refactor: extract MCP config handling to use temp files on Windows

cli/src/claude/claudeLocal.ts

@@ -3,6 +3,7 @@ import { logger } from "@/ui/logger";
 import { restoreTerminalState } from "@/ui/terminalState";
 import { claudeCheckSession } from "./utils/claudeCheckSession";
 import { getProjectPath } from "./utils/path";
+import { appendMcpConfigArg } from "./utils/mcpConfig";
 import { systemPrompt } from "./utils/systemPrompt";
 import { withBunRuntimeEnv } from "@/utils/bunRuntime";
 import { spawnWithAbort } from "@/utils/spawnWithAbort";
@@ -41,6 +42,7 @@ export async function claudeLocal(opts: {
     }
 
     // Spawn the process
+    let cleanupMcpConfig: (() => void) | null = null;
     try {
         // Start the interactive process
         process.stdin.pause();
@@ -54,9 +56,9 @@ export async function claudeLocal(opts: {
             
             args.push('--append-system-prompt', systemPrompt);
 
-            if (opts.mcpServers && Object.keys(opts.mcpServers).length > 0) {
-                args.push('--mcp-config', JSON.stringify({ mcpServers: opts.mcpServers }));
-            }
+            cleanupMcpConfig = appendMcpConfigArg(args, opts.mcpServers, {
+                baseDir: projectDir
+            });
 
             if (opts.allowedTools && opts.allowedTools.length > 0) {
                 args.push('--allowedTools', opts.allowedTools.join(','));
@@ -96,6 +98,7 @@ export async function claudeLocal(opts: {
             }).then(r).catch(reject);
         });
     } finally {
+        cleanupMcpConfig?.();
         process.stdin.resume();
         restoreTerminalState();
     }

cli/src/claude/sdk/query.ts

@@ -27,6 +27,7 @@ import { withBunRuntimeEnv } from '@/utils/bunRuntime'
 import { killProcessByChildProcess } from '@/utils/process'
 import type { Writable } from 'node:stream'
 import { logger } from '@/ui/logger'
+import { appendMcpConfigArg } from '../utils/mcpConfig'
 
 /**
  * Query class manages Claude Code process interaction
@@ -285,6 +286,7 @@ export function query(config: {
 
     // Build command arguments
     const args = ['--output-format', 'stream-json', '--verbose']
+    let cleanupMcpConfig: (() => void) | null = null
 
     if (customSystemPrompt) args.push('--system-prompt', customSystemPrompt)
     if (appendSystemPrompt) args.push('--append-system-prompt', appendSystemPrompt)
@@ -301,9 +303,6 @@ export function query(config: {
     if (settingsPath) args.push('--settings', settingsPath)
     if (allowedTools.length > 0) args.push('--allowedTools', allowedTools.join(','))
     if (disallowedTools.length > 0) args.push('--disallowedTools', disallowedTools.join(','))
-    if (mcpServers && Object.keys(mcpServers).length > 0) {
-        args.push('--mcp-config', JSON.stringify({ mcpServers }))
-    }
     if (strictMcpConfig) args.push('--strict-mcp-config')
     if (permissionMode) args.push('--permission-mode', permissionMode)
 
@@ -334,6 +333,8 @@ export function query(config: {
     const spawnCommand = pathToClaudeCodeExecutable
     const spawnArgs = args
 
+    cleanupMcpConfig = appendMcpConfigArg(spawnArgs, mcpServers)
+
     // Spawn Claude Code process
     // Use clean env for global claude to avoid local node_modules/.bin taking precedence
     const baseEnv = isCommandOnly ? getCleanEnv() : process.env
@@ -394,6 +395,7 @@ export function query(config: {
 
     // Handle process errors
     child.on('error', (error) => {
+        cleanupMcpConfig?.()
         if (config.options?.abort?.aborted) {
             query.setError(new AbortError('Claude Code process aborted by user'))
         } else {
@@ -408,6 +410,7 @@ export function query(config: {
         if (process.env.CLAUDE_SDK_MCP_SERVERS) {
             delete process.env.CLAUDE_SDK_MCP_SERVERS
         }
+        cleanupMcpConfig?.()
     })
 
     return query

cli/src/claude/utils/mcpConfig.ts

@@ -0,0 +1,58 @@
+import { mkdirSync, unlinkSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+export type McpConfigArg = {
+    value: string;
+    cleanup?: () => void;
+};
+
+export type McpConfigOptions = {
+    useFile?: boolean;
+    baseDir?: string;
+};
+
+export function resolveMcpConfigArg(
+    mcpServers: Record<string, unknown>,
+    options?: McpConfigOptions
+): McpConfigArg {
+    const configJson = JSON.stringify({ mcpServers });
+    const useFile = options?.useFile ?? process.platform === 'win32';
+    if (!useFile) {
+        return { value: configJson };
+    }
+
+    const dir = options?.baseDir ?? tmpdir();
+    mkdirSync(dir, { recursive: true });
+
+    const filePath = join(
+        dir,
+        `mcp-config-${process.pid}-${Date.now()}-${Math.random().toString(16).slice(2)}.json`
+    );
+    writeFileSync(filePath, configJson, "utf8");
+
+    return {
+        value: filePath,
+        cleanup: () => {
+            try {
+                unlinkSync(filePath);
+            } catch {
+                // Ignore cleanup errors; config file is optional and short-lived.
+            }
+        }
+    };
+}
+
+export function appendMcpConfigArg(
+    args: string[],
+    mcpServers?: Record<string, unknown>,
+    options?: McpConfigOptions
+): (() => void) | null {
+    if (!mcpServers || Object.keys(mcpServers).length === 0) {
+        return null;
+    }
+
+    const { value, cleanup } = resolveMcpConfigArg(mcpServers, options);
+    args.push('--mcp-config', value);
+    return cleanup ?? null;
+}