async function waitForNextPromptOrShutdown(
           logForDebugging(
             `[inProcessRunner] ${identity.agentName} received new message from ${msg.from} (index ${selectedIndex})`,
           )
-          await markMessageAsReadByIndex(
+          await markMessageAsReadByIdentity(
             identity.agentName,
             identity.teamName,
-            selectedIndex,
+            msg,
           )
           return {
             type: 'new_message',
diff --git a/src/utils/teammateMailbox.ts b/src/utils/teammateMailbox.ts
index eb72fcc21..ad9b22f93 100644
--- a/src/utils/teammateMailbox.ts
+++ b/src/utils/teammateMailbox.ts
@@ -7,7 +7,8 @@
  * Note: Inboxes are keyed by agent name within a team.
  */
 
-import { mkdir, readFile, writeFile } from 'fs/promises'
+import { randomBytes } from 'crypto'
+import { mkdir, readFile, rename, stat, unlink, writeFile } from 'fs/promises'
 import { join } from 'path'
 import { z } from 'zod/v4'
 import { TEAMMATE_MESSAGE_TAG } from '../constants/xml.js'
@@ -40,6 +41,13 @@ const LOCK_OPTIONS = {
   },
 }
 
+export const MAX_MAILBOX_MESSAGES = 1_000
+export const MAX_READ_MAILBOX_MESSAGES = 200
+export const MAX_UNREAD_PROTOCOL_MAILBOX_MESSAGES = 2_000
+export const MAX_MAILBOX_MESSAGE_TEXT_BYTES = 64 * 1024
+export const MAX_MAILBOX_RETAINED_BYTES = 2 * 1024 * 1024
+export const MAX_MAILBOX_FILE_BYTES = 4 * 1024 * 1024
+
 export type TeammateMessage = {
   from: string
   text: string
@@ -49,6 +57,223 @@ export type TeammateMessage = {
   summary?: string // 5-10 word summary shown as preview in the UI
 }
 
+function isJsonLikeMessage(text: string): boolean {
+  const trimmed = text.trimStart()
+  return trimmed.startsWith('{') || trimmed.startsWith('[')
+}
+
+function shouldRetainUnreadAsProtocolMessage(
+  message: TeammateMessage,
+): boolean {
+  if (message.read) return false
+  if (isStructuredProtocolMessage(message.text)) return true
+  if (!isJsonLikeMessage(message.text)) return false
+
+  try {
+    const parsed = jsonParse(message.text)
+    return Boolean(
+      parsed &&
+        typeof parsed === 'object' &&
+        'type' in (parsed as Record<string, unknown>),
+    )
+  } catch {
+    return false
+  }
+}
+
+function sameMailboxMessage(a: TeammateMessage, b: TeammateMessage): boolean {
+  return a.from === b.from && a.timestamp === b.timestamp && a.text === b.text
+}
+
+function mailboxMessageStorageBytes(message: TeammateMessage): number {
+  return Buffer.byteLength(jsonStringify(message), 'utf8')
+}
+
+function assertMailboxMessageSize(message: TeammateMessage): void {
+  const textBytes = Buffer.byteLength(message.text, 'utf8')
+  if (textBytes > MAX_MAILBOX_MESSAGE_TEXT_BYTES) {
+    throw new Error(
+      `Mailbox message text exceeds ${MAX_MAILBOX_MESSAGE_TEXT_BYTES} bytes`,
+    )
+  }
+}
+
+function toMailboxMessage(value: unknown): TeammateMessage {
+  if (!value || typeof value !== 'object') {
+    throw new Error('Invalid mailbox message: expected object')
+  }
+  const record = value as Record<string, unknown>
+  if (
+    typeof record.from !== 'string' ||
+    typeof record.text !== 'string' ||
+    typeof record.timestamp !== 'string' ||
+    typeof record.read !== 'boolean'
+  ) {
+    throw new Error('Invalid mailbox message shape')
+  }
+  const message: TeammateMessage = {
+    from: record.from,
+    text: record.text,
+    timestamp: record.timestamp,
+    read: record.read,
+    ...(typeof record.color === 'string' ? { color: record.color } : {}),
+    ...(typeof record.summary === 'string' ? { summary: record.summary } : {}),
+  }
+  assertMailboxMessageSize(message)
+  return message
+}
+
+function parseMailboxMessages(content: string): TeammateMessage[] {
+  const parsed = jsonParse(content)
+  if (!Array.isArray(parsed)) {
+    throw new Error('Invalid mailbox file: expected message array')
+  }
+  return parsed.map(toMailboxMessage)
+}
+
+async function readMailboxFile(inboxPath: string): Promise<string> {
+  const info = await stat(inboxPath)
+  if (info.size > MAX_MAILBOX_FILE_BYTES) {
+    throw new Error(
+      `Mailbox file exceeds ${MAX_MAILBOX_FILE_BYTES} bytes: ${inboxPath}`,
+    )
+  }
+  return readFile(inboxPath, 'utf-8')
+}
+
+async function readMailboxForMutation(
+  agentName: string,
+  teamName?: string,
+): Promise<TeammateMessage[]> {
+  const inboxPath = getInboxPath(agentName, teamName)
+  return parseMailboxMessages(await readMailboxFile(inboxPath))
+}
+
+async function writeMailboxAtomic(
+  inboxPath: string,
+  content: string,
+): Promise<void> {
+  const bytes = Buffer.byteLength(content, 'utf8')
+  if (bytes > MAX_MAILBOX_FILE_BYTES) {
+    throw new Error(
+      `Compacted mailbox still exceeds ${MAX_MAILBOX_FILE_BYTES} bytes`,
+    )
+  }
+  const tempPath = `${inboxPath}.${process.pid}.${randomBytes(8).toString('hex')}.tmp`
+  try {
+    await writeFile(tempPath, content, 'utf-8')
+    await rename(tempPath, inboxPath)
+  } catch (error) {
+    await unlink(tempPath).catch(() => undefined)
+    throw error
+  }
+}
+
+export function compactMailboxMessages(
+  messages: TeammateMessage[],
+  limits: {
+    maxMessages?: number
+    maxReadMessages?: number
+    maxUnreadProtocolMessages?: number
+    maxRetainedBytes?: number
+  } = {},
+): TeammateMessage[] {
+  const maxMessages = limits.maxMessages ?? MAX_MAILBOX_MESSAGES
+  const maxReadMessages = limits.maxReadMessages ?? MAX_READ_MAILBOX_MESSAGES
+  const maxUnreadProtocolMessages =
+    limits.maxUnreadProtocolMessages ?? MAX_UNREAD_PROTOCOL_MAILBOX_MESSAGES
+  const maxRetainedBytes = limits.maxRetainedBytes ?? MAX_MAILBOX_RETAINED_BYTES
+
+  if (
+    maxRetainedBytes <= 0 ||
+    (maxMessages <= 0 && maxUnreadProtocolMessages <= 0)
+  ) {
+    return []
+  }
+
+  const keepIndexes = new Set<number>()
+  let retainedBytes = 0
+  let keptUnreadProtocolMessages = 0
+  const tryKeep = (index: number): boolean => {
+    if (keepIndexes.has(index)) return true
+    const message = messages[index]
+    if (!message) return false
+    const bytes = mailboxMessageStorageBytes(message)
+    if (bytes > maxRetainedBytes || retainedBytes + bytes > maxRetainedBytes) {
+      return false
+    }
+    keepIndexes.add(index)
+    retainedBytes += bytes
+    return true
+  }
+
+  for (let i = messages.length - 1; i >= 0; i--) {
+    const message = messages[i]
+    if (!message || !shouldRetainUnreadAsProtocolMessage(message)) continue
+    if (keptUnreadProtocolMessages >= maxUnreadProtocolMessages) continue
+    if (tryKeep(i)) keptUnreadProtocolMessages++
+  }
+
+  let keptNonProtocolMessages = 0
+  for (let i = messages.length - 1; i >= 0; i--) {
+    if (keptNonProtocolMessages >= maxMessages) break
+    const message = messages[i]
+    if (
+      message &&
+      !message.read &&
+      !shouldRetainUnreadAsProtocolMessage(message)
+    ) {
+      if (tryKeep(i)) keptNonProtocolMessages++
+    }
+  }
+
+  let keptReadMessages = 0
+  for (let i = messages.length - 1; i >= 0; i--) {
+    if (keptNonProtocolMessages >= maxMessages) break
+    if (keptReadMessages >= maxReadMessages) break
+    const message = messages[i]
+    if (message?.read) {
+      if (tryKeep(i)) {
+        keptReadMessages++
+        keptNonProtocolMessages++
+      }
+    }
+  }
+
+  return messages.filter((_message, index) => keepIndexes.has(index))
+}
+
+function logUnreadMailboxEvictions(
+  original: TeammateMessage[],
+  compacted: TeammateMessage[],
+  context: string,
+): void {
+  const kept = new Set(compacted)
+  const unreadEvicted = original.filter(message => {
+    return !message.read && !kept.has(message)
+  })
+  if (unreadEvicted.length === 0) return
+
+  const protocolEvicted = count(unreadEvicted, message =>
+    shouldRetainUnreadAsProtocolMessage(message),
+  )
+  logError(
+    new Error(
+      `[TeammateMailbox] Compacted ${unreadEvicted.length} unread message(s) in ${context}; protocol_or_unknown=${protocolEvicted}`,
+    ),
+  )
+}
+
+async function writeCompactedMailbox(
+  inboxPath: string,
+  messages: TeammateMessage[],
+  context: string,
+): Promise<void> {
+  const compacted = compactMailboxMessages(messages)
+  logUnreadMailboxEvictions(messages, compacted, context)
+  await writeMailboxAtomic(inboxPath, jsonStringify(compacted, null, 2))
+}
+
 /**
  * Get the path to a teammate's inbox file
  * Structure: ~/.claude/teams/{team_name}/inboxes/{agent_name}.json
@@ -89,8 +314,7 @@ export async function readMailbox(
   logForDebugging(`[TeammateMailbox] readMailbox: path=${inboxPath}`)
 
   try {
-    const content = await readFile(inboxPath, 'utf-8')
-    const messages = jsonParse(content) as TeammateMessage[]
+    const messages = parseMailboxMessages(await readMailboxFile(inboxPath))
     logForDebugging(
       `[TeammateMailbox] readMailbox: read ${messages.length} message(s)`,
     )
@@ -103,7 +327,7 @@ export async function readMailbox(
     }
     logForDebugging(`Failed to read inbox for ${agentName}: ${error}`)
     logError(error)
-    return []
+    throw error
   }
 }
 
@@ -156,7 +380,7 @@ export async function writeToMailbox(
         `[TeammateMailbox] writeToMailbox: failed to create inbox file: ${error}`,
       )
       logError(error)
-      return
+      throw error
     }
   }
 
@@ -168,22 +392,23 @@ export async function writeToMailbox(
     })
 
     // Re-read messages after acquiring lock to get the latest state
-    const messages = await readMailbox(recipientName, teamName)
+    const messages = await readMailboxForMutation(recipientName, teamName)
 
-    const newMessage: TeammateMessage = {
+    const newMessage = toMailboxMessage({
       ...message,
       read: false,
-    }
+    })
 
     messages.push(newMessage)
 
-    await writeFile(inboxPath, jsonStringify(messages, null, 2), 'utf-8')
+    await writeCompactedMailbox(inboxPath, messages, 'writeToMailbox')
     logForDebugging(
       `[TeammateMailbox] Wrote message to ${recipientName}'s inbox from ${message.from}`,
     )
   } catch (error) {
     logForDebugging(`Failed to write to inbox for ${recipientName}: ${error}`)
     logError(error)
+    throw error
   } finally {
     if (release) {
       await release()
@@ -222,7 +447,7 @@ export async function markMessageAsReadByIndex(
     logForDebugging(`[TeammateMailbox] markMessageAsReadByIndex: lock acquired`)
 
     // Re-read messages after acquiring lock to get the latest state
-    const messages = await readMailbox(agentName, teamName)
+    const messages = await readMailboxForMutation(agentName, teamName)
     logForDebugging(
       `[TeammateMailbox] markMessageAsReadByIndex: read ${messages.length} messages after lock`,
     )
@@ -244,7 +469,7 @@ export async function markMessageAsReadByIndex(
 
     messages[messageIndex] = { ...message, read: true }
 
-    await writeFile(inboxPath, jsonStringify(messages, null, 2), 'utf-8')
+    await writeCompactedMailbox(inboxPath, messages, 'markMessageAsReadByIndex')
     logForDebugging(
       `[TeammateMailbox] markMessageAsReadByIndex: marked message at index ${messageIndex} as read`,
     )
@@ -270,6 +495,46 @@ export async function markMessageAsReadByIndex(
   }
 }
 
+export async function markMessageAsReadByIdentity(
+  agentName: string,
+  teamName: string | undefined,
+  expectedMessage: TeammateMessage,
+): Promise<boolean> {
+  const inboxPath = getInboxPath(agentName, teamName)
+  const lockFilePath = `${inboxPath}.lock`
+
+  let release: (() => Promise<void>) | undefined
+  try {
+    release = await lockfile.lock(inboxPath, {
+      lockfilePath: lockFilePath,
+      ...LOCK_OPTIONS,
+    })
+
+    const messages = await readMailboxForMutation(agentName, teamName)
+    const messageIndex = messages.findIndex(message => {
+      return !message.read && sameMailboxMessage(message, expectedMessage)
+    })
+    if (messageIndex < 0) return false
+
+    messages[messageIndex] = { ...messages[messageIndex]!, read: true }
+    await writeCompactedMailbox(
+      inboxPath,
+      messages,
+      'markMessageAsReadByIdentity',
+    )
+    return true
+  } catch (error) {
+    const code = getErrnoCode(error)
+    if (code === 'ENOENT') return false
+    logError(error)
+    return false
+  } finally {
+    if (release) {
+      await release()
+    }
+  }
+}
+
 /**
  * Mark all messages in a teammate's inbox as read
  * Uses file locking to prevent race conditions
@@ -297,7 +562,7 @@ export async function markMessagesAsRead(
     logForDebugging(`[TeammateMailbox] markMessagesAsRead: lock acquired`)
 
     // Re-read messages after acquiring lock to get the latest state
-    const messages = await readMailbox(agentName, teamName)
+    const messages = await readMailboxForMutation(agentName, teamName)
     logForDebugging(
       `[TeammateMailbox] markMessagesAsRead: read ${messages.length} messages after lock`,
     )
@@ -317,7 +582,7 @@ export async function markMessagesAsRead(
     // messages comes from jsonParse — fresh, unshared objects safe to mutate
     for (const m of messages) m.read = true
 
-    await writeFile(inboxPath, jsonStringify(messages, null, 2), 'utf-8')
+    await writeCompactedMailbox(inboxPath, messages, 'markMessagesAsRead')
     logForDebugging(
       `[TeammateMailbox] markMessagesAsRead: WROTE ${unreadCount} message(s) as read to ${inboxPath}`,
     )
@@ -1114,7 +1379,7 @@ export async function markMessagesAsReadByPredicate(
       ...LOCK_OPTIONS,
     })
 
-    const messages = await readMailbox(agentName, teamName)
+    const messages = await readMailboxForMutation(agentName, teamName)
     if (messages.length === 0) {
       return
     }
@@ -1123,7 +1388,11 @@ export async function markMessagesAsReadByPredicate(
       !m.read && predicate(m) ? { ...m, read: true } : m,
     )
 
-    await writeFile(inboxPath, jsonStringify(updatedMessages, null, 2), 'utf-8')
+    await writeCompactedMailbox(
+      inboxPath,
+      updatedMessages,
+      'markMessagesAsReadByPredicate',
+    )
   } catch (error) {
     const code = getErrnoCode(error)
     if (code === 'ENOENT') {
@@ -1161,7 +1430,12 @@ export function getLastPeerDmSummary(messages: Message[]): string | undefined {
     if (!Array.isArray(content)) continue
     for (const block of content) {
       if (typeof block === 'string') continue
-      const b = block as unknown as { type: string; name?: string; input?: Record<string, unknown>; [key: string]: unknown }
+      const b = block as unknown as {
+        type: string
+        name?: string
+        input?: Record<string, unknown>
+        [key: string]: unknown
+      }
       if (
         b.type === 'tool_use' &&
         b.name === SEND_MESSAGE_TOOL_NAME &&
@@ -1177,7 +1451,7 @@ export function getLastPeerDmSummary(messages: Message[]): string | undefined {
         const to = b.input.to as string
         const summary =
           'summary' in b.input && typeof b.input.summary === 'string'
-            ? b.input.summary as string
+            ? (b.input.summary as string)
             : (b.input.message as string).slice(0, 80)
         return `[to ${to}] ${summary}`
       }
diff --git a/src/utils/udsClient.ts b/src/utils/udsClient.ts
index 781f3ddd1..e33ef3fdb 100644
--- a/src/utils/udsClient.ts
+++ b/src/utils/udsClient.ts
@@ -16,7 +16,8 @@ import { errorMessage, isFsInaccessible } from './errors.js'
 import { isProcessRunning } from './genericProcessUtils.js'
 import { jsonParse, jsonStringify } from './slowOperations.js'
 import type { SessionKind } from './concurrentSessions.js'
-import type { UdsMessage } from './udsMessaging.js'
+import { MAX_UDS_FRAME_BYTES, type UdsMessage } from './udsMessaging.js'
+import { attachUdsResponseReader, getChunkBytes } from './udsResponseReader.js'
 
 // ---------------------------------------------------------------------------
 // Types
@@ -104,9 +105,14 @@ export async function listAllLiveSessions(): Promise<PeerSession[]> {
  */
 export async function listPeers(): Promise<PeerSession[]> {
   const all = await listAllLiveSessions()
-  return all.filter(
-    s => s.pid !== process.pid && s.messagingSocketPath != null,
-  )
+  return all.filter(s => s.pid !== process.pid && s.messagingSocketPath != null)
+}
+
+async function findAuthTokenForSocketPath(
+  socketPath: string,
+): Promise<string | undefined> {
+  const { readUdsCapabilityToken } = await import('./udsMessaging.js')
+  return readUdsCapabilityToken(socketPath)
 }
 
 // ---------------------------------------------------------------------------
@@ -117,10 +123,21 @@ export async function listPeers(): Promise<PeerSession[]> {
  * Probe a UDS socket to check if a server is listening (ping/pong).
  * Returns true if the peer responds within the timeout.
  */
-export async function isPeerAlive(socketPath: string, timeoutMs = 3000): Promise<boolean> {
-  return new Promise<boolean>((resolve) => {
+export async function isPeerAlive(
+  socketPath: string,
+  timeoutMs = 3000,
+  authToken?: string,
+): Promise<boolean> {
+  const token = authToken ?? (await findAuthTokenForSocketPath(socketPath))
+  if (!token) return false
+
+  return new Promise<boolean>(resolve => {
     const conn = createConnection(socketPath, () => {
-      const ping: UdsMessage = { type: 'ping', ts: new Date().toISOString() }
+      const ping: UdsMessage = {
+        type: 'ping',
+        ts: new Date().toISOString(),
+        meta: { authToken: token },
+      }
       conn.write(jsonStringify(ping) + '\n')
     })
 
@@ -135,7 +152,19 @@ export async function isPeerAlive(socketPath: string, timeoutMs = 3000): Promise
     }, timeoutMs)
 
     let buffer = ''
-    conn.on('data', (chunk) => {
+    conn.on('data', chunk => {
+      if (
+        Buffer.byteLength(buffer, 'utf8') + getChunkBytes(chunk) >
+        MAX_UDS_FRAME_BYTES
+      ) {
+        if (!resolved) {
+          resolved = true
+          clearTimeout(timer)
+          conn.destroy()
+          resolve(false)
+        }
+        return
+      }
       buffer += chunk.toString()
       if (buffer.includes('"pong"')) {
         if (!resolved) {
@@ -165,6 +194,13 @@ export async function sendToUdsSocket(
   targetSocketPath: string,
   message: string | Record<string, unknown>,
 ): Promise<void> {
+  const { parseUdsTarget } = await import('./udsMessaging.js')
+  const target = parseUdsTarget(targetSocketPath)
+  const authToken = await findAuthTokenForSocketPath(target.socketPath)
+  if (!authToken) {
+    throw new Error(`No auth token found for peer at ${target.socketPath}`)
+  }
+
   const data = typeof message === 'string' ? message : jsonStringify(message)
   const udsMsg: UdsMessage = {
     type: 'text',
@@ -177,18 +213,36 @@ export async function sendToUdsSocket(
   udsMsg.from = getUdsMessagingSocketPath()
 
   return new Promise<void>((resolve, reject) => {
-    const conn = createConnection(targetSocketPath, () => {
-      conn.write(jsonStringify(udsMsg) + '\n', (err) => {
+    let settled = false
+    let conn: ReturnType<typeof createConnection>
+    const finish = (error?: Error): void => {
+      if (settled) return
+      settled = true
+      if (error) {
+        conn.destroy(error)
+        reject(error)
+      } else {
         conn.end()
-        if (err) reject(err)
-        else resolve()
+        resolve()
+      }
+    }
+
+    conn = createConnection(target.socketPath, () => {
+      udsMsg.meta = { ...udsMsg.meta, authToken }
+      conn.write(jsonStringify(udsMsg) + '\n', err => {
+        if (err) finish(err)
       })
     })
-    conn.on('error', (err) => {
-      reject(new Error(`Failed to connect to peer at ${targetSocketPath}: ${errorMessage(err)}`))
+    attachUdsResponseReader(conn, {
+      maxFrameBytes: MAX_UDS_FRAME_BYTES,
+      onSettled: finish,
+      formatSocketError: err =>
+        new Error(
+          `Failed to connect to peer at ${target.socketPath}: ${errorMessage(err)}`,
+        ),
     })
     conn.setTimeout(5000, () => {
-      conn.destroy(new Error('Connection timed out'))
+      finish(new Error('Connection timed out'))
     })
   })
 }
diff --git a/src/utils/udsMessaging.ts b/src/utils/udsMessaging.ts
index 1c95ab63c..b30cba137 100644
--- a/src/utils/udsMessaging.ts
+++ b/src/utils/udsMessaging.ts
@@ -8,14 +8,26 @@
  * but can be overridden via --messaging-socket-path.
  */
 
+import { createHash, randomBytes, timingSafeEqual } from 'crypto'
 import { createServer, type Server, type Socket } from 'net'
-import { mkdir, unlink } from 'fs/promises'
+import {
+  chmod,
+  lstat,
+  mkdir,
+  open,
+  readFile,
+  rename,
+  unlink,
+} from 'fs/promises'
 import { dirname, join } from 'path'
 import { tmpdir } from 'os'
 import { registerCleanup } from './cleanupRegistry.js'
 import { logForDebugging } from './debug.js'
 import { errorMessage } from './errors.js'
+import { getClaudeConfigHomeDir } from './envUtils.js'
 import { attachNdjsonFramer } from './ndjsonFramer.js'
+import { attachUdsResponseReader } from './udsResponseReader.js'
+import { logError } from './log.js'
 import { jsonParse, jsonStringify } from './slowOperations.js'
 
 // ---------------------------------------------------------------------------
@@ -27,6 +39,7 @@ export type UdsMessageType =
   | 'notification'
   | 'query'
   | 'response'
+  | 'error'
   | 'ping'
   | 'pong'
 
@@ -60,6 +73,17 @@ let onEnqueueCb: (() => void) | null = null
 const clients = new Set<Socket>()
 const inbox: UdsInboxEntry[] = []
 let nextId = 1
+let defaultSocketPath: string | null = null
+let authToken: string | null = null
+let capabilityFilePath: string | null = null
+let inboxBytes = 0
+
+export const MAX_UDS_INBOX_ENTRIES = 1_000
+export const MAX_UDS_FRAME_BYTES = 64 * 1024
+export const MAX_UDS_INBOX_BYTES = 2 * 1024 * 1024
+export const MAX_UDS_CLIENTS = 128
+export const UDS_AUTH_TIMEOUT_MS = 2_000
+export const UDS_IDLE_TIMEOUT_MS = 30_000
 
 // ---------------------------------------------------------------------------
 // Public API — socket path helpers
@@ -74,10 +98,19 @@ let nextId = 1
  * transparently, but we use the pipe format on Windows for Node.js compat.
  */
 export function getDefaultUdsSocketPath(): string {
+  if (defaultSocketPath) return defaultSocketPath
+  const nonce = randomBytes(16).toString('hex')
   if (process.platform === 'win32') {
-    return `\\\\.\\pipe\\claude-code-${process.pid}`
+    defaultSocketPath = `\\\\.\\pipe\\claude-code-${process.pid}-${nonce}`
+    return defaultSocketPath
   }
-  return join(tmpdir(), 'claude-code-socks', `${process.pid}.sock`)
+  defaultSocketPath = join(
+    tmpdir(),
+    'claude-code-socks',
+    `${process.pid}-${nonce}`,
+    'messaging.sock',
+  )
+  return defaultSocketPath
 }
 
 /**
@@ -88,6 +121,153 @@ export function getUdsMessagingSocketPath(): string | undefined {
   return socketPath ?? undefined
 }
 
+export function formatUdsAddress(socket: string): string {
+  return `uds:${socket}`
+}
+
+export function parseUdsTarget(target: string): {
+  socketPath: string
+} {
+  if (target.includes('#token=')) {
+    throw new Error(
+      'UDS target must not include an inline auth token; use the ListPeers address',
+    )
+  }
+  return { socketPath: target }
+}
+
+function getCapabilityDir(): string {
+  return join(getClaudeConfigHomeDir(), 'messaging-capabilities')
+}
+
+function getCapabilityPath(socket: string): string {
+  const digest = createHash('sha256').update(socket).digest('hex')
+  return join(getCapabilityDir(), `${digest}.json`)
+}
+
+function isNotFound(error: unknown): boolean {
+  return (
+    typeof error === 'object' &&
+    error !== null &&
+    (error as NodeJS.ErrnoException).code === 'ENOENT'
+  )
+}
+
+async function assertPrivateCapabilityDir(dir: string): Promise<void> {
+  let stat: Awaited<ReturnType<typeof lstat>>
+  try {
+    stat = await lstat(dir)
+  } catch (error) {
+    if (!isNotFound(error)) throw error
+    await mkdir(dir, { recursive: true, mode: 0o700 })
+    stat = await lstat(dir)
+  }
+
+  assertPrivateDirectory(stat, dir, 'capability directory')
+  await chmod(dir, 0o700)
+}
+
+function assertPrivateDirectory(
+  stat: Awaited<ReturnType<typeof lstat>>,
+  dir: string,
+  label: string,
+): void {
+  if (!stat.isDirectory() || stat.isSymbolicLink()) {
+    throw new Error(
+      `[udsMessaging] ${label} is not a private directory: ${dir}`,
+    )
+  }
+  if (process.platform !== 'win32') {
+    const broadMode = Number(stat.mode) & 0o077
+    if (broadMode !== 0) {
+      throw new Error(
+        `[udsMessaging] ${label} permissions are too broad: ${dir}`,
+      )
+    }
+    if (
+      typeof process.getuid === 'function' &&
+      Number(stat.uid) !== process.getuid()
+    ) {
+      throw new Error(
+        `[udsMessaging] ${label} owner does not match current user: ${dir}`,
+      )
+    }
+  }
+}
+
+async function writePrivateFileExclusive(
+  path: string,
+  content: string,
+): Promise<void> {
+  const handle = await open(path, 'wx', 0o600)
+  try {
+    await handle.writeFile(content, 'utf-8')
+  } finally {
+    await handle.close()
+  }
+  await chmod(path, 0o600)
+}
+
+async function ensureSocketParent(path: string): Promise<void> {
+  const dir = dirname(path)
+  try {
+    const stat = await lstat(dir)
+    if (!stat.isDirectory() || stat.isSymbolicLink()) {
+      throw new Error(
+        `[udsMessaging] socket parent is not a directory: ${dir}`,
+      )
+    }
+    assertPrivateDirectory(stat, dir, 'socket parent')
+    return
+  } catch (error) {
+    if (!isNotFound(error)) throw error
+  }
+
+  await mkdir(dir, { recursive: true, mode: 0o700 })
+  await chmod(dir, 0o700)
+}
+
+async function writeCapabilityFile(
+  socket: string,
+  token: string,
+): Promise<void> {
+  const dir = getCapabilityDir()
+  await assertPrivateCapabilityDir(dir)
+  const target = getCapabilityPath(socket)
+  const temp = `${target}.${process.pid}.${randomBytes(8).toString('hex')}.tmp`
+  try {
+    await writePrivateFileExclusive(
+      temp,
+      jsonStringify({ socketPath: socket, authToken: token }),
+    )
+    await rename(temp, target)
+  } catch (error) {
+    try {
+      await unlink(temp)
+    } catch {
+      // Temp file may not exist if exclusive creation failed.
+    }
+    throw error
+  }
+  capabilityFilePath = target
+}
+
+export async function readUdsCapabilityToken(
+  socket: string,
+): Promise<string | undefined> {
+  try {
+    const parsed = jsonParse(
+      await readFile(getCapabilityPath(socket), 'utf-8'),
+    ) as Record<string, unknown>
+    if (parsed.socketPath === socket && typeof parsed.authToken === 'string') {
+      return parsed.authToken
+    }
+  } catch {
+    // Missing or unreadable capability file means the peer is not addressable.
+  }
+  return undefined
+}
+
 // ---------------------------------------------------------------------------
 // Inbox
 // ---------------------------------------------------------------------------
@@ -101,16 +281,121 @@ export function setOnEnqueue(cb: (() => void) | null): void {
 }
 
 /**
- * Drain all pending inbox messages, marking them processed.
+ * Drain all pending inbox messages and release retained history.
  */
 export function drainInbox(): UdsInboxEntry[] {
-  const pending = inbox.filter(e => e.status === 'pending')
+  const pending = inbox.splice(0, inbox.length)
+  inboxBytes = 0
   for (const entry of pending) {
     entry.status = 'processed'
   }
   return pending
 }
 
+function getMessageBytes(message: UdsMessage): number {
+  return Buffer.byteLength(jsonStringify(message), 'utf8')
+}
+
+function enqueueInboxEntry(entry: UdsInboxEntry): boolean {
+  const entryBytes = getMessageBytes(entry.message)
+  if (
+    entryBytes > MAX_UDS_FRAME_BYTES ||
+    inbox.length >= MAX_UDS_INBOX_ENTRIES ||
+    inboxBytes + entryBytes > MAX_UDS_INBOX_BYTES
+  ) {
+    logError(
+      new Error(
+        `[udsMessaging] inbox full (${inbox.length}/${MAX_UDS_INBOX_ENTRIES}, ${inboxBytes}/${MAX_UDS_INBOX_BYTES} bytes); dropping message type=${entry.message.type}`,
+      ),
+    )
+    return false
+  }
+  inbox.push(entry)
+  inboxBytes += entryBytes
+  return true
+}
+
+function ensureAuthToken(): string {
+  if (!authToken) {
+    authToken = randomBytes(32).toString('hex')
+  }
+  return authToken
+}
+
+function getMessageAuthToken(message: UdsMessage): string | undefined {
+  const token = message.meta?.authToken
+  return typeof token === 'string' ? token : undefined
+}
+
+function isAuthorizedMessage(message: UdsMessage): boolean {
+  const provided = getMessageAuthToken(message)
+  if (!provided || !authToken) return false
+  const providedBuffer = Buffer.from(provided, 'utf8')
+  const expectedBuffer = Buffer.from(authToken, 'utf8')
+  if (providedBuffer.length !== expectedBuffer.length) return false
+  return timingSafeEqual(providedBuffer, expectedBuffer)
+}
+
+function writeSocketMessage(socket: Socket, message: UdsMessage): void {
+  if (socket.destroyed) return
+  socket.write(jsonStringify(message) + '\n')
+}
+
+function writeSocketMessageAndDestroy(socket: Socket, message: UdsMessage): void {
+  if (socket.destroyed) return
+  socket.write(jsonStringify(message) + '\n', () => {
+    if (!socket.destroyed) socket.destroy()
+  })
+}
+
+function writeSocketErrorAndDestroy(socket: Socket, data: string): void {
+  writeSocketMessageAndDestroy(socket, {
+    type: 'error',
+    data,
+    ts: new Date().toISOString(),
+  })
+}
+
+function unrefTimer(timer: ReturnType<typeof setTimeout>): void {
+  const maybeUnref = (timer as { unref?: () => void }).unref
+  if (typeof maybeUnref === 'function') {
+    maybeUnref.call(timer)
+  }
+}
+
+async function closeServer(serverToClose: Server): Promise<void> {
+  await new Promise<void>(resolve => {
+    serverToClose.close(() => resolve())
+  })
+}
+
+async function removeSocketPath(path: string): Promise<void> {
+  if (process.platform === 'win32') return
+  try {
+    await unlink(path)
+  } catch {
+    // Already gone.
+  }
+}
+
+function stripAuthToken(message: UdsMessage): UdsMessage {
+  const { authToken: _authToken, ...metaWithoutAuth } = message.meta ?? {}
+  return {
+    ...message,
+    meta: Object.keys(metaWithoutAuth).length > 0 ? metaWithoutAuth : undefined,
+  }
+}
+
+function withRequestAuthToken(message: UdsMessage, token: string): UdsMessage {
+  return {
+    ...message,
+    meta: {
+      ...message.meta,
+      authToken: token,
+    },
+  }
+}
+
 // ---------------------------------------------------------------------------
 // Server
 // ---------------------------------------------------------------------------
@@ -132,7 +417,7 @@ export async function startUdsMessaging(
 
   // Ensure parent directory exists (skip on Windows — pipe paths aren't files)
   if (process.platform !== 'win32') {
-    await mkdir(dirname(path), { recursive: true })
+    await ensureSocketParent(path)
   }
 
   // Clean up stale socket file (skip on Windows — pipe paths aren't files)
@@ -144,69 +429,195 @@ export async function startUdsMessaging(
     }
   }
 
-  socketPath = path
+  const token = ensureAuthToken()
+  let startedServer: Server | null = null
+  let exportedSocketEnv = false
+  try {
+    await new Promise<void>((resolve, reject) => {
+      const srv = createServer(socket => {
+        if (clients.size >= MAX_UDS_CLIENTS) {
+          logForDebugging(
+            `[udsMessaging] rejected client: ${clients.size}/${MAX_UDS_CLIENTS} clients already connected`,
+          )
+          socket.destroy()
+          return
+        }
+        clients.add(socket)
+        logForDebugging(
+          `[udsMessaging] client connected (total: ${clients.size})`,
+        )
+        let authenticated = false
+        let closing = false
+        const closeWithError = (data: string): void => {
+          if (closing || socket.destroyed) return
+          closing = true
+          socket.pause()
+          writeSocketErrorAndDestroy(socket, data)
+        }
+        const authTimer = setTimeout(() => {
+          if (authenticated || socket.destroyed) return
+          logForDebugging('[udsMessaging] closing unauthenticated idle client')
+          closeWithError('authentication timeout')
+        }, UDS_AUTH_TIMEOUT_MS)
+        unrefTimer(authTimer)
+        socket.setTimeout(UDS_IDLE_TIMEOUT_MS, () => {
+          logForDebugging('[udsMessaging] closing idle client')
+          closeWithError('idle timeout')
+        })
+
+        attachNdjsonFramer<UdsMessage>(
+          socket,
+          msg => {
+            if (!isAuthorizedMessage(msg)) {
+              logForDebugging(
+                `[udsMessaging] rejected unauthenticated message type=${msg.type}`,
+              )
+              closeWithError('unauthorized')
+              return
+            }
+            if (!authenticated) {
+              authenticated = true
+              clearTimeout(authTimer)
+            }
 
-  await new Promise<void>((resolve, reject) => {
-    const srv = createServer(socket => {
-      clients.add(socket)
-      logForDebugging(
-        `[udsMessaging] client connected (total: ${clients.size})`,
-      )
+            // Handle ping with automatic pong
+            if (msg.type === 'ping') {
+              writeSocketMessage(socket, {
+                type: 'pong',
+                from: socketPath ?? undefined,
+                ts: new Date().toISOString(),
+              })
+              return
+            }
 
-      attachNdjsonFramer<UdsMessage>(
-        socket,
-        msg => {
-          // Handle ping with automatic pong
-          if (msg.type === 'ping') {
-            const pong: UdsMessage = {
-              type: 'pong',
-              from: socketPath ?? undefined,
-              ts: new Date().toISOString(),
+            // Enqueue into inbox
+            const sanitizedMessage = stripAuthToken(msg)
+            const entry: UdsInboxEntry = {
+              id: `uds-${nextId++}`,
+              message: sanitizedMessage,
+              receivedAt: Date.now(),
+              status: 'pending',
             }
-            if (!socket.destroyed) {
-              socket.write(jsonStringify(pong) + '\n')
+            if (!enqueueInboxEntry(entry)) {
+              closeWithError('inbox full')
+              return
             }
-            return
-          }
+            logForDebugging(
+              `[udsMessaging] enqueued message type=${msg.type} from=${msg.from ?? 'unknown'}`,
+            )
+            writeSocketMessage(socket, {
+              type: 'response',
+              data: 'ok',
+              ts: new Date().toISOString(),
+              meta: { id: entry.id },
+            })
+            onEnqueueCb?.()
+          },
+          text => jsonParse(text) as UdsMessage,
+          {
+            maxFrameBytes: MAX_UDS_FRAME_BYTES,
+            onFrameError: error => {
+              logForDebugging(`[udsMessaging] ${error.message}`)
+              closeWithError(error.message)
+            },
+            onInvalidFrame: error => {
+              logForDebugging(
+                `[udsMessaging] invalid client frame: ${errorMessage(error)}`,
+              )
+              closeWithError('invalid frame')
+            },
+            destroyOnFrameError: false,
+          },
+        )
+
+        socket.on('close', () => {
+          clearTimeout(authTimer)
+          clients.delete(socket)
+        })
+
+        socket.on('error', err => {
+          clearTimeout(authTimer)
+          clients.delete(socket)
+          logForDebugging(`[udsMessaging] client error: ${errorMessage(err)}`)
+        })
+      })
 
-          // Enqueue into inbox
-          const entry: UdsInboxEntry = {
-            id: `uds-${nextId++}`,
-            message: msg,
-            receivedAt: Date.now(),
-            status: 'pending',
-          }
-          inbox.push(entry)
-          logForDebugging(
-            `[udsMessaging] enqueued message type=${msg.type} from=${msg.from ?? 'unknown'}`,
-          )
-          onEnqueueCb?.()
-        },
-        text => jsonParse(text) as UdsMessage,
-      )
+      const rejectBeforeListen = (error: Error): void => {
+        reject(error)
+      }
+      const logRuntimeError = (error: Error): void => {
+        logForDebugging(
+          `[udsMessaging] server error on ${path}${opts?.isExplicit ? ' (explicit)' : ''}: ${errorMessage(error)}`,
+        )
+      }
 
-      socket.on('close', () => {
-        clients.delete(socket)
-      })
+      srv.once('error', rejectBeforeListen)
 
-      socket.on('error', err => {
-        clients.delete(socket)
-        logForDebugging(`[udsMessaging] client error: ${errorMessage(err)}`)
+      srv.listen(path, () => {
+        void (async () => {
+          try {
+            if (process.platform !== 'win32') {
+              await chmod(path, 0o600)
+            }
+            srv.off('error', rejectBeforeListen)
+            srv.on('error', logRuntimeError)
+            server = srv
+            startedServer = srv
+            resolve()
+          } catch (error) {
+            srv.off('error', rejectBeforeListen)
+            const closeError =
+              error instanceof Error ? error : new Error(errorMessage(error))
+            let rejected = false
+            const rejectOnce = (): void => {
+              if (rejected) return
+              rejected = true
+              reject(closeError)
+            }
+            const fallback = setTimeout(rejectOnce, 1_000)
+            unrefTimer(fallback)
+            srv.close(() => {
+              clearTimeout(fallback)
+              rejectOnce()
+            })
+          }
+        })()
       })
     })
 
-    srv.on('error', reject)
-
-    srv.listen(path, () => {
-      server = srv
-      // Export so child processes can discover the socket
-      process.env.CLAUDE_CODE_MESSAGING_SOCKET = path
-      logForDebugging(
-        `[udsMessaging] server listening on ${path}${opts?.isExplicit ? ' (explicit)' : ''}`,
-      )
-      resolve()
-    })
-  })
+    await writeCapabilityFile(path, token)
+    socketPath = path
+    // Export so child processes can discover the socket only after the
+    // capability file exists and the listener is ready.
+    process.env.CLAUDE_CODE_MESSAGING_SOCKET = path
+    exportedSocketEnv = true
+    logForDebugging(
+      `[udsMessaging] server listening on ${path}${opts?.isExplicit ? ' (explicit)' : ''}`,
+    )
+  } catch (error) {
+    if (capabilityFilePath) {
+      try {
+        await unlink(capabilityFilePath)
+      } catch {
+        // Already gone.
+      }
+      capabilityFilePath = null
+    }
+    if (startedServer) {
+      await closeServer(startedServer)
+    }
+    if (server === startedServer) {
+      server = null
+    }
+    await removeSocketPath(path)
+    if (exportedSocketEnv) {
+      delete process.env.CLAUDE_CODE_MESSAGING_SOCKET
+    }
+    socketPath = null
+    defaultSocketPath = null
+    authToken = null
+    throw error
+  }
 
   // Register cleanup so the socket file is removed on exit
   registerCleanup(async () => {
@@ -218,6 +629,7 @@ export async function startUdsMessaging(
  * Stop the UDS messaging server and clean up the socket file.
  */
 export async function stopUdsMessaging(): Promise<void> {
+  defaultSocketPath = null
   if (!server) return
 
   // Close all connected clients
@@ -230,21 +642,27 @@ export async function stopUdsMessaging(): Promise<void> {
     server!.close(() => resolve())
   })
   server = null
+  inbox.length = 0
+  inboxBytes = 0
+  onEnqueueCb = null
 
   // Remove socket file (skip on Windows — pipe paths aren't files)
   if (socketPath) {
-    if (process.platform !== 'win32') {
-      try {
-        await unlink(socketPath)
-      } catch {
-        // Already gone
-      }
-    }
+    await removeSocketPath(socketPath)
     delete process.env.CLAUDE_CODE_MESSAGING_SOCKET
     logForDebugging(
       `[udsMessaging] server stopped, socket removed: ${socketPath}`,
     )
     socketPath = null
+    authToken = null
+  }
+  if (capabilityFilePath) {
+    try {
+      await unlink(capabilityFilePath)
+    } catch {
+      // Already gone
+    }
+    capabilityFilePath = null
   }
 }
 
@@ -255,23 +673,50 @@ export async function stopUdsMessaging(): Promise<void> {
 export async function sendUdsMessage(
   targetSocketPath: string,
   message: UdsMessage,
+  opts: { authToken?: string } = {},
 ): Promise<void> {
   const { createConnection } = await import('net')
-  message.from = message.from ?? socketPath ?? undefined
-  message.ts = message.ts ?? new Date().toISOString()
+  const token = opts.authToken ?? authToken
+  if (!token) {
+    throw new Error('Cannot send UDS message without auth token')
+  }
+  const outbound = withRequestAuthToken(
+    {
+      ...message,
+      from: message.from ?? socketPath ?? undefined,
+      ts: message.ts ?? new Date().toISOString(),
+    },
+    token,
+  )
 
   return new Promise<void>((resolve, reject) => {
-    const conn = createConnection(targetSocketPath, () => {
-      conn.write(jsonStringify(message) + '\n', err => {
+    let settled = false
+    let conn: ReturnType<typeof createConnection>
+    const finish = (error?: Error): void => {
+      if (settled) return
+      settled = true
+      if (error) {
+        conn.destroy(error)
+        reject(error)
+      } else {
         conn.end()
-        if (err) reject(err)
-        else resolve()
+        resolve()
+      }
+    }
+
+    conn = createConnection(targetSocketPath, () => {
+      conn.write(jsonStringify(outbound) + '\n', err => {
+        if (err) finish(err)
       })
     })
-    conn.on('error', reject)
+    attachUdsResponseReader(conn, {
+      maxFrameBytes: MAX_UDS_FRAME_BYTES,
+      acceptPong: true,
+      onSettled: finish,
+    })
     // Timeout so we don't hang on unreachable sockets
     conn.setTimeout(5000, () => {
-      conn.destroy(new Error('Connection timed out'))
+      finish(new Error('Connection timed out'))
     })
   })
 }
diff --git a/src/utils/udsResponseReader.ts b/src/utils/udsResponseReader.ts
new file mode 100644
index 000000000..d86328aab
--- /dev/null
+++ b/src/utils/udsResponseReader.ts
@@ -0,0 +1,120 @@
+import type { Socket } from 'net'
+import { StringDecoder } from 'node:string_decoder'
+import { errorMessage } from './errors.js'
+import { jsonParse } from './slowOperations.js'
+import type { UdsMessage } from './udsMessaging.js'
+
+type UdsResponseReaderOptions = {
+  maxFrameBytes: number
+  acceptPong?: boolean
+  onSettled: (error?: Error) => void
+  formatSocketError?: (error: unknown) => Error
+}
+
+export function getChunkBytes(chunk: string | Buffer): number {
+  return typeof chunk === 'string'
+    ? Buffer.byteLength(chunk, 'utf8')
+    : chunk.byteLength
+}
+
+function parseResponseLine(line: string): UdsMessage {
+  try {
+    return jsonParse(line) as UdsMessage
+  } catch {
+    throw new Error('Invalid UDS response frame')
+  }
+}
+
+export function attachUdsResponseReader(
+  socket: Socket,
+  options: UdsResponseReaderOptions,
+): void {
+  let buffer = ''
+  let bufferBytes = 0
+  let settled = false
+  const decoder = new StringDecoder('utf8')
+
+  function cleanupListeners(): void {
+    socket.off('data', onData)
+    socket.off('error', onError)
+    socket.off('end', onEnd)
+    socket.off('close', onClose)
+  }
+
+  function finish(error?: Error): void {
+    if (settled) return
+    settled = true
+    buffer = ''
+    bufferBytes = 0
+    cleanupListeners()
+    if (error) {
+      socket.destroy()
+    } else {
+      socket.end()
+    }
+    options.onSettled(error)
+  }
+
+  function onData(chunk: Buffer): void {
+    const decoded = decoder.write(chunk)
+    const decodedBytes = Buffer.byteLength(decoded, 'utf8')
+    if (bufferBytes + decodedBytes > options.maxFrameBytes) {
+      finish(new Error('UDS response frame exceeded size limit'))
+      return
+    }
+
+    buffer += decoded
+    bufferBytes += decodedBytes
+    let newlineIndex = buffer.indexOf('\n')
+    while (newlineIndex !== -1) {
+      const line = buffer.slice(0, newlineIndex)
+      const consumed = buffer.slice(0, newlineIndex + 1)
+      buffer = buffer.slice(newlineIndex + 1)
+      bufferBytes -= Buffer.byteLength(consumed, 'utf8')
+      if (!line.trim()) {
+        newlineIndex = buffer.indexOf('\n')
+        continue
+      }
+      let response: UdsMessage
+      try {
+        response = parseResponseLine(line)
+      } catch (error) {
+        finish(error instanceof Error ? error : new Error(errorMessage(error)))
+        return
+      }
+      if (
+        response.type === 'response' ||
+        (options.acceptPong === true && response.type === 'pong')
+      ) {
+        finish()
+        return
+      }
+      if (response.type === 'error') {
+        finish(new Error(response.data ?? 'UDS receiver rejected message'))
+        return
+      }
+      newlineIndex = buffer.indexOf('\n')
+    }
+  }
+
+  function onError(error: Error): void {
+    finish(
+      options.formatSocketError?.(error) ??
+        (error instanceof Error ? error : new Error(errorMessage(error))),
+    )
+  }
+
+  function onEnd(): void {
+    finish(new Error('UDS socket ended before response'))
+  }
+
+  function onClose(hadError: boolean): void {
+    if (hadError) return
+    finish(new Error('UDS socket closed before response'))
+  }
+
+  socket.on('data', onData)
+  socket.on('error', onError)
+  socket.on('end', onEnd)
+  socket.on('close', onClose)
+}