🤖 feat: remove Chat with Mux (#3123)

## Summary

Remove the built-in Chat with Mux workspace and agent, along with the
frontend, backend, docs, and test special-casing that supported it, then
follow through on the compatibility and validation regressions that
surfaced once the feature was gone.

## Background

Chat with Mux added a hidden system workspace, a dedicated built-in
agent, and multiple product-specific exceptions across routing,
workspace creation, tool scope, MCP/secrets handling, docs, Storybook,
and tests. Removing the feature wholesale simplifies those paths, but it
also exposed a few places that still depended on legacy system-workspace
behavior, persisted `mux` agent ids, or test-only globals/module state
that had been masked before.

## Implementation

- delete the built-in Chat with Mux agent, constants, docs page, and
dedicated UI test
- remove service-container bootstrap plus workspace/AI/terminal special
handling for the built-in system workspace
- remove UI entrypoints and affordances, including the sidebar help
button, landing-page card, and F1 shortcut
- update command, routing, and agent-locking behavior to stop treating a
special workspace differently
- preserve documented global mux-tool behavior for legacy hidden system
workspaces, while keeping `_multi` workspaces project-scoped
- remap persisted removed `mux` agent ids to the default built-in
fallback so upgraded installs keep UI/backend agent state aligned
- skip hidden system workspaces in the desktop new-chat startup fallback
so upgraded installs still draft chats in user-visible projects
- stabilize the affected Bun test suites by isolating leaked DOM
globals, module cache state, and context-menu/menu mocks across
full-suite runs

## Validation

- `make static-check`
- `make test`

## Risks

- Existing on-disk leftovers from the removed system workspace are no
longer surfaced as a first-class feature; this change removes the
feature rather than adding a migration UI.
- Legacy hidden system workspaces and removed `mux` agent ids still need
compatibility fallbacks on upgrade, so regressions there remain low-risk
but worth keeping under regression coverage.

---

_Generated with `mux` • Model: `openai:gpt-5.4` • Thinking: `xhigh` •
Cost: `$49.43`_

<!-- mux-attribution: model=openai:gpt-5.4 thinking=xhigh costs=49.43
-->

Author: ammar-agent

docs/agents/agent-skills.mdx

@@ -90,8 +90,6 @@ Set `advertise: false` in the frontmatter to exclude a skill from that index. Un
 - **Still appear** in Mux’s UI lists (for example `/` slash suggestions)
 - **Are useful for**: skills meant only for sub-agents, advanced users, or internal orchestration
 
-- **In Chat with Mux tooling**, `advertise` is authored directly in frontmatter content; there is no separate tool argument
-
 ### Example: `deep-review` skill
 
 The Mux repository includes an unadvertised `deep-review` skill that encourages aggressive use of sub-agents to produce excellent code reviews (correctness, tests, consistency, UX, performance). Invoke it with `/deep-review` when you want a thorough, parallelized review. This skill is defined in `.mux/skills/deep-review/SKILL.md`.

docs/agents/index.mdx

@@ -279,7 +279,7 @@ tools:
     - ask_user_question
     # Internal-only tools
     - system1_keep_ranges
-    # Global config tools are restricted to the mux agent
+    # Global config and catalog tools stay out of general-purpose agents
     - mux_agents_.*
     - agent_skill_write
     - agent_skill_delete
@@ -503,7 +503,7 @@ tools:
   remove:
     # Plan should not apply sub-agent patches.
     - task_apply_git_patch
-    # Global config tools are restricted to the mux agent
+    # Global config and catalog tools stay out of general-purpose agents
     - mux_agents_.*
     - agent_skill_write
     - agent_skill_delete
@@ -568,75 +568,6 @@ provided separately.
 
 </Accordion>
 
-### Chat With Mux (internal)
-
-**Configure Mux settings, skills, and agent instructions**
-
-<Accordion title="View mux.md">
-
-```md
----
-name: Chat With Mux
-description: Configure Mux settings, skills, and agent instructions
-ui:
-  hidden: true
-  routable: true
-subagent:
-  runnable: false
-tools:
-  add:
-    - mux_agents_read
-    - mux_agents_write
-    - mux_config_read
-    - mux_config_write
-    - agent_skill_read
-    - agent_skill_read_file
-    - agent_skill_list
-    - agent_skill_write
-    - agent_skill_delete
-    - skills_catalog_search
-    - skills_catalog_read
-    - ask_user_question
-    - todo_read
-    - todo_write
-    - notify
-    - analytics_query
----
-
-You are the **Mux system assistant**.
-
-Your tools are **context-aware** — they automatically target the right scope:
-
-**In a project workspace**:
-
-- **Project skills**: Create, update, list, and delete project skills (`.mux/skills/`)
-- **Project instructions**: Edit the project's `AGENTS.md`
-
-**In the system workspace** (Chat with Mux):
-
-- **Global skills**: Create, update, list, and delete global skills (`~/.mux/skills/`)
-- **Global instructions**: Edit the mux-wide `~/.mux/AGENTS.md`
-
-**Always global** (regardless of context):
-
-- **App config**: Read and write Mux configuration (`~/.mux/config.json`)
-
-## Safety rules
-
-- You do **not** have access to arbitrary filesystem tools.
-- You do **not** have access to project secrets.
-- Before writing AGENTS.md, you must:
-  1. Read the current file (`mux_agents_read`).
-  2. Propose the exact change (show the new content or a concise diff).
-  3. Ask for explicit confirmation via `ask_user_question`.
-  4. Only then call `mux_agents_write` with `confirm: true`.
-- Before writing a skill, show the proposed `SKILL.md` content and confirm.
-
-If the user declines, do not write anything.
-```
-
-</Accordion>
-
 ### Compact (internal)
 
 **History compaction (internal)**
@@ -718,7 +649,7 @@ tools:
     - ask_user_question
     # Internal-only
     - system1_keep_ranges
-    # Global config tools
+    # Global config and catalog tools
     - mux_agents_.*
     - agent_skill_write
 ---

docs/docs.json

@@ -32,7 +32,6 @@
             "pages": [
               "index",
               "install",
-              "getting-started/chat",
               {
                 "group": "Models",
                 "pages": ["config/models", "config/providers"]

docs/getting-started/chat.mdx

@@ -3,7 +3,6 @@ import { useRouter } from "./contexts/RouterContext";
 import { useLocation, useNavigate } from "react-router-dom";
 import "./styles/globals.css";
 import { useWorkspaceContext, toWorkspaceSelection } from "./contexts/WorkspaceContext";
-import { MUX_HELP_CHAT_WORKSPACE_ID } from "@/common/constants/muxChat";
 import { useProjectContext } from "./contexts/ProjectContext";
 import type { WorkspaceSelection } from "./components/ProjectSidebar/ProjectSidebar";
 import { LeftSidebar } from "./components/LeftSidebar/LeftSidebar";
@@ -111,7 +110,6 @@ function AppInner() {
     setWorkspaceMetadata,
     removeWorkspace,
     updateWorkspaceTitle,
-    refreshWorkspaceMetadata,
     selectedWorkspace,
     setSelectedWorkspace,
     pendingNewWorkspaceProject,
@@ -244,27 +242,6 @@ function AppInner() {
     workspaceMetadataRef.current = workspaceMetadata;
   }, [workspaceMetadata]);
 
-  const handleOpenMuxChat = useCallback(() => {
-    // User requested an F1 shortcut to jump straight into Chat with Mux.
-    const metadata = workspaceMetadataRef.current.get(MUX_HELP_CHAT_WORKSPACE_ID);
-    setSelectedWorkspace(
-      metadata
-        ? toWorkspaceSelection(metadata)
-        : {
-            workspaceId: MUX_HELP_CHAT_WORKSPACE_ID,
-            projectPath: "",
-            projectName: "Mux",
-            namedWorkspacePath: "",
-          }
-    );
-
-    if (!metadata) {
-      refreshWorkspaceMetadata().catch((error) => {
-        console.error("Failed to refresh workspace metadata", error);
-      });
-    }
-  }, [refreshWorkspaceMetadata, setSelectedWorkspace]);
-
   // Update window title based on selected workspace
   // URL syncing is now handled by RouterContext
   useEffect(() => {
@@ -802,9 +779,6 @@ function AppInner() {
             : undefined;
           openCommandPalette(initialQuery);
         }
-      } else if (matchesKeybind(e, KEYBINDS.OPEN_MUX_CHAT)) {
-        e.preventDefault();
-        handleOpenMuxChat();
       } else if (matchesKeybind(e, KEYBINDS.TOGGLE_SIDEBAR)) {
         e.preventDefault();
         setSidebarCollapsed((prev) => !prev);
@@ -831,7 +805,6 @@ function AppInner() {
     return () => window.removeEventListener("keydown", handleKeyDown);
   }, [
     handleNavigateWorkspace,
-    handleOpenMuxChat,
     setSidebarCollapsed,
     isCommandPaletteOpen,
     closeCommandPalette,