fix(test): bound CLI subprocess fan-out so unit (linux) passes on GitHub-hosted runners (LAC-2715)

[lacymorrow]

Paperclip issue

LAC-2715 — Fix unit (linux) CI failures: opencode run (non-interactive subprocess) suite times out at ~30s on GitHub-hosted runners.

Root cause

The suite spawns one cold bun run src/index.ts subprocess per cliIt.concurrent test with unbounded fan-out (~10 at once, some tests spawn 3 sequentially). Each child re-transpiles the entire dependency graph, and the harness's per-test HOME/XDG_CACHE_HOME isolation leaves every child's Bun transpiler cache cold. On a 4-vCPU GitHub-hosted runner the simultaneous cold starts starve each other until every full-session child hits its 30s subprocess timeout with empty stdout (exit -1, Error: Timed out) — exactly the 7 failures on run 29067555482. The tests that survived are the fail-fast ones (unknown model, bad attach) that exit before the heavy boot.

Reproduced locally: fresh install/cold caches → 8 fail; warm second run → 13 pass. Deterministic A/B under 12× CPU-hog stress: unfixed → 5 pass / 8 fail (same signature as CI), fixed → 13 pass.

Fix (no blind timeout raises — root cause + fail-fast diagnostics)

• spawnGate semaphore in test/lib/cli-process.ts caps concurrent short-lived CLI spawns at max(2, min(4, cores/2)). The per-spawn 30s timer starts only once the permit is held, so queue wait is not charged against timeoutMs/durationMs and a genuinely hung subprocess still dies at 30s.
• Shared Bun transpiler cache across children via BUN_RUNTIME_TRANSPILER_CACHE_PATH (content-addressed, so per-test isolation is preserved). Only the first spawn pays the transpile cost; local full test/cli/ runtime dropped 305s → 219s.
• Better timeout diagnostics: AppProcess drops collected stderr on timeout, so the synthesized stderr now includes elapsed time and the budget (Timed out after Xms (timeout 30000ms)) instead of a bare Error: Timed out.
• Per-test bun timeouts → 120s in run-process.test.ts: with gated spawns a test's wall clock includes queueing behind other tests, so the test-level budget must cover serialized suite throughput. Hang detection lives in the per-spawn timeout, not the test timeout. Duration regression assertions (durationMs < 30_000) are unchanged and now measure pure subprocess time.

Acceptance criteria

• unit (linux) reaches success on GitHub-hosted runners → verified by this PR's own CI (base: LAC-2385/blacksmith-to-github-runners).

Testing

• bun test test/cli/run/run-process.test.ts — 13 pass, cold shared cache.
• Same, under 12 concurrent CPU hogs (starved-runner simulation) — 13 pass (control without fix: 8 fail).
• bun test test/cli/ (all 53 files using or adjacent to the fixture) — 414 pass / 0 fail.
• bun run typecheck (packages/opencode) — clean.

[gemini-code-assist]

Code Review

This pull request introduces performance optimizations for the test suite by implementing a concurrency gate (spawnGate) and a shared Bun transpiler cache to prevent resource starvation on CI runners. The changes include adding a semaphore to limit concurrent subprocess spawns and configuring a shared cache directory for transpilation. I have kept the reviewer's suggestion to make the shared cache directory user-specific to avoid potential permission conflicts in multi-tenant environments.

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[gemini-code-assist]

Using a hardcoded directory name like "opencode-test-bun-transpiler-cache" in the shared system temp directory (os.tmpdir()) can lead to permission conflicts (EACCES) in multi-tenant CI environments or on shared local development machines when different users run the tests.

To prevent this, we should make the directory name user-specific by appending the current username.

Suggested change

	const sharedTranspilerCache = path.join(os.tmpdir(), "opencode-test-bun-transpiler-cache")
	fs.mkdirSync(sharedTranspilerCache, { recursive: true })
	const username = os.userInfo?.().username || process.env.USER || "default"
	const sharedTranspilerCache = path.join(os.tmpdir(), "opencode-test-bun-transpiler-cache-" + username)
	fs.mkdirSync(sharedTranspilerCache, { recursive: true })

[lacymorrow]

Applied in 9174c6b — the cache dir is now suffixed with the current username. Used a try/catch around os.userInfo() (it can throw ENOENT in containers without a passwd entry) with USER/USERNAME env fallbacks for POSIX/Windows.