One live-PR predicate, a pinned test store, and a spec correction

- repo_service: extract `isLivePr` (a type guard, so it narrows) — two sites
  encoded "exists && OPEN && not stale" independently, and a change to one would
  silently diverge from the other.
- target_rules fixture: pin MAKIT_WORKTREE_TARGETS_FILE. `worktreeTargetsFile()`
  prefers it over MAKIT_HOME, so a value inherited from another suite would point
  these tests at a shared store.
- SPEC-51: the wire aliases read `||`, not `??` (an empty string must fall
  through), and the wrapUp fallback is `defaultBranchFor()` post-merge.

Author: leduckhc

docs/specs/2026-08-11-SPEC-51-target-branch.md

@@ -67,10 +67,10 @@ A winner equal to the worktree's own branch is discarded and resolution continue
 
 **Rule 1 — one vocabulary.** `base` → `target` across server and app. Two documented exceptions:
 `baseRefName` (GitHub's own field, mirrored from their API) and two **one-release** wire aliases —
-`worktree.create` and `worktree.wrapUp` read `env.targetBranch ?? env.baseBranch`, the app sends
+`worktree.create` and `worktree.wrapUp` read `env.targetBranch || env.baseBranch`, the app sends
 both keys, and `WrapUpReport.fromJson` reads both sets. The wrapUp alias is load-bearing, not
 cosmetic: a client that predates the rename would otherwise send a key the server ignores, the
-manager's `?? detectDefaultBranch()` fallback would fast-forward the **wrong branch**, and the ack
+manager's `?? defaultBranchFor()` fallback would fast-forward the **wrong branch**, and the ack
 would report success. Guarded by a test that fails the day someone deletes the alias without
 shipping the app first.
 

server/src/repo_service.ts

@@ -76,6 +76,22 @@ const PR_CONCURRENCY = 6;
  * result to add PR info without redoing the git work — so the numbers never
  * wait on the network.
  */
+/**
+ * Whether a cached pull request is **authoritative** about where its branch
+ * lands: it exists, it is OPEN, and it is fresh.
+ *
+ * `stale` matters as much as the state. `enrichPrs` deliberately retains the
+ * last-known PR when a lookup could not complete, so during a GitHub outage a
+ * stale record would otherwise let an unverified — possibly closed or
+ * since-retargeted — base overwrite a target the user just chose.
+ *
+ * One predicate, because two sites encoded it independently and a change to one
+ * silently diverged from the other.
+ */
+function isLivePr(pr: PullRequestDTO | null): pr is PullRequestDTO {
+  return pr !== null && !pr.stale && pr.state?.toUpperCase() === "OPEN";
+}
+
 /**
  * Persist the base of any **live** pull request that disagrees with what we have
  * stored, and return the effective map.
@@ -112,7 +128,7 @@ function adoptLivePrTargets(
     // retained by `enrichPrs` when a lookup could not complete; adopting its base
     // during a GitHub outage could overwrite a freshly-chosen user target with an
     // unverified — possibly closed or since-retargeted — base.
-    if (!pr || pr.stale || pr.state?.toUpperCase() !== "OPEN") continue;
+    if (!isLivePr(pr)) continue;
     const base = pr.baseRefName;
     // A PR cannot land in its own head branch; treat that as bad data rather than
     // persisting a self-target we would then have to discard on every read.
@@ -217,7 +233,7 @@ async function repairVanishedTargets(
   for (const e of entries) {
     if (!e.branch) continue;
     const pr = lastKnown(repoPath, e.branch);
-    if (pr && !pr.stale && pr.state?.toUpperCase() === "OPEN" && pr.baseRefName) {
+    if (isLivePr(pr) && pr.baseRefName) {
       live.add(pr.baseRefName);
     }
   }

server/src/target_rules.test.ts

@@ -38,6 +38,11 @@ async function fixture(): Promise<Fixture> {
   const prevWt = process.env.MAKIT_WORKTREE_DIR;
   process.env.MAKIT_HOME = home;
   process.env.MAKIT_WORKTREE_DIR = wtDir;
+  // Pin the targets file explicitly. `worktreeTargetsFile()` prefers
+  // MAKIT_WORKTREE_TARGETS_FILE over MAKIT_HOME, so an inherited value from
+  // another suite would silently point these tests at a shared store.
+  const prevTargets = process.env.MAKIT_WORKTREE_TARGETS_FILE;
+  process.env.MAKIT_WORKTREE_TARGETS_FILE = join(home, "worktree-targets.json");
 
   const g = (cwd: string, ...args: string[]) => execFileSync("git", args, { cwd });
   g(repo, "init", "-q", "-b", "main");
@@ -58,6 +63,8 @@ async function fixture(): Promise<Fixture> {
       else process.env.MAKIT_HOME = prevHome;
       if (prevWt === undefined) delete process.env.MAKIT_WORKTREE_DIR;
       else process.env.MAKIT_WORKTREE_DIR = prevWt;
+      if (prevTargets === undefined) delete process.env.MAKIT_WORKTREE_TARGETS_FILE;
+      else process.env.MAKIT_WORKTREE_TARGETS_FILE = prevTargets;
       rmSync(home, { recursive: true, force: true });
       rmSync(repo, { recursive: true, force: true });
       rmSync(wtDir, { recursive: true, force: true });