diff --git a/bin/backends/herdr.sh b/bin/backends/herdr.sh
index 260d2b666..7d8cc189f 100644
--- a/bin/backends/herdr.sh
+++ b/bin/backends/herdr.sh
@@ -67,8 +67,8 @@ FM_HOME="${FM_HOME:-${FM_ROOT_OVERRIDE:-$FM_ROOT}}"
 FM_BACKEND_HERDR_MIN_PROTOCOL=14
 # events.subscribe (the native pane.agent_status_changed push stream) and its
 # subscription_event schema first shipped at protocol 16 (verified: herdr
-# 0.7.3). Below this, or with the events surface absent from `herdr api schema`,
-# the event fast-path fails closed to the watcher's poll loop
+# 0.7.3). Below this, or with either required capability marker absent from
+# `herdr api schema`, the event fast-path fails closed to the watcher's poll loop
 # (fm_backend_herdr_events_capable). Distinct from FM_BACKEND_HERDR_MIN_PROTOCOL
 # (14): the adapter's spawn/capture/send primitives work on 14, only the push
 # subscriber needs 16.
@@ -1225,8 +1225,10 @@ fm_backend_herdr_socket_path() {  # <session>
 # and both `events.subscribe` and `pane.agent_status_changed` present in `herdr
 # api schema`. FM_BACKEND_HERDR_EVENTS_FORCE overrides the whole verdict for
 # tests (1 = capable, 0 = incapable) without touching the real binary. The
-# `api schema` read is ~220KB, so callers (the watcher) memoize this per session
-# for a process lifetime rather than probing every poll.
+# ~220KB `api schema` is captured exactly once and both markers are matched in
+# that value, avoiding an early-closing pipeline that can SIGPIPE its producer
+# under `pipefail`. Callers (the watcher) memoize this per session for a process
+# lifetime rather than probing every poll.
 fm_backend_herdr_events_capable() {  # <session>
   local session=$1 protocol schema
   case "${FM_BACKEND_HERDR_EVENTS_FORCE:-}" in
@@ -1241,8 +1243,8 @@ fm_backend_herdr_events_capable() {  # <session>
   case "$protocol" in ''|*[!0-9]*) return 1 ;; esac
   [ "$protocol" -ge "$FM_BACKEND_HERDR_MIN_EVENTS_PROTOCOL" ] || return 1
   schema=$(herdr api schema --json 2>/dev/null) || return 1
-  printf '%s' "$schema" | grep -Fq 'events.subscribe' || return 1
-  printf '%s' "$schema" | grep -Fq 'pane.agent_status_changed' || return 1
+  case "$schema" in *events.subscribe*) ;; *) return 1 ;; esac
+  case "$schema" in *pane.agent_status_changed*) ;; *) return 1 ;; esac
   return 0
 }
 
diff --git a/docs/herdr-backend.md b/docs/herdr-backend.md
index 0684bb8f9..1bc68b207 100644
--- a/docs/herdr-backend.md
+++ b/docs/herdr-backend.md
@@ -798,7 +798,8 @@ There is no second watcher process: the reader is a short-lived subprocess of th
 
 **Polling is the permanent fail-closed backstop.**
 The watcher's poll loop runs every cycle regardless, so the event path only ever shortens latency and can never drop an escalation.
-Three documented triggers fall back to pure polling (`fm_backend_herdr_events_capable` and the watcher's runtime-disable counter): a build below protocol 16 or missing the events surface in `herdr api schema`; a connect/subscribe failure; and repeated runtime failures, which disable the fast path for the rest of that watcher process (a restart re-probes).
+Three documented triggers fall back to pure polling (`fm_backend_herdr_events_capable` and the watcher's runtime-disable counter): a build below protocol 16 or a schema missing either required capability marker (`events.subscribe` or `pane.agent_status_changed`); a connect/subscribe failure; and repeated runtime failures, which disable the fast path for the rest of that watcher process (a restart re-probes).
+The capability probe captures the roughly 220 KB schema exactly once and checks both markers in that value, avoiding an early-closing pipeline that can SIGPIPE its producer under `pipefail` and falsely disable the push path.
 
 **Empirical evidence (2026-07-11, herdr 0.7.3, protocol 16, macOS aarch64 Darwin 25.5.0, python3 3.13, jq present).**
 Capability, verified read-only:
@@ -826,7 +827,7 @@ ok - real herdr: the watcher fast-path enqueues a stale wake naming the task win
 ```
 
 The subscriber returned the `blocked` transition in **0.129s** and the watcher fast-path enqueued a durable `stale` wake naming the task window - versus up to `FM_POLL` (15s) plus `FM_STALE_ESCALATE_SECS` (240s) on the poll path this shortcuts.
-Dedupe (one wake per `->blocked` edge, marker cleared when the pane returns to `working`), subscribe-then-reconcile ordering (an already-blocked pane enqueued exactly once while newer edges buffer in the active stream), the `kind=secondmate`/`paused:` exemptions, and the three fail-closed fallbacks are covered by the fake-CLI unit tests in `tests/fm-backend-herdr.test.sh` (the `wait_transition`/`apply_transition` cases), `tests/fm-transition-lib.test.sh`, and `tests/fm-supervision-events.test.sh`.
+Dedupe (one wake per `->blocked` edge, marker cleared when the pane returns to `working`), subscribe-then-reconcile ordering (an already-blocked pane enqueued exactly once while newer edges buffer in the active stream), the `kind=secondmate`/`paused:` exemptions, the three fail-closed fallbacks, and the large-schema capability gate under `pipefail` (both markers present, either marker absent, and exactly one schema read) are covered by the fake-CLI unit tests in `tests/fm-backend-herdr.test.sh` (the `events_capable`, `wait_transition`, and `apply_transition` cases), `tests/fm-transition-lib.test.sh`, and `tests/fm-supervision-events.test.sh`.
 
 ## Away-mode daemon terminal launch (2026-07-12, herdr 0.7.3, protocol 16, macOS aarch64)
 
diff --git a/tests/fm-backend-herdr.test.sh b/tests/fm-backend-herdr.test.sh
index 5186cca2c..7cfedee41 100755
--- a/tests/fm-backend-herdr.test.sh
+++ b/tests/fm-backend-herdr.test.sh
@@ -1740,6 +1740,68 @@ test_no_jq_reserved_keyword_arg_names() {
 # that drives a live idle->blocked transition lives in
 # tests/fm-backend-herdr-eventwait-smoke.test.sh.
 
+write_large_events_schema() {  # <path> <method-marker> <event-marker>
+  local path=$1 method=$2 event=$3
+  {
+    # Keep each capability marker on an early complete line like herdr's
+    # pretty-printed schema, with roughly 256KB still unwritten after grep -q
+    # can exit and close the pipe.
+    printf '{\n"methods":["%s"],\n"events":["%s"],\n"padding":"' "$method" "$event"
+    awk 'BEGIN { for (i = 0; i < 262144; i++) printf "x" }'
+    printf '"}\n'
+  } > "$path"
+}
+
+test_events_capable_accepts_large_schema_under_pipefail() {
+  local dir log resp fb err status schema_calls
+  dir="$TMP_ROOT/events-capable-large"; mkdir -p "$dir/responses"
+  log="$dir/log"; resp="$dir/responses"; err="$dir/stderr"; : > "$log"
+  printf '{"client":{"version":"0.7.3","protocol":16}}\n' > "$resp/1.out"
+  write_large_events_schema "$resp/2.out" "events.subscribe" "pane.agent_status_changed"
+  fb=$(make_herdr_fakebin "$dir")
+
+  PATH="$fb:$PATH" FM_HERDR_LOG="$log" FM_HERDR_RESPONSES="$resp" FM_HERDR_SCRIPT_STATUS=1 \
+    FM_BACKEND_HERDR_EVENT_READER=true \
+    /bin/bash -o pipefail -c '. "$0/bin/backends/herdr.sh"; fm_backend_herdr_events_capable sess' "$ROOT" 2>"$err"
+  status=$?
+
+  expect_code 0 "$status" "events_capable should accept both markers in a large schema under pipefail"
+  [ ! -s "$err" ] || fail "events_capable wrote stderr while scanning a large capable schema: $(cat "$err")"
+  schema_calls=$(grep -c $'\x1f''api'$'\x1f''schema'$'\x1f''--json' "$log")
+  [ "$schema_calls" = 1 ] || fail "events_capable should load the schema exactly once, got $schema_calls calls"
+  pass "fm_backend_herdr_events_capable: a large schema detects both required markers under pipefail without stderr noise"
+}
+
+test_events_capable_large_schema_missing_markers_fails_closed() {
+  local missing dir log resp fb err status schema_calls
+  for missing in events.subscribe pane.agent_status_changed; do
+    dir="$TMP_ROOT/events-capable-missing-${missing%%.*}"; mkdir -p "$dir/responses"
+    log="$dir/log"; resp="$dir/responses"; err="$dir/stderr"; : > "$log"
+    printf '{"client":{"version":"0.7.3","protocol":16}}\n' > "$resp/1.out"
+    case "$missing" in
+      events.subscribe)
+        write_large_events_schema "$resp/2.out" "events.missing" "pane.agent_status_changed"
+        ;;
+      pane.agent_status_changed)
+        write_large_events_schema "$resp/2.out" "events.subscribe" "pane.agent_status_missing"
+        ;;
+    esac
+    fb=$(make_herdr_fakebin "$dir")
+
+    status=0
+    PATH="$fb:$PATH" FM_HERDR_LOG="$log" FM_HERDR_RESPONSES="$resp" FM_HERDR_SCRIPT_STATUS=1 \
+      FM_BACKEND_HERDR_EVENT_READER=true \
+      /bin/bash -o pipefail -c '. "$0/bin/backends/herdr.sh"; fm_backend_herdr_events_capable sess' "$ROOT" 2>"$err" \
+      || status=$?
+
+    [ "$status" -ne 0 ] || fail "events_capable should fail closed when $missing is absent"
+    [ ! -s "$err" ] || fail "events_capable wrote stderr while rejecting a schema missing $missing: $(cat "$err")"
+    schema_calls=$(grep -c $'\x1f''api'$'\x1f''schema'$'\x1f''--json' "$log")
+    [ "$schema_calls" = 1 ] || fail "events_capable should load a schema missing $missing exactly once, got $schema_calls calls"
+  done
+  pass "fm_backend_herdr_events_capable: each missing schema marker fails closed after one large-schema load"
+}
+
 # make_herdr_eventfake: a herdr stub answering exactly the calls the event path
 # makes - `session list --json` (echoes one session, name FM_FAKE_SESSION_NAME,
 # socket FM_FAKE_SOCKET), `status --json`, and `agent get <pane>` (per-pane
@@ -2125,6 +2187,8 @@ test_dispatch_routes_herdr_backend
 test_dispatch_busy_state_unknown_for_tmux
 test_dispatch_composer_state_routes_by_backend
 test_scripts_route_explicit_target_through_meta_backend
+test_events_capable_accepts_large_schema_under_pipefail
+test_events_capable_large_schema_missing_markers_fails_closed
 test_normalize_event_leaves_from_empty
 test_escalation_marker_keys_like_watcher
 test_apply_transition_blocked_requires_commit_to_dedupe
diff --git a/tests/fm-turnend-guard.test.sh b/tests/fm-turnend-guard.test.sh
index 3e5d54f82..ed8e83adb 100755
--- a/tests/fm-turnend-guard.test.sh
+++ b/tests/fm-turnend-guard.test.sh
@@ -785,7 +785,7 @@ SH
 exit 0
 SH
   chmod +x "$repo/bin/fm-turnend-guard.sh" "$repo/bin/fm-arm-pretool-check.sh"
-  out=$(PLUGIN="$ext" FM_HOME="$home" FM_GUARD_LOG="$log" node --input-type=module 2>&1 <<'EOF'
+  out=$(NODE_NO_WARNINGS=1 PLUGIN="$ext" FM_HOME="$home" FM_GUARD_LOG="$log" node --input-type=module 2>&1 <<'EOF'
 import { readFileSync } from "node:fs";
 import { pathToFileURL } from "node:url";
 
@@ -845,7 +845,7 @@ SH
 exit 0
 SH
   chmod +x "$repo/bin/fm-turnend-guard.sh" "$repo/bin/fm-arm-pretool-check.sh"
-  out=$(PLUGIN="$ext" FM_HOME="$home" node --input-type=module 2>&1 <<'EOF'
+  out=$(NODE_NO_WARNINGS=1 PLUGIN="$ext" FM_HOME="$home" node --input-type=module 2>&1 <<'EOF'
 import { pathToFileURL } from "node:url";
 
 const handlers = new Map();
diff --git a/tests/fm-watcher-lock.test.sh b/tests/fm-watcher-lock.test.sh
index 36e1f8dd4..4dc8468bb 100755
--- a/tests/fm-watcher-lock.test.sh
+++ b/tests/fm-watcher-lock.test.sh
@@ -152,7 +152,7 @@ test_guard_warnings() {
   mkdir -p "$dir/config"
   printf 'project=x\n' > "$state/task.meta"
   : > "$dir/config/x-mode.env"
-  FM_ROOT_OVERRIDE="$dir" FM_STATE_OVERRIDE="$state" FM_GUARD_GRACE=1 "$ROOT/bin/fm-guard.sh" 2> "$err" >/dev/null || fail "guard failed"
+  FM_ROOT_OVERRIDE="$dir" FM_STATE_OVERRIDE="$state" FM_CONFIG_OVERRIDE="$dir/config" FM_GUARD_GRACE=1 "$ROOT/bin/fm-guard.sh" 2> "$err" >/dev/null || fail "guard failed"
   grep -F "source '$dir/config/x-mode.env' first" "$err" >/dev/null || fail "guard repair line did not source the X-mode cadence config"
 
   # (2) fresh watcher, empty queue -> silence.