fix: merge main branch and renumber migration 037→040

Resolve all merge conflicts between our automation feature branch and
current main (v0.163.0, 920 commits ahead).

Conflicts resolved:
- app/api/__init__.py: add automation_router alongside main's new routers
  (classification_rules, qr_auth, sessions, system_reset)
- app/config.py: add main's new settings (dropbox_use_global_credentials,
  factory_reset_on_startup, enable_factory_reset)
- app/models.py: add main's new models (ClassificationRuleModel, UserSession,
  QRLoginChallenge, SharePoint integration type)
- app/utils/settings_service.py: merge automation_hooks_enabled with main's
  new metadata entries
- docs/API.md: merge automation API docs with main's classification rules docs
- docs/ConfigurationGuide.md: add factory reset settings
- tests/conftest.py: import both AutomationHook and new main models

Migration renumbered:
- 037_add_automation_hooks → 040_add_automation_hooks
- down_revision: 039_add_classification_rules (was 036_add_document_translation_fields)
- Chain: 036 → 037 → 038 → 039 → 040 (automation hooks)

For all non-automation files with conflicts, main's version was taken since
our branch did not modify those files (conflicts were from a stale prior merge).

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>
Agent-Logs-Url: https://github.com/christianlouis/DocuElevate/sessions/cb62f012-3b69-4415-835e-3857ce3e9f45

docs/DatabaseConfiguration.md

@@ -287,6 +287,27 @@ alembic revision --autogenerate -m "describe your change"
 
 Review the generated file in `migrations/versions/` before applying it.
 
+> **Tip:** For detailed guidance on naming conventions, idempotent patterns, parallel-branch workflows, and resolving merge conflicts, see the [Migration Workflow Guide](MigrationWorkflow.md).
+
+### Validating the Migration Chain
+
+A CI check and pre-commit hook validate that the migration chain has no broken
+references, duplicate revisions, or diverged heads.  Run the check locally:
+
+```bash
+python scripts/check_alembic_migrations.py
+python scripts/check_alembic_migrations.py --verbose   # extra detail
+```
+
+If you see **"Multiple migration heads detected"**, two branches added
+migrations from the same parent.  Create a merge migration:
+
+```bash
+alembic merge heads -m "merge_parallel_branches"
+```
+
+For a complete walk-through, see the [Migration Workflow Guide](MigrationWorkflow.md).
+
 ### Automating Migrations in Docker Compose
 
 Add a short-lived `migrate` service that runs before the API and Worker:
@@ -316,18 +337,26 @@ The Helm chart includes a pre-install and pre-upgrade Job hook that runs `alembi
 
 ## Connection Pooling
 
-SQLAlchemy manages a connection pool automatically.  The defaults are suitable for most deployments.  For high-concurrency or Kubernetes deployments you may want to tune:
+SQLAlchemy manages a connection pool automatically.  DocuElevate selects the pool
+strategy based on the database backend:
+
+- **SQLite** — uses `NullPool` (a fresh connection per request, closed immediately).
+  This avoids the `QueuePool limit reached` `TimeoutError` that can occur under
+  concurrent load because SQLite does not benefit from persistent connection pooling.
+- **PostgreSQL / MySQL** — uses a bounded `QueuePool` whose size is configurable
+  via environment variables.
 
 ```bash
-# Optional — these are set via environment variables if you extend app/database.py
-# Typical production values:
-DB_POOL_SIZE=10         # Number of persistent connections per worker
-DB_MAX_OVERFLOW=20      # Additional connections allowed beyond pool_size
-DB_POOL_TIMEOUT=30      # Seconds to wait for a connection from the pool
-DB_POOL_RECYCLE=1800    # Recycle connections after 30 minutes (avoids stale connections)
+# Tune these for PostgreSQL / MySQL (ignored when using SQLite):
+DB_POOL_SIZE=10         # Number of persistent connections per worker (default: 10)
+DB_MAX_OVERFLOW=20      # Additional connections allowed beyond pool_size (default: 20)
+DB_POOL_TIMEOUT=30      # Seconds to wait for a connection from the pool (default: 30)
+DB_POOL_RECYCLE=1800    # Recycle connections after 30 minutes (default: 1800)
 ```
 
-> **Note:** These environment variables are not exposed in the default `app/config.py`.  If you need to tune them, extend the database engine creation in `app/database.py`.
+All backends also enable `pool_pre_ping`, which sends a lightweight health-check
+before each connection is handed out.  This detects stale or dropped connections
+and transparently reconnects.
 
 For **PgBouncer** (external connection pooling), point `DATABASE_URL` at your PgBouncer instance and use transaction-mode pooling:
 
@@ -491,4 +520,13 @@ Then retry `alembic upgrade head`.
 
 Either increase `max_connections` in `postgresql.conf` or add PgBouncer in front of PostgreSQL.  The default PostgreSQL `max_connections` is `100`; reduce `DB_POOL_SIZE` per worker to stay within this limit.
 
+### "QueuePool limit reached" TimeoutError (SQLite)
+
+If you see `TimeoutError: QueuePool limit of size 5 overflow 10 reached`, your
+deployment is still running an older version of DocuElevate that used a bounded
+connection pool for SQLite.  Upgrade to the latest release — SQLite now uses
+`NullPool`, which eliminates this error entirely.  If you are already on the
+latest version and are still seeing pool exhaustion, ensure you are not
+overriding the engine creation manually.
+
 For more help, see the [Troubleshooting Guide](Troubleshooting.md).