feat(cliproxy): add ToolSanitizationProxy for Gemini 64-char limit

Fixes #219 - MCP tool names exceeding Gemini's 64-character limit
now get sanitized automatically.

- Add tool-name-sanitizer: dedupe segments + smart truncate with hash
- Add tool-name-mapper: bidirectional mapping for response restoration
- Add tool-sanitization-proxy: HTTP proxy layer for all CLIProxy providers
- Chain: Claude CLI → ToolSanitizationProxy → [CodexReasoningProxy] → CLIProxy
- Add unit tests for sanitizer and mapper modules

src/cliproxy/cliproxy-executor.ts

@@ -38,6 +38,7 @@ import { resolveProxyConfig, PROXY_CLI_FLAGS } from './proxy-config-resolver';
 import { getWebSearchHookEnv } from '../utils/websearch-manager';
 import { supportsModelConfig, isModelBroken, getModelIssueUrl, findModel } from './model-catalog';
 import { CodexReasoningProxy } from './codex-reasoning-proxy';
+import { ToolSanitizationProxy } from './tool-sanitization-proxy';
 import {
   findAccountByQuery,
   getProviderAccounts,
@@ -841,6 +842,37 @@ export async function execClaudeWithCLIProxy(
   // This adds thinking suffix like model(high) or model(8192) for CLIProxyAPIPlus
   applyThinkingConfig(envVars, provider, thinkingOverride);
 
+  // Tool sanitization proxy - applies to ALL CLIProxy providers.
+  // Sanitizes MCP tool names exceeding Gemini's 64-char limit.
+  // Chain: Claude CLI → ToolSanitizationProxy → [CodexReasoningProxy] → CLIProxy → Gemini
+  let toolSanitizationProxy: ToolSanitizationProxy | null = null;
+  let toolSanitizationPort: number | null = null;
+
+  if (envVars.ANTHROPIC_BASE_URL) {
+    try {
+      toolSanitizationProxy = new ToolSanitizationProxy({
+        upstreamBaseUrl: envVars.ANTHROPIC_BASE_URL,
+        verbose,
+        warnOnSanitize: true,
+      });
+      toolSanitizationPort = await toolSanitizationProxy.start();
+      log(`Tool sanitization proxy active on port ${toolSanitizationPort}`);
+    } catch (error) {
+      // Non-fatal: continue without sanitization
+      const err = error as Error;
+      toolSanitizationProxy = null;
+      toolSanitizationPort = null;
+      if (verbose) {
+        console.error(warn(`Tool sanitization proxy disabled: ${err.message}`));
+      }
+    }
+  }
+
+  // Determine the effective upstream URL after tool sanitization
+  const postSanitizationBaseUrl = toolSanitizationPort
+    ? `http://127.0.0.1:${toolSanitizationPort}`
+    : envVars.ANTHROPIC_BASE_URL;
+
   // Codex-only: inject OpenAI reasoning effort based on tier model mapping.
   // Maps by request.model:
   // - OPUS/default model → xhigh
@@ -850,7 +882,7 @@ export async function execClaudeWithCLIProxy(
   let codexReasoningProxy: CodexReasoningProxy | null = null;
   let codexReasoningPort: number | null = null;
   if (provider === 'codex') {
-    if (!envVars.ANTHROPIC_BASE_URL) {
+    if (!postSanitizationBaseUrl) {
       log('ANTHROPIC_BASE_URL not set for Codex, reasoning proxy disabled');
     } else {
       try {
@@ -861,7 +893,7 @@ export async function execClaudeWithCLIProxy(
         // because remote CLIProxyAPI uses root paths (/v1/messages), not provider-prefixed
         const stripPathPrefix = useRemoteProxy ? '/api/provider/codex' : undefined;
         codexReasoningProxy = new CodexReasoningProxy({
-          upstreamBaseUrl: envVars.ANTHROPIC_BASE_URL,
+          upstreamBaseUrl: postSanitizationBaseUrl,
           verbose,
           defaultEffort: 'medium',
           traceFilePath: traceEnabled
@@ -890,13 +922,22 @@ export async function execClaudeWithCLIProxy(
     }
   }
 
-  const effectiveEnvVars =
-    codexReasoningProxy && codexReasoningPort
-      ? {
-          ...envVars,
-          ANTHROPIC_BASE_URL: `http://127.0.0.1:${codexReasoningPort}/api/provider/codex`,
-        }
-      : envVars;
+  // Determine the final ANTHROPIC_BASE_URL based on active proxies
+  // Chain order: Claude CLI → [CodexReasoningProxy] → [ToolSanitizationProxy] → CLIProxy
+  // The outermost active proxy becomes the effective base URL
+  let finalBaseUrl = envVars.ANTHROPIC_BASE_URL;
+  if (toolSanitizationPort) {
+    finalBaseUrl = `http://127.0.0.1:${toolSanitizationPort}`;
+  }
+  if (codexReasoningPort) {
+    // Codex reasoning proxy is the outermost layer for codex provider
+    finalBaseUrl = `http://127.0.0.1:${codexReasoningPort}/api/provider/codex`;
+  }
+
+  const effectiveEnvVars = {
+    ...envVars,
+    ANTHROPIC_BASE_URL: finalBaseUrl,
+  };
   const webSearchEnv = getWebSearchHookEnv();
   const env = {
     ...process.env,
@@ -906,16 +947,12 @@ export async function execClaudeWithCLIProxy(
   };
 
   log(`Claude env: ANTHROPIC_BASE_URL=${effectiveEnvVars.ANTHROPIC_BASE_URL}`);
-  log(`Claude env: ANTHROPIC_MODEL=${effectiveEnvVars.ANTHROPIC_MODEL}`);
+  log(`Claude env: ANTHROPIC_MODEL=${envVars.ANTHROPIC_MODEL}`);
   if (Object.keys(webSearchEnv).length > 0) {
     log(`Claude env: WebSearch config=${JSON.stringify(webSearchEnv)}`);
   }
   // Log global env vars for visibility
-  if (
-    effectiveEnvVars.DISABLE_TELEMETRY ||
-    effectiveEnvVars.DISABLE_ERROR_REPORTING ||
-    effectiveEnvVars.DISABLE_BUG_COMMAND
-  ) {
+  if (envVars.DISABLE_TELEMETRY || envVars.DISABLE_ERROR_REPORTING || envVars.DISABLE_BUG_COMMAND) {
     log(`Claude env: Global env applied (telemetry/reporting disabled)`);
   }
 
@@ -983,6 +1020,10 @@ export async function execClaudeWithCLIProxy(
       codexReasoningProxy.stop();
     }
 
+    if (toolSanitizationProxy) {
+      toolSanitizationProxy.stop();
+    }
+
     if (httpsTunnel) {
       httpsTunnel.stop();
     }
@@ -1007,6 +1048,10 @@ export async function execClaudeWithCLIProxy(
       codexReasoningProxy.stop();
     }
 
+    if (toolSanitizationProxy) {
+      toolSanitizationProxy.stop();
+    }
+
     if (httpsTunnel) {
       httpsTunnel.stop();
     }
@@ -1026,6 +1071,10 @@ export async function execClaudeWithCLIProxy(
       codexReasoningProxy.stop();
     }
 
+    if (toolSanitizationProxy) {
+      toolSanitizationProxy.stop();
+    }
+
     if (httpsTunnel) {
       httpsTunnel.stop();
     }

src/cliproxy/index.ts

@@ -189,3 +189,19 @@ export {
   getSyncableProfileCount,
   isProfileSyncable,
 } from './sync';
+
+// Tool name sanitization (for Gemini 64-char limit compliance)
+export type { SanitizeResult } from './tool-name-sanitizer';
+export {
+  sanitizeToolName,
+  isValidToolName,
+  removeDuplicateSegments,
+  smartTruncate,
+  GEMINI_MAX_TOOL_NAME_LENGTH,
+} from './tool-name-sanitizer';
+
+export type { Tool, ToolUseBlock, ContentBlock, SanitizationChange } from './tool-name-mapper';
+export { ToolNameMapper } from './tool-name-mapper';
+
+export type { ToolSanitizationProxyConfig } from './tool-sanitization-proxy';
+export { ToolSanitizationProxy } from './tool-sanitization-proxy';

src/cliproxy/tool-name-mapper.ts

@@ -0,0 +1,153 @@
+/**
+ * Tool Name Mapper
+ *
+ * Bidirectional mapping class to track original ↔ sanitized tool names.
+ * Used to restore original names in API responses after sanitization.
+ *
+ * Flow:
+ * 1. Request: registerTools() sanitizes names and stores mapping
+ * 2. Response: restoreToolUse() restores original names using mapping
+ */
+
+import { sanitizeToolName, type SanitizeResult } from './tool-name-sanitizer';
+
+/** MCP tool definition from Claude API */
+export interface Tool {
+  name: string;
+  description?: string;
+  input_schema?: Record<string, unknown>;
+  [key: string]: unknown;
+}
+
+/** Tool use content block from Claude API response */
+export interface ToolUseBlock {
+  type: 'tool_use';
+  id: string;
+  name: string;
+  input: Record<string, unknown>;
+}
+
+/** Content block from Claude API response (union type) */
+export interface ContentBlock {
+  type: string;
+  [key: string]: unknown;
+}
+
+/** Record of a sanitization change */
+export interface SanitizationChange {
+  original: string;
+  sanitized: string;
+}
+
+/**
+ * Bidirectional mapper for tool name sanitization.
+ *
+ * Maintains a per-request mapping between sanitized and original tool names.
+ * Must be cleared between requests to avoid memory leaks.
+ */
+export class ToolNameMapper {
+  /** Map from sanitized name → original name */
+  private mapping: Map<string, string> = new Map();
+
+  /** List of all changes made during registration */
+  private changes: SanitizationChange[] = [];
+
+  /**
+   * Register tools and sanitize their names.
+   * Stores mapping for later restoration.
+   *
+   * @param tools Array of tool definitions
+   * @returns Array of tools with sanitized names
+   */
+  registerTools(tools: Tool[]): Tool[] {
+    return tools.map((tool) => {
+      const result: SanitizeResult = sanitizeToolName(tool.name);
+
+      if (result.changed) {
+        // Store mapping: sanitized → original
+        this.mapping.set(result.sanitized, tool.name);
+        this.changes.push({
+          original: tool.name,
+          sanitized: result.sanitized,
+        });
+      }
+
+      return {
+        ...tool,
+        name: result.sanitized,
+      };
+    });
+  }
+
+  /**
+   * Restore original tool names in content blocks.
+   * Looks for tool_use blocks and restores their names.
+   *
+   * @param content Array of content blocks from API response
+   * @returns Array with restored tool names
+   */
+  restoreToolUse(content: ContentBlock[]): ContentBlock[] {
+    return content.map((block) => {
+      if (block.type !== 'tool_use') {
+        return block;
+      }
+
+      // Type guard: we know this is a tool_use block
+      const toolUseName = block.name as string | undefined;
+      if (!toolUseName) {
+        return block;
+      }
+
+      const originalName = this.mapping.get(toolUseName);
+
+      if (originalName) {
+        return {
+          ...block,
+          name: originalName,
+        };
+      }
+
+      return block;
+    });
+  }
+
+  /**
+   * Restore tool name in a single tool_use block.
+   * Useful for streaming responses.
+   *
+   * @param name The sanitized tool name
+   * @returns Original name if mapped, otherwise the input name
+   */
+  restoreName(name: string): string {
+    return this.mapping.get(name) ?? name;
+  }
+
+  /**
+   * Check if any sanitization occurred during registration.
+   */
+  hasChanges(): boolean {
+    return this.changes.length > 0;
+  }
+
+  /**
+   * Get all sanitization changes for logging.
+   */
+  getChanges(): SanitizationChange[] {
+    return [...this.changes];
+  }
+
+  /**
+   * Get the number of tools that were sanitized.
+   */
+  getChangeCount(): number {
+    return this.changes.length;
+  }
+
+  /**
+   * Clear all mappings. Call between requests.
+   */
+  clear(): void {
+    this.mapping.clear();
+    this.changes = [];
+  }
+}

src/cliproxy/tool-name-sanitizer.ts

@@ -0,0 +1,130 @@
+/**
+ * Tool Name Sanitizer
+ *
+ * Sanitizes MCP tool names to comply with Gemini API constraints:
+ * - Max 64 characters
+ * - Must start with letter or underscore
+ * - Only a-z A-Z 0-9 _ . : - allowed
+ *
+ * Strategies:
+ * 1. Remove duplicate segments (e.g., gitmcp__foo__foo → gitmcp__foo)
+ * 2. Smart truncate with hash suffix if still >64 chars
+ */
+
+import { createHash } from 'crypto';
+
+/** Maximum tool name length allowed by Gemini API */
+export const GEMINI_MAX_TOOL_NAME_LENGTH = 64;
+
+/** Valid characters pattern for Gemini tool names */
+const VALID_CHARS_REGEX = /^[a-zA-Z_][a-zA-Z0-9_.:/-]*$/;
+
+/** Result of sanitization operation */
+export interface SanitizeResult {
+  /** The sanitized tool name */
+  sanitized: string;
+  /** Whether the name was changed */
+  changed: boolean;
+}
+
+/**
+ * Check if a tool name is valid for Gemini API.
+ *
+ * Requirements:
+ * - Length <= 64 characters
+ * - Starts with letter or underscore
+ * - Contains only valid characters: a-z A-Z 0-9 _ . : -
+ */
+export function isValidToolName(name: string): boolean {
+  if (!name || name.length === 0) {
+    return false;
+  }
+  if (name.length > GEMINI_MAX_TOOL_NAME_LENGTH) {
+    return false;
+  }
+  return VALID_CHARS_REGEX.test(name);
+}
+
+/**
+ * Remove consecutive duplicate segments separated by '__'.
+ *
+ * Examples:
+ * - 'gitmcp__foo__foo' → 'gitmcp__foo'
+ * - 'a__b__c__b__c' → 'a__b__c'
+ * - 'no_dupes' → 'no_dupes'
+ */
+export function removeDuplicateSegments(name: string): string {
+  const segments = name.split('__');
+  const deduped: string[] = [];
+
+  for (const segment of segments) {
+    // Only add if different from previous segment
+    if (deduped.length === 0 || deduped[deduped.length - 1] !== segment) {
+      deduped.push(segment);
+    }
+  }
+
+  return deduped.join('__');
+}
+
+/**
+ * Generate a short hash from a string for truncation suffix.
+ * Uses first 6 characters of MD5 hash (16M combinations).
+ */
+function generateShortHash(input: string): string {
+  return createHash('md5').update(input).digest('hex').slice(0, 6);
+}
+
+/**
+ * Smart truncate a name to fit within maxLen.
+ * Preserves start of name and appends hash suffix for uniqueness.
+ *
+ * Format: <prefix>_<6-char-hash>
+ *
+ * @param name The name to truncate
+ * @param maxLen Maximum allowed length (default: 64)
+ */
+export function smartTruncate(name: string, maxLen: number = GEMINI_MAX_TOOL_NAME_LENGTH): string {
+  if (name.length <= maxLen) {
+    return name;
+  }
+
+  // Format: prefix + '_' + 6-char hash = 7 chars for suffix
+  const hash = generateShortHash(name);
+  const prefixLen = maxLen - 7; // 7 = '_' (1) + hash (6)
+  const prefix = name.slice(0, prefixLen);
+
+  return `${prefix}_${hash}`;
+}
+
+/**
+ * Sanitize a tool name to comply with Gemini API constraints.
+ *
+ * Process:
+ * 1. Remove duplicate segments (always, as duplicates are likely unintentional)
+ * 2. Truncate with hash if >64 chars
+ * 3. Return result with changed flag
+ *
+ * @param name The original tool name
+ * @returns Sanitization result with sanitized name and changed flag
+ */
+export function sanitizeToolName(name: string): SanitizeResult {
+  // Step 1: Always try to remove duplicate segments
+  // Duplicates like gitmcp__foo__foo are likely unintentional from MCP naming
+  let sanitized = removeDuplicateSegments(name);
+
+  // Step 2: Truncate if still too long
+  if (sanitized.length > GEMINI_MAX_TOOL_NAME_LENGTH) {
+    sanitized = smartTruncate(sanitized);
+  }
+
+  // Step 3: If still invalid after sanitization, apply truncation to original
+  if (!isValidToolName(sanitized)) {
+    sanitized = smartTruncate(name);
+  }
+
+  return {
+    sanitized,
+    changed: sanitized !== name,
+  };
+}

src/cliproxy/tool-sanitization-proxy.ts

@@ -0,0 +1,457 @@
+/**
+ * Tool Sanitization Proxy
+ *
+ * HTTP proxy that intercepts Claude CLI → CLIProxy requests to:
+ * 1. Sanitize MCP tool names exceeding Gemini's 64-char limit
+ * 2. Forward sanitized requests to upstream
+ * 3. Restore original names in responses
+ *
+ * Follows CodexReasoningProxy pattern for consistency.
+ */
+
+import * as http from 'http';
+import * as https from 'https';
+import { URL } from 'url';
+import { ToolNameMapper, type Tool, type ContentBlock } from './tool-name-mapper';
+
+export interface ToolSanitizationProxyConfig {
+  /** Upstream CLIProxy URL */
+  upstreamBaseUrl: string;
+  /** Enable verbose logging */
+  verbose?: boolean;
+  /** Log warnings when sanitization occurs */
+  warnOnSanitize?: boolean;
+  /** Request timeout in milliseconds */
+  timeoutMs?: number;
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === 'object' && value !== null && !Array.isArray(value);
+}
+
+export class ToolSanitizationProxy {
+  private server: http.Server | null = null;
+  private port: number | null = null;
+  private readonly config: Required<ToolSanitizationProxyConfig>;
+
+  constructor(config: ToolSanitizationProxyConfig) {
+    this.config = {
+      upstreamBaseUrl: config.upstreamBaseUrl,
+      verbose: config.verbose ?? false,
+      warnOnSanitize: config.warnOnSanitize ?? true,
+      timeoutMs: config.timeoutMs ?? 120000,
+    };
+  }
+
+  private log(message: string): void {
+    if (this.config.verbose) {
+      console.error(`[tool-sanitization-proxy] ${message}`);
+    }
+  }
+
+  private warn(message: string): void {
+    if (this.config.warnOnSanitize) {
+      console.error(`[!] ${message}`);
+    }
+  }
+
+  /**
+   * Start the proxy server on an ephemeral port.
+   * @returns The assigned port number
+   */
+  async start(): Promise<number> {
+    if (this.server) return this.port ?? 0;
+
+    return new Promise((resolve, reject) => {
+      this.server = http.createServer((req, res) => {
+        void this.handleRequest(req, res);
+      });
+
+      this.server.listen(0, '127.0.0.1', () => {
+        const address = this.server?.address();
+        this.port = typeof address === 'object' && address ? address.port : 0;
+        resolve(this.port);
+      });
+
+      this.server.on('error', (err) => reject(err));
+    });
+  }
+
+  /**
+   * Stop the proxy server.
+   */
+  stop(): void {
+    if (!this.server) return;
+    this.server.close();
+    this.server = null;
+    this.port = null;
+  }
+
+  /**
+   * Get the port the proxy is listening on.
+   */
+  getPort(): number | null {
+    return this.port;
+  }
+
+  private readBody(req: http.IncomingMessage): Promise<string> {
+    return new Promise((resolve, reject) => {
+      const chunks: Buffer[] = [];
+      const maxSize = 10 * 1024 * 1024; // 10MB
+      let total = 0;
+
+      req.on('data', (chunk: Buffer) => {
+        total += chunk.length;
+        if (total > maxSize) {
+          req.destroy();
+          reject(new Error('Request body too large (max 10MB)'));
+          return;
+        }
+        chunks.push(chunk);
+      });
+
+      req.on('end', () => resolve(Buffer.concat(chunks).toString('utf8')));
+      req.on('error', reject);
+    });
+  }
+
+  private async handleRequest(req: http.IncomingMessage, res: http.ServerResponse): Promise<void> {
+    const method = req.method || 'GET';
+    const requestPath = req.url || '/';
+    const upstreamBase = new URL(this.config.upstreamBaseUrl);
+    const fullUpstreamUrl = new URL(requestPath, upstreamBase);
+
+    this.log(`${method} ${requestPath} → ${fullUpstreamUrl.href}`);
+
+    // Only buffer+rewrite JSON POST requests
+    const contentType = String(req.headers['content-type'] || '');
+    const isJson = contentType.includes('application/json');
+    const shouldRewrite = isJson && ['POST', 'PUT', 'PATCH'].includes(method.toUpperCase());
+
+    try {
+      if (!shouldRewrite) {
+        await this.forwardRaw(req, res, fullUpstreamUrl);
+        return;
+      }
+
+      const rawBody = await this.readBody(req);
+      let parsed: unknown;
+      try {
+        parsed = rawBody.length ? JSON.parse(rawBody) : {};
+      } catch {
+        res.writeHead(400, { 'Content-Type': 'application/json' });
+        res.end(JSON.stringify({ error: 'Invalid JSON in request body' }));
+        return;
+      }
+
+      // Create mapper for this request
+      const mapper = new ToolNameMapper();
+
+      // Sanitize tools if present
+      let modifiedBody = parsed;
+      if (isRecord(parsed) && Array.isArray(parsed.tools)) {
+        const sanitizedTools = mapper.registerTools(parsed.tools as Tool[]);
+        modifiedBody = { ...parsed, tools: sanitizedTools };
+
+        // Log sanitization warnings
+        if (mapper.hasChanges()) {
+          const changes = mapper.getChanges();
+          for (const change of changes) {
+            this.warn(`Tool name sanitized: "${change.original}" → "${change.sanitized}"`);
+          }
+          this.log(`Sanitized ${changes.length} tool name(s)`);
+        }
+      }
+
+      // Check if streaming is requested
+      const isStreaming = isRecord(parsed) && parsed.stream === true;
+
+      if (isStreaming) {
+        await this.forwardJsonStreaming(req, res, fullUpstreamUrl, modifiedBody, mapper);
+      } else {
+        await this.forwardJsonBuffered(req, res, fullUpstreamUrl, modifiedBody, mapper);
+      }
+    } catch (error) {
+      const err = error as Error;
+      this.log(`Error: ${err.message}`);
+      if (!res.headersSent) {
+        res.writeHead(502, { 'Content-Type': 'application/json' });
+      }
+      res.end(JSON.stringify({ error: err.message }));
+    }
+  }
+
+  private buildForwardHeaders(
+    originalHeaders: http.IncomingHttpHeaders,
+    bodyString?: string
+  ): http.OutgoingHttpHeaders {
+    const headers: http.OutgoingHttpHeaders = {};
+
+    // RFC 7230 hop-by-hop headers that should not be forwarded
+    const hopByHop = new Set([
+      'host',
+      'content-length',
+      'connection',
+      'transfer-encoding',
+      'keep-alive',
+      'proxy-authenticate',
+      'proxy-authorization',
+      'te',
+      'trailer',
+      'upgrade',
+    ]);
+
+    for (const [key, value] of Object.entries(originalHeaders)) {
+      if (!value) continue;
+      const lower = key.toLowerCase();
+      if (hopByHop.has(lower)) continue;
+      headers[key] = value;
+    }
+
+    if (bodyString !== undefined) {
+      headers['Content-Type'] = headers['Content-Type'] || 'application/json';
+      headers['Content-Length'] = Buffer.byteLength(bodyString);
+    }
+
+    return headers;
+  }
+
+  private getRequestFn(url: URL): typeof http.request | typeof https.request {
+    return url.protocol === 'https:' ? https.request : http.request;
+  }
+
+  private forwardRaw(
+    originalReq: http.IncomingMessage,
+    clientRes: http.ServerResponse,
+    upstreamUrl: URL
+  ): Promise<void> {
+    return new Promise((resolve, reject) => {
+      const requestFn = this.getRequestFn(upstreamUrl);
+      const upstreamReq = requestFn(
+        {
+          protocol: upstreamUrl.protocol,
+          hostname: upstreamUrl.hostname,
+          port: upstreamUrl.port,
+          path: upstreamUrl.pathname + upstreamUrl.search,
+          method: originalReq.method,
+          timeout: this.config.timeoutMs,
+          headers: this.buildForwardHeaders(originalReq.headers),
+        },
+        (upstreamRes) => {
+          clientRes.writeHead(upstreamRes.statusCode || 200, upstreamRes.headers);
+          upstreamRes.pipe(clientRes);
+          upstreamRes.on('end', () => resolve());
+          upstreamRes.on('error', reject);
+        }
+      );
+
+      upstreamReq.on('timeout', () => upstreamReq.destroy(new Error('Upstream request timeout')));
+      upstreamReq.on('error', reject);
+      originalReq.pipe(upstreamReq);
+    });
+  }
+
+  /**
+   * Forward JSON request and buffer response for tool name restoration.
+   */
+  private forwardJsonBuffered(
+    originalReq: http.IncomingMessage,
+    clientRes: http.ServerResponse,
+    upstreamUrl: URL,
+    body: unknown,
+    mapper: ToolNameMapper
+  ): Promise<void> {
+    return new Promise((resolve, reject) => {
+      const bodyString = JSON.stringify(body);
+      const requestFn = this.getRequestFn(upstreamUrl);
+      const upstreamReq = requestFn(
+        {
+          protocol: upstreamUrl.protocol,
+          hostname: upstreamUrl.hostname,
+          port: upstreamUrl.port,
+          path: upstreamUrl.pathname + upstreamUrl.search,
+          method: originalReq.method,
+          timeout: this.config.timeoutMs,
+          headers: this.buildForwardHeaders(originalReq.headers, bodyString),
+        },
+        (upstreamRes) => {
+          const chunks: Buffer[] = [];
+
+          upstreamRes.on('data', (chunk: Buffer) => chunks.push(chunk));
+          upstreamRes.on('end', () => {
+            try {
+              const responseBody = Buffer.concat(chunks).toString('utf8');
+              const contentType = upstreamRes.headers['content-type'] || '';
+
+              // Only process JSON responses with tool_use blocks
+              if (contentType.includes('application/json') && mapper.hasChanges()) {
+                try {
+                  const parsed = JSON.parse(responseBody);
+                  if (isRecord(parsed) && Array.isArray(parsed.content)) {
+                    parsed.content = mapper.restoreToolUse(parsed.content as ContentBlock[]);
+                    const modifiedResponse = JSON.stringify(parsed);
+
+                    // Update content-length header
+                    const headers = { ...upstreamRes.headers };
+                    headers['content-length'] = String(Buffer.byteLength(modifiedResponse));
+
+                    clientRes.writeHead(upstreamRes.statusCode || 200, headers);
+                    clientRes.end(modifiedResponse);
+                    resolve();
+                    return;
+                  }
+                } catch {
+                  // JSON parse failed, pass through unchanged
+                }
+              }
+
+              // Pass through unchanged
+              clientRes.writeHead(upstreamRes.statusCode || 200, upstreamRes.headers);
+              clientRes.end(responseBody);
+              resolve();
+            } catch (err) {
+              reject(err);
+            }
+          });
+          upstreamRes.on('error', reject);
+        }
+      );
+
+      upstreamReq.on('timeout', () => upstreamReq.destroy(new Error('Upstream request timeout')));
+      upstreamReq.on('error', reject);
+      upstreamReq.write(bodyString);
+      upstreamReq.end();
+    });
+  }
+
+  /**
+   * Forward JSON request and stream response with tool name restoration.
+   * Handles SSE (Server-Sent Events) format.
+   */
+  private forwardJsonStreaming(
+    originalReq: http.IncomingMessage,
+    clientRes: http.ServerResponse,
+    upstreamUrl: URL,
+    body: unknown,
+    mapper: ToolNameMapper
+  ): Promise<void> {
+    return new Promise((resolve, reject) => {
+      const bodyString = JSON.stringify(body);
+      const requestFn = this.getRequestFn(upstreamUrl);
+      const upstreamReq = requestFn(
+        {
+          protocol: upstreamUrl.protocol,
+          hostname: upstreamUrl.hostname,
+          port: upstreamUrl.port,
+          path: upstreamUrl.pathname + upstreamUrl.search,
+          method: originalReq.method,
+          timeout: this.config.timeoutMs,
+          headers: this.buildForwardHeaders(originalReq.headers, bodyString),
+        },
+        (upstreamRes) => {
+          clientRes.writeHead(upstreamRes.statusCode || 200, upstreamRes.headers);
+
+          // If no changes were made, just pipe through
+          if (!mapper.hasChanges()) {
+            upstreamRes.pipe(clientRes);
+            upstreamRes.on('end', () => resolve());
+            upstreamRes.on('error', reject);
+            return;
+          }
+
+          // Process SSE events for tool name restoration
+          let buffer = '';
+
+          upstreamRes.on('data', (chunk: Buffer) => {
+            buffer += chunk.toString('utf8');
+
+            // Process complete SSE events
+            const events = buffer.split('\n\n');
+            buffer = events.pop() || ''; // Keep incomplete event in buffer
+
+            for (const event of events) {
+              if (!event.trim()) continue;
+
+              const processedEvent = this.processSSEEvent(event, mapper);
+              clientRes.write(processedEvent + '\n\n');
+            }
+          });
+
+          upstreamRes.on('end', () => {
+            // Process any remaining buffer
+            if (buffer.trim()) {
+              const processedEvent = this.processSSEEvent(buffer, mapper);
+              clientRes.write(processedEvent + '\n\n');
+            }
+            clientRes.end();
+            resolve();
+          });
+
+          upstreamRes.on('error', reject);
+        }
+      );
+
+      upstreamReq.on('timeout', () => upstreamReq.destroy(new Error('Upstream request timeout')));
+      upstreamReq.on('error', reject);
+      upstreamReq.write(bodyString);
+      upstreamReq.end();
+    });
+  }
+
+  /**
+   * Process a single SSE event, restoring tool names if present.
+   */
+  private processSSEEvent(event: string, mapper: ToolNameMapper): string {
+    // Parse SSE format: data: {...}
+    const lines = event.split('\n');
+    const processedLines: string[] = [];
+
+    for (const line of lines) {
+      if (line.startsWith('data: ')) {
+        const jsonStr = line.slice(6); // Remove 'data: ' prefix
+
+        // Skip [DONE] marker
+        if (jsonStr.trim() === '[DONE]') {
+          processedLines.push(line);
+          continue;
+        }
+
+        try {
+          const data = JSON.parse(jsonStr);
+
+          // Handle content_block_start with tool_use
+          if (
+            isRecord(data) &&
+            data.type === 'content_block_start' &&
+            isRecord(data.content_block) &&
+            data.content_block.type === 'tool_use' &&
+            typeof data.content_block.name === 'string'
+          ) {
+            const originalName = mapper.restoreName(data.content_block.name);
+            data.content_block.name = originalName;
+            processedLines.push('data: ' + JSON.stringify(data));
+            continue;
+          }
+
+          // Handle message with content array (final message)
+          if (isRecord(data) && Array.isArray(data.content)) {
+            data.content = mapper.restoreToolUse(data.content as ContentBlock[]);
+            processedLines.push('data: ' + JSON.stringify(data));
+            continue;
+          }
+
+          // Pass through unchanged
+          processedLines.push(line);
+        } catch {
+          // Not valid JSON, pass through unchanged
+          processedLines.push(line);
+        }
+      } else {
+        // Non-data lines (event:, id:, etc.) pass through
+        processedLines.push(line);
+      }
+    }
+
+    return processedLines.join('\n');
+  }
+}