fix(tmux-terminal): D5 probe + D6 node prefix (real-tmux execution)

[lantisprime]

Summary

Fixes two bugs surfaced by exercising the implementation against a real tmux server (tmux-terminal/test-fixtures/test-real-tmux-smoke.mjs). Both bugs were invisible to the v5 unit test suite because FakeTmuxExecutor returns configurable responses that don't model defaultTmuxExecutor's actual behavior or tmux's worker-execution semantics.

The bugs

D5 — isAvailable probe (tmux-backend.ts:34)

Before: ["has-session", "-t", "__pi_probe__"]

• __pi_probe__ session doesn't exist by default → has-session returns exit 1
• defaultTmuxExecutor catches non-zero exits and returns {ok: false}
• The D1 result.ok === true check then made isAvailable always return false, even when the tmux server was reachable

Fix: probe with ["list-sessions"] — returns 0 when the server is reachable, regardless of session count. Correctly distinguishes server-reachable from server-unreachable.

D6 — launch argv missing node prefix (tmux-backend.ts:52)

Before: ["new-window", ..., "--", workerPath, manifestPath]

• tmux tries to exec workerPath directly, but bg-worker.ts has no shebang and is mode 644 (not executable)
• Window is created, then immediately destroyed because the command fails to exec
• @pi_run_id and @pi_agent_name user-options are never set
• isAlive returns false, list returns empty

Fix: prepend "node" → ["new-window", ..., "--", "node", workerPath, manifestPath]. node handles the .ts extension via --experimental-strip-types (the same mechanism used by run-p4-4-tests.sh and the other test runners in this repo).

Why these bugs survived the v5 review process

• Plan review (5 rounds): focused on argv construction (Group 3 tests), not on isAvailable probe semantics or worker-execution semantics
• Code review (1 round): verified argv shape against fake-recorded calls, did not exercise real tmux
• Unit tests: FakeTmuxExecutor returns configurable responses; defaultTmuxExecutor's actual return shape (always {ok: false} for non-zero exit, no throw) was hidden behind the fake
• "Manual smoke" done criterion (from v5 plan): "pi -e ./agents/index.ts -e ./tmux-terminal/index.ts then /agents bg scout 'echo hello' launches tmux window" — listed but never executed before merge

The new test-real-tmux-smoke.mjs makes this criterion mechanically verified in CI.

New: real-tmux smoke test

tmux-terminal/test-fixtures/test-real-tmux-smoke.mjs (222 lines) + run-real-tmux-smoke.sh (7 lines):

• Exercises the actual createTmuxBackend against an isolated tmux -L p5-smoke-<pid> socket (does NOT touch the user's default tmux session)
• Cleans up on exit (kill-server + temp dirs)
• 11 verification steps: backend.name, isAvailable probes real tmux, launch creates window, window visible via direct CLI, user-options set, isAlive, list recovers runId/agentName, kill removes window, isAlive after kill, kill idempotent
• Skipped (exit 0) if tmux not on $PATH — opt-in by environment

Test updates

3 assertions in test-tmux-backend.mjs updated to match new contracts:

• Group 2 test 1 (line 43): ["has-session", "-t", "__pi_probe__"] → ["list-sessions"]
• Group 3 test 1 (line 99): deepEqual argv now includes "node" before workerPath
• Group 4 test 1 (line 155): workerIdx + 1 → workerIdx + 2 for manifestPath position; added intermediate "node" check

Verification (all green)

Command	Result
bash tmux-terminal/test-fixtures/run-p5-tests.sh	63/63 pass + 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 pass against real tmux 3.6a
Mutation #1 (realpathSync → path.resolve)	only testWorkerPathIsRealpathed fails ✓
Mutation #2 (WORKER_BASENAMES reorder)	only testWorkerPathPrefersTsOverMjs fails ✓

Files changed (5 files, +246/-7)

• tmux-terminal/lib/tmux-backend.ts — D5 probe + D6 node prefix
• tmux-terminal/test-fixtures/test-tmux-backend.mjs — 3 assertion updates
• tmux-terminal/test-fixtures/test-real-tmux-smoke.mjs — NEW (222 lines)
• tmux-terminal/test-fixtures/run-real-tmux-smoke.sh — NEW (7 lines)
• agents/P3_IMPLEMENTATION_SLICES.md — D5/D6 + smoke test docs

Plan v6 note

D5 and D6 should be incorporated into v6 of the P5 plan as canonical recipe (probe = list-sessions, argv = [..., "--", "node", workerPath, manifestPath]). This PR ships them as post-merge fixes against v5.

🤖 Generated with pi-coding-agent