fix(FN-branch-group): address second-round PR review feedback (#1357)

- syncGroupPrCallback forwards owner/repo to updatePr (multi-project daemons
  could 404 or edit an unrelated same-numbered PR via process-cwd fallback)
- merger background reconcile re-reads the group before persisting and skips
  the write when the PR snapshot changed (stale-write race vs newer open PR)
- branchContext.groupId trimmed on metadata emit/parse round-trip
- triageSlice non-shared invariant assertions (no groupId, no group row)

packages/cli/src/commands/__tests__/task-lifecycle.test.ts

@@ -1366,6 +1366,11 @@ describe("syncGroupPrCallback (U6)", () => {
     const result = await sync({ cwd: "/tmp/project", group: group as never, members });
     expect(result).toEqual({ prNumber: 42, prUrl: "https://github.com/owner/repo/pull/42", prState: "open" });
     expect(github.updatePr).toHaveBeenCalledTimes(1);
+    // T4: owner/repo must be forwarded so multi-project daemons target the
+    // resolved per-project repo, not process.cwd().
+    expect(github.updatePr).toHaveBeenCalledWith(
+      expect.objectContaining({ owner: "owner", repo: "repo", number: 42 }),
+    );
     const body = (github.updatePr.mock.calls[0][0] as { body: string }).body;
     expect(body).toContain("Completion: 0/2 landed");
     expect(body).toContain("FN-A: Alpha");

packages/cli/src/commands/task-lifecycle.ts

@@ -39,7 +39,7 @@ interface GitHubOperations {
   }>;
   mergePr(params: { number: number; method?: "merge" | "squash" | "rebase" }): Promise<PrInfo>;
   getPrStatus(owner: string, repo: string, number: number): Promise<PrInfo>;
-  updatePr(params: { number: number; title?: string; body?: string }): Promise<PrInfo>;
+  updatePr(params: { owner?: string; repo?: string; number: number; title?: string; body?: string }): Promise<PrInfo>;
   closePr(params: { number: number }): Promise<PrInfo>;
 }
 
@@ -287,6 +287,8 @@ export function syncGroupPrCallback(
       return { prNumber: current.number, prUrl: current.url, prState: currentState };
     }
     const updated = await github.updatePr({
+      owner: repo.owner,
+      repo: repo.repo,
       number: group.prNumber,
       title: buildGroupPullRequestTitle(group, members),
       body: buildGroupPrSyncBody(group, members),