feat(repo-cache): handle empty repositories

[AlexanderLanin]

What this achieves

Repository synchronization now handles repositories with no Git references as an expected, reportable state. Organization-wide policy runs skip those repositories instead of attempting to use a checkout that does not exist.

Why this is necessary

Newly created or otherwise empty repositories can appear in the organization listing without a usable Git ref. Treating the resulting clone or fetch failure as an operational error either makes cache synchronization fail or causes the policy-sync consumer to evaluate a missing checkout.

Changes

• Detect empty repositories during initial clone and cached-checkout refresh.
• Expose empty outcomes separately from synchronization failures.
• Report empty repositories in the cache CLI and library documentation.
• Skip empty outcomes in policy synchronization and keep summary counts accurate.
• Add regression coverage for detection, reporting, and downstream policy handling.

[Copilot]

🟡 Changes recommended

Policy reports mislabel empty repositories, and cached-checkout detection lacks regression coverage.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds explicit handling for repositories without Git references across cache synchronization and policy evaluation.

Changes:

• Detects and reports empty repositories separately from failures.
• Skips empty repositories during policy evaluation.
• Adds CLI, documentation, and regression coverage.

File summaries

File	Description
repo_policy_sync/tests/test_runner.py	Tests empty-repository skipping.
repo_policy_sync/src/runner.py	Excludes empty repositories from evaluation.
repo_cache/tests/test_sync.py	Tests empty synchronization outcomes.
repo_cache/tests/test_cli.py	Tests CLI empty-repository reporting.
repo_cache/tests/test_checkout.py	Tests initial empty-repository detection.
repo_cache/src/sync.py	Models and aggregates empty outcomes.
repo_cache/src/errors.py	Defines the empty-repository exception.
repo_cache/src/cli.py	Reports empty repositories and adjusted totals.
repo_cache/src/checkout.py	Detects missing Git references.
repo_cache/README.md	Documents empty-repository behavior.
repo_cache/__init__.py	Exports the new exception.

Review details

• Files reviewed: 11/11 changed files
• Comments generated: 2
• Review effort level: Balanced

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[Copilot]

🟢 Approval recommended

Empty outcomes are consistently detected, propagated, reported, skipped, and covered by regression tests.

Review details

• Files reviewed: 13/13 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[MaximilianSoerenPollak]

Seems alright.