Restore legacy assistant agent fallback

Author: Eric-Guo

packages/opencode/src/session/message-v2.ts

@@ -89,12 +89,15 @@ export const cursor = {
   },
 }
 
-const info = (row: typeof MessageTable.$inferSelect) =>
-  ({
+const info = (row: typeof MessageTable.$inferSelect) => {
+  const data = row.data as typeof row.data & { agent?: string; mode?: string }
+  return {
     ...row.data,
     id: row.id,
     sessionID: row.session_id,
-  }) as Info
+    ...(data.role === "assistant" && data.agent === undefined ? { agent: data.mode ?? "build" } : {}),
+  } as Info
+}
 
 const part = (row: typeof PartTable.$inferSelect) =>
   ({

packages/opencode/test/server/httpapi-session.test.ts

@@ -24,7 +24,7 @@ import { Session } from "@/session/session"
 import { MessageID, PartID, SessionID, type SessionID as SessionIDType } from "../../src/session/schema"
 import { MessageV2 } from "../../src/session/message-v2"
 import { Database } from "@opencode-ai/core/database/database"
-import { SessionMessageTable, SessionTable } from "@opencode-ai/core/session/sql"
+import { MessageTable, SessionMessageTable, SessionTable } from "@opencode-ai/core/session/sql"
 import { SessionMessage } from "@opencode-ai/core/session/message"
 import { ModelV2 } from "@opencode-ai/core/model"
 import { ProviderV2 } from "@opencode-ai/core/provider"
@@ -182,6 +182,37 @@ const insertCorruptV2Message = (sessionID: SessionIDType, time = 1) =>
       .pipe(Effect.orDie)
   })
 
+const insertLegacyMessageV2Assistant = (sessionID: SessionIDType, parentID: MessageID) =>
+  Effect.sync(() => {
+    Database.use((db) =>
+      db
+        .insert(MessageTable)
+        .values({
+          id: MessageID.ascending(),
+          session_id: sessionID,
+          time_created: 1,
+          time_updated: 1,
+          data: {
+            role: "assistant",
+            time: { created: 1, completed: 1 },
+            parentID,
+            modelID: ModelID.make("test"),
+            providerID: ProviderID.make("test"),
+            mode: "build",
+            path: { cwd: "/tmp", root: "/tmp" },
+            cost: 0,
+            tokens: {
+              input: 0,
+              output: 0,
+              reasoning: 0,
+              cache: { read: 0, write: 0 },
+            },
+          } as NonNullable<(typeof MessageTable.$inferInsert)["data"]>,
+        })
+        .run(),
+    )
+  })
+
 const setLegacySummaryDiff = (sessionID: SessionIDType) =>
   Effect.gen(function* () {
     const { db } = yield* Database.Service
@@ -635,6 +666,30 @@ describe("session HttpApi", () => {
     { git: true, config: { formatter: false, lsp: false } },
   )
 
+  it.instance(
+    "serves legacy assistant messages missing agent",
+    () =>
+      Effect.gen(function* () {
+        const test = yield* TestInstance
+        const session = yield* createSession({ title: "legacy assistant" })
+        const message = yield* createTextMessage(session.id, "hello")
+        yield* insertLegacyMessageV2Assistant(session.id, message.info.id)
+
+        const response = yield* request(`${pathFor(SessionPaths.messages, { sessionID: session.id })}?limit=80`, {
+          headers: { "x-opencode-directory": test.directory },
+        })
+
+        expect(response.status).toBe(200)
+        expect(
+          (yield* json<MessageV2.WithParts[]>(response)).find((item) => item.info.role === "assistant")?.info,
+        ).toMatchObject({
+          role: "assistant",
+          agent: "build",
+        })
+      }),
+    { git: true, config: { formatter: false, lsp: false } },
+  )
+
   it.instance(
     "serves lifecycle mutation routes",
     () =>