Write MCP debug logs to ~/.cache/firebase

CHANGELOG.md

@@ -1 +1,2 @@
+- Moved MCP server `firebase-debug.log` to `~/.cache/firebase/firebase-debug.log`. (#9982)
 - Added a prompt to `firebase init` to install Agent Skills for Firebase.

src/bin/mcp.ts

@@ -1,6 +1,8 @@
 #!/usr/bin/env node
 
-import { resolve } from "path";
+import { resolve, join } from "path";
+import { mkdir } from "fs/promises";
+import { homedir } from "os";
 import { parseArgs } from "util";
 import { useFileLogger } from "../logger";
 import { FirebaseMcpServer } from "../mcp/index";
@@ -50,7 +52,7 @@
   -h, --help                Show this help message.
 `;
 
 export async function mcp(): Promise<void> {
   const { values } = parseArgs({
     options: {
       only: { type: "string", default: "" },
@@ -84,7 +86,10 @@
   if (earlyExit) return;
 
   setFirebaseMcp(true);
-  useFileLogger();
+  // Write debug logs to ~/.cache/firebase to avoid polluting the user's project directory.
+  const mcpLogDir = join(homedir(), ".cache", "firebase");
+  await mkdir(mcpLogDir, { recursive: true });
+  useFileLogger(join(mcpLogDir, "firebase-debug.log"));
   const activeFeatures = (values.only || "")
     .split(",")
     .map((f) => f.trim())