feat(agents): mirror Paperclip interactions in case page

Surface issue_thread_interactions (ask_user_questions / request_confirmation /
suggest_tasks) directly inside legal-ai's case detail feed so the user can
answer agent prompts without switching to Paperclip's UI.

Backend (FastAPI):
- paperclip_client.py: 4 new helpers — get_issue_interactions (DB),
  respond_to_interaction / accept_interaction / reject_interaction (REST).
- app.py: extends GET /api/cases/{case_number}/agents to include
  `interactions`, and adds POST /api/cases/{case_number}/agents/interaction-response
  routing to /respond, /accept, /reject in Paperclip.
- paperclip_client.py: also pulls existing httpx calls onto the centralized
  pc_request helper (paperclip_api.py) for consistent auth + run-id headers.

Frontend (web-ui, Next.js 16 + TanStack Query):
- agents.ts: Interaction / InteractionPayload / InteractionStatus types,
  useSubmitInteraction mutation hook (invalidates the activity query).
- agent-activity-feed.tsx: InteractionCard renders radio (single) /
  checkbox (multi) for ask_user_questions, accept/reject + reason for
  request_confirmation, task selection for suggest_tasks. Resolved
  interactions show a read-only summary. Cards are interleaved with
  comments by created_at, so the feed reads chronologically.

Paperclip auto-wakes the issue assignee on a successful response
(queueResolvedInteractionContinuationWakeup) — no explicit wakeup needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web-ui/src/lib/api/agents.ts

@@ -42,10 +42,80 @@ export type PaperclipAgent = {
   last_heartbeat_at: string | null;
 };
 
+export type InteractionKind =
+  | "ask_user_questions"
+  | "request_confirmation"
+  | "suggest_tasks";
+
+export type InteractionStatus =
+  | "pending"
+  | "answered"
+  | "accepted"
+  | "rejected"
+  | "expired"
+  | "failed";
+
+export type InteractionOption = {
+  id: string;
+  label: string;
+  description?: string | null;
+};
+
+export type InteractionQuestion = {
+  id: string;
+  prompt: string;
+  selectionMode?: "single" | "multi";
+  required?: boolean;
+  options: InteractionOption[];
+};
+
+export type InteractionTask = {
+  clientKey: string;
+  parentClientKey?: string | null;
+  title: string;
+  description?: string | null;
+};
+
+/** Free-form payload — shape depends on `kind`. Common fields surfaced for the
+ * UI; everything else is preserved on the wire. */
+export type InteractionPayload = {
+  version?: number;
+  submitLabel?: string;
+  acceptLabel?: string;
+  rejectLabel?: string;
+  questions?: InteractionQuestion[];
+  tasks?: InteractionTask[];
+  body?: string;
+  [key: string]: unknown;
+};
+
+export type Interaction = {
+  id: string;
+  issue_id: string;
+  kind: InteractionKind;
+  status: InteractionStatus;
+  title: string | null;
+  summary: string | null;
+  payload: InteractionPayload;
+  result: Record<string, unknown> | null;
+  created_at: string | null;
+  resolved_at: string | null;
+};
+
 export type AgentActivityResponse = {
   issues: PaperclipIssue[];
   comments: PaperclipComment[];
   agents: PaperclipAgent[];
+  interactions: Interaction[];
+};
+
+export type InteractionAction = "respond" | "accept" | "reject";
+
+export type InteractionSubmitVars = {
+  issue_id: string;
+  interaction_id: string;
+  action: InteractionAction;
+  payload: Record<string, unknown>;
 };
 
 // ── Query Keys ───────────────────────────────────────────────────
@@ -85,3 +155,19 @@ export function useSendComment(caseNumber: string | undefined) {
     },
   });
 }
+
+export function useSubmitInteraction(caseNumber: string | undefined) {
+  const qc = useQueryClient();
+  return useMutation({
+    mutationFn: (vars: InteractionSubmitVars) =>
+      apiRequest<Interaction>(
+        `/api/cases/${caseNumber}/agents/interaction-response`,
+        { method: "POST", body: vars },
+      ),
+    onSuccess: () => {
+      if (caseNumber) {
+        qc.invalidateQueries({ queryKey: agentKeys.activity(caseNumber) });
+      }
+    },
+  });
+}