fix: harden teardown recovery and file descriptor handling

AGENTS.md

@@ -551,7 +551,8 @@ bin/fm-teardown.sh <id>
 ```
 
 The script refuses if the worktree holds uncommitted changes or committed work that has not landed; treat a refusal as a stop-and-investigate, not an obstacle.
-Teardown validates that the recorded project and worktree are exact roots with the expected repository registration, quiesces every ordinary task endpoint, and then runs the final non-destructive safety checks before any Treehouse return.
+Teardown normally validates that the recorded project and worktree are exact roots with the expected repository registration, quiesces every ordinary task endpoint, and then runs the final non-destructive safety checks before any Treehouse return.
+It can also finish bookkeeping for a provably landed worktree whose Treehouse lease was already cleared; `bin/fm-teardown.sh`'s header owns the fail-closed recovery contract.
 For a task whose metadata carries `report_required=1`, teardown also publishes the validated completion report before releasing the account lease or removing the worktree.
 A safety refusal after quiescence leaves the endpoint stopped while preserving all task state for repair and retry.
 `bin/fm-teardown.sh`'s header owns the full landed-work definition (remote-reachable, merged-PR-head containment for the squash-merge-then-delete-branch flow, content already in the default branch, local-only merges) and the `pr=` discovery fallback for merges that skipped `bin/fm-pr-check.sh`.

bin/fm-process-tree-lib.sh

@@ -184,6 +184,17 @@ fm_run_bounded() {
       if (!$command) {
         close $status_write;
         close $finish_read;
+        # Close inherited fds above stderr so the bounded command starts
+        # with a clean fd table.  The boundary walker in
+        # fm_checkout_treehouse_return_locked opens one fd per directory
+        # in the worktree; inherited fds from the parent bash process
+        # consume headroom and cause EMFILE on large trees.
+        if (opendir my $devfd, "/dev/fd") {
+          my @inherited = grep { $_ > 2 }
+            map { /^(\d+)$/ ? $1 : () } readdir $devfd;
+          closedir $devfd;
+          POSIX::close($_) for @inherited;
+        }
         $SIG{HUP} = "DEFAULT";
         $SIG{INT} = "DEFAULT";
         $SIG{QUIT} = "DEFAULT";

bin/fm-spawn.sh

@@ -2817,7 +2817,7 @@ if [ "$KIND" = secondmate ]; then
   fi
   if [ "$ACCOUNT_EFFECTIVE_MODE" = enforce ]; then
     if ! secondmate_home_supports_account_routing "$PROJ_ABS"; then
-      echo "error: refusing account-routed secondmate launch for $PROJ_ABS: the home lacks Agent Fleet routing support. Fast-forward or otherwise reconcile the home to this Firstmate revision, run bin/fm-config-push.sh, and retry." >&2
+      echo "error: refusing account-routed secondmate $ID launch for $PROJ_ABS: the home lacks Agent Fleet routing support. Fast-forward or otherwise reconcile the home to this Firstmate revision, run bin/fm-config-push.sh, and retry." >&2
       exit 1
     fi
   elif ! secondmate_home_supports_account_routing "$PROJ_ABS"; then

tests/fm-teardown.test.sh

@@ -4937,6 +4937,41 @@ test_secondmate_registry_updates_are_locked_and_literal() {
   pass "secondmate registry updates are serialized and compare ids literally"
 }
 
+test_fd_leak_under_low_ulimit() {
+  local case_dir rc dir_count i
+  case_dir=$(make_case fd-leak-ulimit)
+  write_meta "$case_dir" no-mistakes ship
+  wt_commit "$case_dir" "fix the thing"
+  git -C "$case_dir/wt" push -q origin fm/task-x1
+
+  dir_count=200
+  i=0
+  while [ "$i" -lt "$dir_count" ]; do
+    mkdir -p "$case_dir/wt/deep/dir_$i"
+    : > "$case_dir/wt/deep/dir_$i/.keep"
+    i=$((i + 1))
+  done
+  git -C "$case_dir/wt" add -A
+  git -C "$case_dir/wt" -c user.email=t@t -c user.name=t commit -q -m "add dirs"
+  git -C "$case_dir/wt" push -q origin fm/task-x1
+
+  set +e
+  (
+    ulimit -n 256 2>/dev/null || exit 99
+    run_teardown "$case_dir" > "$case_dir/stdout" 2> "$case_dir/stderr"
+  )
+  rc=$?
+  set -e
+
+  [ "$rc" -eq 0 ] || fail "fd-leak-ulimit: teardown failed under low ulimit (rc=$rc): $(cat "$case_dir/stderr")"
+  pass "teardown succeeds under low ulimit -n with many directories (fd leak fix)"
+}
+
+if [ "${FM_TEST_FOCUSED:-}" = fd-leak-ulimit ]; then
+  test_fd_leak_under_low_ulimit
+  exit 0
+fi
+
 if [ "${FM_TEST_FOCUSED:-}" = tasktmp-safety ]; then
   test_teardown_removes_safe_tasktmp_and_accepts_absence
   test_teardown_refuses_unsafe_tasktmp_metadata
@@ -5239,3 +5274,4 @@ test_transient_index_lock_clears_after_first_attempt_and_retry_succeeds
 test_persistent_index_lock_exhausts_retries_and_refuses_loudly
 test_empty_retry_wait_uses_default_without_aborting
 test_fractional_legacy_retry_wait_refuses_without_arithmetic_error
+test_fd_leak_under_low_ulimit