diff --git a/bin/fm-pr-merge.sh b/bin/fm-pr-merge.sh
index 8ffb32cc..13e48230 100755
--- a/bin/fm-pr-merge.sh
+++ b/bin/fm-pr-merge.sh
@@ -87,4 +87,4 @@ if ! caller_has_merge_method "$@"; then
   merge_args=(--squash)
 fi
 
-gh-axi pr merge "$PR_NUMBER" --repo "$PR_OWNER/$PR_REPO" "${merge_args[@]}" "$@"
+gh-axi pr merge "$PR_NUMBER" --repo "$PR_OWNER/$PR_REPO" ${merge_args[@]+"${merge_args[@]}"} "$@"
diff --git a/bin/fm-spawn.sh b/bin/fm-spawn.sh
index 1c4352a6..4c50df11 100755
--- a/bin/fm-spawn.sh
+++ b/bin/fm-spawn.sh
@@ -415,6 +415,45 @@ path_is_ancestor_of() {
   return 1
 }
 
+# Resolve a git worktree's common dir to an absolute real path. `git rev-parse
+# --git-common-dir` may return a path relative to the worktree, so anchor a
+# relative result to the worktree before canonicalizing with pwd -P; this lets
+# two worktrees of the same repository be compared regardless of symlinked paths.
+git_common_dir_real() {
+  local dir=$1 common
+  common=$(git -C "$dir" rev-parse --git-common-dir 2>/dev/null) || return 1
+  [ -n "$common" ] || return 1
+  case "$common" in
+    /*) ;;
+    *) common="$dir/$common" ;;
+  esac
+  [ -d "$common" ] || return 1
+  (cd "$common" && pwd -P)
+}
+
+# A captured pane path is the genuine treehouse lease only when it is a worktree
+# of the SAME repository as the project, resolved distinctly from it. The wait
+# loop below accepts the first pane cwd that differs from the project dir, but
+# shell-init noise (e.g. a transient ~/.oh-my-zsh cwd during zsh startup - itself
+# a git repo, but a DIFFERENT repository) can appear before `treehouse get`
+# lands. Comparing canonical git common dirs distinguishes the real lease from
+# such noise no matter where treehouse.toml places the pool root, and resolving
+# every path with pwd -P keeps a symlinked $HOME from breaking the match. The
+# isolation guard after the loop is the backstop; this keeps the loop from ever
+# selecting the wrong path.
+is_project_worktree() {
+  local candidate=$1 proj_abs=$2 cand_real proj_real cand_common proj_common
+  [ -d "$candidate" ] || return 1
+  [ "$(git -C "$candidate" rev-parse --is-inside-work-tree 2>/dev/null)" = "true" ] || return 1
+  cand_common=$(git_common_dir_real "$candidate") || return 1
+  proj_common=$(git_common_dir_real "$proj_abs") || return 1
+  [ "$cand_common" = "$proj_common" ] || return 1
+  cand_real=$(cd "$candidate" 2>/dev/null && pwd -P) || return 1
+  proj_real=$(cd "$proj_abs" 2>/dev/null && pwd -P) || return 1
+  [ "$cand_real" != "$proj_real" ] || return 1
+  return 0
+}
+
 validate_firstmate_home_for_spawn() {
   local id=$1 home=$2 abs_home abs_active_home abs_root marker_id
   abs_home=$(resolved_existing_dir "$home") || return 1
@@ -634,17 +673,23 @@ spawn_send_key() {  # <target> <key>
 if [ "$KIND" != secondmate ]; then
   spawn_send_text_line "$T" 'treehouse get'
 
-  # Wait for the treehouse subshell: the pane's cwd moves from the project to the worktree.
-  for _ in $(seq 1 60); do
+  # Wait for the treehouse subshell: the pane's cwd moves from the project to the
+  # worktree. Only accept a captured path that is genuinely a worktree of the SAME
+  # repository as the project - a bare "differs from the project dir" check once
+  # recorded shell-init noise (e.g. a transient ~/.oh-my-zsh cwd during zsh startup)
+  # that appears before `treehouse get` lands. This needs no knowledge of the
+  # treehouse pool root, so it works wherever treehouse.toml places it.
+  wt_wait="${FM_SPAWN_WORKTREE_WAIT:-60}"
+  for _ in $(seq 1 "$wt_wait"); do
     p=$(spawn_current_path "$T" || true)
-    if [ -n "$p" ] && [ "$p" != "$PROJ_ABS" ]; then
+    if [ -n "$p" ] && is_project_worktree "$p" "$PROJ_ABS"; then
       WT="$p"
       break
     fi
     sleep 1
   done
   if [ -z "$WT" ]; then
-    echo "error: treehouse get did not enter a worktree within 60s; inspect window $T" >&2
+    echo "error: treehouse get did not enter a worktree within ${wt_wait}s; inspect window $T" >&2
     exit 1
   fi
 
diff --git a/docs/configuration.md b/docs/configuration.md
index 5649c7a6..310c0068 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -213,6 +213,7 @@ FM_FLEET_PRUNE=1        # set to 0 to skip pruning local branches whose upstream
 FM_BUSY_REGEX='esc (to )?interrupt|Working\.\.\.|Ctrl\+c:cancel'   # busy-pane signatures, shared by watcher, fm-crew-state pane fallback, and tmux helper
 FM_COMPOSER_IDLE_RE=    # optional empty-composer regex, applied after dim-ghost and border stripping
 GROK_HOME=              # optional Grok config home for firstmate's global grok turn-end hook; defaults to ~/.grok
+FM_SPAWN_WORKTREE_WAIT=60   # seconds fm-spawn waits for treehouse get to land the pane in a same-repo isolated worktree before aborting
 FM_SEND_RETRIES=3       # fm-send Enter-retry attempts after typing the line once
 FM_SEND_SLEEP=0.4       # seconds between fm-send submit checks
 FM_SEND_SETTLE=1        # seconds fm-send waits after a successful text submit; 0 disables
diff --git a/tests/fm-tangle-guard.test.sh b/tests/fm-tangle-guard.test.sh
index 92a697d8..001d3566 100755
--- a/tests/fm-tangle-guard.test.sh
+++ b/tests/fm-tangle-guard.test.sh
@@ -181,6 +181,7 @@ run_spawn() {
     FM_STATE_OVERRIDE="$home/state" FM_DATA_OVERRIDE="$home/data" \
     FM_PROJECTS_OVERRIDE="$home/projects" FM_CONFIG_OVERRIDE="$home/config" \
     FM_SPAWN_NO_GUARD=1 FM_FAKE_PANE_PATH="$pane" TMUX="fake,1,0" \
+    FM_SPAWN_WORKTREE_WAIT=2 \
     PATH="$fakebin:$PATH" \
     "$ROOT/bin/fm-spawn.sh" "$id" "$proj" codex 2>&1
 }
@@ -196,9 +197,12 @@ test_spawn_isolation_abort() {
   mkdir -p "$TMP_ROOT/spawn-notgit" "$proj/sub"
 
   # Abort: the pane resolves to a plain non-git directory (not a worktree at all).
+  # The wait loop only captures a same-repo worktree, so a persistent non-git pane
+  # is treated as "treehouse never landed" and times out rather than reaching the
+  # isolation guard - still a clean abort (exit 1, no meta recorded).
   out=$(run_spawn "$home" abort-notgit-dd4 "$proj" "$TMP_ROOT/spawn-notgit" "$fakebin"); status=$?
   expect_code 1 "$status" "spawn into a non-worktree dir should abort"
-  assert_contains "$out" "did not yield an isolated worktree" "non-worktree spawn lacked the isolation error"
+  assert_contains "$out" "did not enter a worktree" "non-worktree spawn lacked the timeout abort"
   assert_absent "$home/state/abort-notgit-dd4.meta" "aborted spawn must not record meta"
 
   # Abort: the pane resolves INTO the primary checkout (a subdir of PROJ_ABS).