perf(config): mtime-signature fast path for load_config

[ChuckBuilds]

Summary

PR 6 of the performance series. load_config() did full work on every call — 3 file reads + 3 JSON parses + a recursive template-migration diff — and it's called from ~30 web request handlers, several 2–3× per request.

Now: 3 os.stat calls; if the (mtime_ns, size) signature of config/secrets/template is unchanged since the last successful load, return the already-parsed self.config (identical aliasing semantics to the full path). Signature taken after load+migration so migration write-backs don't retrigger; both save paths refresh it; rollback and raw-file writes self-invalidate through the mtime they change.

Cross-process freshness preserved by construction — the web process's save bumps the mtime, so the display process's next call re-reads (dedicated test). Same-second edits caught by mtime_ns + size.

Verification

7 new tests: zero file opens on the fast path (counted via monkeypatched open), reload on each of the three files changing, same-mtime/different-size edit detection, save-then-load coherence with secrets preserved, and the cross-process pickup. Full config-related suites green (the 2 failures are the pre-existing order-dependent TestConfigAPI double-sided ones on main).

🤖 Generated with Claude Code

https://claude.ai/code/session_01FqzC1nzTWL4kaqgMaQZFam

Summary by CodeRabbit

• Performance

  • Improved configuration loading to avoid unnecessary file reads when configuration files are unchanged.
  • Configuration changes are detected reliably, including edits made within the same timestamp interval.

• Bug Fixes

  • Ensured saved settings remain immediately available without redundant reloads.
  • External updates to configuration files are now detected and reflected correctly.

• Tests

  • Added coverage for caching, file changes, template updates, and save/reload behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 94d9724a-b147-479d-a286-b9813d356994

📥 Commits

Reviewing files that changed from the base of the PR and between 6edd80d and 373fe2e.

📒 Files selected for processing (2)

• src/config_manager.py
• test/test_config_load_cache.py

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📝 Walkthrough

Walkthrough

ConfigManager now caches loaded configuration using (mtime_ns, size) signatures for config, secrets, and template files. Saves refresh the cache signature, while tests cover unchanged loads, file changes, same-mtime edits, migrations, and external updates.

Changes

Config Cache

Layer / File(s)	Summary
Signature cache and save coherence src/config_manager.py	Adds file-signature tracking, a cached-load fast path, post-load signature updates, and signature refreshes after atomic and non-atomic saves.
Cache invalidation and save tests test/test_config_load_cache.py	Tests unchanged-file caching, config/secrets/template changes, same-mtime edits, template migration, save coherence, and cross-process updates.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant ConfigManager
  participant ConfigFiles
  ConfigManager->>ConfigFiles: Compute mtime_ns and size signature
  ConfigFiles-->>ConfigManager: Return current signature
  ConfigManager->>ConfigManager: Compare with _loaded_sig
  ConfigManager-->>ConfigManager: Return cached config or load files

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🚥 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 matches the main change: adding an mtime-signature fast path to load_config for config caching.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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 perf/config-mtime-cache

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 4 complexity · 0 duplication

Metric	Results
Complexity	4
Duplication	0

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