test: stop the suite writing to the real ~/.pi/agent audit log

[carstenlucke]

Problem

Tests that delegate with the default config (auditLog defaults to on, auditLogPath unset) resolve their log path through getAgentDir(), which falls back to the real ~/.pi/agent. Every run therefore appended fixture rows to the developer's production vision-audit.log.

Measured on a clean checkout before the fix:

Audit-Log before test run:  174 lines
Audit-Log after test run:   188 lines
=> one `pnpm test` writes 14 entries into the real audit log

After a handful of runs the log held 84 fixture rows naming providers the user never configured (ollama/minimax-m3:cloud, openrouter/qwen3.5:cloud) for images that never existed (/tmp/vision-delegate-*/pixel.png), interleaved with the genuine ones.

No network traffic occurs — globalThis.fetch is mocked throughout delegate.test.ts — so nothing leaked. But the audit log is precisely the artefact that answers "where did my image bytes actually go?", and fixture noise makes it unusable for that. README.md sells this log as a privacy feature; it should not be forgeable by a test run.

tests/integration.test.ts already guarded itself with an ad-hoc PI_CODING_AGENT_DIR redirect. Nothing else did.

Fix

tests/setup.ts redirects the agent dir to a throwaway temp dir, imported as the first statement of every tests/*.test.ts. Doing it per file rather than via a runner flag means the redirect holds however the suite is started — pnpm test, a bare tsx --test, a single file, or a run from another working directory.

Details worth knowing:

• An inherited PI_CODING_AGENT_DIR is honoured (CI, wrapper scripts) unless it resolves inside ~/.pi, which is exactly the pollution this prevents. The check is separator-aware, so a sibling such as ~/.pi-sandbox stays valid.
• The expanded path is written back, so the env var and getAgentDir() agree even when the dir was passed as ~/….
• Cleanup runs on SIGINT/SIGTERM/SIGHUP as well as exit, so Ctrl-C no longer leaks one temp dir per test file.
• integration.test.ts drops its ad-hoc redirect in favour of the shared one.

Two guards keep it from regressing silently: a meta-test fails if a test file omits the import, and a second test asserts the redirect actually took effect.

Verification

	tests	growth of the real audit log
with the redirect	354 pass	0
without it (counter-check)	353 pass, 1 fail	14

The guard fires exactly when it should. tsc --noEmit clean.

Scope

Test-only — no production code touched, hence the test: prefix. The bug was never about what the suite executes, only about where it writes.

tests/audit.test.ts needed no behavioural change: it passes explicit paths and never calls getAgentDir(). The audit-specific tests in delegate.test.ts (T60 ff.) set auditLogPath themselves and are likewise untouched.

Note

Independent of #20 — different cause, different scope, no shared commits. Either can merge first.