Avoid redundant Pi local-file child sessions

[ymichael]

Human comments

What was wrong

The local-file bridge test wrapped three deterministic input-to-prompt assertions in three independent real fake-Pi session lifecycles. Each case constructed a Pi RPC child, loaded the real extension boundary, delivered one local-file conversion, and tore the child down. The packages shard runs Turbo at concurrency 4 while each package starts a Vitest pool, so CPU/process oversubscription made those avoidable serial child startups cross Vitest's unchanged 5-second case ceiling. Scheduler contention is the reproduction trigger; the root cause is paying three feature-specific subprocess startups for a typed conversion already exposed as extractPiPromptInput.

On the frozen Intel base, the unchanged file passed unloaded in 4.43 seconds of test time (2.197/1.117/1.118 seconds per case). With 32 bounded CPU burners, all three unchanged cases timed out at the existing 5-second ceiling and were reported at 6.927/6.913/8.498 seconds.

What changed

• Added exact mixed text/local-file and file-only assertions to turn-input.test.ts, directly against the typed conversion called by both turn and steer handlers.
• Replaced the generic text prompt in the existing real-process stop{release} lifecycle case with a metadata-bearing local-file-only turn and retained the child shutdown/checkpoint assertions.
• Added a local file to the existing real-process successful steer case and retained its accepted-input, turn-boundary, framing, and no-error assertions.
• Deleted the standalone three-session bridge.local-file.test.ts.

This adds no subprocess startup: the meaningful turn/start and turn/steer protocol checks ride real child sessions already required for lifecycle coverage. No timeout, polling deadline, retry budget, production behavior, protocol field, CLI/SDK surface, or host-daemon wire contract changed, so HOST_DAEMON_PROTOCOL_VERSION is unchanged.

A timeout increase was rejected because the work is deterministic and its repeated process construction is avoidable. A shared feature-specific fake-Pi session was also rejected because it would preserve unnecessary startup exposure and duplicate existing lifecycle sessions. The retained real-process checks continue waiting for observable turn boundaries and child exit, while the conversion matrix itself completes synchronously.

Open PR/issue searches found no owner for bridge.local-file.test.ts or the exact timeout. The only open PR touching the Pi bridge is #3249, for skill-command behavior; it does not touch this test. BB thread searches likewise found no overlapping local-file flake owner. Merged #3302 is the structural precedent for the distinct skill-command suite.

How you verified

Mandatory host gate and every workload ran on enrolled Intel host host_nwqfteeqz4 (Intel(R) Core(TM) i5-1038NG7 CPU @ 2.00GHz, x86_64). HEAD began at and retains merge-base a4f513251851bc357fbc0f28e61c331ea3f9f2e4; origin/main advanced afterward and this branch intentionally kept the frozen base.

• Unchanged-main focused run: 3 passed; 4.43 seconds of test time.
• Unchanged-main 32-burner reproduction: 3/3 timed out at the unchanged 5-second ceiling; 6.927/6.913/8.498 seconds reported.
• Final identical 32-burner conversion run: 12/12 passed in 50 ms of test time; the local-file case took 3 ms.
• Final focused conversion plus reused turn/steer protocol checks: 3/3 passed.
• pnpm exec turbo run test --filter=bb-plugin-provider-pi --force -- --maxWorkers=2: 26 files and 154 tests passed, one file/test skipped.
• The default-worker full package run demonstrated the systemic oversubscription separately: 150 tests passed and four unrelated settings/conformance/lifecycle cases timed out or observed late cleanup; both changed real-process cases passed under that load at 13.413 and 12.637 seconds. No clock was changed in response.
• pnpm exec turbo run typecheck --filter=bb-plugin-provider-pi --force: 4 Turbo tasks passed.
• pnpm exec turbo run build --filter=@bb/host-daemon --force: 5 Turbo tasks passed.
• pnpm exec turbo run test --filter=@bb/plugin-build --force -- --maxWorkers=2: 10 files and 137 tests passed, one skipped, including provider-Pi server and host artifact builds.
• pnpm exec oxfmt --check plugins/provider-pi/src/bridge/bridge.lifecycle.test.ts plugins/provider-pi/src/bridge/bridge.round2.test.ts plugins/provider-pi/src/bridge/turn-input.test.ts
• git diff --check

Every test, build, formatting, and synthetic-load command used an external deadline and a dedicated top-level process group; the load runner trapped EXIT/INT/TERM/HUP and reaped its workers. Post-run process and temporary-directory audits found no surviving burner, Vitest, Turbo, fake-Pi child, or task-specific temporary directory.

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