diff --git a/lib/hook-utils.sh b/lib/hook-utils.sh
index 3f218ce00..1c003435a 100644
--- a/lib/hook-utils.sh
+++ b/lib/hook-utils.sh
@@ -132,6 +132,16 @@ hook::ctx_flush() {
   hook::ctx_reset
 }
 
+# Cheap telemetry opt-in probe — true iff a consumer wired a sink. Producers
+# gate telemetry-payload construction on this (repo-relative path
+# normalization, data JSON) so the unwired default path spawns zero
+# telemetry-only subprocesses. Pure shell test, no subprocess.
+# hook::emit_telemetry re-checks the sink itself, so skipping this probe
+# costs only wasted payload work, never correctness.
+hook::telemetry_enabled() {
+  [[ -n "${HOOK_TELEMETRY_SINK:-}" ]]
+}
+
 # Emit one telemetry envelope per hook run to the consumer-set sink.
 # Fire-and-forget: sink is dispatched in the background; the hook never waits
 # on it and its failure never affects the hook's own exit code or stdout.
diff --git a/lib/hook-utils.test.sh b/lib/hook-utils.test.sh
index d9bbe811e..fda1518ee 100755
--- a/lib/hook-utils.test.sh
+++ b/lib/hook-utils.test.sh
@@ -434,6 +434,32 @@ fi
 
 rm -rf "$PROJ12" "$OUTSIDE12" "$SIB12"
 
+# --- Test 13: hook::telemetry_enabled — cheap sink-presence probe -------------
+# Producers gate telemetry-payload construction on this, so its verdict must
+# track HOOK_TELEMETRY_SINK exactly: unset and empty are disabled, any
+# non-empty value is enabled.
+unset HOOK_TELEMETRY_SINK 2>/dev/null || true
+if hook::telemetry_enabled; then
+  fail "telemetry_enabled: sink unset reported enabled"
+else
+  ok "telemetry_enabled: sink unset → disabled"
+fi
+
+HOOK_TELEMETRY_SINK=""
+if hook::telemetry_enabled; then
+  fail "telemetry_enabled: empty sink reported enabled"
+else
+  ok "telemetry_enabled: empty sink → disabled"
+fi
+
+HOOK_TELEMETRY_SINK="/some/sink.sh"
+if hook::telemetry_enabled; then
+  ok "telemetry_enabled: non-empty sink → enabled"
+else
+  fail "telemetry_enabled: non-empty sink reported disabled"
+fi
+unset HOOK_TELEMETRY_SINK
+
 echo
 echo "PASS=$PASS FAIL=$FAIL"
 [[ $FAIL -eq 0 ]]
diff --git a/plugins/bash-lint/.claude-plugin/plugin.json b/plugins/bash-lint/.claude-plugin/plugin.json
index 8fc6740ea..66cf18fce 100644
--- a/plugins/bash-lint/.claude-plugin/plugin.json
+++ b/plugins/bash-lint/.claude-plugin/plugin.json
@@ -1,7 +1,7 @@
 {
   "$schema": "https://json.schemastore.org/claude-code-plugin-manifest.json",
   "name": "bash-lint",
-  "version": "0.1.3",
+  "version": "0.1.4",
   "description": "Auto-format and lint shell scripts on edit via shfmt + ShellCheck, using the consuming repo's own .editorconfig and .shellcheckrc.",
   "author": {
     "name": "Melodic Software",
diff --git a/plugins/bash-lint/hooks/hook-utils.sh b/plugins/bash-lint/hooks/hook-utils.sh
index 3f218ce00..1c003435a 100644
--- a/plugins/bash-lint/hooks/hook-utils.sh
+++ b/plugins/bash-lint/hooks/hook-utils.sh
@@ -132,6 +132,16 @@ hook::ctx_flush() {
   hook::ctx_reset
 }
 
+# Cheap telemetry opt-in probe — true iff a consumer wired a sink. Producers
+# gate telemetry-payload construction on this (repo-relative path
+# normalization, data JSON) so the unwired default path spawns zero
+# telemetry-only subprocesses. Pure shell test, no subprocess.
+# hook::emit_telemetry re-checks the sink itself, so skipping this probe
+# costs only wasted payload work, never correctness.
+hook::telemetry_enabled() {
+  [[ -n "${HOOK_TELEMETRY_SINK:-}" ]]
+}
+
 # Emit one telemetry envelope per hook run to the consumer-set sink.
 # Fire-and-forget: sink is dispatched in the background; the hook never waits
 # on it and its failure never affects the hook's own exit code or stdout.
diff --git a/plugins/biome-format/.claude-plugin/plugin.json b/plugins/biome-format/.claude-plugin/plugin.json
index cf33e54f5..f0df26423 100644
--- a/plugins/biome-format/.claude-plugin/plugin.json
+++ b/plugins/biome-format/.claude-plugin/plugin.json
@@ -1,7 +1,7 @@
 {
   "$schema": "https://json.schemastore.org/claude-code-plugin-manifest.json",
   "name": "biome-format",
-  "version": "0.1.2",
+  "version": "0.1.3",
   "description": "Auto-format and lint JS/TS/JSX/JSON on edit via Biome, only when a biome.json governs the repo — using the consuming repo's own Biome config.",
   "author": {
     "name": "Melodic Software",
diff --git a/plugins/biome-format/hooks/hook-utils.sh b/plugins/biome-format/hooks/hook-utils.sh
index 3f218ce00..1c003435a 100644
--- a/plugins/biome-format/hooks/hook-utils.sh
+++ b/plugins/biome-format/hooks/hook-utils.sh
@@ -132,6 +132,16 @@ hook::ctx_flush() {
   hook::ctx_reset
 }
 
+# Cheap telemetry opt-in probe — true iff a consumer wired a sink. Producers
+# gate telemetry-payload construction on this (repo-relative path
+# normalization, data JSON) so the unwired default path spawns zero
+# telemetry-only subprocesses. Pure shell test, no subprocess.
+# hook::emit_telemetry re-checks the sink itself, so skipping this probe
+# costs only wasted payload work, never correctness.
+hook::telemetry_enabled() {
+  [[ -n "${HOOK_TELEMETRY_SINK:-}" ]]
+}
+
 # Emit one telemetry envelope per hook run to the consumer-set sink.
 # Fire-and-forget: sink is dispatched in the background; the hook never waits
 # on it and its failure never affects the hook's own exit code or stdout.
diff --git a/plugins/markdown-formatter/.claude-plugin/plugin.json b/plugins/markdown-formatter/.claude-plugin/plugin.json
index 39710b639..8af5daf76 100644
--- a/plugins/markdown-formatter/.claude-plugin/plugin.json
+++ b/plugins/markdown-formatter/.claude-plugin/plugin.json
@@ -1,7 +1,7 @@
 {
   "$schema": "https://json.schemastore.org/claude-code-plugin-manifest.json",
   "name": "markdown-formatter",
-  "version": "0.1.4",
+  "version": "0.1.5",
   "description": "Auto-format and lint Markdown on edit via markdownlint-cli2, using the consuming repo's own markdownlint config.",
   "author": {
     "name": "Melodic Software",
diff --git a/plugins/markdown-formatter/hooks/hook-utils.sh b/plugins/markdown-formatter/hooks/hook-utils.sh
index 3f218ce00..1c003435a 100644
--- a/plugins/markdown-formatter/hooks/hook-utils.sh
+++ b/plugins/markdown-formatter/hooks/hook-utils.sh
@@ -132,6 +132,16 @@ hook::ctx_flush() {
   hook::ctx_reset
 }
 
+# Cheap telemetry opt-in probe — true iff a consumer wired a sink. Producers
+# gate telemetry-payload construction on this (repo-relative path
+# normalization, data JSON) so the unwired default path spawns zero
+# telemetry-only subprocesses. Pure shell test, no subprocess.
+# hook::emit_telemetry re-checks the sink itself, so skipping this probe
+# costs only wasted payload work, never correctness.
+hook::telemetry_enabled() {
+  [[ -n "${HOOK_TELEMETRY_SINK:-}" ]]
+}
+
 # Emit one telemetry envelope per hook run to the consumer-set sink.
 # Fire-and-forget: sink is dispatched in the background; the hook never waits
 # on it and its failure never affects the hook's own exit code or stdout.
diff --git a/plugins/markdown-formatter/hooks/markdown-format.sh b/plugins/markdown-formatter/hooks/markdown-format.sh
index 02f366703..ffcc3c35f 100755
--- a/plugins/markdown-formatter/hooks/markdown-format.sh
+++ b/plugins/markdown-formatter/hooks/markdown-format.sh
@@ -24,12 +24,15 @@ hook::check_enabled "MARKDOWN_FORMAT"
 # under `set -u` would abort before the advisory exit 0, failing every edit.
 start=${EPOCHREALTIME:-}
 
-# Telemetry needs the high-res start stamp. When EPOCHREALTIME is unavailable
-# (Bash < 5.0) the stamp is empty and telemetry is skipped, so the hook still
-# formats on older bash rather than aborting.
+# Emit this run's telemetry envelope: $1 status, $2 findings JSON array.
+# Two guards: the high-res start stamp (EPOCHREALTIME is Bash 5.0+; on older
+# bash it is empty and telemetry is skipped, so the hook still formats rather
+# than aborting) and the sink opt-in. The data payload costs a jq subprocess,
+# so it is built here after both guards — never on the unwired path.
 emit_tel() {
   [[ -n "$start" ]] || return 0
-  hook::emit_telemetry "$@"
+  hook::telemetry_enabled || return 0
+  hook::emit_telemetry "markdown-format" "PostToolUse" "$1" "$start" "$(build_data_json "$2")" "$REPO_ROOT"
 }
 
 INPUT=$(cat)
@@ -40,26 +43,35 @@ case "$FILE" in
   *) exit 0 ;;
 esac
 
-TOOL=$(printf '%s' "$INPUT" | jq -r '.tool_name // empty' 2>/dev/null)
-
 # Resolve repo root early — needed for CWD-anchored config discovery and for
 # computing the schema-required repo-relative path in data.file.
 REPO_ROOT="$(hook::repo_root "$(dirname "$FILE")")"
-# Repo-relative path: schema requires "relative to the consuming repo root".
-# On Windows Git Bash, git rev-parse --show-toplevel returns a drive-letter path
-# while FILE may be in POSIX mount form. Normalize both through cygpath -lm
-# (long name, forward-slash mixed form) when available so the prefix strip
-# compares the same representation. On Linux/macOS, cygpath is absent and both
-# paths are already POSIX. Falls back to raw FILE on any normalization error.
+
+# Telemetry-payload precursors — TOOL and FILE_REL feed only the envelope's
+# data object, so both are built only when a sink is wired: the unwired
+# default path spawns zero telemetry-only subprocesses (the tool_name jq
+# parse, and 2× cygpath on Windows).
+#
+# FILE_REL is the repo-relative path: schema requires "relative to the
+# consuming repo root". On Windows Git Bash, git rev-parse --show-toplevel
+# returns a drive-letter path while FILE may be in POSIX mount form. Normalize
+# both through cygpath -lm (long name, forward-slash mixed form) when
+# available so the prefix strip compares the same representation. On
+# Linux/macOS, cygpath is absent and both paths are already POSIX. Falls back
+# to raw FILE on any normalization error.
+TOOL=""
 FILE_REL="$FILE"
-if command -v cygpath >/dev/null 2>&1; then
-  _file_lm=$(cygpath -lm "$FILE" 2>/dev/null)
-  _root_lm=$(cygpath -lm "$REPO_ROOT" 2>/dev/null)
-  if [[ -n "$_file_lm" && -n "$_root_lm" ]]; then
-    FILE_REL="${_file_lm#"$_root_lm"/}"
+if hook::telemetry_enabled; then
+  TOOL=$(printf '%s' "$INPUT" | jq -r '.tool_name // empty' 2>/dev/null)
+  if command -v cygpath >/dev/null 2>&1; then
+    _file_lm=$(cygpath -lm "$FILE" 2>/dev/null)
+    _root_lm=$(cygpath -lm "$REPO_ROOT" 2>/dev/null)
+    if [[ -n "$_file_lm" && -n "$_root_lm" ]]; then
+      FILE_REL="${_file_lm#"$_root_lm"/}"
+    fi
+  else
+    FILE_REL="${FILE#"$REPO_ROOT"/}"
   fi
-else
-  FILE_REL="${FILE#"$REPO_ROOT"/}"
 fi
 
 # Build the telemetry data object for the current TOOL/FILE_REL. $1 is the
@@ -85,15 +97,13 @@ elif command -v npx >/dev/null 2>&1; then
   MDLINT=(npx markdownlint-cli2)
 else
   # markdownlint unavailable — emit skipped telemetry then exit cleanly.
-  data_json=$(build_data_json '[]')
-  emit_tel "markdown-format" "PostToolUse" "skipped" "$start" "$data_json" "$REPO_ROOT"
+  emit_tel "skipped" '[]'
   exit 0
 fi
 
 if FIX_OUTPUT=$(cd "$REPO_ROOT" && "${MDLINT[@]}" --fix "$FILE" 2>&1); then
   # Clean after fix — emit ok with empty findings.
-  data_json=$(build_data_json '[]')
-  emit_tel "markdown-format" "PostToolUse" "ok" "$start" "$data_json" "$REPO_ROOT"
+  emit_tel "ok" '[]'
   exit 0
 fi
 
@@ -120,6 +130,5 @@ if [[ -n "$findings_raw" ]]; then
   FINDINGS_JSON=$(printf '%s' "$findings_raw" | jq -R . | jq -s . 2>/dev/null) || FINDINGS_JSON='[]'
 fi
 
-data_json=$(build_data_json "$FINDINGS_JSON")
-emit_tel "markdown-format" "PostToolUse" "ok" "$start" "$data_json" "$REPO_ROOT"
+emit_tel "ok" "$FINDINGS_JSON"
 exit 0
diff --git a/plugins/markdown-formatter/hooks/markdown-format.test.sh b/plugins/markdown-formatter/hooks/markdown-format.test.sh
index b4c3fa3fa..592bc8af0 100755
--- a/plugins/markdown-formatter/hooks/markdown-format.test.sh
+++ b/plugins/markdown-formatter/hooks/markdown-format.test.sh
@@ -379,6 +379,92 @@ else
 fi
 rm -f "$TEL_LEAK"
 
+# --- Unwired producer runs zero telemetry-only subprocesses -------------------
+# The telemetry payload (tool_name jq parse, cygpath path normalization, data
+# JSON build) must be gated on sink presence. Count the hook's subprocess
+# spawns via PATH shims: a cygpath shim that logs and echoes its last argument
+# unchanged (a plausible `-lm` result on any host, so the Windows branch is
+# exercised even on Linux), and a jq shim that logs then delegates to the real
+# jq so hook behavior is unaffected. cygpath assertions filter on the hook's
+# `-lm` flag: on Windows, npm/npx launcher shims may call `cygpath -w` on
+# their own, which is not the hook's doing.
+SHIM_DIR="$WORK/shims"
+mkdir -p "$SHIM_DIR"
+CYG_LOG="$WORK/cygpath.log"
+JQ_LOG="$WORK/jq.log"
+REAL_JQ="$(command -v jq)"
+cat >"$SHIM_DIR/cygpath" <<EOF
+#!/usr/bin/env bash
+printf '%s\n' "\$*" >>"$CYG_LOG"
+printf '%s\n' "\${!#}"
+EOF
+cat >"$SHIM_DIR/jq" <<EOF
+#!/usr/bin/env bash
+printf '%s\n' "\$*" >>"$JQ_LOG"
+exec "$REAL_JQ" "\$@"
+EOF
+chmod +x "$SHIM_DIR/cygpath" "$SHIM_DIR/jq"
+
+count_lm() { grep -c -- '-lm' "$CYG_LOG" 2>/dev/null || true; }
+
+# Unwired (sink unset), clean fixture: the only legitimate jq spawn is
+# hook::read_file_path's file_path parse — TOOL, FILE_REL and data_json are
+# all telemetry-only and must not be built.
+: >"$CYG_LOG"
+: >"$JQ_LOG"
+printf '# Gate Doc\n\nClean text.\n' >"$REPO/fixtureGate.md"
+OUT_GATE="$(cd "$UNRELATED" && printf '{"tool_input":{"file_path":"%s"},"tool_name":"Write"}' "$REPO/fixtureGate.md" \
+  | env -u CLAUDE_PROJECT_DIR -u HOOK_TELEMETRY_SINK HOOK_MARKDOWN_FORMAT_ENABLED=true PATH="$SHIM_DIR:$PATH" bash "$HOOK")"
+RC_GATE=$?
+if [[ $RC_GATE -eq 0 && -z "$OUT_GATE" ]]; then
+  ok "telemetry-gate/unwired: exit 0, empty stdout"
+else
+  fail "telemetry-gate/unwired: rc=$RC_GATE out=$OUT_GATE"
+fi
+CYG_LM_UNWIRED="$(count_lm)"
+if [[ "$CYG_LM_UNWIRED" -eq 0 ]]; then
+  ok "telemetry-gate/unwired: zero cygpath -lm spawns"
+else
+  fail "telemetry-gate/unwired: $CYG_LM_UNWIRED cygpath -lm spawns: $(cat "$CYG_LOG")"
+fi
+JQ_UNWIRED="$(wc -l <"$JQ_LOG")"
+if [[ "$JQ_UNWIRED" -eq 1 ]]; then
+  ok "telemetry-gate/unwired: exactly 1 jq spawn (file_path parse only)"
+else
+  fail "telemetry-gate/unwired: expected 1 jq spawn, got $JQ_UNWIRED: $(cat "$JQ_LOG")"
+fi
+
+# Wired (stub sink), same fixture shape: the payload construction must still
+# run — positive control proving the shims observe the telemetry spawns (the
+# unwired zeroes above would otherwise pass vacuously).
+: >"$CYG_LOG"
+: >"$JQ_LOG"
+TEL_GATE="$(mktemp)"
+GATE_SINK="$(make_sink "cat >\"$TEL_GATE\"")"
+printf '# Gate Doc Wired\n\nClean text.\n' >"$REPO/fixtureGateWired.md"
+# shellcheck disable=SC2034  # stdout captured for timing correctness; content checked via TEL_GATE
+_OUT_GW="$(cd "$UNRELATED" && printf '{"tool_input":{"file_path":"%s"},"tool_name":"Write"}' "$REPO/fixtureGateWired.md" \
+  | env -u CLAUDE_PROJECT_DIR HOOK_MARKDOWN_FORMAT_ENABLED=true HOOK_TELEMETRY_SINK="$GATE_SINK" PATH="$SHIM_DIR:$PATH" bash "$HOOK")"
+wait_for_sink "$TEL_GATE"
+CYG_LM_WIRED="$(count_lm)"
+if [[ "$CYG_LM_WIRED" -eq 2 ]]; then
+  ok "telemetry-gate/wired: 2 cygpath -lm spawns (FILE + REPO_ROOT normalization)"
+else
+  fail "telemetry-gate/wired: expected 2 cygpath -lm spawns, got $CYG_LM_WIRED: $(cat "$CYG_LOG")"
+fi
+JQ_WIRED="$(wc -l <"$JQ_LOG")"
+if [[ "$JQ_WIRED" -gt 1 ]]; then
+  ok "telemetry-gate/wired: payload jq spawns present ($JQ_WIRED total)"
+else
+  fail "telemetry-gate/wired: expected >1 jq spawns, got $JQ_WIRED: $(cat "$JQ_LOG")"
+fi
+if [[ -s "$TEL_GATE" ]] && jq -e '.data.tool == "Write"' "$TEL_GATE" >/dev/null 2>&1; then
+  ok "telemetry-gate/wired: envelope delivered with data.tool intact"
+else
+  fail "telemetry-gate/wired: envelope missing or data.tool wrong: $(cat "$TEL_GATE" 2>/dev/null)"
+fi
+rm -f "$TEL_GATE"
+
 echo
 echo "PASS=$PASS FAIL=$FAIL"
 [[ $FAIL -eq 0 ]]
diff --git a/plugins/ruff-format/.claude-plugin/plugin.json b/plugins/ruff-format/.claude-plugin/plugin.json
index 42dc94af6..eb6af8e55 100644
--- a/plugins/ruff-format/.claude-plugin/plugin.json
+++ b/plugins/ruff-format/.claude-plugin/plugin.json
@@ -1,7 +1,7 @@
 {
   "$schema": "https://json.schemastore.org/claude-code-plugin-manifest.json",
   "name": "ruff-format",
-  "version": "0.1.2",
+  "version": "0.1.3",
   "description": "Auto-format and lint Python on edit via Ruff, only when a Ruff config governs the repo — using the consuming repo's own Ruff config.",
   "author": {
     "name": "Melodic Software",
diff --git a/plugins/ruff-format/hooks/hook-utils.sh b/plugins/ruff-format/hooks/hook-utils.sh
index 3f218ce00..1c003435a 100644
--- a/plugins/ruff-format/hooks/hook-utils.sh
+++ b/plugins/ruff-format/hooks/hook-utils.sh
@@ -132,6 +132,16 @@ hook::ctx_flush() {
   hook::ctx_reset
 }
 
+# Cheap telemetry opt-in probe — true iff a consumer wired a sink. Producers
+# gate telemetry-payload construction on this (repo-relative path
+# normalization, data JSON) so the unwired default path spawns zero
+# telemetry-only subprocesses. Pure shell test, no subprocess.
+# hook::emit_telemetry re-checks the sink itself, so skipping this probe
+# costs only wasted payload work, never correctness.
+hook::telemetry_enabled() {
+  [[ -n "${HOOK_TELEMETRY_SINK:-}" ]]
+}
+
 # Emit one telemetry envelope per hook run to the consumer-set sink.
 # Fire-and-forget: sink is dispatched in the background; the hook never waits
 # on it and its failure never affects the hook's own exit code or stdout.