diff --git a/lib/worktree.ts b/lib/worktree.ts
index 1e68884b..8854a840 100644
--- a/lib/worktree.ts
+++ b/lib/worktree.ts
@@ -259,6 +259,11 @@ export class WorktreeManager {
 
         const entryPath = path.join(worktreeBase, entry);
         try {
+          // Skip recent worktrees (< 1 hour old) to avoid killing
+          // worktrees from concurrent test runs still in progress
+          const stat = fs.statSync(entryPath);
+          const ageMs = Date.now() - stat.mtimeMs;
+          if (ageMs < 3600_000) continue;
           fs.rmSync(entryPath, { recursive: true, force: true });
         } catch { /* non-fatal */ }
       }
diff --git a/test/helpers/session-runner.ts b/test/helpers/session-runner.ts
index 7101e30c..c0f2ac00 100644
--- a/test/helpers/session-runner.ts
+++ b/test/helpers/session-runner.ts
@@ -303,12 +303,13 @@ export async function runSkillTest(options: {
 
   // Use resultLine for structured result data
   if (resultLine) {
-    if (resultLine.is_error) {
+    if (resultLine.subtype === 'success' && resultLine.is_error) {
       // claude -p can return subtype=success with is_error=true (e.g. API connection failure)
       exitReason = 'error_api';
     } else if (resultLine.subtype === 'success') {
       exitReason = 'success';
     } else if (resultLine.subtype) {
+      // Preserve known subtypes like error_max_turns even if is_error is set
       exitReason = resultLine.subtype;
     }
   }
diff --git a/test/worktree.test.ts b/test/worktree.test.ts
index be1533ae..47a58d23 100644
--- a/test/worktree.test.ts
+++ b/test/worktree.test.ts
@@ -231,6 +231,9 @@ describe('WorktreeManager', () => {
     spawnSync('git', ['worktree', 'remove', '--force', oldPath], { cwd: repo, stdio: 'pipe' });
     // Recreate the directory to simulate orphaned state
     fs.mkdirSync(oldPath, { recursive: true });
+    // Backdate mtime to simulate a stale worktree (> 1 hour old)
+    const staleTime = new Date(Date.now() - 7200_000);
+    fs.utimesSync(oldRunDir, staleTime, staleTime);
 
     // New manager should prune the old run's directory
     const newMgr = new WorktreeManager(repo);