fix: harden browser existing-session flows

src/browser/chrome-mcp.ts

@@ -39,6 +39,7 @@ const DEFAULT_CHROME_MCP_ARGS = [
 ];
 
 const sessions = new Map<string, ChromeMcpSession>();
+const pendingSessions = new Map<string, Promise<ChromeMcpSession>>();
 let sessionFactory: ChromeMcpSessionFactory | null = null;
 
 function asRecord(value: unknown): Record<string, unknown> | null {
@@ -144,6 +145,11 @@ function extractMessageText(result: ChromeMcpToolResult): string {
   return blocks.find((block) => block.trim()) ?? "";
 }
 
+function extractToolErrorMessage(result: ChromeMcpToolResult, name: string): string {
+  const message = extractMessageText(result).trim();
+  return message || `Chrome MCP tool "${name}" failed.`;
+}
+
 function extractJsonMessage(result: ChromeMcpToolResult): unknown {
   const candidates = [extractMessageText(result), ...extractTextContent(result)].filter((text) =>
     text.trim(),
@@ -207,8 +213,22 @@ async function getSession(profileName: string): Promise<ChromeMcpSession> {
     session = undefined;
   }
   if (!session) {
-    session = await (sessionFactory ?? createRealSession)(profileName);
-    sessions.set(profileName, session);
+    let pending = pendingSessions.get(profileName);
+    if (!pending) {
+      pending = (async () => {
+        const created = await (sessionFactory ?? createRealSession)(profileName);
+        sessions.set(profileName, created);
+        return created;
+      })();
+      pendingSessions.set(profileName, pending);
+    }
+    try {
+      session = await pending;
+    } finally {
+      if (pendingSessions.get(profileName) === pending) {
+        pendingSessions.delete(profileName);
+      }
+    }
   }
   try {
     await session.ready;
@@ -229,10 +249,14 @@ async function callTool(
 ): Promise<ChromeMcpToolResult> {
   const session = await getSession(profileName);
   try {
-    return (await session.client.callTool({
+    const result = (await session.client.callTool({
       name,
       arguments: args,
     })) as ChromeMcpToolResult;
+    if (result.isError) {
+      throw new Error(extractToolErrorMessage(result, name));
+    }
+    return result;
   } catch (err) {
     sessions.delete(profileName);
     await session.client.close().catch(() => {});
@@ -268,6 +292,7 @@ export function getChromeMcpPid(profileName: string): number | null {
 }
 
 export async function closeChromeMcpSession(profileName: string): Promise<boolean> {
+  pendingSessions.delete(profileName);
   const session = sessions.get(profileName);
   if (!session) {
     return false;
@@ -508,5 +533,6 @@ export function setChromeMcpSessionFactoryForTest(factory: ChromeMcpSessionFacto
 
 export async function resetChromeMcpSessionsForTest(): Promise<void> {
   sessionFactory = null;
+  pendingSessions.clear();
   await stopAllChromeMcpSessions();
 }