2 files changed, 102 insertions, 16 deletions

diff --git a/packages/core/src/ide/ide-client.ts b/packages/core/src/ide/ide-client.ts
index fe605eb2..94107f21 100644
--- a/packages/core/src/ide/ide-client.ts
+++ b/packages/core/src/ide/ide-client.ts
@@ -5,7 +5,6 @@
  */
 
 import * as fs from 'node:fs';
-import * as path from 'node:path';
 import { detectIde, DetectedIde, getIdeInfo } from '../ide/detect-ide.js';
 import {
   ideContext,
@@ -15,8 +14,11 @@ import {
   CloseDiffResponseSchema,
   DiffUpdateResult,
 } from '../ide/ideContext.js';
+import { getIdeProcessId } from './process-utils.js';
 import { Client } from '@modelcontextprotocol/sdk/client/index.js';
 import { StreamableHTTPClientTransport } from '@modelcontextprotocol/sdk/client/streamableHttp.js';
+import * as os from 'node:os';
+import * as path from 'node:path';
 
 const logger = {
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -95,12 +97,27 @@ export class IdeClient {
       return;
     }
 
-    const port = this.getPortFromEnv();
-    if (!port) {
-      return;
+    const portFromFile = await this.getPortFromFile();
+    if (portFromFile) {
+      const connected = await this.establishConnection(portFromFile);
+      if (connected) {
+        return;
+      }
     }
 
-    await this.establishConnection(port);
+    const portFromEnv = this.getPortFromEnv();
+    if (portFromEnv) {
+      const connected = await this.establishConnection(portFromEnv);
+      if (connected) {
+        return;
+      }
+    }
+
+    this.setState(
+      IDEConnectionStatus.Disconnected,
+      `Failed to connect to IDE companion extension for ${this.currentIdeDisplayName}. Please ensure the extension is running and try restarting your terminal. To install the extension, run /ide install.`,
+      true,
+    );
   }
 
   /**
@@ -264,16 +281,26 @@ export class IdeClient {
   private getPortFromEnv(): string | undefined {
     const port = process.env['GEMINI_CLI_IDE_SERVER_PORT'];
     if (!port) {
-      this.setState(
-        IDEConnectionStatus.Disconnected,
-        `Failed to connect to IDE companion extension for ${this.currentIdeDisplayName}. Please ensure the extension is running and try restarting your terminal. To install the extension, run /ide install.`,
-        true,
-      );
       return undefined;
     }
     return port;
   }
 
+  private async getPortFromFile(): Promise<string | undefined> {
+    try {
+      const ideProcessId = await getIdeProcessId();
+      const portFile = path.join(
+        os.tmpdir(),
+        `gemini-ide-server-${ideProcessId}.json`,
+      );
+      const portFileContents = await fs.promises.readFile(portFile, 'utf8');
+      const port = JSON.parse(portFileContents).port;
+      return port.toString();
+    } catch (_) {
+      return undefined;
+    }
+  }
+
   private registerClientHandlers() {
     if (!this.client) {
       return;
@@ -328,7 +355,7 @@ export class IdeClient {
     );
   }
 
-  private async establishConnection(port: string) {
+  private async establishConnection(port: string): Promise<boolean> {
     let transport: StreamableHTTPClientTransport | undefined;
     try {
       this.client = new Client({
@@ -342,12 +369,8 @@ export class IdeClient {
       await this.client.connect(transport);
       this.registerClientHandlers();
       this.setState(IDEConnectionStatus.Connected);
+      return true;
     } catch (_error) {
-      this.setState(
-        IDEConnectionStatus.Disconnected,
-        `Failed to connect to IDE companion extension for ${this.currentIdeDisplayName}. Please ensure the extension is running and try restarting your terminal. To install the extension, run /ide install.`,
-        true,
-      );
       if (transport) {
         try {
           await transport.close();
@@ -355,6 +378,7 @@ export class IdeClient {
           logger.debug('Failed to close transport:', closeError);
         }
       }
+      return false;
     }
   }
 }
diff --git a/packages/core/src/ide/process-utils.ts b/packages/core/src/ide/process-utils.ts
new file mode 100644
index 00000000..40e16a73
--- /dev/null
+++ b/packages/core/src/ide/process-utils.ts
@@ -0,0 +1,62 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { exec } from 'child_process';
+import { promisify } from 'util';
+import os from 'os';
+
+const execAsync = promisify(exec);
+
+/**
+ * Traverses up the process tree from the current process to find the top-level ancestor process ID.
+ * This is useful for identifying the main application process that spawned the current script,
+ * such as the main VS Code window process.
+ *
+ * @returns A promise that resolves to the numeric PID of the top-level process.
+ * @throws Will throw an error if the underlying shell commands fail unexpectedly.
+ */
+export async function getIdeProcessId(): Promise<number> {
+  const platform = os.platform();
+  let currentPid = process.pid;
+
+  // Loop upwards through the process tree, with a depth limit to prevent infinite loops.
+  const MAX_TRAVERSAL_DEPTH = 32;
+  for (let i = 0; i < MAX_TRAVERSAL_DEPTH; i++) {
+    let parentPid: number;
+
+    try {
+      // Use wmic for Windows
+      if (platform === 'win32') {
+        const command = `wmic process where "ProcessId=${currentPid}" get ParentProcessId /value`;
+        const { stdout } = await execAsync(command);
+        const match = stdout.match(/ParentProcessId=(\d+)/);
+        parentPid = match ? parseInt(match[1], 10) : 0; // Top of the tree is 0
+      }
+      // Use ps for macOS, Linux, and other Unix-like systems
+      else {
+        const command = `ps -o ppid= -p ${currentPid}`;
+        const { stdout } = await execAsync(command);
+        const ppid = parseInt(stdout.trim(), 10);
+        parentPid = isNaN(ppid) ? 1 : ppid; // Top of the tree is 1
+      }
+    } catch (_) {
+      // This can happen if a process in the chain dies during execution.
+      // We'll break the loop and return the last valid PID we found.
+      break;
+    }
+
+    // Define the root PID for the current OS
+    const rootPid = platform === 'win32' ? 0 : 1;
+
+    // If the parent is the root process or invalid, we've found our target.
+    if (parentPid === rootPid || parentPid <= 0) {
+      break;
+    }
+    // Move one level up the tree for the next iteration.
+    currentPid = parentPid;
+  }
+  return currentPid;
+}