feat: improve AI agent detection for MCP server

### Description
Improve the reliability of AI agent detection when running as an MCP server by utilizing the client information provided during the MCP `initialize` request. This replaces the reliance on environment variables which were proving to be unreliable in some environments.

### Scenarios Tested
- Verified that `detectAIAgent` returns "unknown" by default.
- Verified that `detectAIAgent` returns mapped name from env vars.
- Verified that `detectAIAgent` returns normalized MCP client name when in MCP mode.
- Verified that it falls back to env vars if no client name is set in MCP mode.
- Verified that MCP client name is ignored if not in MCP mode.

### Sample Commands
Ran unit tests:
npx mocha src/env.spec.ts

Author: joehan

src/env.spec.ts

@@ -0,0 +1,55 @@
+import { expect } from "chai";
+import { detectAIAgent, setFirebaseMcp, setMcpClientName } from "./env";
+
+describe("env", () => {
+  const originalEnv = { ...process.env };
+
+  beforeEach(() => {
+    // Clear all well-known env vars
+    delete process.env.ANTIGRAVITY_CLI_ALIAS;
+    delete process.env.CLAUDECODE;
+    delete process.env.CLINE_ACTIVE;
+    delete process.env.CODEX_SANDBOX;
+    delete process.env.CURSOR_AGENT;
+    delete process.env.GEMINI_CLI;
+    delete process.env.OPENCODE;
+    
+    setFirebaseMcp(false);
+    // We can't easily reset module-level variables if they don't have a reset function,
+    // but passing empty string will make it falsy in detectAIAgent.
+    setMcpClientName("");
+  });
+
+  afterEach(() => {
+    process.env = { ...originalEnv };
+  });
+
+  describe("detectAIAgent", () => {
+    it("should return unknown by default", () => {
+      expect(detectAIAgent()).to.equal("unknown");
+    });
+
+    it("should detect agent from env var", () => {
+      process.env.CURSOR_AGENT = "true";
+      expect(detectAIAgent()).to.equal("cursor");
+    });
+
+    it("should detect agent from MCP client name when in MCP mode", () => {
+      setFirebaseMcp(true);
+      setMcpClientName("Claude Desktop");
+      expect(detectAIAgent()).to.equal("claude_desktop");
+    });
+
+    it("should fallback to env vars if in MCP mode but no client name set", () => {
+      setFirebaseMcp(true);
+      process.env.CURSOR_AGENT = "true";
+      expect(detectAIAgent()).to.equal("cursor");
+    });
+
+    it("should ignore MCP client name if not in MCP mode", () => {
+      setMcpClientName("Claude Desktop");
+      process.env.CURSOR_AGENT = "true";
+      expect(detectAIAgent()).to.equal("cursor");
+    });
+  });
+});

src/env.ts

@@ -17,8 +17,17 @@ export function setFirebaseMcp(value: boolean) {
   isFirebaseMcpFlag = value;
 }
 
+let mcpClientNameFlag: string | undefined;
+
+export function setMcpClientName(name: string) {
+  mcpClientNameFlag = name;
+}
+
 // Detect if the CLI was invoked by a coding agent, based on well-known env vars.
 export function detectAIAgent(): string {
+  if (isFirebaseMcp() && mcpClientNameFlag) {
+    return mcpClientNameFlag.toLowerCase().replace(/ /g, "_");
+  }
   if (process.env.ANTIGRAVITY_CLI_ALIAS) return "antigravity";
   if (process.env.CLAUDECODE) return "claude_code";
   if (process.env.CLINE_ACTIVE) return "cline";

src/mcp/index.ts

@@ -30,7 +30,7 @@ import { Config } from "../config";
 import { configstore } from "../configstore";
 import { EmulatorHubClient } from "../emulator/hubClient";
 import { Emulators } from "../emulator/types";
-import { isFirebaseStudio } from "../env";
+import { isFirebaseStudio, setMcpClientName } from "../env";
 import { Options } from "../options";
 import { getProjectId } from "../projectUtils";
 import { loadRC } from "../rc";
@@ -131,6 +131,7 @@ export class FirebaseMcpServer {
       const clientInfo = this.server.getClientVersion();
       this.clientInfo = clientInfo;
       if (clientInfo?.name) {
+        setMcpClientName(clientInfo.name);
         void this.trackGA4("mcp_client_connected");
       }
       if (!this.clientInfo?.name) this.clientInfo = { name: "<unknown-client>" };