Speed up integration-test fixtures on Windows (shrink copied transcripts; skip symlink tests when unavailable)

[cboos]

Part of #248.

Problem

The test suite is far slower on Windows than Linux. Profiling the worst
offenders — the test_integration_realistic.py family (18 of the 25
slowest tests, 30–45s each) — showed the cost is not the
shutil.copytree of the fixture data (~0.15s) but the repeated
rendering + cache build of the large fixture transcripts, which every
function-scoped test re-does. A couple of fixture session files are ~5 MB
each and dominate.

Change

• Shrink oversized transcripts in the copied fixture data only
  (_shrink_large_transcripts), leaving the source tree pristine so
  volume-sensitive tests (test_performance, test_dag*, …) keep the
  full data. The truncation is a leading-prefix cut, which is DAG-safe:
  an entry's parentUuid always refers to an earlier line, so dropping
  the tail removes only leaf descendants. agent-/subagents files and
  content-sensitive fixtures stay below the 600 KB threshold.
• Skip the symlink-based aggregate tests when symlinks aren't
  available. On Windows without Developer Mode/elevation, os.symlink
  raises OSError [WinError 1314]; the tests now probe capability once
  and skipif, so they still run everywhere symlinks work
  (Linux/macOS/elevated Windows).

Results (local Windows)

Scope	Before	After
test_integration_realistic.py (serial)	150.3s	93.2s (−38%)
Full unit suite (-n auto)	185.7s	146.9s (−21%)

No production code is touched; the coverage trade-off is documented in the
fixture module. This is an absolute speedup (it helps Linux
proportionally too); the Windows/Linux ratio is addressed by the
companion PRs tracked in #248.

Summary by CodeRabbit

• Bug Fixes
  • Improved test reliability and speed by reducing oversized temporary transcript files during realistic integration runs.
  • Adjusted scan/characterization tests to automatically skip on platforms that don’t permit symlink creation, avoiding failures in restricted environments.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

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Run ID: 486f3dd3-6c65-4733-b514-9d0276d0ce89

📥 Commits

Reviewing files that changed from the base of the PR and between f3bc27c and 9014816.

📒 Files selected for processing (1)

• test/test_integration_realistic.py

🚧 Files skipped from review as they are similar to previous changes (1)

• test/test_integration_realistic.py

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📝 Walkthrough

Walkthrough

Integration test fixtures now shrink oversized standalone JSONL transcripts after copying project trees, and characterization tests now skip symlink-dependent coverage when symlink creation is unavailable.

Changes

Test Stability Improvements

Layer / File(s)	Summary
Large transcript shrinking in integration fixtures test/test_integration_realistic.py	Adds module-level constants and a _shrink_large_transcripts(projects_dir) helper; temp_projects_copy and projects_with_cache fixtures call it after shutil.copytree.
Symlink capability probe and skipif guard test/test_session_scan_characterization.py	Adds module-level _symlinks_supported() probe and _SYMLINKS_SUPPORTED constant; applies pytest.mark.skipif to the index inline-aggregate characterization test class.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• daaain/claude-code-log#186: Introduced the index inline-aggregate characterization tests in test/test_session_scan_characterization.py that are now guarded with the symlink skipif decorator.

Poem

🐇 Hop hop, the tests grow light,
Trimming transcripts down just right.
Where symlinks cannot start their dance,
The tests take a respectful chance.

🚥 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 summarizes the main changes: speeding up Windows integration tests by shrinking copied transcripts and skipping symlink tests when unsupported.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
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.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch dev/win-test-speedup

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[coderabbitai]

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 `@test/test_integration_realistic.py`:
- Around line 71-77: The truncation logic in the JSONL fixture copy path can
still write a partial record when no complete line exists within the kept
prefix. Update the truncation step around the `cut`/`last_newline` handling so
that `load_transcript()` only receives complete JSONL lines: if `last_newline`
is not found within the kept prefix, skip writing the truncated file (or
otherwise avoid writing any partial object) before `jsonl_file.write_bytes` is
called.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ba425536-a218-4d4d-8a49-0e92d235b323

📥 Commits

Reviewing files that changed from the base of the PR and between 4bd633f and f3bc27c.

📒 Files selected for processing (2)

• test/test_integration_realistic.py
• test/test_session_scan_characterization.py