diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..e458ed5
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+.worktrees/
diff --git a/bin/agent-hook-session-end-claude b/bin/agent-hook-session-end-claude
index cb4e6b2..1da8cf4 100755
--- a/bin/agent-hook-session-end-claude
+++ b/bin/agent-hook-session-end-claude
@@ -18,17 +18,12 @@ _agentguard_claude_session_end() {
   # Already titled — skip
   _agentguard_transcript_has_custom_title "$transcript_path" && return 0
 
-  local timeout_prefix=()
-  if command -v timeout >/dev/null 2>&1; then
-    timeout_prefix=(timeout 60)
-  elif command -v gtimeout >/dev/null 2>&1; then
-    timeout_prefix=(gtimeout 60)
-  fi
+  _hook_timeout_prefix 60
 
   # Fire-and-forget: nohup so naming survives hook exit, with a timeout when
   # the platform provides one.
   # shellcheck disable=SC2016
-  nohup "${timeout_prefix[@]}" bash -c '
+  nohup "${_HOOK_TIMEOUT_PREFIX[@]}" bash -c '
   transcript_has_custom_title() {
     jq -e -R "$2" "$1" >/dev/null 2>&1
   }
diff --git a/lib/agentguard/hook-helpers.sh b/lib/agentguard/hook-helpers.sh
index b89dab3..1495114 100644
--- a/lib/agentguard/hook-helpers.sh
+++ b/lib/agentguard/hook-helpers.sh
@@ -585,6 +585,54 @@ _hook_hm_warn_once() {
   _hook_once_per_session "hm-warn-$key" && _hook_warn "$message"
 }
 
+# Inline `bash -c` script backing _hook_timeout_prefix's fallback when
+# neither `timeout` nor `gtimeout` is on PATH — confirmed missing on stock
+# macOS (no coreutils) including GitHub's macOS runners. Takes the budget in
+# seconds as $1 and the guarded command as the rest; polls every 0.1s and,
+# past budget, TERMs then KILLs the child and exits 124 to match GNU
+# timeout's convention, which _hook_hm_event already checks for. Must be a
+# real executable (not a shell function) so it works as a plain word in
+# _HOOK_TIMEOUT_PREFIX even when a caller execs it via `env` (env can only
+# exec real binaries, not the calling shell's functions) — `bash` itself is
+# always present since this whole library requires it already, so this adds
+# no new dependency.
+# shellcheck disable=SC2016 # single-quoted on purpose: expands later, inside the bash -c it's passed to.
+_HOOK_PORTABLE_TIMEOUT_SCRIPT='
+  seconds="$1"; shift
+  "$@" &
+  pid=$!
+  waited=0
+  budget=$((seconds * 10))
+  while kill -0 "$pid" 2>/dev/null; do
+    if [ "$waited" -ge "$budget" ]; then
+      kill -TERM "$pid" 2>/dev/null
+      sleep 0.1
+      kill -KILL "$pid" 2>/dev/null
+      wait "$pid" 2>/dev/null
+      exit 124
+    fi
+    sleep 0.1
+    waited=$((waited + 1))
+  done
+  wait "$pid"
+'
+
+# Best-effort external timeout guard for a slow subprocess, general-purpose
+# (not Hive Memory-specific). Sets the _HOOK_TIMEOUT_PREFIX array to prepend
+# to the guarded command, preferring a real `timeout`/`gtimeout` binary and
+# falling back to the portable bash implementation above so the guard is
+# never silently absent for want of an external dependency.
+_hook_timeout_prefix() {
+  local seconds="$1"
+  if command -v timeout >/dev/null 2>&1; then
+    _HOOK_TIMEOUT_PREFIX=(timeout "$seconds")
+  elif command -v gtimeout >/dev/null 2>&1; then
+    _HOOK_TIMEOUT_PREFIX=(gtimeout "$seconds")
+  else
+    _HOOK_TIMEOUT_PREFIX=(bash -c "$_HOOK_PORTABLE_TIMEOUT_SCRIPT" _ "$seconds")
+  fi
+}
+
 _hook_hm_event() {
   _hook_hm_available || return 0
 
@@ -617,6 +665,15 @@ _hook_hm_event() {
       ;;
   esac
   hm_args+=(--json "$@")
+
+  # `hm`'s canonical store for a given alias can be a network-backed mount
+  # (e.g. an rclone/cloud-synced Google Drive path) with no latency bound of
+  # its own. Guard the call with a short external timeout so a slow or
+  # unreachable store degrades to "skip memory context this turn" well
+  # inside the hook runner's own timeout budget, instead of risking the
+  # whole hook process getting killed later and its output discarded.
+  _hook_timeout_prefix "${AGENTGUARD_HIVE_MEMORY_TIMEOUT:-2}"
+
   if [ "$project_infer" -eq 0 ]; then
     response=$(
       env -u HIVE_MEMORY_PROJECT \
@@ -624,7 +681,7 @@ _hook_hm_event() {
         HIVE_MEMORY_SESSION_ID="$_HOOK_SESSION_KEY" \
         HIVE_MEMORY_PROJECT_INFER=0 \
         HIVE_MEMORY_HOOK_ACTIVE=1 \
-        hm "${hm_args[@]}" 2>"$err"
+        "${_HOOK_TIMEOUT_PREFIX[@]}" hm "${hm_args[@]}" 2>"$err"
     )
   else
     response=$(
@@ -633,12 +690,14 @@ _hook_hm_event() {
       HIVE_MEMORY_PROJECT="$project" \
       HIVE_MEMORY_PROJECT_INFER="$project_infer" \
       HIVE_MEMORY_HOOK_ACTIVE=1 \
-        hm "${hm_args[@]}" 2>"$err"
+        "${_HOOK_TIMEOUT_PREFIX[@]}" hm "${hm_args[@]}" 2>"$err"
     )
   fi
   rc=$?
   if [ "$rc" -ne 0 ]; then
-    if [ -s "$err" ]; then
+    if [ "$rc" -eq 124 ]; then
+      _hook_hm_warn_once "timeout" "Hive Memory hook timed out after ${AGENTGUARD_HIVE_MEMORY_TIMEOUT:-2}s — skipping memory context this turn"
+    elif [ -s "$err" ]; then
       _hook_hm_warn_once "failed" "Hive Memory hook failed: $(tr '\n' ' ' <"$err")"
     else
       _hook_hm_warn_once "failed" "Hive Memory hook failed with status $rc"
diff --git a/test/suites/agent-hook-helpers-test b/test/suites/agent-hook-helpers-test
index 46128a2..af04247 100755
--- a/test/suites/agent-hook-helpers-test
+++ b/test/suites/agent-hook-helpers-test
@@ -504,6 +504,17 @@ case "${HM_MODE:-empty}" in
     printf 'backend offline\n' >&2
     exit 42
     ;;
+  hang)
+    # Simulates a canonical store that never responds (e.g. an unreachable
+    # network mount) so the timeout guard has something real to bound.
+    # `exec` so this process *becomes* sleep rather than forking a child of
+    # it — the real hm binary is a single process blocked on I/O, not a
+    # shell forking a subprocess, and a forked child here would become an
+    # orphan that outlives a plain `kill` on this script's own PID, keeping
+    # any pipe it inherited (like a caller's stdout capture) open until it
+    # finishes on its own regardless of whether the timeout guard fired.
+    exec sleep 10
+    ;;
   *)
     printf '%s\n' '{"warnings":[],"actions":[]}'
     ;;
@@ -887,6 +898,178 @@ HOME="$HM_HOME" \
 hm_fail_count=$(grep -c 'Hive Memory hook failed' "$hm_fail_err" || true)
 _assert_eq "hm hook: repeated failures warn once per session" "1" "$hm_fail_count"
 
+# `hm`'s canonical store can be a network-backed mount with no bound of its
+# own (a real incident: an rclone/cloud-synced Google Drive mount going
+# through a slow revalidation caused prompt-submit to blow past the host
+# agent's own hook timeout). `_hook_hm_event` must guard the call so a
+# hung/unreachable store degrades to "skip memory context this turn" well
+# inside a short, configurable budget instead of running unbounded.
+#
+# _hook_hm_prompt_submit returns early on an empty prompt, before ever
+# calling _hook_hm_event — so, unlike the mocked-response cases above, this
+# needs real prompt text in _HOOK_INPUT to actually reach the guarded `hm`
+# call.
+: >"$HM_LOG"
+hm_hang_err="$HM_MOCK_ROOT/hang.err"
+hm_hang_start=$(date +%s)
+HOME="$HM_HOME" \
+  PATH="$HM_BIN:$PATH" \
+  TMPDIR="$HM_TMP" \
+  HM_LOG="$HM_LOG" \
+  HM_MODE=hang \
+  AGENTGUARD_HIVE_MEMORY_HOOKS=1 \
+  AGENTGUARD_HIVE_MEMORY_TIMEOUT=1 \
+  AGENTGUARD_NAME=codex \
+  CODEX_THREAD_ID="hm-hang-session" \
+  bash -c '
+    source "$1"
+    _HOOK_INPUT='"'"'{"prompt":"remember this"}'"'"'
+    _hook_hm_prompt_submit
+  ' _ "$HELPERS" >/dev/null 2>"$hm_hang_err"
+hm_hang_elapsed=$(($(date +%s) - hm_hang_start))
+# The mock sleeps 10s; a working guard returns close to the 1s budget. Bound
+# well below 10s so this only fails if the guard genuinely isn't cutting the
+# call short, not on ordinary CI scheduling jitter around 1s.
+if [ "$hm_hang_elapsed" -lt 6 ]; then
+  _pass "hm hook: a hung store is cut off near the configured timeout, not left to run"
+else
+  _fail "hm hook: a hung store is cut off near the configured timeout, not left to run"
+fi
+_assert_contains "hm hook: a timeout is reported distinctly from a hard failure" \
+  "Hive Memory hook timed out after 1s" "$(cat "$hm_hang_err")"
+
+# The timeout is advisory infrastructure, not a hard failure: the calling
+# hook must still exit cleanly and simply proceed without memory context.
+hm_hang_rc=0
+HOME="$HM_HOME" \
+  PATH="$HM_BIN:$PATH" \
+  TMPDIR="$HM_TMP" \
+  HM_LOG="$HM_LOG" \
+  HM_MODE=hang \
+  AGENTGUARD_HIVE_MEMORY_HOOKS=1 \
+  AGENTGUARD_HIVE_MEMORY_TIMEOUT=1 \
+  AGENTGUARD_NAME=codex \
+  CODEX_THREAD_ID="hm-hang-session-2" \
+  bash -c '
+    source "$1"
+    _HOOK_INPUT='"'"'{"prompt":"remember this"}'"'"'
+    _hook_hm_prompt_submit
+  ' _ "$HELPERS" >/dev/null 2>/dev/null || hm_hang_rc=$?
+_assert_eq "hm hook: a timed-out call still returns success to the caller" "0" "$hm_hang_rc"
+
+# Lock in the actual default (AGENTGUARD_HIVE_MEMORY_TIMEOUT unset) rather
+# than only ever exercising it overridden for test speed above — a future
+# change to the hardcoded default in hook-helpers.sh should fail this
+# assertion, not silently drift from what's documented/expected. Costs a
+# real ~2s of wall clock since it deliberately does not override the value.
+: >"$HM_LOG"
+hm_hang_default_err="$HM_MOCK_ROOT/hang-default.err"
+HOME="$HM_HOME" \
+  PATH="$HM_BIN:$PATH" \
+  TMPDIR="$HM_TMP" \
+  HM_LOG="$HM_LOG" \
+  HM_MODE=hang \
+  AGENTGUARD_HIVE_MEMORY_HOOKS=1 \
+  AGENTGUARD_NAME=codex \
+  CODEX_THREAD_ID="hm-hang-default-session" \
+  bash -c '
+    unset AGENTGUARD_HIVE_MEMORY_TIMEOUT
+    source "$1"
+    _HOOK_INPUT='"'"'{"prompt":"remember this"}'"'"'
+    _hook_hm_prompt_submit
+  ' _ "$HELPERS" >/dev/null 2>"$hm_hang_default_err"
+_assert_contains "hm hook: default timeout is 2s when unconfigured" \
+  "Hive Memory hook timed out after 2s" "$(cat "$hm_hang_default_err")"
+
+# End-to-end proof for the exact scenario that failed on GitHub's macOS CI
+# runners (no timeout, no gtimeout on PATH): going through the real
+# _hook_hm_prompt_submit path — not just the isolated _hook_timeout_prefix
+# unit test below — against a genuinely hung mock hm. The curated PATH omits
+# only timeout/gtimeout, mirroring real stock macOS (which ships dirname,
+# jq, etc. as base OS tools — the only thing actually missing without
+# Homebrew coreutils is a `timeout` binary); everything else hook-helpers.sh
+# and its detect.sh dependency need stays available so this isolates the
+# timeout-specific behavior instead of tripping over unrelated missing tools.
+: >"$HM_LOG"
+NO_TIMEOUT_HM_BIN=$(_tmpdir)
+for _no_timeout_tool in bash sleep dirname basename ps sed tr cat jq mktemp; do
+  ln -s "$(command -v "$_no_timeout_tool")" "$NO_TIMEOUT_HM_BIN/$_no_timeout_tool"
+done
+hm_hang_no_timeout_err="$HM_MOCK_ROOT/hang-no-timeout.err"
+hm_hang_no_timeout_start=$SECONDS
+HOME="$HM_HOME" \
+  PATH="$NO_TIMEOUT_HM_BIN:$HM_BIN" \
+  TMPDIR="$HM_TMP" \
+  HM_LOG="$HM_LOG" \
+  HM_MODE=hang \
+  AGENTGUARD_HIVE_MEMORY_HOOKS=1 \
+  AGENTGUARD_HIVE_MEMORY_TIMEOUT=1 \
+  AGENTGUARD_NAME=codex \
+  CODEX_THREAD_ID="hm-hang-no-timeout-session" \
+  bash -c '
+    source "$1"
+    _HOOK_INPUT='"'"'{"prompt":"remember this"}'"'"'
+    _hook_hm_prompt_submit
+  ' _ "$HELPERS" >/dev/null 2>"$hm_hang_no_timeout_err"
+hm_hang_no_timeout_elapsed=$((SECONDS - hm_hang_no_timeout_start))
+if [ "$hm_hang_no_timeout_elapsed" -lt 6 ]; then
+  _pass "hm hook: guard still bounds a hang without any external timeout binary on PATH"
+else
+  _fail "hm hook: guard still bounds a hang without any external timeout binary on PATH"
+fi
+_assert_contains "hm hook: timeout warning still fires without an external timeout binary" \
+  "Hive Memory hook timed out after 1s" "$(cat "$hm_hang_no_timeout_err")"
+
+# _hook_timeout_prefix (general-purpose, not Hive Memory-specific): absent
+# timeout/gtimeout falls back to the portable bash implementation, not to
+# leaving a guarded command unbounded — this is what CI caught missing on
+# GitHub's macOS runners (no coreutils, so neither binary exists there) and
+# what makes clark2 or any other stock-macOS machine in the fleet actually
+# protected. Curate a PATH with only `bash` and `sleep` (both required to
+# even run this test) so timeout/gtimeout are genuinely absent, then confirm
+# the resulting prefix actually cuts off a real 5s sleep near the 1s budget
+# rather than running the full 5s.
+NO_TIMEOUT_BIN=$(_tmpdir)
+ln -s "$(command -v bash)" "$NO_TIMEOUT_BIN/bash"
+ln -s "$(command -v sleep)" "$NO_TIMEOUT_BIN/sleep"
+timeout_prefix_fallback_result=$(
+  PATH="$NO_TIMEOUT_BIN" bash -c '
+    source "$1"
+    _hook_timeout_prefix 1
+    start=$SECONDS
+    "${_HOOK_TIMEOUT_PREFIX[@]}" sleep 5
+    rc=$?
+    printf "%s %s" "$((SECONDS - start))" "$rc"
+  ' _ "$HELPERS"
+)
+timeout_prefix_fallback_elapsed="${timeout_prefix_fallback_result%% *}"
+timeout_prefix_fallback_rc="${timeout_prefix_fallback_result##* }"
+if [ "$timeout_prefix_fallback_elapsed" -lt 3 ]; then
+  _pass "hook timeout prefix: portable fallback cuts off a hang near the budget, not the full duration"
+else
+  _fail "hook timeout prefix: portable fallback cuts off a hang near the budget, not the full duration"
+fi
+_assert_eq "hook timeout prefix: portable fallback reports 124 like GNU timeout" \
+  "124" "$timeout_prefix_fallback_rc"
+
+FAKE_TIMEOUT_BIN=$(_tmpdir)
+cat >"$FAKE_TIMEOUT_BIN/timeout" <<'SCRIPT'
+#!/usr/bin/env bash
+shift
+exec "$@"
+SCRIPT
+chmod +x "$FAKE_TIMEOUT_BIN/timeout"
+timeout_prefix_present=$(
+  bash -c '
+    source "$1"
+    PATH="$2"
+    _hook_timeout_prefix 5
+    printf "%s\n" "${_HOOK_TIMEOUT_PREFIX[*]}"
+  ' _ "$HELPERS" "$FAKE_TIMEOUT_BIN"
+)
+_assert_eq "hook timeout prefix: prepends the available timeout binary and duration" \
+  "timeout 5" "$timeout_prefix_present"
+
 # _hook_agent_name returns "codex" when CODEX_INTERNAL_ORIGINATOR_OVERRIDE is set
 # shellcheck disable=SC2034  # env vars consumed by sourced helpers, not direct use
 (