refactor: unify active assignment checks and add project-type guards

- Replace all UnitAssignment "active" checks from `status == "active"` to
  `assigned_until == None` in both project_locations.py and projects.py.
  This aligns with the canonical definition: active = no end date set.
  (status field is still set in sync, but is no longer the query criterion)

- Add `_require_sound_project()` helper to both routers and call it at the
  top of every sound-monitoring-specific endpoint (FTP browser, FTP downloads,
  RND file viewer, all Excel report endpoints, combined report wizard,
  upload-all, NRL live status, NRL data upload). Vibration projects hitting
  these endpoints now receive a clear 400 instead of silently failing or
  returning empty results.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/routers/project_locations.py

@@ -35,6 +35,19 @@ from backend.templates_config import templates
 router = APIRouter(prefix="/api/projects/{project_id}", tags=["project-locations"])
 
 
+# ============================================================================
+# Shared helpers
+# ============================================================================
+
+def _require_sound_project(project) -> None:
+    """Raise 400 if the project is not a sound_monitoring project."""
+    if not project or project.project_type_id != "sound_monitoring":
+        raise HTTPException(
+            status_code=400,
+            detail="This feature is only available for Sound Monitoring projects.",
+        )
+
+
 # ============================================================================
 # Session period helpers
 # ============================================================================
@@ -98,11 +111,11 @@ async def get_project_locations(
     # Enrich with assignment info
     locations_data = []
     for location in locations:
-        # Get active assignment
+        # Get active assignment (active = assigned_until IS NULL)
         assignment = db.query(UnitAssignment).filter(
             and_(
                 UnitAssignment.location_id == location.id,
-                UnitAssignment.status == "active",
+                UnitAssignment.assigned_until == None,
             )
         ).first()
 
@@ -258,11 +271,11 @@ async def delete_location(
     if not location:
         raise HTTPException(status_code=404, detail="Location not found")
 
-    # Check if location has active assignments
+    # Check if location has active assignments (active = assigned_until IS NULL)
     active_assignments = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.location_id == location_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).count()
 
@@ -569,9 +582,9 @@ async def get_available_units(
         )
     ).all()
 
-    # Filter out units that already have active assignments
+    # Filter out units that already have active assignments (active = assigned_until IS NULL)
     assigned_unit_ids = db.query(UnitAssignment.unit_id).filter(
-        UnitAssignment.status == "active"
+        UnitAssignment.assigned_until == None
     ).distinct().all()
     assigned_unit_ids = [uid[0] for uid in assigned_unit_ids]
 
@@ -747,6 +760,9 @@ async def upload_nrl_data(
     from datetime import datetime
 
     # Verify project and location exist
+    project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
+
     location = db.query(MonitoringLocation).filter_by(
         id=location_id, project_id=project_id
     ).first()
@@ -925,15 +941,18 @@ async def get_nrl_live_status(
     Fetch cached status from SLMM for the unit assigned to this NRL and
     return a compact HTML status card. Used in the NRL overview tab for
     connected NRLs. Gracefully shows an offline message if SLMM is unreachable.
+    Sound Monitoring projects only.
     """
     import os
     import httpx
 
-    # Find the assigned unit
+    _require_sound_project(db.query(Project).filter_by(id=project_id).first())
+
+    # Find the assigned unit (active = assigned_until IS NULL)
     assignment = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.location_id == location_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).first()
 

backend/routers/projects.py

@@ -45,6 +45,21 @@ router = APIRouter(prefix="/api/projects", tags=["projects"])
 logger = logging.getLogger(__name__)
 
 
+# ============================================================================
+# Shared helpers
+# ============================================================================
+
+def _require_sound_project(project: Project) -> None:
+    """Raise 400 if the project is not a sound_monitoring project.
+    Call this at the top of any endpoint that only makes sense for sound projects
+    (report generation, FTP browser, RND file viewer, etc.)."""
+    if not project or project.project_type_id != "sound_monitoring":
+        raise HTTPException(
+            status_code=400,
+            detail="This feature is only available for Sound Monitoring projects.",
+        )
+
+
 # ============================================================================
 # RND file normalization — maps AU2 (older Rion) column names to the NL-43
 # equivalents so report generation and the web viewer work for both formats.
@@ -398,11 +413,11 @@ async def get_projects_list(
             project_id=project.id
         ).scalar()
 
-        # Count assigned units
+        # Count assigned units (active = assigned_until IS NULL)
         unit_count = db.query(func.count(UnitAssignment.id)).filter(
             and_(
                 UnitAssignment.project_id == project.id,
-                UnitAssignment.status == "active",
+                UnitAssignment.assigned_until == None,
             )
         ).scalar()
 
@@ -806,11 +821,11 @@ async def get_project_dashboard(
     # Get locations
     locations = db.query(MonitoringLocation).filter_by(project_id=project_id).all()
 
-    # Get assigned units with details
+    # Get assigned units with details (active = assigned_until IS NULL)
     assignments = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.project_id == project_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).all()
 
@@ -899,11 +914,11 @@ async def get_project_units(
     """
     from backend.models import DataFile
 
-    # Get all assignments for this project
+    # Get all assignments for this project (active = assigned_until IS NULL)
     assignments = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.project_id == project_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).all()
 
@@ -1160,15 +1175,18 @@ async def get_ftp_browser(
 ):
     """
     Get FTP browser interface for downloading files from assigned SLMs.
-    Returns HTML partial with FTP browser.
+    Returns HTML partial with FTP browser. Sound Monitoring projects only.
     """
     from backend.models import DataFile
 
-    # Get all assignments for this project
+    project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
+
+    # Get all assignments for this project (active = assigned_until IS NULL)
     assignments = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.project_id == project_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).all()
 
@@ -1202,6 +1220,7 @@ async def ftp_download_to_server(
     """
     Download a file from an SLM to the server via FTP.
     Creates a DataFile record and stores the file in data/Projects/{project_id}/
+    Sound Monitoring projects only.
     """
     import httpx
     import os
@@ -1209,6 +1228,8 @@ async def ftp_download_to_server(
     from pathlib import Path
     from backend.models import DataFile
 
+    _require_sound_project(db.query(Project).filter_by(id=project_id).first())
+
     data = await request.json()
     unit_id = data.get("unit_id")
     remote_path = data.get("remote_path")
@@ -1367,12 +1388,15 @@ async def ftp_download_folder_to_server(
     Download an entire folder from an SLM to the server via FTP.
     Extracts all files from the ZIP and preserves folder structure.
     Creates individual DataFile records for each file.
+    Sound Monitoring projects only.
     """
     import httpx
     import os
     import hashlib
     import zipfile
     import io
+
+    _require_sound_project(db.query(Project).filter_by(id=project_id).first())
     from pathlib import Path
     from backend.models import DataFile
 
@@ -1915,6 +1939,7 @@ async def view_rnd_file(
 
     # Get project info
     project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
 
     # Get location info if available
     location = None
@@ -1958,12 +1983,15 @@ async def get_rnd_data(
     """
     Get parsed RND file data as JSON.
     Returns the measurement data for charts and tables.
+    Sound Monitoring projects only.
     """
     from backend.models import DataFile
     from pathlib import Path
     import csv
     import io
 
+    _require_sound_project(db.query(Project).filter_by(id=project_id).first())
+
     # Get the file record
     file_record = db.query(DataFile).filter_by(id=file_id).first()
     if not file_record:
@@ -2120,6 +2148,7 @@ async def generate_excel_report(
 
     # Get related data for report context
     project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
     location = db.query(MonitoringLocation).filter_by(id=session.location_id).first() if session.location_id else None
 
     # Build full file path
@@ -2550,6 +2579,7 @@ async def preview_report_data(
 
     # Get related data for report context
     project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
     location = db.query(MonitoringLocation).filter_by(id=session.location_id).first() if session.location_id else None
 
     # Build full file path
@@ -2761,6 +2791,7 @@ async def generate_report_from_preview(
         raise HTTPException(status_code=403, detail="File does not belong to this project")
 
     project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
     location = db.query(MonitoringLocation).filter_by(id=session.location_id).first() if session.location_id else None
 
     # Extract data from request
@@ -3041,6 +3072,7 @@ async def generate_combined_excel_report(
     project = db.query(Project).filter_by(id=project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
+    _require_sound_project(project)
 
     # Get all sessions with measurement files
     sessions = db.query(MonitoringSession).filter_by(project_id=project_id).all()
@@ -3386,6 +3418,7 @@ async def combined_report_wizard(
     project = db.query(Project).filter_by(id=project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
+    _require_sound_project(project)
 
     sessions = db.query(MonitoringSession).filter_by(project_id=project_id).order_by(MonitoringSession.started_at).all()
 
@@ -3655,6 +3688,7 @@ async def generate_combined_from_preview(
     project = db.query(Project).filter_by(id=project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
+    _require_sound_project(project)
 
     report_title = data.get("report_title", "Background Noise Study")
     project_name = data.get("project_name", project.name)
@@ -4130,6 +4164,7 @@ async def upload_all_project_data(
     project = db.query(Project).filter_by(id=project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
+    _require_sound_project(project)
 
     # Load all sound monitoring locations for this project
     locations = db.query(MonitoringLocation).filter_by(