test(e2e): isolate HOME in Setup Journey + Init Edge Cases blocks

[orendi84]

The bug

The E2E: Setup Journey block in test/e2e/mechanical.test.ts runs gbrain init --non-interactive --url $DATABASE_URL in a subprocess that inherits the real HOME env var. gbrain init calls saveConfig() (src/commands/init.ts:198) which writes to ~/.gbrain/config.json in whatever homedir() returns - i.e. the developer's real home directory.

Run this exact command from CONTRIBUTING.md:

DATABASE_URL=postgresql://postgres:postgres@localhost:5434/gbrain_test bun run test:e2e

...and your real ~/.gbrain/config.json gets silently overwritten with:

{"engine":"postgres","database_url":"postgresql://postgres:postgres@localhost:5434/gbrain_test"}

Any Supabase URL and API keys that were in the config are gone. The gbrain CLI then fails with 28P01 password authentication failed on the next real-brain query.

I hit this on my 13k-page brain today running migrations. Cost ~90 minutes of debugging before we realized tests had clobbered the config.

The fix

Override process.env.HOME to a fresh mkdtempSync() dir in beforeAll, restore in afterAll, and pass HOME explicitly to spawned subprocesses. This is the same pattern already used in test/e2e/migration-flow.test.ts (see lines 62-73, 80-90) - that file is the only other e2e test that had the discipline to isolate HOME correctly.

Applied the same fix defensively to E2E: Init Edge Cases even though its current test strips DATABASE_URL before spawning. If a future test in that block calls gbrain init with a URL, the isolation is already there.

Scope

• One file changed: test/e2e/mechanical.test.ts
• +36 lines, -4 lines
• Zero production code changes
• Zero new dependencies (mkdtempSync, rmSync, tmpdir, join already imported)
• Test behavior unchanged, just safer re: developer's real config

Verification

Locally: file builds clean via bun build, matches the migration-flow.test.ts pattern which is already known-good in the existing E2E suite.