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/routes/costs.ts

@@ -14,6 +14,7 @@ import {
   financeService,
   companyService,
   agentService,
+  issueService,
   heartbeatService,
   logActivity,
 } from "../services/index.js";
@@ -58,6 +59,14 @@ export function costRoutes(
   const budgets = budgetService(db, budgetHooks);
   const companies = companyService(db);
   const agents = agentService(db);
+  const issues = issueService(db);
+
+  async function resolveIssueByRef(rawId: string) {
+    if (/^[A-Z]+-\d+$/i.test(rawId)) {
+      return issues.getByIdentifier(rawId);
+    }
+    return issues.getById(rawId);
+  }
 
   router.post("/companies/:companyId/cost-events", validate(createCostEventSchema), async (req, res) => {
     const companyId = req.params.companyId as string;
@@ -126,6 +135,18 @@ export function costRoutes(
     res.json(summary);
   });
 
+  router.get("/issues/:id/cost-summary", async (req, res) => {
+    const rawId = req.params.id as string;
+    const issue = await resolveIssueByRef(rawId);
+    if (!issue) {
+      res.status(404).json({ error: "Issue not found" });
+      return;
+    }
+    assertCompanyAccess(req, issue.companyId);
+    const summary = await costs.issueTreeSummary(issue.companyId, issue.id);
+    res.json(summary);
+  });
+
   router.get("/companies/:companyId/costs/by-agent", async (req, res) => {
     const companyId = req.params.companyId as string;
     assertCompanyAccess(req, companyId);