feat: add conversation and conversation_messages tables for concurrent messaging (#8182)

.skills/db-migrations-schema-changes/SKILL.md

@@ -90,6 +90,36 @@ Workflow for Postgres-targeted migration:
    - `uv run alembic upgrade head`
    - `uv run alembic revision --autogenerate -m "..."`
 
+### 5. Resetting local Postgres for clean migration generation
+
+If your local Postgres database has drifted from main (e.g., applied migrations
+that no longer exist, or has stale schema), you can reset it to generate a clean
+migration.
+
+From the repo root (`/Users/sarahwooders/repos/letta-cloud`):
+
+```bash
+# 1. Remove postgres data directory
+rm -rf ./data/postgres
+
+# 2. Stop the running postgres container
+docker stop $(docker ps -q --filter ancestor=ankane/pgvector)
+
+# 3. Restart services (creates fresh postgres)
+just start-services
+
+# 4. Wait a moment for postgres to be ready, then apply all migrations
+cd apps/core
+export LETTA_PG_URI=postgresql+pg8000://postgres:postgres@localhost:5432/letta-core
+uv run alembic upgrade head
+
+# 5. Now generate your new migration
+uv run alembic revision --autogenerate -m "your migration message"
+```
+
+This ensures the migration is generated against a clean database state matching
+main, avoiding spurious diffs from local-only schema changes.
+
 ## Troubleshooting
 
 - **"Target database is not up to date" when autogenerating**
@@ -101,7 +131,7 @@ Workflow for Postgres-targeted migration:
     changed model is imported in Alembic env context.
 - **Autogenerated migration has unexpected drops/renames**
   - Review model changes; consider explicit operations instead of relying on
-    autogenerate.
+    autogenerate. Reset local Postgres (see workflow 5) to get a clean baseline.
 
 ## References