docs(AGENTS): state explicit preference against mocks; dedupe root section

- Add 'Testing without Mocks (preferred)' guidance in both AGENTS.md and docs/AGENTS.md
- Deduplicate accidentally duplicated section in root AGENTS.md

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Author: ammar-agent

docs/AGENTS.md

@@ -280,18 +280,6 @@ await env.mockIpcRenderer.invoke(IPC_CHANNELS.WORKSPACE_CREATE, projectPath, bra
 - 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.
 
-### Testing without Mocks (preferred)
-
-- Prefer exercising real behavior over substituting test doubles. Do not stub `child_process`, `fs`, or discovery logic.
-- Use temporary directories and real processes in unit tests where feasible. Clean up with `fs.rmSync(temp, { recursive: true, force: true })` in `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.
 
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