🤖 feat: VS Code-style extension system with global host architecture

.gitignore

@@ -102,6 +102,7 @@ __pycache__
 
 tmpfork
 .cmux-agent-cli
+.cmux/*.tmp.*
 storybook-static/
 *.tgz
 src/test-workspaces/

bun.lock

@@ -17,6 +17,7 @@
         "@radix-ui/react-tooltip": "^1.2.8",
         "ai": "^5.0.72",
         "ai-tokenizer": "^1.0.3",
+        "capnweb": "^0.2.0",
         "chalk": "^5.6.2",
         "cors": "^2.8.5",
         "crc-32": "^1.2.2",
@@ -1131,6 +1132,8 @@
 
     "caniuse-lite": ["caniuse-lite@1.0.30001751", "", {}, "sha512-A0QJhug0Ly64Ii3eIqHu5X51ebln3k4yTUkY1j8drqpWHVreg/VLijN48cZ1bYPiqOQuqpkIKnzr/Ul8V+p6Cw=="],
 
+    "capnweb": ["capnweb@0.2.0", "", {}, "sha512-fQSW5h6HIefRM4rHZMyAsWcu/qE/6Qr2OC8B99whifjDJatI5KLFcODSykKmpyCCKF50N3HvZ5lB26YBdh0fRg=="],
+
     "ccount": ["ccount@2.0.1", "", {}, "sha512-eyrF0jiFpY+3drT6383f1qhkbGsLSifNAjA61IUjZjmLCWjItY6LB9ft9YhoDgwfmclB2zhu51Lc7+95b8NRAg=="],
 
     "chai": ["chai@5.3.3", "", { "dependencies": { "assertion-error": "^2.0.1", "check-error": "^2.1.1", "deep-eql": "^5.0.1", "loupe": "^3.1.0", "pathval": "^2.0.0" } }, "sha512-4zNhdJD/iOjSH0A05ea+Ke6MU5mmpQcbQsSOkgdaUMJ9zTlDTD/GYlwohmIE2u0gaxHYiVHEn1Fw9mZ/ktJWgw=="],

docs/AGENTS.md

@@ -270,6 +270,20 @@ await env.mockIpcRenderer.invoke(IPC_CHANNELS.WORKSPACE_CREATE, projectPath, bra
 - Verifying filesystem state (like checking if files exist) after IPC operations complete
 - Loading existing data to avoid expensive API calls in test setup
 
+### Testing without Mocks (preferred)
+
+- Prefer exercising real behavior over substituting test doubles. Do not stub `child_process`, `fs`, or discovery logic.
+- **Use async fs operations (`fs/promises`) in tests, never sync fs**. This keeps tests fast and allows parallelization.
+- **Use `test.concurrent()` for unit tests** to enable parallel execution. Avoid global variables in test files—use local variables in each test or `beforeEach` to ensure test isolation.
+- Use temporary directories and real processes in unit tests where feasible. Clean up with `await fs.rm(temp, { recursive: true, force: true })` in async `afterEach`.
+- For extension system tests:
+  - Spawn the real global extension host via `ExtensionManager.initializeGlobal()`.
+  - Create real on-disk extensions in a temp `~/.cmux/ext` or project `.cmux/ext` folder.
+  - Register/unregister real workspaces and verify through actual tool execution.
+- Integration tests must go through real IPC. Use the test harness's `mockIpcRenderer.invoke()` to traverse the production IPC path (this is a façade, not a Jest mock).
+- Avoid spies and partial mocks. If a mock seems necessary, consider fixing the test harness or refactoring code to make the behavior testable without mocks.
+- Acceptable exceptions: isolating nondeterminism (e.g., time) or external network calls. Prefer dependency injection with in-memory fakes over broad module mocks.
+
 If IPC is hard to test, fix the test infrastructure or IPC layer, don't work around it by bypassing IPC.
 
 ## Command Palette (Cmd+Shift+P)

docs/SUMMARY.md

@@ -20,6 +20,7 @@
 - [Instruction Files](./instruction-files.md)
 - [Project Secrets](./project-secrets.md)
   - [Agentic Git Identity](./agentic-git-identity.md)
+- [Extensions](./extensions.md)
 
 # Advanced