chore(node): preserve pre-canonicalization experiment snapshot

Historical working copy retained for audit before consolidation into main. The canonicalized plugin architecture and later fixes already live in main; this snapshot is not a release or a request to restore obsolete source layout.

src/k1link/web/runtime_diagnostics.py

@@ -18,6 +18,7 @@ _EXTRA_FIELDS: Final = (
     "connection_mode",
     "error_category",
     "error_code",
+    "transport_error_code",
     "reason_code",
     "failed_phase",
     "dialogue_stage",
@@ -32,6 +33,20 @@ _EXTRA_FIELDS: Final = (
     "device_write_confirmed",
     "ble_att_error_code",
     "ble_att_error_name",
+    "resolved_write_mode",
+    "max_write_without_response_size",
+    "mtu_size",
+    "frame_length",
+    "bridge_frame_length",
+    "quick_connect_frame_length",
+    "scan_elapsed_ms",
+    "scanner_start_ms",
+    "initial_window_ms",
+    "first_candidate_ms",
+    "scan_extended",
+    "candidate_count",
+    "likely_k1_candidate_count",
+    "discovery_generation",
     "helper_stage",
     "helper_elapsed_ms",
     "status_reconciliation",
@@ -102,6 +117,26 @@ class ScannerDiagnosticJsonFormatter(logging.Formatter):
             value = getattr(record, field, None)
             if value is not None and isinstance(value, (str, int, bool)):
                 document[field] = value
+        if record.exc_info is not None:
+            exception_type, _exception, traceback = record.exc_info
+            if exception_type is not None:
+                document["exception_type"] = exception_type.__name__[:128]
+            if traceback is not None:
+                while traceback.tb_next is not None:
+                    traceback = traceback.tb_next
+                code = traceback.tb_frame.f_code
+                # Preserve the failure location, never exception text, locals,
+                # source lines or absolute paths that may contain private data.
+                document["exception_site"] = (
+                    f"{Path(code.co_filename).name}:{traceback.tb_lineno}:{code.co_name}"
+                )[:256]
+        properties = getattr(record, "write_characteristic_properties", None)
+        if isinstance(properties, (list, tuple)) and all(
+            isinstance(value, str)
+            and value in {"read", "write", "write-without-response", "notify", "indicate"}
+            for value in properties
+        ):
+            document["write_characteristic_properties"] = sorted(set(properties))
         return json.dumps(document, ensure_ascii=False, separators=(",", ":"))