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__/issue-blocker-attention.test.ts

@@ -76,6 +76,7 @@ describeEmbeddedPostgres("issue blocker attention", () => {
     status: string;
     parentId?: string | null;
     assigneeAgentId?: string | null;
+    assigneeUserId?: string | null;
     originKind?: string | null;
     originId?: string | null;
     originFingerprint?: string | null;
@@ -90,6 +91,7 @@ describeEmbeddedPostgres("issue blocker attention", () => {
       priority: "medium",
       parentId: input.parentId ?? null,
       assigneeAgentId: input.assigneeAgentId ?? null,
+      assigneeUserId: input.assigneeUserId ?? null,
       originKind: input.originKind ?? "manual",
       originId: input.originId ?? null,
       originFingerprint: input.originFingerprint ?? "default",
@@ -147,6 +149,55 @@ describeEmbeddedPostgres("issue blocker attention", () => {
     });
   });
 
+  it("classifies an assigned backlog blocker leaf without a waiting path as attention-needed", async () => {
+    const { companyId, agentId } = await createCompany("PBB");
+    const parentId = await insertIssue({ companyId, identifier: "PBB-1", title: "Parent", status: "blocked" });
+    const blockerId = await insertIssue({
+      companyId,
+      identifier: "PBB-2",
+      title: "Parked assigned blocker",
+      status: "backlog",
+      assigneeAgentId: agentId,
+    });
+    await block({ companyId, blockerIssueId: blockerId, blockedIssueId: parentId });
+
+    const parent = (await svc.list(companyId, { status: "blocked" })).find((issue) => issue.id === parentId);
+
+    expect(parent?.blockerAttention).toMatchObject({
+      state: "needs_attention",
+      reason: "attention_required",
+      unresolvedBlockerCount: 1,
+      coveredBlockerCount: 0,
+      stalledBlockerCount: 0,
+      attentionBlockerCount: 1,
+      sampleBlockerIdentifier: "PBB-2",
+    });
+  });
+
+  it("treats a human-owned backlog blocker as a covered waiting path", async () => {
+    const { companyId } = await createCompany("PBU");
+    const parentId = await insertIssue({ companyId, identifier: "PBU-1", title: "Parent", status: "blocked" });
+    const blockerId = await insertIssue({
+      companyId,
+      identifier: "PBU-2",
+      title: "Human-owned parked blocker",
+      status: "backlog",
+      assigneeUserId: "board-user-1",
+    });
+    await block({ companyId, blockerIssueId: blockerId, blockedIssueId: parentId });
+
+    const parent = (await svc.list(companyId, { status: "blocked" })).find((issue) => issue.id === parentId);
+
+    expect(parent?.blockerAttention).toMatchObject({
+      state: "covered",
+      reason: "active_dependency",
+      unresolvedBlockerCount: 1,
+      coveredBlockerCount: 1,
+      attentionBlockerCount: 0,
+      sampleBlockerIdentifier: "PBU-2",
+    });
+  });
+
   it("keeps mixed blockers attention-required when any path lacks active work", async () => {
     const { companyId, agentId } = await createCompany("PBM");
     const parentId = await insertIssue({ companyId, identifier: "PBM-1", title: "Parent", status: "blocked" });