diff --git a/bin/fm-spawn.sh b/bin/fm-spawn.sh
index 825bc74fd6..9d0cd110a7 100755
--- a/bin/fm-spawn.sh
+++ b/bin/fm-spawn.sh
@@ -1426,6 +1426,12 @@ if [ "$KIND" != secondmate ]; then
       fi
       ;;
   esac
+  # Every branch below unconditionally truncates and rewrites its hook
+  # artifact (cat/printf >, never appended or skip-if-exists), so a worktree
+  # treehouse hands back from its reuse pool always gets hooks bound to THIS
+  # incarnation's id and $BUSY_GEN, never a prior tenant's. Keep new adapter
+  # wiring the same way; tests/fm-spawn-reused-worktree-hooks.test.sh guards
+  # the claude case end to end.
   case "$HARNESS" in
     claude*)
       # Semantic busy-state hooks (bin/fm-busy-lib.sh): UserPromptSubmit opens
diff --git a/tests/fm-spawn-reused-worktree-hooks.test.sh b/tests/fm-spawn-reused-worktree-hooks.test.sh
new file mode 100755
index 0000000000..d1ac95e066
--- /dev/null
+++ b/tests/fm-spawn-reused-worktree-hooks.test.sh
@@ -0,0 +1,132 @@
+#!/usr/bin/env bash
+# Regression test: when treehouse hands fm-spawn.sh a REUSED, pooled worktree
+# (the same on-disk path a prior, now-torn-down task used), the claude
+# busy-hook contract fm-spawn.sh installs into that worktree
+# (.claude/settings.local.json) must reference the CURRENT task's own id and
+# busy-gen only. A stale hook still naming the PRIOR tenant would let the new
+# task's Claude session keep touching the old task's turn-ended marker and
+# reporting busy/idle under the old task's id, confusing the watcher's
+# liveness tracking. bin/fm-spawn.sh's hook-install writes are unconditional
+# (`cat >`, truncate-and-rewrite) and bin/fm-teardown.sh scrubs the same
+# artifacts before a worktree returns to the pool; this test exercises the
+# real spawn -> teardown -> respawn-into-the-same-worktree sequence end to end
+# to prove neither path leaves or reintroduces a stale hook.
+set -u
+
+# shellcheck source=tests/lib.sh
+. "$(dirname "${BASH_SOURCE[0]}")/lib.sh"
+fm_git_identity fmtest fmtest@example.invalid
+
+SPAWN="$ROOT/bin/fm-spawn.sh"
+TEARDOWN="$ROOT/bin/fm-teardown.sh"
+TMP_ROOT=$(fm_test_tmproot fm-spawn-reused-worktree-hooks)
+
+make_fakebin() {
+  local dir=$1 fakebin
+  fakebin=$(fm_fakebin "$dir")
+  cat > "$fakebin/tmux" <<'SH'
+#!/usr/bin/env bash
+set -u
+case "$*" in
+  *"#{pane_current_path}"*) printf '%s\n' "${FM_FAKE_PANE_PATH:-}"; exit 0 ;;
+esac
+case "${1:-}" in
+  display-message) printf 'firstmate\n'; exit 0 ;;
+  list-windows) exit 0 ;;
+  has-session|new-session|new-window|kill-window|send-keys) exit 0 ;;
+esac
+exit 0
+SH
+  chmod +x "$fakebin/tmux"
+  fm_fake_exit0 "$fakebin" treehouse pi opencode claude codex gh-axi gh
+  printf '%s\n' "$fakebin"
+}
+
+# One home + project + worktree shared across two successive spawns, modeling
+# treehouse returning the identical pooled worktree path for an unrelated
+# second task after the first task's teardown returns it to the pool.
+CASE_DIR="$TMP_ROOT/reuse"
+HOME_DIR="$CASE_DIR/home"
+PROJ_DIR="$CASE_DIR/project"
+WT_DIR="$CASE_DIR/wt"
+FAKEBIN_DIR=$(make_fakebin "$CASE_DIR/fake")
+mkdir -p "$HOME_DIR/data" "$HOME_DIR/projects" "$HOME_DIR/state" "$HOME_DIR/config"
+printf 'claude\n' > "$HOME_DIR/config/crew-harness"
+fm_git_worktree "$PROJ_DIR" "$WT_DIR" "wt-reuse"
+touch "$HOME_DIR/state/.last-watcher-beat"
+
+ID_A=reuse-hooks-a1
+ID_B=reuse-hooks-b2
+mkdir -p "$HOME_DIR/data/$ID_A" "$HOME_DIR/data/$ID_B"
+printf 'brief for %s\n' "$ID_A" > "$HOME_DIR/data/$ID_A/brief.md"
+printf 'brief for %s\n' "$ID_B" > "$HOME_DIR/data/$ID_B/brief.md"
+
+run_spawn() {  # <id>
+  FM_ROOT_OVERRIDE='' FM_HOME="$HOME_DIR" \
+    FM_STATE_OVERRIDE="$HOME_DIR/state" FM_DATA_OVERRIDE="$HOME_DIR/data" \
+    FM_PROJECTS_OVERRIDE="$HOME_DIR/projects" FM_CONFIG_OVERRIDE="$HOME_DIR/config" \
+    FM_SPAWN_NO_GUARD=1 FM_FAKE_PANE_PATH="$WT_DIR" TMUX="fake,1,0" \
+    GROK_HOME="$HOME_DIR/grok-home" PATH="$FAKEBIN_DIR:$PATH" \
+    "$SPAWN" "$1" "$PROJ_DIR" 2>&1
+}
+
+run_teardown() {  # <id>
+  FM_ROOT_OVERRIDE="$ROOT" \
+    FM_STATE_OVERRIDE="$HOME_DIR/state" FM_CONFIG_OVERRIDE="$HOME_DIR/config" \
+    PATH="$FAKEBIN_DIR:$PATH" \
+    "$TEARDOWN" "$1" 2>&1
+}
+
+run_claude_hook() {  # <settings.json> <hook-event>
+  local cmd
+  cmd=$(jq -r ".hooks[\"$2\"][0].hooks[0].command" "$1")
+  [ -n "$cmd" ] && [ "$cmd" != null ] || fail "no $2 hook command in $1"
+  sh -c "$cmd"
+}
+
+test_reused_pool_worktree_gets_fresh_hooks_not_prior_tenants() {
+  local out settings state gen_a gen_b
+
+  state="$HOME_DIR/state"
+  settings="$WT_DIR/.claude/settings.local.json"
+
+  out=$(run_spawn "$ID_A")
+  expect_code 0 $? "spawn A should succeed: $out"
+  assert_present "$settings" "spawn A did not write hook settings"
+  assert_grep "$ID_A" "$settings" "A's hooks do not reference A's own id"
+  gen_a=$(cat "$state/$ID_A.busy-gen")
+
+  out=$(run_teardown "$ID_A")
+  expect_code 0 $? "teardown A should succeed: $out"
+  assert_absent "$settings" "teardown left a stale settings.local.json in the pooled worktree"
+  assert_absent "$state/$ID_A.meta" "teardown did not remove A's meta"
+
+  # treehouse hands the exact same worktree path back out for the unrelated
+  # second task - FM_FAKE_PANE_PATH stays pointed at the same $WT_DIR to model
+  # the reuse-pool scenario.
+  out=$(run_spawn "$ID_B")
+  expect_code 0 $? "spawn B into the reused worktree should succeed: $out"
+  assert_present "$settings" "spawn B did not write hook settings into the reused worktree"
+  gen_b=$(cat "$state/$ID_B.busy-gen")
+  [ "$gen_b" != "$gen_a" ] || fail "B armed the same busy-gen as A; incarnations must be distinguishable"
+
+  assert_grep "$ID_B" "$settings" "B's hooks do not reference B's own id"
+  assert_no_grep "$ID_A" "$settings" \
+    "B's hooks still reference A's id - stale hook inheritance from the reused worktree"
+  assert_no_grep "$gen_a" "$settings" \
+    "B's hooks still embed A's busy-gen - stale hook inheritance from the reused worktree"
+
+  # Firing B's Stop hook must only ever touch B's own turn-ended marker, never
+  # resurrect A's.
+  rm -f "$state/$ID_A.turn-ended" "$state/$ID_B.turn-ended"
+  run_claude_hook "$settings" Stop || fail "B's Stop hook command failed"
+  assert_present "$state/$ID_B.turn-ended" "B's Stop hook did not touch B's own turn-ended marker"
+  assert_absent "$state/$ID_A.turn-ended" \
+    "B's Stop hook touched A's (dead) turn-ended marker - stale hook inheritance"
+
+  pass "fm-spawn.sh refreshes claude hooks to the current task's id and busy-gen when reusing a pooled worktree, never inheriting the prior tenant's"
+}
+
+test_reused_pool_worktree_gets_fresh_hooks_not_prior_tenants
+
+echo "all fm-spawn-reused-worktree-hooks tests passed"