fix(structural): preserve parser failure blob provenance

[nia-sg-bot]

Summary

• include the immutable pre/post blob ID in every Tree-sitter PARSE_FAILURE warning
• retain the exact post-change parser-failure golden fixture and cover a fixed pre-change syntax error
• keep parser dependency failures reproducible against the staged blob identity

Validation

• python3 -m pytest (205 passed)
• git diff --check

Part of #22

Remaining work: expand deterministic Tree-sitter coverage beyond this parser-failure provenance slice.

Summary by CodeRabbit

• Bug Fixes
  • Parse failure reports now identify whether the error came from the pre-change or post-change snapshot and include the relevant blob ID and error details.
  • Added regression coverage for syntax errors in committed snapshots, even when the worktree has been repaired.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: 83908fde-b2e7-4dd6-906f-85a4ffdadebe

📥 Commits

Reviewing files that changed from the base of the PR and between 864a3de and 7a27788.

📒 Files selected for processing (3)

• diffgraph/structural.py
• tests/fixtures/python_parser_failure.json
• tests/test_structural.py

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Walkthrough

Parse failure warnings now identify whether the failure occurred in the pre- or post-change snapshot and include that snapshot’s blob object ID. Tests cover a committed syntax error and updated post-change parser dependency warning details.

Changes

Parse Failure Details

Layer / File(s)	Summary
Format and verify parse failure warnings diffgraph/structural.py, tests/test_structural.py, tests/fixtures/python_parser_failure.json	A shared helper formats warnings with the snapshot side, blob object ID or absent, exception type, and error detail. Both parse failure branches use the helper and retain skip-and-continue handling. Tests check the pre-change syntax error and post-change parser dependency warning details.

Priority: ⬇️ Low

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

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 7a277

Parse-failure warnings now identify the affected snapshot, and file-skipping behavior is unchanged. No concrete merge-blocking risk remains.

Security Architecture Review

Security architecture risk: ⚪ Minimal · up to 7a277

The change adds precise source-version information to parser warnings without changing what is read, how parsing failures are handled, or who can invoke analysis. The same blob identifiers were already included in analysis output. No material security risk was found in the changed behavior.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The changed exposure is diagnostic text delivered to existing analysis-output consumers. The production diff introduces no additional repository reads, parser calls, or authority-bearing operation.

Trust Boundaries and Controls

• observed — The routed public-entrypoint ranges exercise analyze_local_diff from tests. The reviewed production change leaves its interface and parsing controls unchanged; it only enriches warnings after an existing parser failure.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 62.50% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 functions across 2 files. (1 skipped: 1…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 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 main change: preserving parser failure blob provenance in structural analysis.
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.

Full details: Docstring Coverage

Explanation

Docstring coverage is 62.50% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 functions across 2 files. (1 skipped: 1 unsupported.)

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