fix(tmux-terminal): D7 resolveWorkerPath walks up to find agents/lib/bg-worker (symlink loading)

[lantisprime]

Summary

Fixes D7: resolveWorkerPath() production mode looked for bg-worker.ts in the wrong directory (tmux-terminal/ instead of agents/lib/), causing the extension to silently skip registration when loaded via symlink (~/.pi/agent/extensions/tmux-terminal).

Bug surfaced by the user's interactive test — after running ln -s and restarting pi, /agents bg scout "..." still said "No terminal backend installed". This bug was invisible to all 63 unit tests + the real-tmux smoke test (see "Why previous tests missed it" below).

The bug

tmux-terminal/lib/resolve-worker-path.ts computed the production-mode baseDir as:

path.dirname(path.dirname(fileURLToPath(import.meta.url)))

For a module at tmux-terminal/lib/resolve-worker-path.ts, this resolves to tmux-terminal/ — but bg-worker.ts actually lives at agents/lib/bg-worker.ts. The production-mode path looked in the wrong directory and returned null. The extension's registerBgTerminalBackend was silently skipped (console.debug("tmux-terminal: worker not found, skipping registration")), and getBgTerminalBackend() in agents/index.ts returned null, producing the "No terminal backend installed" warning.

The fix

Production mode now walks UP from the module's directory, checking for agents/lib/bg-worker.{ts,mjs,js} at each level until found or root reached. Robust to:

• Symlinked extensions (~/.pi/agent/extensions/tmux-terminal)
• Arbitrary repo depth (the agents/ dir may be N levels above)
• ts vs mjs vs js worker variants

let dir = path.dirname(fileURLToPath(import.meta.url));
const root = path.parse(dir).root;
while (dir !== root) {
  const agentsLibDir = path.join(dir, "agents", "lib");
  for (const basename of WORKER_BASENAMES) {
    const candidate = path.join(agentsLibDir, basename);
    if (fs.existsSync(candidate)) return fs.realpathSync(candidate);
  }
  const parent = path.dirname(dir);
  if (parent === dir) break;
  dir = parent;
}
return null;

New test

testProductionModeFindsWorkerByWalkingUp in test-fixtures/test-helpers.mjs:

• Sets up a fake repo layout in a tmpdir: agents/lib/bg-worker.ts + fake-extension/lib/{resolve-worker-path,constants}.ts
• Uses copy (not symlink) so Node ESM doesn't resolve import.meta.url to the real path
• Spawns a child node process to verify production-mode path resolution
• Verified to FAIL when the production-mode walk-up is reverted to the broken version

Why previous tests missed it

Test	Why it missed D7
testWorkerPathIsRealpathed	Uses resolveWorkerPath(searchDir) — bypasses production-mode path
testWorkerPathPrefersTsOverMjs	Same — uses searchDir
test-real-tmux-smoke.mjs	Passes workerPath directly to createTmuxBackend, never going through resolveWorkerPath
Manual smoke (load both extensions via -e)	Worked because Node loads via real path, not symlink — import.meta.url happens to give a path where dirname(dirname(...)) finds agents/lib/

Lesson: any production-mode code that depends on import.meta.url for path computation needs at least one test that simulates symlink loading via copy + child process.

Verification

• bash tmux-terminal/test-fixtures/run-p5-tests.sh: 64/64 (was 63) + REQ-13 OK
• bash agents/test-fixtures/run-p4-4-tests.sh: green (regression intact)
• node tmux-terminal/test-fixtures/test-real-tmux-smoke.mjs: 11/11 against real tmux
• New D7 test against broken version: FAILS (regression guard works)
• Mutation Harden Prompt Shield and Secure Web Search #1 (realpathSync → path.resolve): fails only realpath test
• Mutation Fix Prompt Shield deny/approve flow and prevent stale cache #2 (WORKER_BASENAMES reorder): fails only precedence test

Files changed (3 files, +60/-5)

• tmux-terminal/lib/resolve-worker-path.ts — walk-up logic for production mode
• tmux-terminal/test-fixtures/test-helpers.mjs — new D7 regression test
• agents/P3_IMPLEMENTATION_SLICES.md — D7 documented in deviations list

User-visible fix

After this PR merges + symlink exists, /agents bg scout "echo hello" should launch a tmux window (no more "No terminal backend installed" warning).

🤖 Generated with pi-coding-agent