fix(mcp): exit stdio server on parent death

scripts/test.sh

@@ -60,4 +60,8 @@ scripts/clean.sh
 # Step 2 + 3: Build and run tests (with arch prefix on macOS)
 $ARCH_PREFIX make -j"$NPROC" -f Makefile.cbm test $MAKE_ARGS
 
+# Step 4: Build the stdio MCP binary and verify it exits when its parent dies.
+$ARCH_PREFIX make -j"$NPROC" -f Makefile.cbm cbm $MAKE_ARGS
+bash tests/test_parent_watchdog.sh
+
 echo "=== All tests passed ==="

src/main.c

@@ -27,13 +27,15 @@ enum {
     MAIN_FLAG_OFF = 5, /* strlen("--ui=") */
     MAIN_PORT_OFF = 7, /* strlen("--port=") */
     MAIN_MAX_PORT = 65536,
+    PARENT_WATCHDOG_STACK_SIZE = 64 * CBM_SZ_1K,
 };
 #define MAIN_RAM_FRACTION 0.5
 
 #define SLEN(s) (sizeof(s) - 1)
 #include "foundation/log.h"
 #include "foundation/diagnostics.h"
 #include "foundation/platform.h"
+#include "foundation/compat.h"
 #include "foundation/compat_thread.h"
 #include "foundation/mem.h"
 #include "foundation/profile.h"
@@ -59,9 +61,10 @@ static cbm_mcp_server_t *g_server = NULL;
 static cbm_http_server_t *g_http_server = NULL;
 static atomic_int g_shutdown = 0;
 
-static void signal_handler(int sig) {
-    (void)sig;
-    atomic_store(&g_shutdown, 1);
+static void request_shutdown(void) {
+    if (atomic_exchange(&g_shutdown, 1)) {
+        return;
+    }
 
     /* Cancel any in-progress pipeline (async-signal-safe: only does atomic_store) */
     if (g_server) {
@@ -83,6 +86,37 @@ static void signal_handler(int sig) {
     (void)fclose(stdin);
 }
 
+static void signal_handler(int sig) {
+    (void)sig;
+    request_shutdown();
+}
+
+/* ── Parent process watchdog ───────────────────────────────────── */
+
+#ifndef _WIN32
+static void *parent_watchdog_thread(void *arg) {
+    pid_t initial_ppid = *(pid_t *)arg;
+    const unsigned int interval_us = 500000;
+
+    while (!atomic_load(&g_shutdown)) {
+        cbm_usleep(interval_us);
+
+        if (atomic_load(&g_shutdown)) {
+            break;
+        }
+
+        pid_t current_ppid = getppid();
+        if (initial_ppid > 1 && current_ppid != initial_ppid) {
+            cbm_log_warn("parent.exited", "reason", "ppid_changed");
+            request_shutdown();
+            exit(0);
+        }
+    }
+
+    return NULL;
+}
+#endif
+
 /* ── Watcher background thread ──────────────────────────────────── */
 
 static void *watcher_thread(void *arg) {
@@ -345,6 +379,24 @@ int main(int argc, char **argv) {
         return subcmd;
     }
 
+#ifndef _WIN32
+    pid_t initial_ppid = getppid();
+    if (initial_ppid <= 1) {
+        return 0;
+    }
+
+    cbm_thread_t parent_watchdog_tid;
+    bool parent_watchdog_started = false;
+    int parent_watchdog_rc = cbm_thread_create(&parent_watchdog_tid, PARENT_WATCHDOG_STACK_SIZE,
+                                               parent_watchdog_thread, &initial_ppid);
+    if (parent_watchdog_rc == 0) {
+        parent_watchdog_started = true;
+    } else {
+        cbm_log_int(CBM_LOG_WARN, "parent.watchdog.unavailable", "rc", parent_watchdog_rc);
+        return SKIP_ONE;
+    }
+#endif
+
     /* Default: MCP server on stdio */
     cbm_mem_init(MAIN_RAM_FRACTION); /* 50% of RAM — safe now because mimalloc tracks ALL
                                       * memory (C + C++ allocations) via global override.
@@ -391,6 +443,12 @@ int main(int argc, char **argv) {
     if (!g_server) {
         cbm_log_error("server.err", "msg", "failed to create server");
         cbm_config_close(runtime_config);
+#ifndef _WIN32
+        atomic_store(&g_shutdown, 1);
+        if (parent_watchdog_started) {
+            cbm_thread_join(&parent_watchdog_tid);
+        }
+#endif
         return SKIP_ONE;
     }
 
@@ -430,10 +488,17 @@ int main(int argc, char **argv) {
 
     /* Run MCP event loop (blocks until EOF or signal) */
     int rc = cbm_mcp_server_run(g_server, stdin, stdout);
+    atomic_store(&g_shutdown, 1);
 
     /* Shutdown */
     cbm_log_info("server.shutdown");
 
+#ifndef _WIN32
+    if (parent_watchdog_started) {
+        cbm_thread_join(&parent_watchdog_tid);
+    }
+#endif
+
     if (http_started) {
         cbm_http_server_stop(g_http_server);
         cbm_thread_join(&http_tid);

tests/test_parent_watchdog.sh

@@ -0,0 +1,82 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+BINARY="${ROOT}/build/c/codebase-memory-mcp"
+
+case "$(uname -s)" in
+  MINGW*|MSYS*|CYGWIN*)
+    echo "skipping parent watchdog test on Windows"
+    exit 0
+    ;;
+esac
+
+if [[ ! -x "${BINARY}" ]]; then
+  echo "missing binary: ${BINARY}" >&2
+  exit 2
+fi
+
+tmpdir="$(mktemp -d)"
+cleanup() {
+  if [[ -f "${tmpdir}/child.pid" ]]; then
+    child_pid="$(cat "${tmpdir}/child.pid" 2>/dev/null || true)"
+    if [[ -n "${child_pid}" ]]; then
+      kill "${child_pid}" 2>/dev/null || true
+    fi
+  fi
+  if [[ -n "${wrapper_pid:-}" ]]; then
+    kill "${wrapper_pid}" 2>/dev/null || true
+  fi
+  rm -rf "${tmpdir}"
+}
+trap cleanup EXIT
+
+cat >"${tmpdir}/wrapper.sh" <<'SH'
+#!/usr/bin/env bash
+set -euo pipefail
+exec 3<>"${FIFO}"
+"${CBM_BINARY}" <&3 >/dev/null 2>"${TMPDIR_PATH}/child.err" &
+echo "$!" >"${TMPDIR_PATH}/child.pid"
+wait
+SH
+chmod +x "${tmpdir}/wrapper.sh"
+mkfifo "${tmpdir}/stdin"
+
+CBM_BINARY="${BINARY}" FIFO="${tmpdir}/stdin" TMPDIR_PATH="${tmpdir}" "${tmpdir}/wrapper.sh" &
+wrapper_pid=$!
+
+for _ in {1..50}; do
+  [[ -s "${tmpdir}/child.pid" ]] && break
+  sleep 0.1
+done
+
+if [[ ! -s "${tmpdir}/child.pid" ]]; then
+  echo "child pid file was not written" >&2
+  if [[ -s "${tmpdir}/child.err" ]]; then
+    cat "${tmpdir}/child.err" >&2
+  fi
+  exit 3
+fi
+
+child_pid="$(cat "${tmpdir}/child.pid")"
+if ! kill -0 "${child_pid}" 2>/dev/null; then
+  echo "child did not start" >&2
+  exit 3
+fi
+
+kill -9 "${wrapper_pid}"
+wait "${wrapper_pid}" 2>/dev/null || true
+
+deadline=$((SECONDS + 6))
+while (( SECONDS < deadline )); do
+  if ! kill -0 "${child_pid}" 2>/dev/null; then
+    exit 0
+  fi
+  sleep 0.2
+done
+
+echo "codebase-memory-mcp child ${child_pid} survived parent death" >&2
+if [[ -s "${tmpdir}/child.err" ]]; then
+  cat "${tmpdir}/child.err" >&2
+fi
+exit 1