feat(unit-detail): editable deployment timeline

Each assignment row in the timeline now gets an inline edit (pencil)
that opens a modal with `assigned_at`, `assigned_until`, and notes.
Save calls the existing `PATCH /api/projects/{pid}/assignments/{aid}`;
delete (for misclicks) calls the existing `DELETE`.  Open-ended
checkbox clears `assigned_until` and the endpoint flips status back
to "active".

Adds an "+ Add deployment record" button at the top of the timeline
for backfilling historical windows when orphan events sit outside any
assignment.  Modal: project → location → assigned_at → assigned_until
(optional open-ended) → notes.

Backend: the `/locations/{loc}/assign` endpoint now accepts an
`assigned_at` form field and a closed-window assignment.  The previous
blanket "location already has an active assignment" check is replaced
with same-location overlap detection — closed historical windows that
don't overlap an existing assignment are accepted (which is exactly
the backfill case).

After any save/delete the timeline reloads and the SFM-events list
re-fetches so previously-orphaned events flip to "attributed" when
their timestamp now falls inside an assignment window.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/routers/project_locations.py

@@ -723,6 +723,19 @@ async def assign_unit_to_location(
 ):
     """
     Assign a unit to a monitoring location.
+
+    Accepts form fields:
+      - unit_id        — required
+      - assigned_at    — optional ISO datetime; defaults to now.  Set this
+                         when backfilling a historical deployment whose
+                         events landed in the orphan bucket.
+      - assigned_until — optional ISO datetime; absent = open-ended /
+                         active.
+      - notes          — optional free text
+
+    Refuses only when the *new window would overlap* an existing active
+    open-ended assignment at the same location.  Closed historical windows
+    that don't overlap are allowed (and required for orphan-event backfill).
     """
     location = db.query(MonitoringLocation).filter_by(
         id=location_id,
@@ -748,32 +761,65 @@ async def assign_unit_to_location(
             detail=f"Unit type '{unit.device_type}' does not match location type '{location.location_type}'",
         )
 
-    # Check if location already has an active assignment (active = assigned_until IS NULL)
+    # Parse dates.
-    existing_assignment = db.query(UnitAssignment).filter(
+    assigned_at_str    = form_data.get("assigned_at")
-        and_(
+    assigned_until_str = form_data.get("assigned_until")
-            UnitAssignment.location_id == location_id,
+    try:
-            UnitAssignment.assigned_until == None,
+        assigned_at = (
+            datetime.fromisoformat(assigned_at_str)
+            if assigned_at_str else datetime.utcnow()
+        )
+    except (TypeError, ValueError):
+        raise HTTPException(
+            status_code=400, detail=f"Invalid assigned_at: {assigned_at_str!r}"
+        )
+    try:
+        assigned_until = (
+            datetime.fromisoformat(assigned_until_str)
+            if assigned_until_str else None
+        )
+    except (TypeError, ValueError):
+        raise HTTPException(
+            status_code=400, detail=f"Invalid assigned_until: {assigned_until_str!r}"
+        )
+    if assigned_until is not None and assigned_until <= assigned_at:
+        raise HTTPException(
+            status_code=400, detail="assigned_until must be after assigned_at.",
         )
-    ).first()
 
-    if existing_assignment:
+    # Reject only if the new window overlaps an existing assignment at the
+    # SAME location.  Closed historical windows that sit before the current
+    # active assignment are fine — that's the backfill case.
+    new_end_for_overlap = assigned_until or datetime.utcnow()
+    existing = db.query(UnitAssignment).filter(
+        UnitAssignment.location_id == location_id
+    ).all()
+    for other in existing:
+        other_start = other.assigned_at
+        other_end   = other.assigned_until or datetime.utcnow()
+        if assigned_at < other_end and new_end_for_overlap > other_start:
+            other_window = (
+                f"{other.assigned_at:%Y-%m-%d}"
+                + (f" → {other.assigned_until:%Y-%m-%d}" if other.assigned_until else " → present")
+            )
             raise HTTPException(
                 status_code=400,
-            detail=f"Location already has an active unit assignment ({existing_assignment.unit_id}). Use swap to replace it.",
+                detail=(
+                    f"New window overlaps an existing assignment at this "
+                    f"location ({other.unit_id} {other_window}). Use swap or "
+                    f"edit that record instead."
+                ),
             )
 
-    # Create new assignment
-    assigned_until_str = form_data.get("assigned_until")
-    assigned_until = datetime.fromisoformat(assigned_until_str) if assigned_until_str else None
-
     assignment = UnitAssignment(
         id=str(uuid.uuid4()),
         unit_id=unit_id,
         location_id=location_id,
         project_id=project_id,
         device_type=unit.device_type,
+        assigned_at=assigned_at,
         assigned_until=assigned_until,
-        status="active",
+        status="active" if assigned_until is None else "completed",
         notes=form_data.get("notes"),
     )
 

templates/unit_detail.html

@@ -281,12 +281,17 @@
             <!-- Deployment Timeline (Phase 4 unified view — derived from
                  unit_assignments + unit_history + SFM event overlay) -->
             <div class="border-t border-gray-200 dark:border-gray-700 pt-6">
-                <div class="flex justify-between items-center mb-4">
+                <div class="flex justify-between items-center mb-4 flex-wrap gap-2">
                     <h3 class="text-lg font-semibold text-gray-900 dark:text-white">Deployment Timeline</h3>
+                    <div class="flex items-center gap-2">
+                        <button onclick="openAddAssignmentModal()" class="px-3 py-1.5 text-sm rounded-lg bg-seismo-orange hover:bg-orange-600 text-white">
+                            + Add deployment record
+                        </button>
                         <button onclick="loadDeploymentTimeline()" class="px-3 py-1.5 text-sm rounded-lg border border-gray-300 dark:border-gray-600 hover:bg-gray-50 dark:hover:bg-gray-700 text-gray-700 dark:text-gray-300">
                             ↻ Refresh
                         </button>
                     </div>
+                </div>
 
                 <!-- Gantt chart — visual timeline of all deployments.  Click
                      a bar to jump to its row in the list below. -->
@@ -302,6 +307,119 @@
                 </div>
             </div>
 
+            <!-- Edit-assignment modal -->
+            <div id="editAssignmentModal" class="hidden fixed inset-0 bg-black/60 z-50 flex items-center justify-center p-4">
+                <div class="bg-white dark:bg-slate-800 rounded-xl shadow-2xl w-full max-w-md max-h-[90vh] overflow-y-auto">
+                    <div class="sticky top-0 bg-white dark:bg-slate-800 border-b border-gray-200 dark:border-gray-700 px-5 py-4 flex items-center justify-between">
+                        <h3 class="text-lg font-semibold text-gray-900 dark:text-white">Edit deployment record</h3>
+                        <button onclick="closeEditAssignmentModal()" class="text-2xl text-gray-500 hover:text-gray-700 dark:hover:text-gray-300">&times;</button>
+                    </div>
+                    <div class="p-5 space-y-4">
+                        <div class="text-sm text-gray-500 dark:text-gray-400">
+                            <span id="editAssignmentLocation">—</span>
+                            <span class="text-xs">·</span>
+                            <span id="editAssignmentProject" class="text-xs">—</span>
+                        </div>
+                        <label class="block">
+                            <span class="text-sm font-medium text-gray-700 dark:text-gray-300">Assigned at</span>
+                            <input id="editAssignedAt" type="datetime-local" step="60"
+                                   class="mt-1 w-full px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-slate-700 text-gray-900 dark:text-white">
+                        </label>
+                        <label class="block">
+                            <span class="text-sm font-medium text-gray-700 dark:text-gray-300">Assigned until</span>
+                            <div class="mt-1 flex items-center gap-2">
+                                <input id="editAssignedUntil" type="datetime-local" step="60"
+                                       class="flex-1 px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-slate-700 text-gray-900 dark:text-white">
+                                <label class="inline-flex items-center gap-1 text-xs text-gray-700 dark:text-gray-300 whitespace-nowrap">
+                                    <input id="editAssignedUntilOpen" type="checkbox" onchange="_toggleEditOpenEnded()">
+                                    open-ended
+                                </label>
+                            </div>
+                            <p class="text-xs text-gray-500 dark:text-gray-400 mt-1">Check "open-ended" to mark this assignment active (no end date).</p>
+                        </label>
+                        <label class="block">
+                            <span class="text-sm font-medium text-gray-700 dark:text-gray-300">Notes</span>
+                            <textarea id="editAssignmentNotes" rows="2"
+                                      class="mt-1 w-full px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-slate-700 text-gray-900 dark:text-white"></textarea>
+                        </label>
+                        <div id="editAssignmentError" class="hidden text-sm text-red-600"></div>
+                    </div>
+                    <div class="sticky bottom-0 bg-white dark:bg-slate-800 border-t border-gray-200 dark:border-gray-700 px-5 py-3 flex items-center justify-between gap-2">
+                        <button onclick="deleteAssignmentFromModal()" class="px-3 py-2 text-sm rounded-lg border border-red-300 text-red-700 dark:border-red-700 dark:text-red-300 hover:bg-red-50 dark:hover:bg-red-900/20">
+                            Delete
+                        </button>
+                        <div class="flex gap-2">
+                            <button onclick="closeEditAssignmentModal()" class="px-4 py-2 text-sm rounded-lg border border-gray-300 dark:border-gray-600 text-gray-700 dark:text-gray-300 hover:bg-gray-50 dark:hover:bg-gray-700">
+                                Cancel
+                            </button>
+                            <button id="editAssignmentSaveBtn" onclick="saveEditAssignment()" class="px-4 py-2 text-sm rounded-lg bg-seismo-orange hover:bg-orange-600 text-white">
+                                Save
+                            </button>
+                        </div>
+                    </div>
+                </div>
+            </div>
+
+            <!-- Add-historical-assignment modal -->
+            <div id="addAssignmentModal" class="hidden fixed inset-0 bg-black/60 z-50 flex items-center justify-center p-4">
+                <div class="bg-white dark:bg-slate-800 rounded-xl shadow-2xl w-full max-w-md max-h-[90vh] overflow-y-auto">
+                    <div class="sticky top-0 bg-white dark:bg-slate-800 border-b border-gray-200 dark:border-gray-700 px-5 py-4 flex items-center justify-between">
+                        <h3 class="text-lg font-semibold text-gray-900 dark:text-white">Add deployment record</h3>
+                        <button onclick="closeAddAssignmentModal()" class="text-2xl text-gray-500 hover:text-gray-700 dark:hover:text-gray-300">&times;</button>
+                    </div>
+                    <div class="p-5 space-y-4">
+                        <p class="text-xs text-gray-500 dark:text-gray-400">
+                            Create a deployment record for this unit — usually to backfill a historical window so orphan events get attributed.
+                        </p>
+                        <label class="block">
+                            <span class="text-sm font-medium text-gray-700 dark:text-gray-300">Project</span>
+                            <select id="addAssignmentProject" onchange="_addAssignmentProjectChanged()"
+                                    class="mt-1 w-full px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-slate-700 text-gray-900 dark:text-white">
+                                <option value="">Loading…</option>
+                            </select>
+                        </label>
+                        <label class="block">
+                            <span class="text-sm font-medium text-gray-700 dark:text-gray-300">Location</span>
+                            <select id="addAssignmentLocation"
+                                    class="mt-1 w-full px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-slate-700 text-gray-900 dark:text-white" disabled>
+                                <option value="">Pick a project first</option>
+                            </select>
+                        </label>
+                        <label class="block">
+                            <span class="text-sm font-medium text-gray-700 dark:text-gray-300">Assigned at</span>
+                            <input id="addAssignedAt" type="datetime-local" step="60"
+                                   class="mt-1 w-full px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-slate-700 text-gray-900 dark:text-white">
+                        </label>
+                        <label class="block">
+                            <span class="text-sm font-medium text-gray-700 dark:text-gray-300">Assigned until</span>
+                            <div class="mt-1 flex items-center gap-2">
+                                <input id="addAssignedUntil" type="datetime-local" step="60"
+                                       class="flex-1 px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-slate-700 text-gray-900 dark:text-white">
+                                <label class="inline-flex items-center gap-1 text-xs text-gray-700 dark:text-gray-300 whitespace-nowrap">
+                                    <input id="addAssignedUntilOpen" type="checkbox" onchange="_toggleAddOpenEnded()">
+                                    open-ended
+                                </label>
+                            </div>
+                        </label>
+                        <label class="block">
+                            <span class="text-sm font-medium text-gray-700 dark:text-gray-300">Notes</span>
+                            <textarea id="addAssignmentNotes" rows="2"
+                                      placeholder="e.g. Backfilled to attribute orphan events 2026-03-16 — 2026-03-25"
+                                      class="mt-1 w-full px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-slate-700 text-gray-900 dark:text-white"></textarea>
+                        </label>
+                        <div id="addAssignmentError" class="hidden text-sm text-red-600"></div>
+                    </div>
+                    <div class="sticky bottom-0 bg-white dark:bg-slate-800 border-t border-gray-200 dark:border-gray-700 px-5 py-3 flex justify-end gap-2">
+                        <button onclick="closeAddAssignmentModal()" class="px-4 py-2 text-sm rounded-lg border border-gray-300 dark:border-gray-600 text-gray-700 dark:text-gray-300 hover:bg-gray-50 dark:hover:bg-gray-700">
+                            Cancel
+                        </button>
+                        <button id="addAssignmentSaveBtn" onclick="saveAddAssignment()" class="px-4 py-2 text-sm rounded-lg bg-seismo-orange hover:bg-orange-600 text-white">
+                            Create
+                        </button>
+                    </div>
+                </div>
+            </div>
+
             <!-- SFM Events (seismographs only) -->
             <div id="sfmEventsSection" class="border-t border-gray-200 dark:border-gray-700 pt-6 hidden">
                 <div class="flex justify-between items-center mb-4">
@@ -2141,6 +2259,16 @@ function _dtRenderAssignment(e) {
         ? `<div class="mt-2 text-xs text-gray-600 dark:text-gray-400 italic">${_dtEsc(e.notes)}</div>`
         : '';
 
+    // Edit/delete actions live on the right of the date row.  Only shown
+    // for assignment entries with a real assignment_id (synthesized legacy
+    // entries without one are read-only).
+    const actionButtons = e.assignment_id
+        ? `<button type="button" onclick='openEditAssignmentModal(${JSON.stringify(e.assignment_id)})'
+              class="text-xs text-gray-500 hover:text-seismo-orange p-1 rounded" title="Edit dates / notes">
+              ✏️
+           </button>`
+        : '';
+
     return `<div class="flex gap-3 transition-shadow rounded-lg" data-assignment-row="${_dtEsc(e.assignment_id)}">
         <div class="flex flex-col items-center pt-1">
             <span class="w-3 h-3 rounded-full ${e.is_active ? 'bg-green-500' : 'bg-seismo-orange'}"></span>
@@ -2153,6 +2281,7 @@ function _dtRenderAssignment(e) {
                 <div class="flex items-center gap-2">
                     ${mergeableBadge}
                     ${activeBadge}
+                    ${actionButtons}
                 </div>
             </div>
             <div class="mt-1">${locLink}</div>
@@ -2455,6 +2584,261 @@ function renderDeploymentTimeline(entries, container, mergeGroups) {
     container.innerHTML = bannerHtml + '<div class="space-y-3">' + html + '</div>';
 }
 
+// ── Deployment-timeline editor ──────────────────────────────────────────────
+// Edit / delete an existing UnitAssignment row, or create a historical one
+// (backfill orphan-event windows).  All three operations hit endpoints that
+// already exist on the project-locations router; after a save we just
+// reload the timeline + events.
+
+let _editAssignmentCtx = null;   // { assignment_id, project_id, location_name, project_name }
+
+function _iso_to_local_input(iso) {
+    // The PATCH/POST endpoints accept "YYYY-MM-DDTHH:MM[:SS]" strings
+    // (datetime.fromisoformat).  datetime-local inputs emit the same shape
+    // without timezone.  We just strip the trailing "Z" if present and
+    // truncate to minutes.
+    if (!iso) return '';
+    let s = String(iso).replace('Z', '');
+    // Slice down to YYYY-MM-DDTHH:MM (16 chars).
+    return s.slice(0, 16);
+}
+
+function openEditAssignmentModal(assignmentId) {
+    const entry = (_dtCurrentTimeline.entries || []).find(
+        e => e.kind === 'assignment' && e.assignment_id === assignmentId
+    );
+    if (!entry) {
+        alert('Could not find this assignment in the loaded timeline.');
+        return;
+    }
+    _editAssignmentCtx = {
+        assignment_id:  entry.assignment_id,
+        project_id:     entry.project_id,
+        location_name:  entry.location_name || 'unnamed location',
+        project_name:   entry.project_name  || '',
+    };
+
+    document.getElementById('editAssignmentLocation').textContent = _editAssignmentCtx.location_name;
+    document.getElementById('editAssignmentProject').textContent  = _editAssignmentCtx.project_name;
+
+    document.getElementById('editAssignedAt').value    = _iso_to_local_input(entry.starts_at);
+    const endsAtInput  = document.getElementById('editAssignedUntil');
+    const openCheckbox = document.getElementById('editAssignedUntilOpen');
+    if (entry.is_active) {
+        endsAtInput.value = '';
+        endsAtInput.disabled = true;
+        openCheckbox.checked = true;
+    } else {
+        endsAtInput.value = _iso_to_local_input(entry.ends_at);
+        endsAtInput.disabled = false;
+        openCheckbox.checked = false;
+    }
+    document.getElementById('editAssignmentNotes').value = entry.notes || '';
+    document.getElementById('editAssignmentError').classList.add('hidden');
+    document.getElementById('editAssignmentModal').classList.remove('hidden');
+}
+
+function closeEditAssignmentModal() {
+    document.getElementById('editAssignmentModal').classList.add('hidden');
+    _editAssignmentCtx = null;
+}
+
+function _toggleEditOpenEnded() {
+    const open  = document.getElementById('editAssignedUntilOpen').checked;
+    const input = document.getElementById('editAssignedUntil');
+    input.disabled = open;
+    if (open) input.value = '';
+}
+
+async function saveEditAssignment() {
+    if (!_editAssignmentCtx) return;
+    const err = document.getElementById('editAssignmentError');
+    err.classList.add('hidden');
+
+    const assignedAt = document.getElementById('editAssignedAt').value;
+    if (!assignedAt) {
+        err.textContent = 'Assigned-at is required.';
+        err.classList.remove('hidden');
+        return;
+    }
+    const open        = document.getElementById('editAssignedUntilOpen').checked;
+    const assignedUntil = open ? null : (document.getElementById('editAssignedUntil').value || null);
+    const notes       = document.getElementById('editAssignmentNotes').value;
+
+    const btn = document.getElementById('editAssignmentSaveBtn');
+    btn.disabled = true; btn.textContent = 'Saving…';
+
+    try {
+        const url = `/api/projects/${encodeURIComponent(_editAssignmentCtx.project_id)}/assignments/${encodeURIComponent(_editAssignmentCtx.assignment_id)}`;
+        const r = await fetch(url, {
+            method:  'PATCH',
+            headers: { 'Content-Type': 'application/json' },
+            body:    JSON.stringify({
+                assigned_at:    assignedAt,
+                assigned_until: assignedUntil,
+                notes:          notes,
+            }),
+        });
+        if (!r.ok) {
+            const e = await r.json().catch(() => ({detail: 'HTTP ' + r.status}));
+            throw new Error(e.detail || 'HTTP ' + r.status);
+        }
+        closeEditAssignmentModal();
+        await loadDeploymentTimeline();
+        if (typeof loadUnitEvents === 'function' && currentUnit && currentUnit.device_type === 'seismograph') {
+            loadUnitEvents();
+        }
+    } catch (e) {
+        err.textContent = e.message;
+        err.classList.remove('hidden');
+    } finally {
+        btn.disabled = false; btn.textContent = 'Save';
+    }
+}
+
+async function deleteAssignmentFromModal() {
+    if (!_editAssignmentCtx) return;
+    if (!confirm('Hard-delete this deployment record?\n\nThe assignment row and its history audit entry are removed.  Use this only for misclicks — to end a real deployment, edit the "assigned until" date instead.')) return;
+    const err = document.getElementById('editAssignmentError');
+    err.classList.add('hidden');
+    try {
+        const url = `/api/projects/${encodeURIComponent(_editAssignmentCtx.project_id)}/assignments/${encodeURIComponent(_editAssignmentCtx.assignment_id)}`;
+        const r = await fetch(url, { method: 'DELETE' });
+        if (!r.ok) {
+            const e = await r.json().catch(() => ({detail: 'HTTP ' + r.status}));
+            throw new Error(e.detail || 'HTTP ' + r.status);
+        }
+        closeEditAssignmentModal();
+        await loadDeploymentTimeline();
+        if (typeof loadUnitEvents === 'function' && currentUnit && currentUnit.device_type === 'seismograph') {
+            loadUnitEvents();
+        }
+    } catch (e) {
+        err.textContent = e.message;
+        err.classList.remove('hidden');
+    }
+}
+
+// ── Add-historical-assignment modal ─────────────────────────────────────────
+let _addAssignmentProjectsCache = null;
+
+async function openAddAssignmentModal() {
+    if (!currentUnit) return;
+    document.getElementById('addAssignmentError').classList.add('hidden');
+    document.getElementById('addAssignedAt').value    = '';
+    document.getElementById('addAssignedUntil').value = '';
+    document.getElementById('addAssignedUntilOpen').checked = false;
+    document.getElementById('addAssignedUntil').disabled    = false;
+    document.getElementById('addAssignmentNotes').value     = '';
+
+    const locSel = document.getElementById('addAssignmentLocation');
+    locSel.disabled = true;
+    locSel.innerHTML = '<option value="">Pick a project first</option>';
+
+    const projSel = document.getElementById('addAssignmentProject');
+    projSel.innerHTML = '<option value="">Loading…</option>';
+
+    document.getElementById('addAssignmentModal').classList.remove('hidden');
+
+    try {
+        if (!_addAssignmentProjectsCache) {
+            const r = await fetch('/api/projects/search-json?limit=50');
+            if (!r.ok) throw new Error('HTTP ' + r.status);
+            _addAssignmentProjectsCache = await r.json();
+        }
+        projSel.innerHTML = '<option value="">— pick project —</option>'
+            + _addAssignmentProjectsCache.map(p =>
+                `<option value="${_dtEsc(p.id)}">${_dtEsc(p.name)}${p.project_number ? ' (' + _dtEsc(p.project_number) + ')' : ''}</option>`
+            ).join('');
+    } catch (e) {
+        projSel.innerHTML = `<option value="">Load failed: ${_dtEsc(e.message)}</option>`;
+    }
+}
+
+function closeAddAssignmentModal() {
+    document.getElementById('addAssignmentModal').classList.add('hidden');
+}
+
+function _toggleAddOpenEnded() {
+    const open  = document.getElementById('addAssignedUntilOpen').checked;
+    const input = document.getElementById('addAssignedUntil');
+    input.disabled = open;
+    if (open) input.value = '';
+}
+
+async function _addAssignmentProjectChanged() {
+    const projectId = document.getElementById('addAssignmentProject').value;
+    const locSel = document.getElementById('addAssignmentLocation');
+    if (!projectId) {
+        locSel.disabled = true;
+        locSel.innerHTML = '<option value="">Pick a project first</option>';
+        return;
+    }
+    locSel.disabled = true;
+    locSel.innerHTML = '<option value="">Loading locations…</option>';
+    // Match the device type to the location_type filter.
+    const wantType = (currentUnit && currentUnit.device_type === 'slm') ? 'sound' : 'vibration';
+    try {
+        const r = await fetch(`/api/projects/${encodeURIComponent(projectId)}/locations-json?location_type=${wantType}`);
+        if (!r.ok) throw new Error('HTTP ' + r.status);
+        const locs = await r.json();
+        if (!locs.length) {
+            locSel.innerHTML = '<option value="">No matching locations in this project</option>';
+            return;
+        }
+        locSel.disabled = false;
+        locSel.innerHTML = '<option value="">— pick location —</option>'
+            + locs.map(l => `<option value="${_dtEsc(l.id)}">${_dtEsc(l.name)}</option>`).join('');
+    } catch (e) {
+        locSel.innerHTML = `<option value="">Load failed: ${_dtEsc(e.message)}</option>`;
+    }
+}
+
+async function saveAddAssignment() {
+    if (!currentUnit) return;
+    const err = document.getElementById('addAssignmentError');
+    err.classList.add('hidden');
+
+    const projectId  = document.getElementById('addAssignmentProject').value;
+    const locationId = document.getElementById('addAssignmentLocation').value;
+    const assignedAt = document.getElementById('addAssignedAt').value;
+    const open       = document.getElementById('addAssignedUntilOpen').checked;
+    const assignedUntil = open ? '' : document.getElementById('addAssignedUntil').value;
+    const notes      = document.getElementById('addAssignmentNotes').value;
+
+    if (!projectId)  { err.textContent = 'Pick a project.';  err.classList.remove('hidden'); return; }
+    if (!locationId) { err.textContent = 'Pick a location.'; err.classList.remove('hidden'); return; }
+    if (!assignedAt) { err.textContent = 'Assigned-at is required.'; err.classList.remove('hidden'); return; }
+
+    const btn = document.getElementById('addAssignmentSaveBtn');
+    btn.disabled = true; btn.textContent = 'Creating…';
+
+    try {
+        const fd = new FormData();
+        fd.append('unit_id',     currentUnit.id);
+        fd.append('assigned_at', assignedAt);
+        if (assignedUntil) fd.append('assigned_until', assignedUntil);
+        if (notes)         fd.append('notes',          notes);
+
+        const url = `/api/projects/${encodeURIComponent(projectId)}/locations/${encodeURIComponent(locationId)}/assign`;
+        const r = await fetch(url, { method: 'POST', body: fd });
+        if (!r.ok) {
+            const e = await r.json().catch(() => ({detail: 'HTTP ' + r.status}));
+            throw new Error(e.detail || 'HTTP ' + r.status);
+        }
+        closeAddAssignmentModal();
+        await loadDeploymentTimeline();
+        if (typeof loadUnitEvents === 'function' && currentUnit.device_type === 'seismograph') {
+            loadUnitEvents();
+        }
+    } catch (e) {
+        err.textContent = e.message;
+        err.classList.remove('hidden');
+    } finally {
+        btn.disabled = false; btn.textContent = 'Create';
+    }
+}
+
 // ── SFM Events section ──────────────────────────────────────────────────────
 function clearUnitEventFilters() {
     document.getElementById('ue-filter-bucket').value = 'all';