refactor(server): extract the loops routes into routers/loops.py (R3) (#839)

Third router. Practice loops (saved A/B regions per song): GET/POST/DELETE
/api/loops, meta_db-only (0 setattr targets, 0 helpers to relocate per
router_scan.py). Bodies verbatim; @app -> @router, meta_db -> appstate.meta_db.
include_router at the original site; 143-route table identical to origin/main.

server.py: 9,337 -> 9,301.

No test retargeting (test_demo_mode only names the paths in middleware regexes).
Verified: pyflakes clean; route table identical; pytest 2398 passed; packaging
guard green; eslint 0; boot smoke drives POST (auto-names "Loop N") / GET / DELETE
/ missing-fields error, and demo mode 403s both writes while allowing the read.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -26,7 +26,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   next root-level module can't ship broken.
 
 ### Added
-- **`routers/` — extracting `server.py`'s route layer, cheapest-first (R3).** Each PR moves a cohesive route group into a `fastapi.APIRouter` under `lib/routers/`, mounted with `app.include_router(...)` at its original site (FastAPI matches in registration order; the full route table stays byte-identical). Bodies are verbatim — only the decorator receiver (`@app` → `@router`) and singleton reads (`meta_db` → `appstate.meta_db`, resolved at call time) change. So far: `audio_effects` (5 routes), `artist_aliases` (5 routes — the Tidy-up/P4 alias overrides). The next cut is picked by a dependency-closure scan that ranks groups by how many `monkeypatch.setattr(server, …)` targets they'd drag along.
+- **`routers/` — extracting `server.py`'s route layer, cheapest-first (R3).** Each PR moves a cohesive route group into a `fastapi.APIRouter` under `lib/routers/`, mounted with `app.include_router(...)` at its original site (FastAPI matches in registration order; the full route table stays byte-identical). Bodies are verbatim — only the decorator receiver (`@app` → `@router`) and singleton reads (`meta_db` → `appstate.meta_db`, resolved at call time) change. So far: `audio_effects` (5), `artist_aliases` (5), `loops` (3 — saved A/B practice regions). The next cut is picked by a dependency-closure scan that ranks groups by how many `monkeypatch.setattr(server, …)` targets they'd drag along.
 - **`routers/` — the first extracted route module (R3).** The five audio-effects mapping
   endpoints move out of `server.py` into `lib/routers/audio_effects.py` as a
   `fastapi.APIRouter`, mounted with `app.include_router(...)` **at the point in the file

docs/size-exemptions.md

@@ -55,8 +55,8 @@ without a *signed* exemption" is unenforceable.
 ## Planned, NOT exempt (owned by split plans — listed so nothing falls between states)
 
 core `static/app.js` (11,852) · `static/highway.js` (4,168, whole file) · `server.py`
-(9,337 — was 14,037; ratcheted by the R3 `MetadataDB` + `AudioEffectsMappingDB`
-extractions and the first two `routers/` modules) ·
+(9,302 — was 14,037; ratcheted by the R3 `MetadataDB` + `AudioEffectsMappingDB`
+extractions and the first three `routers/` modules) ·
 `lib/metadata_db.py` (4,373 — new in R3; the `MetadataDB` class alone is 4,018 lines
 and is a monolith in its own right, to be split per-table once the router train
 lands) · `static/v3/songs.js` (4,134) · `static/capabilities/audio-session.js`

lib/routers/loops.py

@@ -0,0 +1,52 @@
+"""Practice loops — saved A/B regions per song.
+
+Extracted verbatim from ``server.py`` (R3); only the decorator receiver
+(``@app`` -> ``@router``) and the singleton reads (``meta_db`` ->
+``appstate.meta_db``) changed. See ``appstate.py`` for why the reads stay
+module attributes.
+"""
+
+from fastapi import APIRouter
+
+import appstate
+
+router = APIRouter()
+
+
+@router.get("/api/loops")
+def list_loops(filename: str):
+    rows = appstate.meta_db.conn.execute(
+        "SELECT id, name, start_time, end_time FROM loops WHERE filename = ? ORDER BY start_time",
+        (filename,)
+    ).fetchall()
+    return [{"id": r[0], "name": r[1], "start": r[2], "end": r[3]} for r in rows]
+
+
+@router.post("/api/loops")
+def save_loop(data: dict):
+    filename = data.get("filename", "")
+    name = data.get("name", "").strip()
+    start = data.get("start")
+    end = data.get("end")
+    if not filename or start is None or end is None:
+        return {"error": "Missing fields"}
+    if not name:
+        count = appstate.meta_db.conn.execute(
+            "SELECT COUNT(*) FROM loops WHERE filename = ?", (filename,)
+        ).fetchone()[0]
+        name = f"Loop {count + 1}"
+    with appstate.meta_db._lock:
+        appstate.meta_db.conn.execute(
+            "INSERT INTO loops (filename, name, start_time, end_time) VALUES (?, ?, ?, ?)",
+            (filename, name, float(start), float(end))
+        )
+        appstate.meta_db.conn.commit()
+    return {"ok": True, "name": name}
+
+
+@router.delete("/api/loops/{loop_id}")
+def delete_loop(loop_id: int):
+    with appstate.meta_db._lock:
+        appstate.meta_db.conn.execute("DELETE FROM loops WHERE id = ?", (loop_id,))
+        appstate.meta_db.conn.commit()
+    return {"ok": True}

server.py

@@ -71,7 +71,7 @@ from audio_effects_db import AudioEffectsMappingDB
 # Lives in lib/ because that is the one core dir every packaging path copies.
 import appstate
 # Extracted route modules. They import `appstate`, never `server` — one-way graph.
-from routers import audio_effects, artist_aliases
+from routers import audio_effects, artist_aliases, loops
 import sloppak as sloppak_mod
 import drums as drums_mod
 import notation as notation_mod
@@ -5903,44 +5903,9 @@ def api_remove_wanted(wanted_id: int):
 
 
 # ── Loops API ────────────────────────────────────────────────────────────────
-
-@app.get("/api/loops")
-def list_loops(filename: str):
-    rows = meta_db.conn.execute(
-        "SELECT id, name, start_time, end_time FROM loops WHERE filename = ? ORDER BY start_time",
-        (filename,)
-    ).fetchall()
-    return [{"id": r[0], "name": r[1], "start": r[2], "end": r[3]} for r in rows]
-
-
-@app.post("/api/loops")
-def save_loop(data: dict):
-    filename = data.get("filename", "")
-    name = data.get("name", "").strip()
-    start = data.get("start")
-    end = data.get("end")
-    if not filename or start is None or end is None:
-        return {"error": "Missing fields"}
-    if not name:
-        count = meta_db.conn.execute(
-            "SELECT COUNT(*) FROM loops WHERE filename = ?", (filename,)
-        ).fetchone()[0]
-        name = f"Loop {count + 1}"
-    with meta_db._lock:
-        meta_db.conn.execute(
-            "INSERT INTO loops (filename, name, start_time, end_time) VALUES (?, ?, ?, ?)",
-            (filename, name, float(start), float(end))
-        )
-        meta_db.conn.commit()
-    return {"ok": True, "name": name}
-
-
-@app.delete("/api/loops/{loop_id}")
-def delete_loop(loop_id: int):
-    with meta_db._lock:
-        meta_db.conn.execute("DELETE FROM loops WHERE id = ?", (loop_id,))
-        meta_db.conn.commit()
-    return {"ok": True}
+# Mounted here, where these routes used to be defined (FastAPI matches in
+# registration order). Implementation in lib/routers/loops.py.
+app.include_router(loops.router)
 
 
 # ── Audio Effects Mapping API ───────────────────────────────────────────────