diff --git a/packages/core/src/ide/ide-client.test.ts b/packages/core/src/ide/ide-client.test.ts
index 7ec7e53124..64bfc022b1 100644
--- a/packages/core/src/ide/ide-client.test.ts
+++ b/packages/core/src/ide/ide-client.test.ts
@@ -23,6 +23,7 @@ import { StdioClientTransport } from '@modelcontextprotocol/sdk/client/stdio.js'
 import { detectIde, IDE_DEFINITIONS } from './detect-ide.js';
 import * as os from 'node:os';
 import * as path from 'node:path';
+import { getIdeServerHost } from './ide-client.js';
 
 vi.mock('node:fs', async (importOriginal) => {
   const actual = await importOriginal<typeof fs>();
@@ -34,7 +35,7 @@ vi.mock('node:fs', async (importOriginal) => {
       readdir: vi.fn(),
     },
     realpathSync: (p: string) => p,
-    existsSync: () => false,
+    existsSync: vi.fn(() => false),
   };
 });
 vi.mock('./process-utils.js');
@@ -110,7 +111,7 @@ describe('IdeClient', () => {
       await ideClient.connect();
 
       expect(fs.promises.readFile).toHaveBeenCalledWith(
-        path.join('/tmp/', 'gemini-ide-server-12345.json'),
+        path.join('/tmp', 'gemini', 'ide', 'gemini-ide-server-12345.json'),
         'utf8',
       );
       expect(StreamableHTTPClientTransport).toHaveBeenCalledWith(
@@ -277,7 +278,7 @@ describe('IdeClient', () => {
 
       expect(result).toEqual(config);
       expect(fs.promises.readFile).toHaveBeenCalledWith(
-        path.join('/tmp', 'gemini-ide-server-12345.json'),
+        path.join('/tmp', 'gemini', 'ide', 'gemini-ide-server-12345.json'),
         'utf8',
       );
     });
@@ -324,7 +325,7 @@ describe('IdeClient', () => {
 
       expect(result).toEqual(config);
       expect(fs.promises.readFile).toHaveBeenCalledWith(
-        path.join('/tmp/gemini/ide', 'gemini-ide-server-12345-123.json'),
+        path.join('/tmp', 'gemini', 'ide', 'gemini-ide-server-12345-123.json'),
         'utf8',
       );
     });
@@ -517,11 +518,11 @@ describe('IdeClient', () => {
 
       expect(result).toEqual(validConfig);
       expect(fs.promises.readFile).toHaveBeenCalledWith(
-        path.join('/tmp/gemini/ide', 'gemini-ide-server-12345-111.json'),
+        path.join('/tmp', 'gemini', 'ide', 'gemini-ide-server-12345-111.json'),
         'utf8',
       );
       expect(fs.promises.readFile).not.toHaveBeenCalledWith(
-        path.join('/tmp/gemini/ide', 'not-a-config-file.txt'),
+        path.join('/tmp', 'gemini', 'ide', 'not-a-config-file.txt'),
         'utf8',
       );
     });
@@ -956,3 +957,178 @@ describe('IdeClient', () => {
     });
   });
 });
+
+describe('getIdeServerHost', () => {
+  let existsSyncMock: Mock;
+  let originalSshConnection: string | undefined;
+  let originalVscodeRemoteSession: string | undefined;
+  let originalRemoteContainers: string | undefined;
+
+  beforeEach(() => {
+    existsSyncMock = vi.mocked(fs.existsSync);
+    existsSyncMock.mockClear();
+    originalSshConnection = process.env['SSH_CONNECTION'];
+    originalVscodeRemoteSession =
+      process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    originalRemoteContainers = process.env['REMOTE_CONTAINERS'];
+
+    delete process.env['SSH_CONNECTION'];
+    delete process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    delete process.env['REMOTE_CONTAINERS'];
+  });
+
+  afterEach(() => {
+    vi.clearAllMocks();
+    if (originalSshConnection !== undefined) {
+      process.env['SSH_CONNECTION'] = originalSshConnection;
+    } else {
+      delete process.env['SSH_CONNECTION'];
+    }
+    if (originalVscodeRemoteSession !== undefined) {
+      process.env['VSCODE_REMOTE_CONTAINERS_SESSION'] =
+        originalVscodeRemoteSession;
+    } else {
+      delete process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    }
+    if (originalRemoteContainers !== undefined) {
+      process.env['REMOTE_CONTAINERS'] = originalRemoteContainers;
+    } else {
+      delete process.env['REMOTE_CONTAINERS'];
+    }
+  });
+
+  // Helper to set existsSync mock behavior
+  const setupFsMocks = (
+    dockerenvExists: boolean,
+    containerenvExists: boolean,
+  ) => {
+    existsSyncMock.mockImplementation((path: string) => {
+      if (path === '/.dockerenv') {
+        return dockerenvExists;
+      }
+      if (path === '/run/.containerenv') {
+        return containerenvExists;
+      }
+      return false;
+    });
+  };
+
+  it('should return 127.0.0.1 when not in container and no SSH_CONNECTION or Dev Container env vars', () => {
+    setupFsMocks(false, false);
+    delete process.env['SSH_CONNECTION'];
+    delete process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    delete process.env['REMOTE_CONTAINERS'];
+    expect(getIdeServerHost()).toBe('127.0.0.1');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/run/.containerenv');
+  });
+
+  it('should return 127.0.0.1 when not in container but SSH_CONNECTION is set', () => {
+    setupFsMocks(false, false);
+    process.env['SSH_CONNECTION'] = 'some_ssh_value';
+    delete process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    delete process.env['REMOTE_CONTAINERS'];
+    expect(getIdeServerHost()).toBe('127.0.0.1');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/run/.containerenv');
+  });
+
+  it('should return host.docker.internal when in .dockerenv container and no SSH_CONNECTION or Dev Container env vars', () => {
+    setupFsMocks(true, false);
+    delete process.env['SSH_CONNECTION'];
+    delete process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    delete process.env['REMOTE_CONTAINERS'];
+    expect(getIdeServerHost()).toBe('host.docker.internal');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).not.toHaveBeenCalledWith(
+      '/run/.containerenv',
+    ); // Short-circuiting
+  });
+
+  it('should return 127.0.0.1 when in .dockerenv container and SSH_CONNECTION is set', () => {
+    setupFsMocks(true, false);
+    process.env['SSH_CONNECTION'] = 'some_ssh_value';
+    delete process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    delete process.env['REMOTE_CONTAINERS'];
+    expect(getIdeServerHost()).toBe('127.0.0.1');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).not.toHaveBeenCalledWith(
+      '/run/.containerenv',
+    ); // Short-circuiting
+  });
+
+  it('should return 127.0.0.1 when in .dockerenv container and VSCODE_REMOTE_CONTAINERS_SESSION is set', () => {
+    setupFsMocks(true, false);
+    delete process.env['SSH_CONNECTION'];
+    process.env['VSCODE_REMOTE_CONTAINERS_SESSION'] = 'some_session_id';
+    expect(getIdeServerHost()).toBe('127.0.0.1');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).not.toHaveBeenCalledWith(
+      '/run/.containerenv',
+    ); // Short-circuiting
+  });
+
+  it('should return host.docker.internal when in .containerenv container and no SSH_CONNECTION or Dev Container env vars', () => {
+    setupFsMocks(false, true);
+    delete process.env['SSH_CONNECTION'];
+    delete process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    delete process.env['REMOTE_CONTAINERS'];
+    expect(getIdeServerHost()).toBe('host.docker.internal');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/run/.containerenv');
+  });
+
+  it('should return 127.0.0.1 when in .containerenv container and SSH_CONNECTION is set', () => {
+    setupFsMocks(false, true);
+    process.env['SSH_CONNECTION'] = 'some_ssh_value';
+    delete process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    delete process.env['REMOTE_CONTAINERS'];
+    expect(getIdeServerHost()).toBe('127.0.0.1');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/run/.containerenv');
+  });
+
+  it('should return 127.0.0.1 when in .containerenv container and REMOTE_CONTAINERS is set', () => {
+    setupFsMocks(false, true);
+    delete process.env['SSH_CONNECTION'];
+    process.env['REMOTE_CONTAINERS'] = 'true';
+    expect(getIdeServerHost()).toBe('127.0.0.1');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/run/.containerenv');
+  });
+
+  it('should return host.docker.internal when in both containers and no SSH_CONNECTION or Dev Container env vars', () => {
+    setupFsMocks(true, true);
+    delete process.env['SSH_CONNECTION'];
+    delete process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    delete process.env['REMOTE_CONTAINERS'];
+    expect(getIdeServerHost()).toBe('host.docker.internal');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).not.toHaveBeenCalledWith(
+      '/run/.containerenv',
+    ); // Short-circuiting
+  });
+
+  it('should return 127.0.0.1 when in both containers and SSH_CONNECTION is set', () => {
+    setupFsMocks(true, true);
+    process.env['SSH_CONNECTION'] = 'some_ssh_value';
+    delete process.env['VSCODE_REMOTE_CONTAINERS_SESSION'];
+    delete process.env['REMOTE_CONTAINERS'];
+    expect(getIdeServerHost()).toBe('127.0.0.1');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).not.toHaveBeenCalledWith(
+      '/run/.containerenv',
+    ); // Short-circuiting
+  });
+
+  it('should return 127.0.0.1 when in both containers and VSCODE_REMOTE_CONTAINERS_SESSION is set', () => {
+    setupFsMocks(true, true);
+    delete process.env['SSH_CONNECTION'];
+    process.env['VSCODE_REMOTE_CONTAINERS_SESSION'] = 'some_session_id';
+    expect(getIdeServerHost()).toBe('127.0.0.1');
+    expect(vi.mocked(fs.existsSync)).toHaveBeenCalledWith('/.dockerenv');
+    expect(vi.mocked(fs.existsSync)).not.toHaveBeenCalledWith(
+      '/run/.containerenv',
+    ); // Short-circuiting
+  });
+});
diff --git a/packages/core/src/ide/ide-client.ts b/packages/core/src/ide/ide-client.ts
index d8e0577e28..a4d9234bd0 100644
--- a/packages/core/src/ide/ide-client.ts
+++ b/packages/core/src/ide/ide-client.ts
@@ -585,6 +585,8 @@ export class IdeClient {
     try {
       const portFile = path.join(
         os.tmpdir(),
+        'gemini',
+        'ide',
         `gemini-ide-server-${this.ideProcessInfo.pid}.json`,
       );
       const portFileContents = await fs.promises.readFile(portFile, 'utf8');
@@ -671,11 +673,11 @@ export class IdeClient {
     return validWorkspaces[0];
   }
 
-  private createProxyAwareFetch() {
-    // ignore proxy for '127.0.0.1' by default to allow connecting to the ide mcp server
+  private async createProxyAwareFetch(ideServerHost: string) {
+    // ignore proxy for the IDE server host to allow connecting to the ide mcp server
     const existingNoProxy = process.env['NO_PROXY'] || '';
     const agent = new EnvHttpProxyAgent({
-      noProxy: [existingNoProxy, '127.0.0.1'].filter(Boolean).join(','),
+      noProxy: [existingNoProxy, ideServerHost].filter(Boolean).join(','),
     });
     const undiciPromise = import('undici');
     // Suppress unhandled rejection if the promise is not awaited immediately.
@@ -777,23 +779,28 @@ export class IdeClient {
   private async establishHttpConnection(port: string): Promise<boolean> {
     let transport: StreamableHTTPClientTransport | undefined;
     try {
+      const ideServerHost = getIdeServerHost();
+      const portNumber = parseInt(port, 10);
+      // validate port to prevent Server-Side Request Forgery (SSRF) vulnerability
+      if (isNaN(portNumber) || portNumber <= 0 || portNumber > 65535) {
+        return false;
+      }
+      const serverUrl = `http://${ideServerHost}:${portNumber}/mcp`;
       logger.debug('Attempting to connect to IDE via HTTP SSE');
+      logger.debug(`Server URL: ${serverUrl}`);
       this.client = new Client({
         name: 'streamable-http-client',
         // TODO(#3487): use the CLI version here.
         version: '1.0.0',
       });
-      transport = new StreamableHTTPClientTransport(
-        new URL(`http://${getIdeServerHost()}:${port}/mcp`),
-        {
-          fetch: this.createProxyAwareFetch(),
-          requestInit: {
-            headers: this.authToken
-              ? { Authorization: `Bearer ${this.authToken}` }
-              : {},
-          },
+      transport = new StreamableHTTPClientTransport(new URL(serverUrl), {
+        fetch: await this.createProxyAwareFetch(ideServerHost),
+        requestInit: {
+          headers: this.authToken
+            ? { Authorization: `Bearer ${this.authToken}` }
+            : {},
         },
-      );
+      });
       await this.client.connect(transport);
       this.registerClientHandlers();
       await this.discoverTools();
@@ -846,8 +853,31 @@ export class IdeClient {
   }
 }
 
-function getIdeServerHost() {
-  const isInContainer =
-    fs.existsSync('/.dockerenv') || fs.existsSync('/run/.containerenv');
-  return isInContainer ? 'host.docker.internal' : '127.0.0.1';
+export function getIdeServerHost() {
+  let host: string;
+  host = '127.0.0.1';
+  if (isInContainer()) {
+    // when ssh-connection (e.g. remote-ssh) or devcontainer setup:
+    // --> host must be '127.0.0.1' to have cli companion working
+    if (!isSshConnected() && !isDevContainer()) {
+      host = 'host.docker.internal';
+    }
+  }
+  logger.debug(`[getIdeServerHost] Mapping IdeServerHost to '${host}'`);
+  return host;
+}
+
+function isInContainer() {
+  return fs.existsSync('/.dockerenv') || fs.existsSync('/run/.containerenv');
+}
+
+function isSshConnected() {
+  return !!process.env['SSH_CONNECTION'];
+}
+
+function isDevContainer() {
+  return !!(
+    process.env['VSCODE_REMOTE_CONTAINERS_SESSION'] ||
+    process.env['REMOTE_CONTAINERS']
+  );
 }