diff --git a/src/cli/cli.h b/src/cli/cli.h
index 27ef4e3ec..de4939c74 100644
--- a/src/cli/cli.h
+++ b/src/cli/cli.h
@@ -477,6 +477,20 @@ char *cbm_hook_augment_lifecycle_json_for(const char *input, const char *forced_
 void cbm_hook_augment_arm_deadline(void);
 char *cbm_hook_augment_read_stdin(void);
 
+/* Why a hook client is not augmenting. The hook caller only ever sees stdout,
+ * so each reason that is actionable by the user must have a stdout notice
+ * (#1388: a build-conflicted daemon used to report on stderr alone, which is
+ * invisible in-session and reads as silent skips). */
+typedef enum {
+    CBM_HOOK_ADMISSION_DAEMON_ABSENT = 0, /* no daemon running: `daemon start` heals it */
+    CBM_HOOK_ADMISSION_BUILD_CONFLICT     /* daemon runs another build: needs `daemon stop` */
+} cbm_hook_admission_t;
+
+/* The JSON systemMessage a hook client must print on stdout for `reason`, or
+ * NULL when nothing should be printed. hook_dialect NULL = Claude Code, the
+ * only dialect that surfaces a stdout systemMessage to the user. */
+const char *cbm_hook_admission_notice(cbm_hook_admission_t reason, const char *hook_dialect);
+
 /* Process one already-read hook payload using a caller-owned MCP session.
  * Returns a malloc-owned hook output JSON string, or NULL for fail-open/no
  * augmentation. This is the daemon entry; it never arms a process-global
diff --git a/src/cli/hook_augment.c b/src/cli/hook_augment.c
index 404d71eb4..73ad1c45b 100644
--- a/src/cli/hook_augment.c
+++ b/src/cli/hook_augment.c
@@ -1437,3 +1437,24 @@ int cbm_cmd_hook_augment(int argc, char **argv) {
     free(input);
     return 0;
 }
+
+const char *cbm_hook_admission_notice(cbm_hook_admission_t reason, const char *hook_dialect) {
+    /* Only Claude Code (the NULL dialect) consumes a bare stdout JSON object;
+     * emitting it into another dialect's channel would corrupt that protocol. */
+    if (hook_dialect) {
+        return NULL;
+    }
+    switch (reason) {
+    case CBM_HOOK_ADMISSION_DAEMON_ABSENT:
+        return "{\"systemMessage\":\"codebase-memory-mcp: no CBM daemon is running, so graph "
+               "augmentation is currently skipped. Run `codebase-memory-mcp daemon start` (or "
+               "open an MCP session) to enable it.\"}";
+    case CBM_HOOK_ADMISSION_BUILD_CONFLICT:
+        return "{\"systemMessage\":\"codebase-memory-mcp: graph augmentation is skipped: the "
+               "active CBM daemon runs a different build than this binary (usually an update was "
+               "installed while the old daemon kept running). Run `codebase-memory-mcp daemon "
+               "stop`, then retry - the next command starts a matching daemon.\"}";
+    default:
+        return NULL;
+    }
+}
diff --git a/src/main.c b/src/main.c
index b12ebc77e..6a03d0624 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1483,12 +1483,9 @@ static void main_hook_report_absent_daemon(const char *hook_dialect) {
     (void)fprintf(stderr, "codebase-memory-mcp: no CBM daemon is running, so graph "
                           "augmentation is skipped. Start an MCP session or run "
                           "`codebase-memory-mcp daemon start` to enable it.\n");
-    if (!hook_dialect) {
-        /* Claude hook output: a systemMessage is surfaced to the user. */
-        (void)fputs("{\"systemMessage\":\"codebase-memory-mcp: no CBM daemon is running, so "
-                    "graph augmentation is currently skipped. Run `codebase-memory-mcp daemon "
-                    "start` (or open an MCP session) to enable it.\"}",
-                    stdout);
+    const char *notice = cbm_hook_admission_notice(CBM_HOOK_ADMISSION_DAEMON_ABSENT, hook_dialect);
+    if (notice) {
+        (void)fputs(notice, stdout);
         (void)fflush(stdout);
     }
 }
@@ -1503,12 +1500,11 @@ static void main_hook_report_conflicted_daemon(const char *hook_dialect) {
     if (hook_dialect || !main_hook_absent_notice_due()) {
         return;
     }
-    (void)fputs("{\"systemMessage\":\"codebase-memory-mcp: graph augmentation is skipped: the "
-                "active CBM daemon runs a different build than this binary (usually an update "
-                "was installed while the old daemon kept running). Run `codebase-memory-mcp "
-                "daemon stop`, then retry - the next command starts a matching daemon.\"}",
-                stdout);
-    (void)fflush(stdout);
+    const char *notice = cbm_hook_admission_notice(CBM_HOOK_ADMISSION_BUILD_CONFLICT, hook_dialect);
+    if (notice) {
+        (void)fputs(notice, stdout);
+        (void)fflush(stdout);
+    }
 }
 
 static int main_run_hook_frontend(cbm_daemon_runtime_client_t *client, const char *hook_event,
diff --git a/tests/test_cli.c b/tests/test_cli.c
index c1f9d4e82..cc0de91a2 100644
--- a/tests/test_cli.c
+++ b/tests/test_cli.c
@@ -4670,6 +4670,33 @@ TEST(cli_agent_reinstall_preserves_foreign_policy_entries) {
     PASS();
 }
 
+/* Regression for #1388: a hook client blocked by a daemon BUILD CONFLICT must
+ * emit a stdout systemMessage. stdout is the only channel a hook caller sees,
+ * so the pre-fix stderr-only reporting was indistinguishable from "no matches"
+ * and produced silent skips for the whole session. The absent-daemon notice
+ * must stay distinct: it points at `daemon start`, which cannot heal a build
+ * conflict. Non-Claude dialects take no bare stdout JSON at all. */
+TEST(cli_hook_conflict_emits_stdout_notice_issue1388) {
+    const char *conflict = cbm_hook_admission_notice(CBM_HOOK_ADMISSION_BUILD_CONFLICT, NULL);
+    ASSERT_NOT_NULL(conflict);
+    ASSERT_NOT_NULL(strstr(conflict, "systemMessage"));
+    ASSERT_NOT_NULL(strstr(conflict, "different build"));
+    /* The actionable step: a conflicted daemon must be STOPPED, not started. */
+    ASSERT_NOT_NULL(strstr(conflict, "daemon stop"));
+
+    const char *absent = cbm_hook_admission_notice(CBM_HOOK_ADMISSION_DAEMON_ABSENT, NULL);
+    ASSERT_NOT_NULL(absent);
+    ASSERT_NOT_NULL(strstr(absent, "daemon start"));
+    /* Distinct diagnoses: the conflict notice must never claim no daemon runs. */
+    ASSERT_TRUE(strcmp(conflict, absent) != 0);
+    ASSERT_NULL(strstr(conflict, "no CBM daemon is running"));
+
+    /* Other dialects do not consume a bare stdout JSON object. */
+    ASSERT_NULL(cbm_hook_admission_notice(CBM_HOOK_ADMISSION_BUILD_CONFLICT, "codex"));
+    ASSERT_NULL(cbm_hook_admission_notice(CBM_HOOK_ADMISSION_DAEMON_ABSENT, "codex"));
+    PASS();
+}
+
 TEST(cli_existing_agents_install_durable_child_context) {
     char tmpdir[256];
     snprintf(tmpdir, sizeof(tmpdir), "/tmp/cli-durable-agents-XXXXXX");
@@ -11936,6 +11963,7 @@ SUITE(cli) {
     RUN_TEST(cli_new_agent_install_plans_use_documented_paths);
     RUN_TEST(cli_new_agent_configs_use_documented_schemas);
     RUN_TEST(cli_agent_reinstall_preserves_foreign_policy_entries);
+    RUN_TEST(cli_hook_conflict_emits_stdout_notice_issue1388);
     RUN_TEST(cli_existing_agents_install_durable_child_context);
     RUN_TEST(cli_durable_profiles_follow_current_vendor_paths);
     RUN_TEST(cli_cline_data_dir_only_redirects_data_state);