Fix attribution debug self-check timeouts

[svarlamov]

Summary

• give asynchronous attribution polling a fresh bounded deadline after the synthetic commit
• run the configured and terminal Git self-checks sequentially to avoid daemon-side contention
• resolve self-check repositories from the active daemon home so every process recognizes them consistently
• skip session-event recovery and agent-usage throttling for synthetic git-ai debug checkpoints
• add a TestRepo regression that validates the daemon-home path, both self-check targets, and every expected attribution class

Root cause

The attribution self-check shared its three-second deadline between repository setup, three checkpoints, commit processing, and result polling. A new two-second post-commit session-event recovery preflight consumed most of that budget, while the two self-check repositories competed concurrently. In installed debug builds, the synthetic mock_ai checkpoint also opened the production metrics throttle database even though mock metrics are discarded.

The remaining Windows failure exposed a split-home bug in the test harness: the debug subprocess created repositories beneath its isolated process home, while the shared daemon determined the self-check root from GIT_AI_DAEMON_HOME. Because those paths differed, the daemon did not recognize the repositories as synthetic and still ran the recovery path. Windows latency then exhausted the fresh polling deadline.

Impact

git-ai debug now waits for attribution with its own bounded budget, creates diagnostic repositories beneath the active daemon's internal directory, and avoids production-only recovery and telemetry work that cannot affect the synthetic result. Normal checkpoint, recovery, and trace2 ingestion behavior is unchanged.

Validation

• task test TEST_FILTER=attribution_self_checks_do_not_timeout
• task test
• task build
• task lint
• task fmt
• task dev
• installed git-ai debug smoke test: both attribution self-checks passed with untracked, known-human, and AI lines correctly classified

[svarlamov]

• Fix attribution debug self-check timeouts #1944 👈 (View in Graphite)
• main

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.