backend/routers/project_locations.py

@@ -830,6 +830,92 @@ async def update_assignment(
     }
 
 
+@router.delete("/assignments/{assignment_id}")
+async def delete_assignment(
+    project_id: str,
+    assignment_id: str,
+    db: Session = Depends(get_db),
+):
+    """
+    Hard-delete an assignment record.
+
+    Use case: operator clicked Assign by mistake (or 8 times in a row) and
+    wants the bogus records gone — not just closed with an `assigned_until`
+    timestamp.  The standard close-via-unassign path is for legitimate
+    deployments that ended; this is for mis-clicks that never actually
+    happened.
+
+    Safety:
+      - Refuses if any MonitoringSession exists for the same (unit, location)
+        within this assignment's window — that suggests the deployment was
+        real, and the operator should use unassign instead.
+      - Refuses if the assignment is the ONLY active assignment for a unit
+        currently shown as deployed AND a recording session is in progress.
+
+    Audit:
+      - Records UnitHistory `assignment_deleted` so the unit's deployment
+        timeline shows the deletion happened (even though the row itself
+        is gone).
+    """
+    assignment = db.query(UnitAssignment).filter_by(
+        id=assignment_id,
+        project_id=project_id,
+    ).first()
+
+    if not assignment:
+        raise HTTPException(status_code=404, detail="Assignment not found")
+
+    # Safety: is there a real recording history for this (unit, location)
+    # within the assignment's time window?  If so, this isn't a mis-click —
+    # the operator should close it via unassign, not delete it.
+    window_start = assignment.assigned_at
+    window_end   = assignment.assigned_until or datetime.utcnow()
+    real_sessions = db.query(MonitoringSession).filter(
+        and_(
+            MonitoringSession.location_id == assignment.location_id,
+            MonitoringSession.unit_id == assignment.unit_id,
+            MonitoringSession.start_time >= window_start,
+            MonitoringSession.start_time <= window_end,
+        )
+    ).count()
+
+    if real_sessions > 0:
+        raise HTTPException(
+            status_code=400,
+            detail=(
+                f"Cannot delete this assignment — {real_sessions} monitoring "
+                f"session(s) were recorded under it.  Use Unassign to close "
+                f"the window instead, which preserves the audit trail."
+            ),
+        )
+
+    # Resolve location name for audit log before deletion.
+    location = db.query(MonitoringLocation).filter_by(
+        id=assignment.location_id
+    ).first()
+    location_label = location.name if location else assignment.location_id
+
+    _record_assignment_history(
+        db,
+        unit_id=assignment.unit_id,
+        change_type="assignment_deleted",
+        old_value=f"{location_label} ({assignment.assigned_at:%Y-%m-%d} → "
+                  f"{assignment.assigned_until and assignment.assigned_until.strftime('%Y-%m-%d') or 'active'})",
+        new_value="deleted",
+        notes=(
+            "Assignment row removed — created in error or accidental duplicate."
+        ),
+    )
+
+    db.delete(assignment)
+    db.commit()
+
+    return {
+        "success": True,
+        "message": "Assignment deleted.",
+    }
+
+
 @router.post("/locations/{location_id}/swap")
 async def swap_unit_on_location(
     project_id: str,

templates/vibration_location_detail.html

@@ -583,6 +583,14 @@ function renderAssignmentsUsed(assignments) {
                         <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M11 5H6a2 2 0 00-2 2v11a2 2 0 002 2h11a2 2 0 002-2v-5m-1.414-9.414a2 2 0 112.828 2.828L11.828 15H9v-2.828l8.586-8.586z"></path>
                     </svg>
                 </button>
+                <button type="button"
+                        onclick="deleteAssignment('${esc(a.assignment_id)}', '${esc(a.unit_id)}', '${start} → ${end}')"
+                        title="Delete this assignment record (for mis-clicks / duplicates)"
+                        class="text-gray-400 hover:text-red-600 transition-colors p-1">
+                    <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                        <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M19 7l-.867 12.142A2 2 0 0116.138 21H7.862a2 2 0 01-1.995-1.858L5 7m5 4v6m4-6v6M1 7h22M9 7V4a1 1 0 011-1h4a1 1 0 011 1v3"/>
+                    </svg>
+                </button>
             </div>
             <span class="text-sm text-gray-700 dark:text-gray-300 whitespace-nowrap">${(a.events_in_window || 0).toLocaleString()} event${a.events_in_window === 1 ? '' : 's'}</span>
         </div>`;
@@ -608,6 +616,33 @@ function openAssignmentEditModal(encodedJson) {
     document.getElementById('assignment-edit-modal').classList.remove('hidden');
 }
 
+async function deleteAssignment(assignmentId, unitId, windowLabel) {
+    // For mis-clicks / accidental duplicate assignments.  Backend refuses
+    // if there's a real recording session inside the window — those should
+    // go through Edit or Unassign instead.
+    const msg = `Delete this assignment?\n\n`
+              + `Unit: ${unitId}\n`
+              + `Window: ${windowLabel}\n\n`
+              + `This is for assignments created in error.  Events that fell `
+              + `in this window will become unattributed.  The unit's deployment `
+              + `history will log the deletion for audit.\n\n`
+              + `If the unit actually was deployed here, use Edit or Unassign instead.`;
+    if (!confirm(msg)) return;
+
+    try {
+        const r = await fetch(`/api/projects/${projectId}/assignments/${assignmentId}`, {
+            method: 'DELETE',
+        });
+        if (!r.ok) {
+            const err = await r.json().catch(() => ({detail: 'HTTP ' + r.status}));
+            throw new Error(err.detail || 'HTTP ' + r.status);
+        }
+        await loadLocationEvents();   // Refresh stats + table without this assignment.
+    } catch (err) {
+        alert(err.message || 'Failed to delete assignment.');
+    }
+}
+
 function closeAssignmentEditModal() {
     document.getElementById('assignment-edit-modal').classList.add('hidden');
 }