chore(dev): self-contained local dev stack (own Postgres + scheduler)

localdev no longer points at the shared .118 database; it now runs its own
local Postgres and its own scheduler, fully decoupled. Removes the shared-DB
migration coupling (no more .118 redeploy after migrations) and lets the
background scheduler actually run during local dev.

docker-compose.localdev.yml

@@ -1,22 +1,34 @@
-# Local development against the central Postgres (an always-on host that also runs the scheduler).
+# Self-contained local development stack — Postgres + API + scheduler, all on this machine.
 #
-# Runs only the webapp/API — no local database, no scheduler — pointed at the shared
-# DB on the server. You see the same live data the 24/7 backfill is filling, and you
-# never run a second scheduler against it.
+# Fully decoupled: its own local database (a Docker volume) and its own scheduler, so there
+# is no shared DB and no migration coupling with any other instance. Edit code, rebuild, and
+# everything (including the background sync) runs right here.
 #
-# Setup: in .env set
-#   DATABASE_URL=postgresql+psycopg://subfeed:<password>@your-db-host:5432/subfeed
-# (use the central DB's host/port and the real POSTGRES_PASSWORD), then:
-#   docker compose -f docker-compose.localdev.yml up --build
+#   docker compose -f docker-compose.localdev.yml up -d --build
 #
-# Browse at http://localhost:8080 — Google login works here because the OAuth redirect
-# is http://localhost:8080/auth/callback.
-#
-# Note: the API runs `alembic upgrade head` on startup, so launching this with newer
-# local migrations will apply them to the shared DB. For risky schema work, point
-# DATABASE_URL at a throwaway local Postgres instead.
+# Browse at http://localhost:8080 — Google login works because the OAuth redirect is
+# http://localhost:8080/auth/callback. The API runs `alembic upgrade head` on startup, so it
+# applies local migrations to THIS local DB only. Seed the catalog once with a pg_dump from
+# another instance if you want real data (see RUNBOOK).
 
 services:
+  db:
+    image: postgres:16-alpine
+    environment:
+      POSTGRES_USER: ${POSTGRES_USER:-subfeed}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-subfeed}
+      POSTGRES_DB: ${POSTGRES_DB:-subfeed}
+    volumes:
+      - pgdata:/var/lib/postgresql/data
+    security_opt:
+      - apparmor:unconfined
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-subfeed} -d ${POSTGRES_DB:-subfeed}"]
+      interval: 5s
+      timeout: 5s
+      retries: 12
+    restart: unless-stopped
+
   api:
     build:
       context: .
@@ -27,11 +39,19 @@ services:
         BUILD_DATE: ${BUILD_DATE:-}
     env_file: .env
     environment:
-      # Exactly one scheduler may write to the shared DB; the server owns it.
-      SCHEDULER_ENABLED: "false"
+      # Own local database (overrides whatever DATABASE_URL is in .env).
+      DATABASE_URL: postgresql+psycopg://${POSTGRES_USER:-subfeed}:${POSTGRES_PASSWORD:-subfeed}@db:5432/${POSTGRES_DB:-subfeed}
+      # This instance owns its scheduler now (its own DB, so no double-write concern).
+      SCHEDULER_ENABLED: "true"
+    depends_on:
+      db:
+        condition: service_healthy
     # Harmless on Docker Desktop; needed if ever run under Docker-in-LXC.
     security_opt:
       - apparmor:unconfined
     ports:
       - "${APP_PORT:-8080}:8000"
     restart: unless-stopped
+
+volumes:
+  pgdata: