feat(gemini): persist and replay thoughtSignature with session namespace

- Add open-sse/services/thoughtSignatureStore.js managing LRU Map (2k) + SQLite kv table
- Store thoughtSignature with sessionId namespace and toolCallId fallback
- Replay cached signature by sessionId:tool_call_id to prevent multi-process collisions
- Normalize Antigravity sessionId to numeric int64 format

Co-Authored-By: Claude Code <noreply@anthropic.com>

open-sse/utils/stream.js

@@ -49,7 +49,8 @@ export function createSSEStream(options = {}) {
     connectionId = null,
     body = null,
     onStreamComplete = null,
-    apiKey = null
+    apiKey = null,
+    credentials = null
   } = options;
 
   let buffer = "";
@@ -59,7 +60,7 @@ export function createSSEStream(options = {}) {
   const decoder = new TextDecoder("utf-8", { fatal: false });
 
   const state = mode === STREAM_MODE.TRANSLATE
-    ? { ...initState(sourceFormat), provider, toolNameMap, customToolNames: new Set(customToolNames || []), model }
+    ? { ...initState(sourceFormat), provider, toolNameMap, customToolNames: new Set(customToolNames || []), model, sessionId: credentials?._clientSessionId || null }
     : null;
 
   let totalContentLength = 0;
@@ -487,7 +488,7 @@ export function createSSEStream(options = {}) {
   });
 }
 
-export function createSSETransformStreamWithLogger(targetFormat, sourceFormat, provider = null, reqLogger = null, toolNameMap = null, model = null, connectionId = null, body = null, onStreamComplete = null, apiKey = null, customToolNames = null) {
+export function createSSETransformStreamWithLogger(targetFormat, sourceFormat, provider = null, reqLogger = null, toolNameMap = null, model = null, connectionId = null, body = null, onStreamComplete = null, apiKey = null, customToolNames = null, credentials = null) {
   return createSSEStream({
     mode: STREAM_MODE.TRANSLATE,
     targetFormat,
@@ -500,7 +501,8 @@ export function createSSETransformStreamWithLogger(targetFormat, sourceFormat, p
     connectionId,
     body,
     onStreamComplete,
-    apiKey
+    apiKey,
+    credentials
   });
 }