Guard assigned backlog liveness (#5428)

## Thinking Path

> - Paperclip orchestrates AI agents for zero-human companies
> - The issue graph and liveness recovery system decide whether assigned
work is executable or parked
> - Assigned issues created without an explicit status could silently
land in backlog, making parents look blocked with no productive wake
path
> - The server, shared validators, recovery analysis, and UI all need to
agree on that execution semantic
> - This pull request makes assigned issue creation default to `todo`,
flags assigned backlog blockers, and surfaces the state in the board
> - The benefit is that parked assigned work becomes intentional and
visible instead of creating silent liveness stalls

## What Changed

- Adds contract tests for assigned issue creation defaults.
- Defaults assigned issue creation to `todo` when status is omitted
while preserving explicit `backlog` parking.
- Exposes `resolveCreateIssueStatusDefault` through shared validators.
- Teaches liveness/blocker attention paths to distinguish assigned
backlog blockers.
- Adds UI notices, row/header badges, and issue detail safeguards for
assigned backlog blockers.
- Adds Storybook fixtures and execution-semantics documentation for the
assigned-backlog behavior.

## Verification

- `pnpm run preflight:workspace-links && pnpm exec vitest run
packages/shared/src/validators/issue.test.ts
server/src/__tests__/issue-assigned-backlog-contract-routes.test.ts
server/src/__tests__/issue-blocker-attention.test.ts
server/src/__tests__/issue-liveness.test.ts
server/src/__tests__/heartbeat-issue-liveness-escalation.test.ts
ui/src/components/IssueAssignedBacklogNotice.test.tsx
ui/src/components/IssueRow.test.tsx` — 50 passed, 23 skipped.
- Skipped tests were embedded Postgres suites on this host with the repo
skip message: `Postgres init script exited with code null. Please check
the logs for extra info. The data directory might already exist.`
- Pairwise merge check against the issue-controls PR branch completed
without conflicts via `git merge --no-commit --no-ff` in a temporary
worktree.
- Screenshots for assigned-backlog UI states:
[light](docs/pr-screenshots/pr-5428/assigned-backlog-light.png),
[dark](docs/pr-screenshots/pr-5428/assigned-backlog-dark.png).
- Follow-up checks: `pnpm --filter /ui typecheck`; `pnpm --filter
/mcp-server build`; `pnpm --filter /mcp-server test`; `pnpm exec vitest
run packages/shared/src/validators/issue.test.ts`; focused UI component
tests.
- Remote PR checks on head `6300b3c`: policy, verify, serialized server
shards 1/4-4/4, Canary Dry Run, e2e, Greptile Review, and Snyk all
passed.

## Risks

- Medium: changes status defaulting for assigned issue creation when the
caller omits status. Explicit `backlog` remains supported, and
server/shared tests cover both paths.
- Medium: liveness classification changes can affect blocker attention
labels; focused service and UI tests cover the new assigned-backlog
state.

> 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 coding agent, GPT-5 model family (`gpt-5`), tool-enabled
Paperclip heartbeat environment. Context window and internal reasoning
mode are not exposed by the runtime.

## 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__/heartbeat-issue-liveness-escalation.test.ts

@@ -117,7 +117,11 @@ describeEmbeddedPostgres("heartbeat issue graph liveness escalation", () => {
     });
   }
 
-  async function seedBlockedChain(opts: { outsideLookback?: boolean } = {}) {
+  async function seedBlockedChain(opts: {
+    outsideLookback?: boolean;
+    blockerStatus?: string;
+    blockerAssigneeAgentId?: "coder" | "manager" | null;
+  } = {}) {
     const companyId = randomUUID();
     const managerId = randomUUID();
     const coderId = randomUUID();
@@ -178,8 +182,13 @@ describeEmbeddedPostgres("heartbeat issue graph liveness escalation", () => {
         id: blockerIssueId,
         companyId,
         title: "Missing unblock owner",
-        status: "todo",
+        status: opts.blockerStatus ?? "todo",
         priority: "medium",
+        assigneeAgentId: opts.blockerAssigneeAgentId === "coder"
+          ? coderId
+          : opts.blockerAssigneeAgentId === "manager"
+            ? managerId
+            : null,
         issueNumber: 2,
         identifier: `${issuePrefix}-2`,
         createdAt: issueTimestamp,
@@ -283,6 +292,46 @@ describeEmbeddedPostgres("heartbeat issue graph liveness escalation", () => {
     expect(result.escalationsCreated).toBe(0);
   });
 
+  it("creates one bounded escalation for an assigned backlog blocker leaf", async () => {
+    await enableAutoRecovery();
+    const { companyId, coderId, blockedIssueId, blockerIssueId } = await seedBlockedChain({
+      blockerStatus: "backlog",
+      blockerAssigneeAgentId: "coder",
+    });
+    const heartbeat = heartbeatService(db);
+
+    const first = await heartbeat.reconcileIssueGraphLiveness();
+    const second = await heartbeat.reconcileIssueGraphLiveness();
+
+    expect(first.findings).toBe(1);
+    expect(first.escalationsCreated).toBe(1);
+    expect(second.findings).toBe(0);
+    expect(second.escalationsCreated).toBe(0);
+
+    const escalations = await db
+      .select()
+      .from(issues)
+      .where(and(eq(issues.companyId, companyId), eq(issues.originKind, "harness_liveness_escalation")));
+    expect(escalations).toHaveLength(1);
+    expect(escalations[0]).toMatchObject({
+      parentId: blockerIssueId,
+      assigneeAgentId: coderId,
+      originId: [
+        "harness_liveness",
+        companyId,
+        blockedIssueId,
+        "blocked_by_assigned_backlog_issue",
+        blockerIssueId,
+      ].join(":"),
+      originFingerprint: [
+        "harness_liveness_leaf",
+        companyId,
+        "blocked_by_assigned_backlog_issue",
+        blockerIssueId,
+      ].join(":"),
+    });
+  });
+
   it("creates one manager escalation, preserves blockers, and records owner selection", async () => {
     await enableAutoRecovery();
     const { companyId, managerId, blockedIssueId, blockerIssueId } = await seedBlockedChain();