refactor(server): extract /api/tunings into routers/tunings.py + lib/appconfig.py (R3)

[byrongamatos]

The merged-tuning-catalog route → lib/routers/tunings.py, verbatim except @app→@router, CONFIG_DIR→appstate.config_dir, and two reusable seam substrates:

• lib/appconfig.py — the pure config.json reader _load_config (used by ~11 server sites + future config-reading routers). server.py re-imports it, so those call sites and any server._load_config test reference are unchanged.
• appstate.tuning_providers — the TuningProviderRegistry instance injected by reference (a stable object mutated in place via register()/unregister()), so the router reads the same registry plugins populate via plugin_context. The instance stays defined in server.py, so server.tuning_providers still resolves — zero test retargets.

Tuning constants (DEFAULT_REFERENCE_PITCH, TUNING_PRESET_MIDIS, freqs_to_midis) already live in lib/tunings.py and import directly.

server.py: 6,960 → 6,917.

Verification

• Route table identical (143); pyflakes clean bar the pre-existing unused tuning_name import.
• Full pytest 2400 passed (110 tuning/config cases); npm run lint 0; Codex 0 findings.
• Boot smoke: /api/tunings serves referencePitch + tunings + tuningMidis.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added a tuning catalog API that returns available tunings, reference pitch, and MIDI representations.
  • Added support for shared tuning configuration and provider data across the application.

• Bug Fixes

  • Invalid or missing reference-pitch settings now safely fall back to the default value.

• Documentation

  • Updated size-exemption tracking for the latest routing changes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 5e616abf-0b23-4dff-bfa0-1d0e6446772c

📥 Commits

Reviewing files that changed from the base of the PR and between cce95cb and 5641a89.

📒 Files selected for processing (6)

• CHANGELOG.md
• docs/size-exemptions.md
• lib/appconfig.py
• lib/appstate.py
• lib/routers/tunings.py
• server.py

---

📝 Walkthrough

Walkthrough

The tuning API implementation moves from server.py into routers/tunings.py. Configuration loading becomes shared, the provider registry is injected through appstate, and the server registers the new router while removing the inline endpoint.

Changes

Tuning API extraction

Layer / File(s)	Summary
Shared configuration and state seams lib/appconfig.py, lib/appstate.py	Adds _load_config() for safe JSON dictionary loading and exposes tuning_providers through the appstate injection slots.
Tuning router endpoint lib/routers/tunings.py	Adds GET /api/tunings, including reference-pitch validation, merged tuning retrieval, MIDI metadata generation, and response construction.
Server wiring and release metadata server.py, CHANGELOG.md, docs/size-exemptions.md	Registers the tuning router, publishes the server-owned provider registry, removes the inline implementation, and updates related tracking entries.

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

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant get_tunings
  participant _load_config
  participant tuning_providers
  Client->>get_tunings: GET /api/tunings
  get_tunings->>_load_config: Read config.json
  get_tunings->>tuning_providers: get_merged(referencePitch)
  tuning_providers-->>get_tunings: Merged tunings
  get_tunings-->>Client: referencePitch, tunings, tuningMidis

Loading

🚥 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 accurately summarizes the main refactor: moving /api/tunings into routers/tunings.py and adding lib/appconfig.py.
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 refactor/r3-router-tunings

---

_{Comment @coderabbitai help to get the list of available commands.}