test(git): cover regular-to-symlink provenance

[nia-sg-bot]

Summary

• add a deterministic regression covering a regular-file → symlink type transition
• verify exact pre/post paths, modes, and immutable blob IDs for unstaged, staged, and two-dot commit-range resolution
• prove symlink identity is the raw target blob, not a clean-filtered file artifact

Part of #21.

Validation

• python3 -m pytest -q (204 passed)
• python3 -m compileall -q diffgraph tests
• python3 -m diffgraph.cli --help
• git diff --check origin/main...HEAD

Compatibility

No production CLI or schema behavior changes. This locks in the existing versioned snapshot-provenance contract used by downstream consumers.

Remaining work

Issue #21 retains its broader comparison-mode and resolver edge-case acceptance criteria.

Summary by CodeRabbit

• Tests
  • Added coverage for detecting file-to-symlink changes, including their status, modes, and blob IDs across unstaged, staged, and commit-range resolutions.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Plan: Advanced

Run ID: 84ec9b80-1da8-4ef3-871b-8ac09a90027f

📥 Commits

Reviewing files that changed from the base of the PR and between 773e1d0 and baf4da5.

📒 Files selected for processing (1)

• tests/test_git_snapshot.py

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Walkthrough

Adds test coverage for regular-file-to-symlink transitions in unstaged, staged, and commit-range snapshots. The tests check the type-change status, endpoint modes, and blob identities.

Changes

Snapshot provenance tests

Layer / File(s)	Summary
Verify type-change provenance tests/test_git_snapshot.py	Adds assertions for unstaged status T, modes 100644 and 120000, and blob identities. It checks that staged and commit-range resolution match the preceding snapshot entries.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to baf4d

This test-only change strengthens symlink provenance coverage without changing production behavior. No actionable merge-blocking risk is established.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely identifies the added Git test for regular-file-to-symlink provenance. It matches the main change in the pull request.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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