Fix Codex marketplace credential cleanup gate

[ericjuta]

Summary

• retry and verify repository credential deletion before any finalizer-launched Codex cleanup command
• skip plugin remove and marketplace remove when credentials remain in the isolated HOME
• add a falsifiable injected removal-failure regression proving only marketplace-add can run and scoped temporary state still disappears

Verification

• bun --bun node_modules/.bin/vp test --run packages/evals/__tests__/check-codex-marketplace.test.ts — 1 file, 7 tests
• bun run check
• bun run test — 15 files, 134 tests
• bun run effect-tsgo:diagnostics — 62 files, 0 diagnostics
• bun audit — 320 packages, 0 vulnerabilities
• bun run check:public-boundary with Node 24.18.0 — 270 files, 11 archives, 0 findings
• focused security review — no findings
• attested external review — no findings, patch correct (94% confidence)

Context

Forward fix for the post-merge credential-lifetime finding on #28. The trusted marketplace-add process remains the only child allowed to receive GIT_ASKPASS; all subsequent normal and cleanup commands require successful deletion and absence verification first.

[ericjuta]

Delivered to main as 21484b15698a532d546af413b2441cf9cd8272e1.

Main CI passed: https://github.com/askgina/plugins/actions/runs/33017864779

The immutable-revision Smoke Codex marketplace at published revision step succeeded, and the full suite includes the new deletion-failure regression: removal is retried, no later normal or cleanup Codex command starts while credentials remain, and scoped temporary state is still removed.