diff --git a/.pql/changelog/ticket_history/2026-06.sql b/.pql/changelog/ticket_history/2026-06.sql
index ac411854..66d7c54e 100644
--- a/.pql/changelog/ticket_history/2026-06.sql
+++ b/.pql/changelog/ticket_history/2026-06.sql
@@ -3999,3 +3999,5 @@ INSERT INTO ticket_history (ticket_record_id, field, old_value, new_value, chang
 INSERT INTO ticket_history (ticket_record_id, field, old_value, new_value, changed_by, changed_at, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('06FBHD098CV2N73823KX4Z99P4', 'status', 'in_progress', 'done', NULL, '2026-06-11 23:04:46', '2026-06-11 23:04:46', '2026-06-11 23:04:46', NULL, '5d8d8c7a17da4894510db957e7af3c3f', 2) ON CONFLICT(hash) DO NOTHING;
 INSERT INTO ticket_history (ticket_record_id, field, old_value, new_value, changed_by, changed_at, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('06FBHCP03EJ9CDBGZGRPD19N8W', 'status', 'backlog', 'in_progress', NULL, '2026-06-11 23:05:16', '2026-06-11 23:05:16', '2026-06-11 23:05:16', NULL, '252a8c28446f3c86876ec826fce03987', 2) ON CONFLICT(hash) DO NOTHING;
 INSERT INTO ticket_history (ticket_record_id, field, old_value, new_value, changed_by, changed_at, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('06FBHCP03EJ9CDBGZGRPD19N8W', 'status', 'in_progress', 'done', NULL, '2026-06-11 23:06:26', '2026-06-11 23:06:26', '2026-06-11 23:06:26', NULL, '4e1cc82f703d717f7592890e230caf00', 2) ON CONFLICT(hash) DO NOTHING;
+INSERT INTO ticket_history (ticket_record_id, field, old_value, new_value, changed_by, changed_at, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('06FBHC90B72A270CAKA7AP1ZX8', 'status', 'backlog', 'in_progress', NULL, '2026-06-11 23:07:01', '2026-06-11 23:07:01', '2026-06-11 23:07:01', NULL, '795c139edb5acd0d2a187dac6a3066c7', 2) ON CONFLICT(hash) DO NOTHING;
+INSERT INTO ticket_history (ticket_record_id, field, old_value, new_value, changed_by, changed_at, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('06FBHC90B72A270CAKA7AP1ZX8', 'status', 'in_progress', 'done', NULL, '2026-06-11 23:08:13', '2026-06-11 23:08:13', '2026-06-11 23:08:13', NULL, 'f83a2fc13f3839070957bea6ac7fdc5f', 2) ON CONFLICT(hash) DO NOTHING;
diff --git a/.pql/changelog/tickets/2026-06.sql b/.pql/changelog/tickets/2026-06.sql
index f905f89b..d3c8f52f 100644
--- a/.pql/changelog/tickets/2026-06.sql
+++ b/.pql/changelog/tickets/2026-06.sql
@@ -4099,3 +4099,13 @@ INSERT INTO tickets (record_id, type, parent_record_id, title, description, stat
 Fix: pass the active workspace root as the spawn cwd (and re-derive it on project switch for new panes).
 
 Acceptance: test that a terminal pane''s SpawnSpec.cwd equals the workspace root, not Directory.current.', 'done', 'medium', NULL, NULL, NULL, '2026-06-11 21:59:42', '2026-06-11 23:06:26', NULL, '8cad068c28a7a0cb6772a5fbdcbc34c3', 2) ON CONFLICT(record_id) DO UPDATE SET type=excluded.type, parent_record_id=excluded.parent_record_id, title=excluded.title, description=excluded.description, status=excluded.status, priority=excluded.priority, assigned_to=excluded.assigned_to, team=excluded.team, decision_ref=excluded.decision_ref, updated_at=excluded.updated_at, deleted_at=excluded.deleted_at, hash=excluded.hash, canonical_version=excluded.canonical_version WHERE excluded.updated_at > tickets.updated_at OR (excluded.updated_at = tickets.updated_at AND excluded.hash > tickets.hash);
+INSERT INTO tickets (record_id, type, parent_record_id, title, description, status, priority, assigned_to, team, decision_ref, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('06FBHC90B72A270CAKA7AP1ZX8', 'bug', '06FBHBGHNEQTAEPGNJKN42C1E8', 'Orchestrator.spawn() races itself — concurrent spawns for one id leak a live claude process', 'lib/builtin/claude/src/session_orchestrator.dart:191-249 — spawn() does check-then-act on the sessions map across two awaits (transcript-tail read, process start). Two concurrent spawns for the same session id both pass the check; the loser''s live claude process is orphaned, never killed, never observed.
+
+Fix: hold a Map<String, Future<ManagedSession>> — first caller installs the future synchronously, later callers await the same future; remove the entry on failure.
+
+Acceptance: test issuing two concurrent spawn() calls for one id yields the same ManagedSession instance and exactly one process spawn (count via injected spawner); failure path clears the in-flight entry so a retry can proceed.', 'in_progress', 'medium', NULL, NULL, NULL, '2026-06-11 21:57:56', '2026-06-11 23:07:01', NULL, 'f2df2148315332d48e2bf66cc2942bd3', 2) ON CONFLICT(record_id) DO UPDATE SET type=excluded.type, parent_record_id=excluded.parent_record_id, title=excluded.title, description=excluded.description, status=excluded.status, priority=excluded.priority, assigned_to=excluded.assigned_to, team=excluded.team, decision_ref=excluded.decision_ref, updated_at=excluded.updated_at, deleted_at=excluded.deleted_at, hash=excluded.hash, canonical_version=excluded.canonical_version WHERE excluded.updated_at > tickets.updated_at OR (excluded.updated_at = tickets.updated_at AND excluded.hash > tickets.hash);
+INSERT INTO tickets (record_id, type, parent_record_id, title, description, status, priority, assigned_to, team, decision_ref, created_at, updated_at, deleted_at, hash, canonical_version) VALUES ('06FBHC90B72A270CAKA7AP1ZX8', 'bug', '06FBHBGHNEQTAEPGNJKN42C1E8', 'Orchestrator.spawn() races itself — concurrent spawns for one id leak a live claude process', 'lib/builtin/claude/src/session_orchestrator.dart:191-249 — spawn() does check-then-act on the sessions map across two awaits (transcript-tail read, process start). Two concurrent spawns for the same session id both pass the check; the loser''s live claude process is orphaned, never killed, never observed.
+
+Fix: hold a Map<String, Future<ManagedSession>> — first caller installs the future synchronously, later callers await the same future; remove the entry on failure.
+
+Acceptance: test issuing two concurrent spawn() calls for one id yields the same ManagedSession instance and exactly one process spawn (count via injected spawner); failure path clears the in-flight entry so a retry can proceed.', 'done', 'medium', NULL, NULL, NULL, '2026-06-11 21:57:56', '2026-06-11 23:08:13', NULL, 'fde3f9e912ea1d25256003ef56dcf491', 2) ON CONFLICT(record_id) DO UPDATE SET type=excluded.type, parent_record_id=excluded.parent_record_id, title=excluded.title, description=excluded.description, status=excluded.status, priority=excluded.priority, assigned_to=excluded.assigned_to, team=excluded.team, decision_ref=excluded.decision_ref, updated_at=excluded.updated_at, deleted_at=excluded.deleted_at, hash=excluded.hash, canonical_version=excluded.canonical_version WHERE excluded.updated_at > tickets.updated_at OR (excluded.updated_at = tickets.updated_at AND excluded.hash > tickets.hash);
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ca0cf08d..42833ffb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -94,6 +94,11 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
   app process's working directory — `$HOME` for desktop launches, and the
   wrong repo after a project switch. (T-381)
 
+- **Two simultaneous spawns of the same Claude session no longer leak a
+  process.** Concurrent spawn calls for one pane id both passed the registry
+  check and the loser's live process was orphaned; spawns for an id are now
+  coalesced onto one in-flight future. (T-374)
+
 - **Accepting ExitPlanMode now leaves plan mode in the conversation panel.**
   Approving Claude's plan (the ExitPlanMode tool) transitioned the underlying
   session out of plan mode, but clide's tracked permission mode didn't follow,
diff --git a/lib/builtin/claude/src/session_orchestrator.dart b/lib/builtin/claude/src/session_orchestrator.dart
index 98125c08..5674f698 100644
--- a/lib/builtin/claude/src/session_orchestrator.dart
+++ b/lib/builtin/claude/src/session_orchestrator.dart
@@ -188,7 +188,28 @@ class ClaudeSessionOrchestrator extends ChangeNotifier {
   /// (T-269): the existing session belongs to the old repo, so it is torn down
   /// and a fresh one spawned for the new repo — a pane must never inherit
   /// another workspace's conversation.
-  Future<ManagedSession> spawn(SpawnSpec spec) async {
+  Future<ManagedSession> spawn(SpawnSpec spec) {
+    // Serialize concurrent spawns per id (T-374): the body check-then-acts
+    // on _sessions across two awaits, so two racing callers would both
+    // pass the check and the loser's live claude process would be orphaned.
+    // The first caller installs the future synchronously; the rest await
+    // it. (A racing different-cwd spawn for the same id also coalesces —
+    // the workspace-switch flow is sequential, so that pair never races.)
+    final inFlight = _spawning[spec.id];
+    if (inFlight != null) return inFlight;
+    final f = _spawn(spec);
+    _spawning[spec.id] = f;
+    unawaited(
+      f.then<void>((_) {}, onError: (Object _) {}).whenComplete(() {
+        if (identical(_spawning[spec.id], f)) _spawning.remove(spec.id);
+      }),
+    );
+    return f;
+  }
+
+  final Map<String, Future<ManagedSession>> _spawning = {};
+
+  Future<ManagedSession> _spawn(SpawnSpec spec) async {
     final existing = _sessions[spec.id];
     if (existing != null) {
       if (existing.cwd == spec.cwd) return existing;
diff --git a/test/builtin/claude/session_orchestrator_test.dart b/test/builtin/claude/session_orchestrator_test.dart
index a7a14bb5..50b68ac6 100644
--- a/test/builtin/claude/session_orchestrator_test.dart
+++ b/test/builtin/claude/session_orchestrator_test.dart
@@ -60,6 +60,32 @@ void main() {
     expect(created, hasLength(1));
   });
 
+  // T-374: spawn() check-then-acts across awaits; without the in-flight
+  // map, two CONCURRENT spawns both passed the registry check and the
+  // loser's live claude process was orphaned.
+  test('two concurrent spawns for one id share one session and one process (T-374)', () async {
+    final (a, b) = await (orch.spawn(spec('primary')), orch.spawn(spec('primary'))).wait;
+    expect(identical(a, b), isTrue);
+    expect(created, hasLength(1));
+  });
+
+  test('a failed spawn clears the in-flight entry so a retry can proceed (T-374)', () async {
+    var calls = 0;
+    final flaky = ClaudeSessionOrchestrator(
+      processFactory: ({required sessionArgs, required cwd, env}) async {
+        calls++;
+        if (calls == 1) throw StateError('spawn blew up');
+        final p = _FakeProc();
+        created.add(p);
+        return p;
+      },
+    );
+    await expectLater(flaky.spawn(spec('primary')), throwsStateError);
+    final m = await flaky.spawn(spec('primary'));
+    expect(m.id, 'primary');
+    expect(calls, 2);
+  });
+
   test('hide keeps the process alive and in the registry; show restores it', () async {
     await orch.spawn(spec('primary'));
     orch.hide('primary');