Fix runtime issues found during live testing

- Fix jinja2.sandbox import: use `from jinja2.sandbox import
  SandboxedEnvironment` (dotted attribute access doesn't work)
  in templates.py, sync.py, and notifier.py
- Fix greenlet crash in tracker trigger: SQLAlchemy async sessions
  can't survive across aiohttp.ClientSession context managers.
  Eagerly load all tracker/server data before entering HTTP context.
  Split check_tracker into check_tracker (scheduler, own session)
  and check_tracker_with_session (API, reuses route session).
- Fix _check_album to accept pre-loaded params instead of tracker
  object (avoids lazy-load access after greenlet context break)

Tested end-to-end against live Immich server:
- Server connection + album browsing: OK (39 albums)
- Template creation + preview: OK
- Webhook target creation: OK
- Tracker creation + trigger: OK (initialized 4 assets)
- Second trigger: OK (no_changes detected)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/server/src/immich_watcher_server/api/sync.py

@@ -6,6 +6,7 @@ from sqlmodel import select
 from sqlmodel.ext.asyncio.session import AsyncSession
 
 import jinja2
+from jinja2.sandbox import SandboxedEnvironment
 
 from ..database.engine import get_session
 from ..database.models import (
@@ -136,7 +137,7 @@ async def render_template(
         raise HTTPException(status_code=404, detail="Template not found")
 
     try:
-        env = jinja2.sandbox.SandboxedEnvironment(autoescape=False)
+        env = SandboxedEnvironment(autoescape=False)
         tmpl = env.from_string(template.body)
         rendered = tmpl.render(**body.context)
         return {"rendered": rendered}

packages/server/src/immich_watcher_server/api/templates.py

@@ -6,6 +6,7 @@ from sqlmodel import select
 from sqlmodel.ext.asyncio.session import AsyncSession
 
 import jinja2
+from jinja2.sandbox import SandboxedEnvironment
 
 from ..auth.dependencies import get_current_user
 from ..database.engine import get_session
@@ -124,7 +125,7 @@ async def preview_template(
     """Render a template with sample data."""
     template = await _get_user_template(session, template_id, user.id)
     try:
-        env = jinja2.sandbox.SandboxedEnvironment(autoescape=False)
+        env = SandboxedEnvironment(autoescape=False)
         tmpl = env.from_string(template.body)
         rendered = tmpl.render(**_SAMPLE_CONTEXT)
         return {"rendered": rendered}

packages/server/src/immich_watcher_server/api/trackers.py

@@ -128,9 +128,8 @@ async def trigger_tracker(
 ):
     """Force an immediate check for a tracker."""
     tracker = await _get_user_tracker(session, tracker_id, user.id)
-    # Import here to avoid circular imports
-    from ..services.watcher import check_tracker
-    result = await check_tracker(tracker.id)
+    from ..services.watcher import check_tracker_with_session
+    result = await check_tracker_with_session(tracker.id, session)
     return {"triggered": True, "result": result}