ffi+drain: route OCaml diagnostics to logcat and trace apply call sites

flutter/lib/logseq_chat_native_bridge.dart

@@ -2,6 +2,7 @@ import 'dart:ffi';
 import 'dart:isolate';
 
 import 'package:ffi/ffi.dart';
+import 'package:flutter/foundation.dart';
 
 import 'lui_dispatch.dart';
 import 'native_effect_drain.dart';
@@ -228,6 +229,7 @@ final class LogseqChatNativeBridge
     required String message,
   }) {
     if (_runtimeScheduler.isCoreBusy) {
+      debugPrint('[NativeBridge] resolveEffect id=$id queued (core busy)');
       _runtimeScheduler.runUi(
         () => _apply(
           _resolveEffectWithMessage(
@@ -239,9 +241,14 @@ final class LogseqChatNativeBridge
       );
       return '';
     }
-    return _read(
+    debugPrint('[NativeBridge] resolveEffect id=$id call');
+    final result = _read(
       _resolveEffectWithMessage(id: id, succeeded: succeeded, message: message),
     );
+    debugPrint(
+      '[NativeBridge] resolveEffect id=$id returned chars=${result.length}',
+    );
+    return result;
   }
 
   Pointer<Utf8> _resolveEffectWithMessage({
@@ -260,12 +267,21 @@ final class LogseqChatNativeBridge
   @override
   String applySnapshot(String response) {
     if (_runtimeScheduler.isCoreBusy) {
+      debugPrint(
+        '[NativeBridge] applySnapshot queued (core busy) '
+        'chars=${response.length}',
+      );
       _runtimeScheduler.runUi(
         () => _apply(_applySnapshotWithResponse(response)),
       );
       return '';
     }
-    return _read(_applySnapshotWithResponse(response));
+    debugPrint('[NativeBridge] applySnapshot call chars=${response.length}');
+    final result = _read(_applySnapshotWithResponse(response));
+    debugPrint(
+      '[NativeBridge] applySnapshot returned chars=${result.length}',
+    );
+    return result;
   }
 
   Pointer<Utf8> _applySnapshotWithResponse(String response) {
@@ -280,12 +296,19 @@ final class LogseqChatNativeBridge
   @override
   String applyHostUpdate({required String kind, required String payload}) {
     if (_runtimeScheduler.isCoreBusy) {
+      debugPrint('[NativeBridge] applyHostUpdate kind=$kind queued (core busy)');
       _runtimeScheduler.runUi(
         () => _apply(_applyHostUpdateWithPayload(kind, payload)),
       );
       return '';
     }
-    return _read(_applyHostUpdateWithPayload(kind, payload));
+    debugPrint('[NativeBridge] applyHostUpdate kind=$kind call');
+    final result = _read(_applyHostUpdateWithPayload(kind, payload));
+    debugPrint(
+      '[NativeBridge] applyHostUpdate kind=$kind returned '
+      'chars=${result.length}',
+    );
+    return result;
   }
 
   Pointer<Utf8> _applyHostUpdateWithPayload(String kind, String payload) {

flutter/lib/native_effect_drain.dart

@@ -249,7 +249,9 @@ final class NativeEffectDrain {
 
   void _apply(String patch, String source) {
     if (patch.isNotEmpty) {
+      trace('applying patch from $source chars=${patch.length}');
       applyPatch(patch);
+      trace('applied patch from $source');
     } else {
       // An OCaml exception in a lui_* FFI call surfaces as an empty patch —
       // log the producer so a wedged pipeline is visible in the drain trace.

shared/native/logseq_chat_core_ffi.c

@@ -11,6 +11,19 @@
 #include <stdlib.h>
 #include <string.h>
 
+#ifdef __ANDROID__
+#include <android/log.h>
+#define LOGSEQ_CHAT_LOG(...) \
+  __android_log_print(ANDROID_LOG_ERROR, "logseq_chat", __VA_ARGS__)
+#else
+#define LOGSEQ_CHAT_LOG(...) \
+  do { \
+    fprintf(stderr, "logseq_chat: "); \
+    fprintf(stderr, __VA_ARGS__); \
+    fputc('\n', stderr); \
+  } while (0)
+#endif
+
 static pthread_once_t logseq_chat_runtime_once = PTHREAD_ONCE_INIT;
 static pthread_t logseq_chat_runtime_thread;
 static _Thread_local char *logseq_chat_response = NULL;
@@ -122,29 +135,27 @@ static const char *missing_lui_callback(void) {
    cannot ride back in-band — the host would try to parse it as a patch.
    An empty patch is silently skipped by the drain, which is exactly the
    wedge signature we hit when an exception wedged the pipeline: log the
-   exception to stderr (logcat on Android, console on iOS) so the failure
-   is diagnosable instead of invisible. */
+   exception via the platform logger (stderr does not reach logcat on
+   Android) so the failure is diagnosable instead of invisible. */
 static const char *lui_no_callback(const char *name) {
-  fprintf(stderr, "logseq_chat: OCaml LUI callback is not registered: %s\n",
-          name);
+  LOGSEQ_CHAT_LOG("OCaml LUI callback is not registered: %s", name);
   return missing_lui_callback();
 }
 
 static const char *lui_bad_argument(const char *name) {
-  fprintf(stderr, "logseq_chat: NULL argument passed to %s\n", name);
+  LOGSEQ_CHAT_LOG("NULL argument passed to %s", name);
   return missing_lui_callback();
 }
 
 static const char *lui_exception(const char *name, value result) {
   char *message = caml_format_exception(Extract_exception(result));
-  fprintf(stderr, "logseq_chat: OCaml exception in %s: %s\n",
-          name, message == NULL ? "(unprintable)" : message);
+  LOGSEQ_CHAT_LOG("OCaml exception in %s: %s",
+                  name, message == NULL ? "(unprintable)" : message);
   return missing_lui_callback();
 }
 
 static const char *lui_thread_registration_failed(void) {
-  fprintf(stderr, "logseq_chat: could not register calling thread "
-                  "with the OCaml runtime\n");
+  LOGSEQ_CHAT_LOG("could not register calling thread with the OCaml runtime");
   return missing_lui_callback();
 }
 
@@ -417,15 +428,14 @@ int64_t logseq_chat_lui_root_node(void) {
   if (registration < 0) return node;
   const value *callback = caml_named_value("logseq_chat_lui_root_node");
   if (callback == NULL) {
-    fprintf(stderr, "logseq_chat: OCaml LUI callback is not registered: "
-                    "logseq_chat_lui_root_node\n");
+    LOGSEQ_CHAT_LOG("OCaml LUI callback is not registered: "
+                    "logseq_chat_lui_root_node");
   } else {
     value result = caml_callback_exn(*callback, Val_unit);
     if (Is_exception_result(result)) {
       char *message = caml_format_exception(Extract_exception(result));
-      fprintf(stderr, "logseq_chat: OCaml exception in "
-                      "logseq_chat_lui_root_node: %s\n",
-              message == NULL ? "(unprintable)" : message);
+      LOGSEQ_CHAT_LOG("OCaml exception in logseq_chat_lui_root_node: %s",
+                      message == NULL ? "(unprintable)" : message);
     } else {
       node = Long_val(result);
     }