Fix stale commit extraction resume failures

[apstenku123]

Summary

• ignore stale repo-level commit extraction failures once commit_plan plus exact ranges prove completion
• persist a derived aggregate completion sentinel that clears the stale failure
• keep failed range keys fail-closed

Verification

• 7 focused commit completion tests passed
• 89 conveyor and problem-repo regression tests passed
• py_compile and git diff --check passed

[github-actions]

🤖 Hi @apstenku123, I've received your request, and I'm working on it now! You can track my progress in the logs for more details.

[Copilot]

Pull request overview

This PR addresses resume failures caused by stale repo-level repo::commits failure records by treating exact range coverage (validated against an authoritative repo::commit_plan) as the source of truth for completion, and persisting a derived aggregate “complete” sentinel that clears the stale failure.

Changes:

• Update manifest_complete_commit_ranges() to ignore stale repo::commits failures while still failing closed on any failed range key (repo::r*).
• Add mark_commit_stream_complete() to persist a derived aggregate completion record (repo::commits) once exact plan+range coverage proves completion (and clear any stale aggregate failure).
• Extend tests to cover stale aggregate failure handling and ensure failed range keys still prevent completion.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
scripts/streaming_conveyor.py	Adjusts commit completion proof logic to ignore stale aggregate failures, adds a derived completion sentinel, and wires it into resume/cleanup decisions.
tests/test_streaming_conveyor_progress.py	Adds regression tests for stale aggregate failure ignoring, failed-range fail-closed behavior, and sentinel persistence/failed-key clearing.

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