feat(greenfield): rebuild SlabUploader M1-M3 on clean foundation, all gates green

Clean re-implementation of the full product (not a port of the old M3 tree):
- P0 foundation: 13-table schema + per-call sqlite factory (thread-safe),
  FastAPI app (health, JSON logging + secret redaction, CORS, startup guard).
- P1 M1 Capture: mask/sheetKeep, geometry/rect (min-area rect), measure,
  png crop/inventory/overlay, EXIF decodeOrientedBitmap.
- P2 M2 Photos: stateful capture session (batch, pick-cal, apply mask/crop
  to batch) + photos-ready lineup.
- P3 M3 Create: real backend (crypto, woo client, taxonomy sync, pricing,
  inference Call1/Call2, review, publish, settings, slabs, photos) + real FE
  review/publish/settings screens consuming the API (no hardcoded Woo ids).
- P4 gate exit: check_requirements + check_coverage both exit 0
  (137/155 IDs, 0 gaps); backend 130/130, frontend 150/150, build green.

Cite: docs/REQUIREMENTS.md (155 rows), docs/MILESTONES.md M1-M3.

backend/tests/test_inference.py

@@ -15,25 +15,54 @@ import backend.db as db_mod
 @pytest.fixture
 def env(monkeypatch):
     tmp = tempfile.mkdtemp(prefix="inf_")
-    os.environ["SLAB_DB_PATH"] = os.path.join(tmp, "i.db")
-    os.environ["SLAB_IMAGES_DIR"] = tmp
-    os.environ["WOO_BASE_URL"] = "https://x.com"
-    os.environ["SLAB_AES_KEY"] = base64.b64encode(b"0123456789abcdef0123456789abcdef").decode()
-    db_mod._reset_for_tests()
+    monkeypatch.setenv("SLAB_DB_PATH", os.path.join(tmp, "i.db"))
+    monkeypatch.setenv("SLAB_IMAGES_DIR", tmp)
+    monkeypatch.setenv("WOO_BASE_URL", "https://x.com")
+    monkeypatch.setenv("SLAB_AES_KEY", base64.b64encode(b"0123456789abcdef0123456789abcdef").decode())
     from backend.crypto import encrypt
 
-    conn = db_mod.init_db()
+    db_mod.init_db()
+
+    conn = db_mod.get_connection()
     conn.execute("INSERT OR REPLACE INTO settings(key,value,value_enc) VALUES ('inference_base_url',NULL,?)", (encrypt("https://infer.example.com"),))
     conn.execute("INSERT OR REPLACE INTO settings(key,value,value_enc) VALUES ('inference_api_key',NULL,?)", (encrypt("sk-test"),))
     conn.execute("INSERT OR REPLACE INTO settings(key,value,value_enc) VALUES ('inference_model','gpt-test',NULL)")
     conn.commit()
+    conn.close()
     from backend.app import app
 
-    yield TestClient(app), conn
-    db_mod._reset_for_tests()
+    # Yield a lazy connection: opening it eagerly would hold a WAL read slot
+    # during the app's first write (prompt seed), whose recovery checkpoint
+    # needs a brief exclusive lock and would deadlock on the open reader.
+    lazy = _LazyConn()
+    with TestClient(app) as c:
+        yield c, lazy
     shutil.rmtree(tmp, ignore_errors=True)
 
 
+class _LazyConn:
+    """Defers the sqlite connection to first use (see fixture note)."""
+
+    def __init__(self):
+        self._conn = None
+
+    def _get(self):
+        if self._conn is None:
+            self._conn = db_mod.get_connection()
+        return self._conn
+
+    def execute(self, *a, **k):
+        return self._get().execute(*a, **k)
+
+    def commit(self):
+        return self._get().commit()
+
+    def close(self):
+        if self._conn is not None:
+            self._conn.close()
+            self._conn = None
+
+
 def test_prompt_seed_and_revision(env):
     client, conn = env
     r = client.get("/api/v1/prompts/call1")
@@ -77,19 +106,19 @@ def test_call1_seed_is_locked_expert_prompt(env):
     assert "character\":" not in CALL1_SEED.replace(" ", "")
 
 
-def test_taxonomy_lists_call1_closed_shape():
+def test_taxonomy_lists_call1_closed_shape(monkeypatch):
     """#86: Call 1 lists are closed Woo picks only — no grade/thickness/moisture; feat names stripped."""
     import tempfile, os, shutil
     tmp = tempfile.mkdtemp(prefix="tax_")
-    os.environ["SLAB_DB_PATH"] = os.path.join(tmp, "t.db")
-    os.environ["SLAB_IMAGES_DIR"] = tmp
-    os.environ.setdefault("WOO_BASE_URL", "https://x.com")
-    os.environ.setdefault(
+    monkeypatch.setenv("SLAB_DB_PATH", os.path.join(tmp, "t.db"))
+    monkeypatch.setenv("SLAB_IMAGES_DIR", tmp)
+    monkeypatch.setenv("WOO_BASE_URL", "https://x.com")
+    monkeypatch.setenv(
         "SLAB_AES_KEY",
         base64.b64encode(b"0123456789abcdef0123456789abcdef").decode(),
     )
-    db_mod._reset_for_tests()
-    conn = db_mod.init_db()
+    db_mod.init_db()
+    conn = db_mod.get_connection()
     conn.execute("INSERT INTO woo_categories(id,name,slug,parent_id,woo_id) VALUES (10,'Species','species',NULL,10)")
     conn.execute("INSERT INTO woo_categories(id,name,slug,parent_id,woo_id) VALUES (11,'Walnut','walnut',10,11)")
     conn.execute("INSERT INTO woo_categories(id,name,slug,parent_id,woo_id) VALUES (20,'Wcat','wcat',NULL,20)")
@@ -120,7 +149,6 @@ def test_taxonomy_lists_call1_closed_shape():
     assert "grade_terms" not in tax
     assert "thickness_terms" not in tax
     assert "moisture_terms" not in tax
-    db_mod._reset_for_tests()
     shutil.rmtree(tmp, ignore_errors=True)