feat(scheduling): node tags + service placement_tags affinity (#58)

Operator-set node labels (node_agents.tags) gate which nodes a service
may schedule onto: services.placement_tags requires every listed tag.
auto and spread filter eligible agents by tags; tags are re-evaluated
each reconcile so retagging a node re-spreads replicas. Pin + tags and
local + tags rejected; empty array clears the requirement.

Surfaces: --placement-tags on services create/update, nodes update
--tags, MCP args, OpenAPI, node-detail tag editor, service-detail
placement-tags input.

Generated with [Devin](https://devin.ai)

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/frontend/src/features/nodes/NodeDetailPage.tsx

@@ -47,6 +47,7 @@ export function NodeDetailPage() {
   const [confirmDelete, setConfirmDelete] = useState(false);
   const [confirmVolumes, setConfirmVolumes] = useState(false);
   const [confirmDrain, setConfirmDrain] = useState(false);
+  const [tagDraft, setTagDraft] = useState<string | null>(null);
 
   const agentQuery = useQuery({
     queryKey: ['node-agent', id],
@@ -79,8 +80,8 @@ export function NodeDetailPage() {
     queryClient.invalidateQueries({ queryKey: ['usage-agents'] });
   };
   const updateMutation = useMutation({
-    mutationFn: (body: { name?: string; auto_prune?: boolean }) => updateAgent(id, body),
-    onSuccess: () => { setRename(null); invalidate(); },
+    mutationFn: (body: { name?: string; auto_prune?: boolean; tags?: string[] }) => updateAgent(id, body),
+    onSuccess: () => { setRename(null); setTagDraft(null); invalidate(); },
   });
   const pruneMutation = useMutation({
     mutationFn: (volumes: boolean) => pruneAgent(id, { volumes }),
@@ -177,6 +178,46 @@ export function NodeDetailPage() {
                   mesh: {meshAddresses(agent).map(([iface, ip]) => `${iface}=${ip}`).join(' · ')}
                 </p>
               )}
+              <p className="v-mono mt-1 text-[11px] text-[var(--text-tertiary)] flex items-center gap-1.5 flex-wrap">
+                tags:
+                {tagDraft === null ? (
+                  <>
+                    {agent.tags.length > 0
+                      ? agent.tags.map((t) => (
+                          <span key={t} className="px-1.5 py-0.5 rounded border border-[var(--border-subtle)] text-[var(--text-secondary)]">{t}</span>
+                        ))
+                      : <span className="text-[var(--text-muted)]">none</span>}
+                    {isAdmin && (
+                      <button
+                        onClick={() => setTagDraft(agent.tags.join(', '))}
+                        className="text-[var(--text-muted)] hover:text-[var(--text-primary)]"
+                        title="Edit placement tags — services can require them via placement_tags"
+                      >
+                        <Pencil size={11} />
+                      </button>
+                    )}
+                  </>
+                ) : (
+                  <>
+                    <input
+                      value={tagDraft}
+                      onChange={(e) => setTagDraft(e.target.value)}
+                      onKeyDown={(e) => {
+                        if (e.key === 'Enter') updateMutation.mutate({ tags: tagDraft.split(',').map((t) => t.trim()).filter(Boolean) });
+                        if (e.key === 'Escape') setTagDraft(null);
+                      }}
+                      autoFocus
+                      placeholder="eu-west, gpu"
+                      className="rounded-md border border-[var(--border-subtle)] bg-[var(--bg-tertiary)] px-2 py-0.5 text-[11px] text-[var(--text-primary)] w-52"
+                    />
+                    <button
+                      onClick={() => updateMutation.mutate({ tags: tagDraft.split(',').map((t) => t.trim()).filter(Boolean) })}
+                      className="text-[var(--accent-primary)] hover:underline"
+                    >save</button>
+                    <button onClick={() => setTagDraft(null)} className="text-[var(--text-muted)] hover:underline">cancel</button>
+                  </>
+                )}
+              </p>
             </div>
             <div className="flex items-center gap-3">
               <span className={`v-mono text-[11px] px-2 py-1 rounded-md border ${online

app/frontend/src/features/service/pages/ServiceDetailPage.tsx

@@ -2452,6 +2452,30 @@ export function ServiceDetailPage() {
                     <span className="text-[var(--text-tertiary)]">running on {service.nodeName}</span>
                   )}
                 </div>
+                {!service.nodeId && (
+                  <div className="mt-3 flex items-center gap-2 text-xs">
+                    <label className="text-[var(--text-tertiary)]" htmlFor="placement-tags">
+                      required node tags
+                    </label>
+                    <input
+                      id="placement-tags"
+                      type="text"
+                      placeholder="e.g. eu-west, gpu — empty = any node"
+                      defaultValue={(service.placementTags ?? []).join(', ')}
+                      disabled={updateServiceMutation.isPending}
+                      title="Remote placement only targets nodes carrying every tag. Re-resolved each reconcile — the service follows the tag, not a stored node."
+                      onBlur={(e) => {
+                        const next = e.target.value.split(',').map((t) => t.trim()).filter(Boolean);
+                        const prev = service.placementTags ?? [];
+                        if (next.join('|') !== prev.join('|')) {
+                          updateServiceMutation.mutate({ placement_tags: next });
+                        }
+                      }}
+                      onKeyDown={(e) => { if (e.key === 'Enter') (e.target as HTMLInputElement).blur(); }}
+                      className="px-2 py-1.5 rounded-[var(--radius-md)] bg-[var(--surface-muted)] border border-[var(--border-subtle)] text-sm text-[var(--text-primary)] w-72"
+                    />
+                  </div>
+                )}
                 {updateServiceMutation.isError && (
                   <p className="mt-2 text-xs text-[var(--error)]">{(updateServiceMutation.error as Error).message}</p>
                 )}