Prefer fetched PR head SHA over cached status SHA for PR checks

On mobile, a create command can commit before opening the review,
meaning the fetched PR's head SHA is fresher than the route's cached
status SHA. Prioritizing the fetched PR head SHA ensures we fetch checks
for the most up-to-date commit.

mobile/src/session/mobile-pr-sidebar-state.ts

@@ -103,7 +103,9 @@ export async function loadPrSidebarData(
     const pr = prOutcome.result
     const checksOutcome = await deps.fetchPRChecks(args.worktreeId, {
       prNumber: pr.number,
-      headSha: args.headSha ?? pr.headSha ?? null,
+      // Why: mobile create can commit before opening the review; the fetched PR
+      // head is fresher than the route's cached git.status head.
+      headSha: pr.headSha ?? args.headSha ?? null,
       // Prefer the fetched PR's own repo identity so fork PRs key their cached
       // checks correctly; fall back to an explicit override then null.
       prRepo: pr.prRepo ?? args.prRepo ?? null

mobile/src/session/use-mobile-pr-sidebar-controller.test.ts

@@ -85,10 +85,10 @@ describe('loadPrSidebarData', () => {
     expect(d.fetchWorkItemDetails).not.toHaveBeenCalled()
     // forBranch's PR number is threaded into prForBranch as the linked hint.
     expect(d.fetchPRForBranch).toHaveBeenCalledWith('w', { branch: 'feat', linkedPRNumber: 7 })
-    // headSha forwarded to checks (status SHA wins over pr.headSha).
+    // The fetched PR head wins over the route's cached status SHA.
     expect(d.fetchPRChecks).toHaveBeenCalledWith('w', {
       prNumber: 7,
-      headSha: 'sha-status',
+      headSha: 'sha-pr',
       prRepo: null
     })
   })