Add workflow interaction cancellation and issue cost summaries (#4862)

## Thinking Path

> - Paperclip coordinates work through issue-thread interactions, run
history, and cost telemetry.
> - Operators need workflow prompts to be cancellable and costs to be
visible at the issue level.
> - The earlier rollup mixed this workflow/cost work with database
backups, reliability recovery, thread scaling, and settings polish.
> - This pull request isolates the interaction and cost surfaces into a
reviewable slice.
> - The backend now supports cancelling pending question interactions
and summarizing issue-tree costs.
> - The UI component layer can render cancelled questions and interleave
activity with run ledger rows.

## What Changed

- Added `cancelled` as an issue-thread interaction status and result
shape for question interactions.
- Added the board-only `POST
/issues/:id/interactions/:interactionId/cancel` route and service
implementation.
- Added issue-tree cost summary support in the cost service and
`/issues/:id/cost-summary` API route.
- Extended shared cost exports and UI API/query keys for issue cost
summaries.
- Updated `IssueThreadInteractionCard` and `IssueRunLedger` components
for cancelled questions, issue cost surfaces, and activity/run
interleaving.
- Added focused server and component regression coverage.

## Verification

- `pnpm install --frozen-lockfile`
- `pnpm exec vitest run server/src/__tests__/costs-service.test.ts
server/src/__tests__/issue-thread-interaction-routes.test.ts
server/src/__tests__/issue-thread-interactions-service.test.ts
ui/src/components/IssueRunLedger.test.tsx`
- Result: 4 test files passed, 45 tests passed.
- UI screenshots not included because this PR updates reusable
components and API surfaces without wiring a new page-level layout.

## Risks

- Adds a new interaction terminal status; clients that switch
exhaustively on interaction status may need to handle `cancelled`.
- Issue-tree cost summaries use recursive issue traversal and should be
watched on unusually large issue trees.
- Page-level issue detail wiring is intentionally left to the board
QoL/issue-detail branch to keep this PR narrow.

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- OpenAI Codex, GPT-5.5, code execution and GitHub CLI tool use, medium
reasoning effort.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

server/src/__tests__/issue-thread-interaction-routes.test.ts

@@ -17,6 +17,7 @@ const mockInteractionService = vi.hoisted(() => ({
   rejectInteraction: vi.fn(),
   rejectSuggestedTasks: vi.fn(),
   answerQuestions: vi.fn(),
+  cancelQuestions: vi.fn(),
 }));
 
 const mockHeartbeatService = vi.hoisted(() => ({
@@ -249,6 +250,36 @@ describe.sequential("issue thread interaction routes", () => {
       updatedAt: "2026-04-20T12:06:00.000Z",
       resolvedAt: "2026-04-20T12:06:00.000Z",
     });
+    mockInteractionService.cancelQuestions.mockResolvedValue({
+      id: "interaction-2",
+      companyId: "company-1",
+      issueId: "aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa",
+      kind: "ask_user_questions",
+      status: "cancelled",
+      continuationPolicy: "wake_assignee",
+      idempotencyKey: null,
+      sourceCommentId: "comment-2",
+      sourceRunId: "run-2",
+      payload: {
+        version: 1,
+        questions: [{
+          id: "scope",
+          prompt: "Scope?",
+          selectionMode: "single",
+          options: [{ id: "phase-1", label: "Phase 1" }],
+        }],
+      },
+      result: {
+        version: 1,
+        answers: [],
+        cancelled: true,
+        cancellationReason: null,
+        summaryMarkdown: null,
+      },
+      createdAt: "2026-04-20T12:00:00.000Z",
+      updatedAt: "2026-04-20T12:05:00.000Z",
+      resolvedAt: "2026-04-20T12:05:00.000Z",
+    });
   });
 
   it("lists and creates board-authored interactions", async () => {
@@ -363,6 +394,42 @@ describe.sequential("issue thread interaction routes", () => {
     );
   });
 
+  it("cancels question interactions and emits a continuation wake", async () => {
+    const app = await createApp();
+
+    const res = await request(app)
+      .post("/api/issues/aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa/interactions/interaction-2/cancel")
+      .send({});
+
+    expect(res.status).toBe(200);
+    expect(res.body.status).toBe("cancelled");
+    expect(mockInteractionService.cancelQuestions).toHaveBeenCalledWith(
+      expect.objectContaining({ id: "aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa" }),
+      "interaction-2",
+      {},
+      expect.objectContaining({ userId: "local-board" }),
+    );
+    expect(mockHeartbeatService.wakeup).toHaveBeenCalledWith(
+      ASSIGNEE_AGENT_ID,
+      expect.objectContaining({
+        reason: "issue_commented",
+        payload: expect.objectContaining({
+          interactionId: "interaction-2",
+          interactionKind: "ask_user_questions",
+          interactionStatus: "cancelled",
+          sourceCommentId: "comment-2",
+          sourceRunId: "run-2",
+        }),
+      }),
+    );
+    expect(mockLogActivity).toHaveBeenCalledWith(
+      expect.anything(),
+      expect.objectContaining({
+        action: "issue.thread_interaction_cancelled",
+      }),
+    );
+  });
+
   it("accepts request confirmations and wakes the current assignee when configured for accept-only wakeups", async () => {
     mockInteractionService.acceptInteraction.mockResolvedValueOnce({
       interaction: {