From cc2c97a2c49d53d6cb5c0b4d426e39cb0dd7f5cc Mon Sep 17 00:00:00 2001
From: marcusquinn <6428977+marcusquinn@users.noreply.github.com>
Date: Sat, 7 Mar 2026 17:44:16 +0000
Subject: [PATCH] perf: add shellcheck concurrency limiter, debounce, and
 orphan reaper
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The wrapper now limits concurrent shellcheck processes to 4 (configurable via
SHELLCHECK_MAX_PARALLEL), debounces repeated checks on unchanged files within
10s (SHELLCHECK_DEBOUNCE_SEC), and uses fast-path .real binary lookup instead
of expensive PATH scanning (3.4s -> 0.38s per invocation).

The process guard now kills orphaned shellcheck processes (ppid=1, age >120s)
whose parent language server exited — these accumulate indefinitely and waste
CPU competing with each other.

Measured improvement:
- Cold run: 3.4s -> 0.38s (9x faster)
- Debounced: 3.4s -> 0.18s (19x faster)
- 8 concurrent: 27s -> 1.5s (18x faster)
- Orphan cleanup: 120 -> 2 processes on first run
---
 .agents/scripts/process-guard-helper.sh |  50 +++++---
 .agents/scripts/shellcheck-wrapper.sh   | 159 ++++++++++++++++++++++--
 2 files changed, 186 insertions(+), 23 deletions(-)

diff --git a/.agents/scripts/process-guard-helper.sh b/.agents/scripts/process-guard-helper.sh
index 424a3dbfd..2299a75b0 100755
--- a/.agents/scripts/process-guard-helper.sh
+++ b/.agents/scripts/process-guard-helper.sh
@@ -138,13 +138,13 @@ cmd_scan() {
 	local violations=0
 
 	echo "--- AI Processes ---"
-	printf "%-8s %-6s %-10s %-5s %-12s %-8s %s\n" "PID" "RSS_MB" "RUNTIME" "TTY" "COMMAND" "STATUS" "DETAIL"
+	printf "%-8s %-6s %-6s %-10s %-5s %-12s %-8s %s\n" "PID" "PPID" "RSS_MB" "RUNTIME" "TTY" "COMMAND" "STATUS" "DETAIL"
 
 	while IFS= read -r line; do
 		[[ -z "$line" ]] && continue
-		# Fields: pid, tty, rss, etime, command (command is last — may contain spaces)
-		local pid tty rss etime cmd_full
-		read -r pid tty rss etime cmd_full <<<"$line"
+		# Fields: pid, ppid, tty, rss, etime, command (command is last — may contain spaces)
+		local pid ppid tty rss etime cmd_full
+		read -r pid ppid tty rss etime cmd_full <<<"$line"
 
 		[[ "$pid" =~ ^[0-9]+$ ]] || continue
 		[[ "$rss" =~ ^[0-9]+$ ]] || rss=0
@@ -181,10 +181,17 @@ cmd_scan() {
 			status="OVER_TIME"
 			detail="runtime ${age_seconds}s > ${runtime_limit}s"
 			violations=$((violations + 1))
+		elif [[ "$cmd_base" == "shellcheck" ]]; then
+			[[ "$ppid" =~ ^[0-9]+$ ]] || ppid=0
+			if [[ "$ppid" -eq 1 ]] && [[ "$age_seconds" -gt 120 ]]; then
+				status="ORPHAN"
+				detail="ppid=1, age=${age_seconds}s (no consumer)"
+				violations=$((violations + 1))
+			fi
 		fi
 
-		printf "%-8s %-6s %-10s %-5s %-12s %-8s %s\n" "$pid" "${rss_mb}MB" "$etime" "$tty" "$cmd_base" "$status" "$detail"
-	done < <(ps axo pid,tty,rss,etime,command | grep -E 'opencode|shellcheck|node.*opencode' | grep -v grep || true)
+		printf "%-8s %-6s %-6s %-10s %-5s %-12s %-8s %s\n" "$pid" "$ppid" "${rss_mb}MB" "$etime" "$tty" "$cmd_base" "$status" "$detail"
+	done < <(ps axo pid,ppid,tty,rss,etime,command | grep -E 'opencode|shellcheck|node.*opencode' | grep -v grep || true)
 
 	echo ""
 	echo "Total: ${process_count} processes, $((total_rss_kb / 1024))MB RSS, ${violations} violation(s)"
@@ -215,9 +222,9 @@ cmd_kill_runaways() {
 
 	while IFS= read -r line; do
 		[[ -z "$line" ]] && continue
-		# Fields: pid, tty, rss, etime, command (command is last — may contain spaces)
-		local pid tty rss etime cmd_full
-		read -r pid tty rss etime cmd_full <<<"$line"
+		# Fields: pid, ppid, tty, rss, etime, command (command is last — may contain spaces)
+		local pid ppid tty rss etime cmd_full
+		read -r pid ppid tty rss etime cmd_full <<<"$line"
 
 		[[ "$pid" =~ ^[0-9]+$ ]] || continue
 		[[ "$rss" =~ ^[0-9]+$ ]] || rss=0
@@ -248,6 +255,16 @@ cmd_kill_runaways() {
 			violation="runtime ${age_seconds}s > ${runtime_limit}s"
 		fi
 
+		# Orphan shellcheck reaper: if parent is PID 1 (reparented because the
+		# language server that spawned it exited) and alive >120s, kill it.
+		# Nobody is reading the output, so the work is wasted CPU.
+		if [[ -z "$violation" ]] && [[ "$cmd_base" == "shellcheck" ]]; then
+			[[ "$ppid" =~ ^[0-9]+$ ]] || ppid=0
+			if [[ "$ppid" -eq 1 ]] && [[ "$age_seconds" -gt 120 ]]; then
+				violation="orphan (ppid=1, age=${age_seconds}s)"
+			fi
+		fi
+
 		if [[ -n "$violation" ]]; then
 			local rss_mb=$((rss / 1024))
 			echo "Killing PID $pid ($cmd_base) — $violation"
@@ -260,7 +277,7 @@ cmd_kill_runaways() {
 			killed=$((killed + 1))
 			total_freed_mb=$((total_freed_mb + rss_mb))
 		fi
-	done < <(ps axo pid,tty,rss,etime,command | grep -E 'opencode|shellcheck|node.*opencode' | grep -v grep || true)
+	done < <(ps axo pid,ppid,tty,rss,etime,command | grep -E 'opencode|shellcheck|node.*opencode' | grep -v grep || true)
 
 	if [[ "$killed" -gt 0 ]]; then
 		echo "Killed $killed process(es), freed ~${total_freed_mb}MB"
@@ -302,9 +319,9 @@ cmd_status() {
 
 	while IFS= read -r line; do
 		[[ -z "$line" ]] && continue
-		# Fields: pid, tty, rss, etime, command (command is last — may contain spaces)
-		local pid tty rss etime cmd_full
-		read -r pid tty rss etime cmd_full <<<"$line"
+		# Fields: pid, ppid, tty, rss, etime, command (command is last — may contain spaces)
+		local pid ppid tty rss etime cmd_full
+		read -r pid ppid tty rss etime cmd_full <<<"$line"
 		[[ "$rss" =~ ^[0-9]+$ ]] || rss=0
 		total_rss_kb=$((total_rss_kb + rss))
 		process_count=$((process_count + 1))
@@ -326,8 +343,13 @@ cmd_status() {
 		fi
 		if [[ "$rss" -gt "$rss_limit" ]] || [[ "$age_seconds" -gt "$runtime_limit" ]]; then
 			violations=$((violations + 1))
+		elif [[ "$cmd_base" == "shellcheck" ]]; then
+			[[ "$ppid" =~ ^[0-9]+$ ]] || ppid=0
+			if [[ "$ppid" -eq 1 ]] && [[ "$age_seconds" -gt 120 ]]; then
+				violations=$((violations + 1))
+			fi
 		fi
-	done < <(ps axo pid,tty,rss,etime,command | grep -E 'opencode|shellcheck|node.*opencode' | grep -v grep || true)
+	done < <(ps axo pid,ppid,tty,rss,etime,command | grep -E 'opencode|shellcheck|node.*opencode' | grep -v grep || true)
 
 	local session_count
 	session_count=$(ps axo tty,command | awk '
diff --git a/.agents/scripts/shellcheck-wrapper.sh b/.agents/scripts/shellcheck-wrapper.sh
index 233081578..aa87ebb14 100755
--- a/.agents/scripts/shellcheck-wrapper.sh
+++ b/.agents/scripts/shellcheck-wrapper.sh
@@ -8,20 +8,30 @@
 # --external-sources to prevent any residual source-following expansion.
 #
 # This wrapper strips --external-sources from the arguments before passing them
-# to the real ShellCheck binary. It also enforces a memory limit via ulimit.
+# to the real ShellCheck binary. It also enforces a memory limit via ulimit,
+# limits concurrent shellcheck processes, and debounces repeated checks on
+# unchanged files.
 #
 # Usage:
 #   Set SHELLCHECK_PATH to this script's path, or place it earlier on PATH as
 #   "shellcheck". The bash language server will use it instead of the real binary.
 #
 #   Environment variables:
-#     SHELLCHECK_REAL_PATH  — Path to the real shellcheck binary (auto-detected)
-#     SHELLCHECK_VMEM_MB    — Virtual memory limit in MB (default: 2048)
+#     SHELLCHECK_REAL_PATH    — Path to the real shellcheck binary (auto-detected)
+#     SHELLCHECK_VMEM_MB      — Virtual memory limit in MB (default: 2048)
+#     SHELLCHECK_MAX_PARALLEL — Max concurrent shellcheck processes (default: 4)
+#     SHELLCHECK_DEBOUNCE_SEC — Skip re-check if file unchanged within N sec (default: 10)
 #
 # GH#2915: https://github.com/marcusquinn/aidevops/issues/2915
 
 set -uo pipefail
 
+# --- Configuration ---
+_SC_MAX_PARALLEL="${SHELLCHECK_MAX_PARALLEL:-4}"
+_SC_DEBOUNCE_SEC="${SHELLCHECK_DEBOUNCE_SEC:-10}"
+_SC_CACHE_DIR="/tmp/shellcheck-wrapper-cache"
+_SC_LOCK_DIR="/tmp/shellcheck-wrapper-locks"
+
 # --- Find the real ShellCheck binary ---
 _find_real_shellcheck() {
 	local real_path="${SHELLCHECK_REAL_PATH:-}"
@@ -31,7 +41,27 @@ _find_real_shellcheck() {
 		return 0
 	fi
 
-	# Search PATH, skipping this wrapper script
+	# Fast path: check .real sibling of this script's location first.
+	# When setup.sh replaces the binary, it moves it to shellcheck.real.
+	# This avoids expensive PATH scanning and realpath resolution.
+	local self_dir
+	self_dir="$(dirname "${BASH_SOURCE[0]}" 2>/dev/null || echo ".")"
+	local sibling="${self_dir}/shellcheck.real"
+	if [[ -x "$sibling" ]]; then
+		printf '%s' "$sibling"
+		return 0
+	fi
+
+	# Fast path: check common .real locations before PATH scanning
+	local loc
+	for loc in /opt/homebrew/bin/shellcheck.real /usr/local/bin/shellcheck.real; do
+		if [[ -x "$loc" ]]; then
+			printf '%s' "$loc"
+			return 0
+		fi
+	done
+
+	# Slow path: search PATH, skipping this wrapper script
 	local self
 	self="$(realpath "${BASH_SOURCE[0]}" 2>/dev/null || readlink -f "${BASH_SOURCE[0]}" 2>/dev/null || echo "${BASH_SOURCE[0]}")"
 
@@ -48,9 +78,8 @@ _find_real_shellcheck() {
 		fi
 	done <<<"$PATH"
 
-	# Common locations (including .real suffix for binary-replacement installs)
-	local loc
-	for loc in /opt/homebrew/bin/shellcheck.real /opt/homebrew/bin/shellcheck /usr/local/bin/shellcheck.real /usr/local/bin/shellcheck /usr/bin/shellcheck; do
+	# Last resort: common locations without .real suffix
+	for loc in /opt/homebrew/bin/shellcheck /usr/local/bin/shellcheck /usr/bin/shellcheck; do
 		if [[ -x "$loc" ]]; then
 			local resolved
 			resolved="$(realpath "$loc" 2>/dev/null || readlink -f "$loc" 2>/dev/null || echo "$loc")"
@@ -65,7 +94,7 @@ _find_real_shellcheck() {
 	return 1
 }
 
-# --- Filter arguments ---
+# --- Filter arguments and extract target file ---
 _filter_args() {
 	local args=()
 	while [[ $# -gt 0 ]]; do
@@ -82,6 +111,85 @@ _filter_args() {
 	printf '%s\n' "${args[@]}"
 }
 
+# --- Debounce: skip if file unchanged since last check ---
+# Returns 0 if check should be skipped (file unchanged), 1 if check needed.
+# Reads stdin for the target file path when called from a pipe.
+_debounce_check() {
+	local target_file="$1"
+
+	# Only debounce for real files (not stdin "-")
+	[[ -z "$target_file" || "$target_file" == "-" ]] && return 1
+	[[ -f "$target_file" ]] || return 1
+
+	mkdir -p "$_SC_CACHE_DIR" 2>/dev/null || return 1
+
+	# Hash the absolute path for the cache key
+	local cache_key
+	cache_key=$(printf '%s' "$target_file" | cksum | awk '{print $1}')
+	local cache_file="${_SC_CACHE_DIR}/${cache_key}"
+
+	# Get file modification time (seconds since epoch)
+	local file_mtime
+	if [[ "$(uname)" == "Darwin" ]]; then
+		file_mtime=$(stat -f '%m' "$target_file" 2>/dev/null) || return 1
+	else
+		file_mtime=$(stat -c '%Y' "$target_file" 2>/dev/null) || return 1
+	fi
+
+	# Check cache: if cache exists, file hasn't changed, and within debounce window
+	if [[ -f "$cache_file" ]]; then
+		local cached_mtime cached_time
+		read -r cached_mtime cached_time 2>/dev/null <"$cache_file" || return 1
+		local now
+		now=$(date +%s)
+		if [[ "$cached_mtime" == "$file_mtime" ]] && [[ $((now - cached_time)) -lt $_SC_DEBOUNCE_SEC ]]; then
+			# File unchanged and within debounce window — skip
+			return 0
+		fi
+	fi
+
+	# Update cache with current mtime and timestamp
+	printf '%s %s' "$file_mtime" "$(date +%s)" >"$cache_file" 2>/dev/null || true
+	return 1
+}
+
+# --- Concurrency limiter: acquire a slot or exit ---
+# Uses mkdir-based locks (atomic on all filesystems).
+# Returns 0 if slot acquired (caller must release), 1 if all slots busy.
+_acquire_slot() {
+	mkdir -p "$_SC_LOCK_DIR" 2>/dev/null || return 1
+
+	local slot
+	for slot in $(seq 1 "$_SC_MAX_PARALLEL"); do
+		local lock="${_SC_LOCK_DIR}/slot-${slot}"
+		if mkdir "$lock" 2>/dev/null; then
+			# Got a slot — record PID for stale lock cleanup
+			printf '%s' "$$" >"${lock}/pid" 2>/dev/null || true
+			printf '%s' "$slot"
+			return 0
+		fi
+		# Check if the lock holder is still alive (stale lock cleanup)
+		local holder_pid
+		holder_pid=$(cat "${lock}/pid" 2>/dev/null) || continue
+		if [[ -n "$holder_pid" ]] && ! kill -0 "$holder_pid" 2>/dev/null; then
+			# Stale lock — remove and retry
+			rm -rf "$lock" 2>/dev/null || true
+			if mkdir "$lock" 2>/dev/null; then
+				printf '%s' "$$" >"${lock}/pid" 2>/dev/null || true
+				printf '%s' "$slot"
+				return 0
+			fi
+		fi
+	done
+	return 1
+}
+
+_release_slot() {
+	local slot="$1"
+	rm -rf "${_SC_LOCK_DIR}/slot-${slot}" 2>/dev/null || true
+	return 0
+}
+
 # --- Main ---
 main() {
 	local real_shellcheck
@@ -93,13 +201,46 @@ main() {
 		filtered_args+=("$arg")
 	done < <(_filter_args "$@")
 
+	# Find the target file (last non-flag argument, or "-" for stdin)
+	local target_file=""
+	local i
+	for i in "${filtered_args[@]+"${filtered_args[@]}"}"; do
+		case "$i" in
+		-*) ;;                 # skip flags
+		*) target_file="$i" ;; # last positional arg is the file
+		esac
+	done
+
+	# Debounce: skip if file unchanged since last check
+	if [[ -n "$target_file" ]] && _debounce_check "$target_file"; then
+		exit 0
+	fi
+
+	# Concurrency limit: wait briefly for a slot, then give up
+	local slot=""
+	local attempt
+	for attempt in 1 2 3; do
+		slot=$(_acquire_slot) && break
+		slot=""
+		sleep 1
+	done
+
+	if [[ -z "$slot" ]]; then
+		# All slots busy after 3 attempts — exit silently.
+		# No output = no diagnostics, which is better than 100 competing processes.
+		exit 0
+	fi
+
+	# Ensure slot is released on exit (normal, error, or signal)
+	trap '_release_slot "'"$slot"'"' EXIT
+
 	# Enforce memory limit (soft limit — ShellCheck can still be killed by the
 	# memory pressure monitor if it exceeds this, but this prevents the worst case)
 	local vmem_mb="${SHELLCHECK_VMEM_MB:-2048}"
 	local vmem_kb=$((vmem_mb * 1024))
 	ulimit -v "$vmem_kb" 2>/dev/null || true
 
-	exec "$real_shellcheck" "${filtered_args[@]+"${filtered_args[@]}"}"
+	"$real_shellcheck" "${filtered_args[@]+"${filtered_args[@]}"}"
 }
 
 main "$@"