Allow Phase 2 memory claims after retry exhaustion

[jif-oai]

Why

The Phase 2 memories job row is only the global lock for the git-backed memory workspace. Manual memory edits do not enqueue new Stage 1 work, so a Phase 2 row with retry_remaining = 0 could be skipped before the worker ever claimed the lock and generated phase2_workspace_diff.md.

That left workspace-only changes unconsolidated after repeated failures, even when retry backoff had elapsed and the filesystem had real diffable work.

What Changed

• Allow try_claim_global_phase2_job to claim the Phase 2 lock after the retry budget is exhausted, while still respecting active retry_at backoff and fresh running leases.
• Treat SkippedRetryUnavailable for Phase 2 as backoff-only, and update the outcome docs to match.
• Clamp Phase 2 retry bookkeeping at zero when failed attempts are recorded.

Verification

• Added phase2_global_lock_can_be_claimed_after_retry_budget_is_exhausted to cover the exhausted-budget lock claim path.
• Ran cargo test -p codex-state.

[jif-oai]

@codex review

[jif-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🎉

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