feat(bootstrapper): record bootstrap stack state on each loop iteration

[dhellmann]

Summary

Writes bootstrap-stack.json to the work directory before each iteration of the DFS loop in Bootstrapper.bootstrap(). The file is a JSON array where index 0 is the next item to be processed (stack[-1]), overwritten on each iteration. Each entry captures identity and accumulated state fields (req, req_type, phase, resolved_version, source_url, why, parent, dep sets); heavy build objects (build_env, paths, build_result) are intentionally excluded.

Enables debugging, progress inspection, and post-mortem analysis of interrupted runs.

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📥 Commits

Reviewing files that changed from the base of the PR and between 27e56a7 and 0abe106.

📒 Files selected for processing (2)

• src/fromager/bootstrapper.py
• tests/test_bootstrapper.py

🚧 Files skipped from review as they are similar to previous changes (2)

• tests/test_bootstrapper.py
• src/fromager/bootstrapper.py

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📝 Walkthrough

Walkthrough

The PR adds persistent stack recording to the bootstrap resolver. Bootstrapper now sets a _stack_filename in the constructor, calls _record_stack_state(stack) at the start of each DFS iteration, and implements _record_stack_state to serialize pending WorkItems (fields: req/req_type/phase/resolved_version/source_url/build_sdist_only, why_snapshot, optional parent, sorted build-dep sets) and overwrite bootstrap-stack.json. Tests add fixtures and assertions validating serialization shape, deterministic dep-set ordering, file creation/overwrite semantics, pop-order preservation, and that bootstrap() calls the recorder.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: adding stack state recording to each bootstrap loop iteration.
Description check	✅ Passed	The description clearly explains the feature, its implementation details, and purpose for debugging and 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.

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/fromager/bootstrapper.py`:
- Around line 1305-1307: The current bootstrap() snapshot write using
open(self._stack_filename, "w") may truncate the file and abort bootstrap on
error; instead, serialize the reversed(stack) into records and write JSON
atomically by writing to a temporary file in the same directory (e.g., use
tempfile.NamedTemporaryFile or a .tmp path) and then atomically replace the
target with os.replace; catch and log any exceptions (use the existing logger on
the object, e.g., self._logger or fallback logger) as a non-fatal warning so
bootstrap() continues on failure, referencing the existing serialize() call and
self._stack_filename to locate the change.

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Fix all unresolved CodeRabbit comments on this PR:

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⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

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Run ID: 876da36e-8403-4513-abee-eb324d8b2989

📥 Commits

Reviewing files that changed from the base of the PR and between bd86c56 and 27e56a7.

📒 Files selected for processing (2)

• src/fromager/bootstrapper.py
• tests/test_bootstrapper.py