Keep PR refreshes anchored to cached review numbers (#2541)

- Use fallback PR numbers after branch lookup misses, including detached HEAD
- Preserve review cards for forked or deleted-head PRs across manual refreshes
- Clear stale GitHub PR cache entries when unlinking worktree review metadata

src/main/github/client.ts

@@ -1727,6 +1727,46 @@ async function getPRByNumber(
   }
 }
 
+async function lookupPRByNumber(args: {
+  candidates: OwnerRepo[]
+  number: number
+  ghOptions: ReturnType<typeof ghRepoExecOptions>
+}): Promise<{ data: PullRequestLookupData | null; dataRepo: OwnerRepo | null }> {
+  for (const candidate of args.candidates) {
+    try {
+      const linkedData = await getPRByNumber(candidate, args.number, args.ghOptions)
+      if (!linkedData) {
+        continue
+      }
+      return { data: linkedData, dataRepo: candidate }
+    } catch (err) {
+      if (shouldStopAfterExactLookupError(err)) {
+        throw err
+      }
+      // Candidate probing is best-effort; another repo may own the PR.
+    }
+  }
+
+  if (args.candidates.length > 0) {
+    return { data: null, dataRepo: null }
+  }
+
+  try {
+    const { stdout } = await ghExecFileAsync(
+      ['pr', 'view', String(args.number), '--json', PR_LOOKUP_JSON_FIELDS],
+      args.ghOptions
+    )
+    return { data: JSON.parse(stdout), dataRepo: null }
+  } catch (err) {
+    if (isNoPullRequestError(err)) {
+      // Why: stale cached fallback numbers should not turn every poll into an
+      // error when the PR was deleted or belonged to a different repo.
+      return { data: null, dataRepo: null }
+    }
+    throw err
+  }
+}
+
 function isNotFoundGhError(err: unknown): boolean {
   const stderr = err instanceof Error ? err.message : String(err)
   return classifyGhError(stderr).type === 'not_found'
@@ -1746,14 +1786,23 @@ function shouldStopAfterExactLookupError(err: unknown): boolean {
  * "create from PR" worktrees whose local branch differs from the PR head ref,
  * and prevents a coalesced linked-PR refresh from fanning out an unrelated
  * branch lookup result to sibling aliases.
+ * `fallbackPRNumber` is weaker: branch lookup still wins, and exact lookup is
+ * used only after branch lookup misses.
  */
 export async function getPRForBranch(
   repoPath: string,
   branch: string,
   linkedPRNumber?: number | null,
-  connectionId?: string | null
+  connectionId?: string | null,
+  fallbackPRNumber?: number | null
 ): Promise<PRInfo | null> {
-  const outcome = await getPRForBranchOutcome(repoPath, branch, linkedPRNumber, connectionId)
+  const outcome = await getPRForBranchOutcome(
+    repoPath,
+    branch,
+    linkedPRNumber,
+    connectionId,
+    fallbackPRNumber
+  )
   return outcome.kind === 'found' ? outcome.pr : null
 }
 
@@ -1761,11 +1810,14 @@ export async function getPRForBranchOutcome(
   repoPath: string,
   branch: string,
   linkedPRNumber?: number | null,
-  connectionId?: string | null
+  connectionId?: string | null,
+  fallbackPRNumber?: number | null
 ): Promise<PRRefreshOutcome> {
   // Strip refs/heads/ prefix if present
   const branchName = branch.replace(/^refs\/heads\//, '')
-  if (!branchName && typeof linkedPRNumber !== 'number') {
+  // Why: detached HEAD cannot use branch lookup, but an exact linked/fallback
+  // PR number remains safe to query and keeps review state visible.
+  if (!branchName && typeof linkedPRNumber !== 'number' && typeof fallbackPRNumber !== 'number') {
     return { kind: 'no-pr', fetchedAt: Date.now() }
   }
   const context = githubRepoContext(repoPath, connectionId)
@@ -1778,39 +1830,13 @@ export async function getPRForBranchOutcome(
     let dataRepo: OwnerRepo | null = null
 
     if (typeof linkedPRNumber === 'number') {
-      for (const candidate of candidates) {
-        try {
-          const linkedData = await getPRByNumber(candidate, linkedPRNumber, ghOptions)
-          if (!linkedData) {
-            continue
-          }
-          data = linkedData
-          dataRepo = candidate
-          break
-        } catch (err) {
-          if (shouldStopAfterExactLookupError(err)) {
-            throw err
-          }
-          // Candidate probing is best-effort; another repo may own the PR.
-        }
-      }
-
-      if (!data && candidates.length === 0) {
-        const args = ['pr', 'view', String(linkedPRNumber), '--json', PR_LOOKUP_JSON_FIELDS]
-        try {
-          const { stdout } = await ghExecFileAsync(args, ghOptions)
-          data = JSON.parse(stdout)
-        } catch (err) {
-          if (!isNoPullRequestError(err)) {
-            return prRefreshUpstreamError(err)
-          }
-          // Why: a stale linkedPRNumber (PR deleted, wrong repo, ...) makes
-          // `gh pr view <number>` reject. Treat that as the no-PR case so
-          // callers see the historical `null` semantics instead of a thrown
-          // error every poll cycle.
-          data = null
-        }
-      }
+      const exactLookup = await lookupPRByNumber({
+        candidates,
+        number: linkedPRNumber,
+        ghOptions
+      })
+      data = exactLookup.data
+      dataRepo = exactLookup.dataRepo
     } else if (branchName) {
       // During a rebase the worktree is in detached HEAD and branch is empty.
       // An empty --head filter causes gh to return an arbitrary PR.
@@ -1852,6 +1878,15 @@ export async function getPRForBranchOutcome(
         }
       }
     }
+    if (!data && typeof linkedPRNumber !== 'number' && typeof fallbackPRNumber === 'number') {
+      const fallbackLookup = await lookupPRByNumber({
+        candidates,
+        number: fallbackPRNumber,
+        ghOptions
+      })
+      data = fallbackLookup.data
+      dataRepo = fallbackLookup.dataRepo
+    }
     if (!data) {
       return { kind: 'no-pr', fetchedAt: Date.now() }
     }