src/mcplocal/src/http/mcp-endpoint.ts

@@ -13,6 +13,7 @@ import { StreamableHTTPServerTransport } from '@modelcontextprotocol/sdk/server/
 import type { JSONRPCMessage } from '@modelcontextprotocol/sdk/types.js';
 import type { McpRouter } from '../router.js';
 import type { JsonRpcRequest } from '../types.js';
+import { WireNameCodec, routeWithWireNames } from '../util/wire-names.js';
 
 interface SessionEntry {
   transport: StreamableHTTPServerTransport;
@@ -20,6 +21,9 @@ interface SessionEntry {
 
 export function registerMcpEndpoint(app: FastifyInstance, router: McpRouter): void {
   const sessions = new Map<string, SessionEntry>();
+  // One codec for the shared router: serve OpenAI-safe tool names on the wire,
+  // map tools/call names back to the internal `server/tool` form.
+  const wireCodec = new WireNameCodec();
 
   // POST /mcp — JSON-RPC requests (initialize, tools/call, etc.)
   app.post('/mcp', async (request, reply) => {
@@ -52,7 +56,11 @@ export function registerMcpEndpoint(app: FastifyInstance, router: McpRouter): vo
     transport.onmessage = async (message: JSONRPCMessage) => {
       // The transport sends us JSON-RPC messages; route them through McpRouter
       if ('method' in message && 'id' in message) {
-        const response = await router.route(message as unknown as JsonRpcRequest);
+        const response = await routeWithWireNames(
+          wireCodec,
+          (req) => router.route(req),
+          message as unknown as JsonRpcRequest,
+        );
         await transport.send(response as unknown as JSONRPCMessage);
       }
       // Notifications (no id) are ignored — router doesn't handle inbound notifications

src/mcplocal/src/http/project-mcp-endpoint.ts

@@ -27,6 +27,7 @@ import { createFavouriteIndexPlugin } from '../proxymodel/plugins/favourite-inde
 import { composePlugins } from '../proxymodel/plugins/compose.js';
 import type { ProxyModelPlugin } from '../proxymodel/plugin.js';
 import { AuditCollector } from '../audit/collector.js';
+import { WireNameCodec, routeWithWireNames } from '../util/wire-names.js';
 
 interface ProjectCacheEntry {
   router: McpRouter;
@@ -45,6 +46,10 @@ export function registerProjectMcpEndpoint(app: FastifyInstance, mcpdClient: Mcp
   let resolvedUserName: string | null | undefined; // undefined = not yet resolved
   const projectCache = new Map<string, ProjectCacheEntry>();
   const sessions = new Map<string, SessionEntry>();
+  // Wire-name codecs are keyed per project and OUTLIVE the router cache TTL:
+  // a client may call a tool it listed minutes ago through a refreshed router,
+  // and the mapping must still resolve.
+  const wireCodecs = new Map<string, WireNameCodec>();
 
   /** Resolve the mcplocal owner's userName once from /auth/me using mcplocal's own credentials. */
   async function ensureUserName(): Promise<string | null> {
@@ -331,7 +336,18 @@ export function registerProjectMcpEndpoint(app: FastifyInstance, mcpdClient: Mcp
         });
 
         const ctx = transport.sessionId ? { sessionId: transport.sessionId, correlationId } : { correlationId };
-        const response = await router.route(message as unknown as JsonRpcRequest, ctx);
+        // Wire-name translation happens HERE, at the client boundary, so the
+        // router, plugins and audit all keep canonical `server/tool` names.
+        let codec = wireCodecs.get(projectName);
+        if (!codec) {
+          codec = new WireNameCodec();
+          wireCodecs.set(projectName, codec);
+        }
+        const response = await routeWithWireNames(
+          codec,
+          (req) => router.route(req, ctx),
+          message as unknown as JsonRpcRequest,
+        );
 
         // Forward queued notifications BEFORE the response — the response send
         // closes the POST SSE stream, so notifications must go first.

src/mcplocal/src/util/wire-names.ts

@@ -0,0 +1,126 @@
+/**
+ * Wire-safe tool-name codec for client-facing MCP endpoints.
+ *
+ * Internally the proxy namespaces tools as `server/tool`, and presentation
+ * plugins add `favourite/<tool>`, `all/<server>/<tool>` and
+ * `agent-<name>/chat`. A `/` is not a valid character in OpenAI-style
+ * function names (`^[a-zA-Z0-9_.-]{1,64}$`), so hosts that forward MCP tool
+ * names verbatim as LLM function names (LibreChat) depend on the model
+ * faithfully echoing an illegal name. deepseek-v4-flash intermittently drops
+ * the `server/` prefix; the host's registry lookup then fails and it reports
+ * the tool's "MCP server is temporarily unavailable" while nothing is down
+ * (the librechat fetch_content incident, 2026-08-25). Claude Code and the pi
+ * extension dodge this only because they sanitize names client-side.
+ *
+ * The codec translates ONLY at the HTTP boundary:
+ *   - tools/list responses are rewritten to wire-safe names (`/` → `_`),
+ *   - tools/call requests are mapped back to the presented (internal) name
+ *     via an exact-match reverse map.
+ *
+ * Everything inside the proxy — routing maps, plugins, favourites config,
+ * audit events — keeps the canonical names. Inbound names with no map entry
+ * (legacy clients echoing slash names, virtual tools called before any
+ * tools/list) pass through unchanged, so existing clients keep working.
+ *
+ * The maps live per project router (not per session) so a client that
+ * reconnects mid-conversation still resolves names listed on its previous
+ * session, as long as the process is alive. After a restart the first
+ * tools/list (which every MCP client performs on initialize) repopulates them.
+ */
+import type { JsonRpcRequest, JsonRpcResponse } from '../types.js';
+
+/** Replace every character that is invalid in an OpenAI-style function name. */
+export function sanitizeWireName(name: string): string {
+  return name.replace(/[^A-Za-z0-9_.-]/g, '_');
+}
+
+export class WireNameCodec {
+  /** wire name → presented (internal) name */
+  private toPresented = new Map<string, string>();
+  /** presented (internal) name → wire name */
+  private toWire = new Map<string, string>();
+
+  /**
+   * Wire name for a presented tool name. Stable for the codec's lifetime.
+   *
+   * Collisions (two presented names sanitizing to the same string, or a
+   * sanitized name shadowing a tool that already uses that exact name) get a
+   * numeric suffix — first registration wins the plain name. This keeps the
+   * reverse map unambiguous; order within one tools/list pass is stable, so
+   * suffixes are deterministic in practice.
+   */
+  encodeName(presented: string): string {
+    const existing = this.toWire.get(presented);
+    if (existing !== undefined) return existing;
+
+    const base = sanitizeWireName(presented);
+    let wire = base;
+    for (let i = 2; this.toPresented.has(wire) && this.toPresented.get(wire) !== presented; i++) {
+      wire = `${base}_${String(i)}`;
+    }
+    if (wire !== base) {
+      console.warn(`[wire-names] collision: '${presented}' presented as '${wire}' (base '${base}' taken by '${this.toPresented.get(base) ?? '?'}')`);
+    }
+    this.toWire.set(presented, wire);
+    this.toPresented.set(wire, presented);
+    return wire;
+  }
+
+  /** The presented name a wire name maps to, or the input unchanged if unknown. */
+  decodeName(wire: string): string {
+    return this.toPresented.get(wire) ?? wire;
+  }
+
+  /**
+   * Rewrite a tools/list response's tool names to wire-safe names,
+   * registering each mapping. Non-list responses and errors pass through.
+   */
+  encodeToolsList(response: JsonRpcResponse): JsonRpcResponse {
+    if (response.error !== undefined) return response;
+    if (response.result === null || typeof response.result !== 'object') return response;
+    const result = response.result as Record<string, unknown>;
+    const tools: unknown = result['tools'];
+    if (!Array.isArray(tools)) return response;
+
+    let changed = false;
+    const encoded = (tools as unknown[]).map((tool) => {
+      if (tool === null || typeof tool !== 'object' || typeof (tool as { name?: unknown }).name !== 'string') return tool;
+      const presented = (tool as { name: string }).name;
+      const wire = this.encodeName(presented);
+      if (wire === presented) return tool;
+      changed = true;
+      return { ...(tool as Record<string, unknown>), name: wire };
+    });
+
+    if (!changed) return response;
+    return { ...response, result: { ...result, tools: encoded } };
+  }
+
+  /**
+   * Map a tools/call request's wire name back to the presented name.
+   * Requests for unknown names (or without a name) pass through unchanged.
+   */
+  decodeToolCall(request: JsonRpcRequest): JsonRpcRequest {
+    const params = request.params;
+    const name = params?.['name'];
+    if (typeof name !== 'string') return request;
+    const presented = this.toPresented.get(name);
+    if (presented === undefined || presented === name) return request;
+    return { ...request, params: { ...params, name: presented } };
+  }
+}
+
+/**
+ * Route one client request through `route` with wire-name translation:
+ * decode the tool name on the way in (tools/call), encode tool names on the
+ * way out (tools/list). Every other method is untouched.
+ */
+export async function routeWithWireNames(
+  codec: WireNameCodec,
+  route: (request: JsonRpcRequest) => Promise<JsonRpcResponse>,
+  request: JsonRpcRequest,
+): Promise<JsonRpcResponse> {
+  const inbound = request.method === 'tools/call' ? codec.decodeToolCall(request) : request;
+  const response = await route(inbound);
+  return request.method === 'tools/list' ? codec.encodeToolsList(response) : response;
+}

src/mcplocal/tests/mcp-endpoint-wire-names.test.ts

@@ -0,0 +1,100 @@
+import { describe, it, expect, vi } from 'vitest';
+import Fastify from 'fastify';
+import { registerMcpEndpoint } from '../src/http/mcp-endpoint.js';
+import type { McpRouter } from '../src/router.js';
+import type { JsonRpcRequest, JsonRpcResponse } from '../src/types.js';
+
+/**
+ * End-to-end over the Streamable HTTP transport: the /mcp endpoint must serve
+ * OpenAI-safe tool names on tools/list and map them back to the router's
+ * canonical `server/tool` names on tools/call (the librechat fetch_content
+ * incident, 2026-08-25).
+ */
+
+function parseSse(body: string): JsonRpcResponse {
+  const dataLine = body.split('\n').find((l) => l.startsWith('data: '));
+  if (!dataLine) throw new Error(`no SSE data line in: ${body}`);
+  return JSON.parse(dataLine.slice('data: '.length)) as JsonRpcResponse;
+}
+
+describe('registerMcpEndpoint wire names', () => {
+  it('lists wire-safe names and routes calls back to canonical names', async () => {
+    const routed: JsonRpcRequest[] = [];
+    const fakeRouter = {
+      route: vi.fn(async (req: JsonRpcRequest): Promise<JsonRpcResponse> => {
+        routed.push(req);
+        switch (req.method) {
+          case 'initialize':
+            return {
+              jsonrpc: '2.0',
+              id: req.id,
+              result: {
+                protocolVersion: '2024-11-05',
+                serverInfo: { name: 'test', version: '0' },
+                capabilities: { tools: {} },
+              },
+            };
+          case 'tools/list':
+            return {
+              jsonrpc: '2.0',
+              id: req.id,
+              result: { tools: [{ name: 'websearch/fetch_content', inputSchema: { type: 'object' } }] },
+            };
+          case 'tools/call':
+            return {
+              jsonrpc: '2.0',
+              id: req.id,
+              result: { content: [{ type: 'text', text: 'ok' }] },
+            };
+          default:
+            return { jsonrpc: '2.0', id: req.id, result: {} };
+        }
+      }),
+    } as unknown as McpRouter;
+
+    const app = Fastify();
+    registerMcpEndpoint(app, fakeRouter);
+    await app.ready();
+    try {
+      const headers = {
+        'content-type': 'application/json',
+        accept: 'application/json, text/event-stream',
+      };
+
+      const init = await app.inject({
+        method: 'POST',
+        url: '/mcp',
+        headers,
+        payload: { jsonrpc: '2.0', id: 1, method: 'initialize', params: { protocolVersion: '2024-11-05', capabilities: {}, clientInfo: { name: 't', version: '0' } } },
+      });
+      expect(init.statusCode).toBe(200);
+      const sessionId = init.headers['mcp-session-id'] as string;
+      expect(sessionId).toBeTruthy();
+      const sessionHeaders = { ...headers, 'mcp-session-id': sessionId };
+
+      const list = await app.inject({
+        method: 'POST',
+        url: '/mcp',
+        headers: sessionHeaders,
+        payload: { jsonrpc: '2.0', id: 2, method: 'tools/list' },
+      });
+      const listResponse = parseSse(list.body);
+      const tools = (listResponse.result as { tools: Array<{ name: string }> }).tools;
+      expect(tools.map((t) => t.name)).toEqual(['websearch_fetch_content']);
+
+      const call = await app.inject({
+        method: 'POST',
+        url: '/mcp',
+        headers: sessionHeaders,
+        payload: { jsonrpc: '2.0', id: 3, method: 'tools/call', params: { name: 'websearch_fetch_content', arguments: { url: 'https://x' } } },
+      });
+      const callResponse = parseSse(call.body);
+      expect(callResponse.error).toBeUndefined();
+
+      const routedCall = routed.find((r) => r.method === 'tools/call');
+      expect(routedCall?.params?.['name']).toBe('websearch/fetch_content');
+    } finally {
+      await app.close();
+    }
+  });
+});

src/mcplocal/tests/wire-names.test.ts

@@ -0,0 +1,168 @@
+import { describe, it, expect, vi } from 'vitest';
+import { sanitizeWireName, WireNameCodec, routeWithWireNames } from '../src/util/wire-names.js';
+import type { JsonRpcRequest, JsonRpcResponse } from '../src/types.js';
+
+describe('sanitizeWireName', () => {
+  it('replaces slashes with underscores', () => {
+    expect(sanitizeWireName('websearch/fetch_content')).toBe('websearch_fetch_content');
+    expect(sanitizeWireName('all/websearch/fetch_content')).toBe('all_websearch_fetch_content');
+  });
+
+  it('keeps names that are already OpenAI-safe', () => {
+    expect(sanitizeWireName('begin_session')).toBe('begin_session');
+    expect(sanitizeWireName('my-grafana.tool')).toBe('my-grafana.tool');
+  });
+
+  it('replaces every character outside [A-Za-z0-9_.-]', () => {
+    expect(sanitizeWireName('a b:c/d')).toBe('a_b_c_d');
+  });
+});
+
+describe('WireNameCodec', () => {
+  it('round-trips a namespaced tool name', () => {
+    const codec = new WireNameCodec();
+    const wire = codec.encodeName('websearch/fetch_content');
+    expect(wire).toBe('websearch_fetch_content');
+    expect(codec.decodeName(wire)).toBe('websearch/fetch_content');
+  });
+
+  it('is stable across repeated encodes', () => {
+    const codec = new WireNameCodec();
+    expect(codec.encodeName('searxng/web_url_read')).toBe('searxng_web_url_read');
+    expect(codec.encodeName('searxng/web_url_read')).toBe('searxng_web_url_read');
+  });
+
+  it('passes unknown inbound names through unchanged', () => {
+    const codec = new WireNameCodec();
+    // Legacy client echoing the slash form, or a virtual tool never listed.
+    expect(codec.decodeName('websearch/fetch_content')).toBe('websearch/fetch_content');
+    expect(codec.decodeName('begin_session')).toBe('begin_session');
+  });
+
+  it('suffixes on collision, first registration wins the plain name', () => {
+    const warn = vi.spyOn(console, 'warn').mockImplementation(() => {});
+    try {
+      const codec = new WireNameCodec();
+      expect(codec.encodeName('foo_bar/baz')).toBe('foo_bar_baz');
+      expect(codec.encodeName('foo/bar_baz')).toBe('foo_bar_baz_2');
+      // Both decode back to their own presented names.
+      expect(codec.decodeName('foo_bar_baz')).toBe('foo_bar/baz');
+      expect(codec.decodeName('foo_bar_baz_2')).toBe('foo/bar_baz');
+      // And stay stable.
+      expect(codec.encodeName('foo/bar_baz')).toBe('foo_bar_baz_2');
+      expect(warn).toHaveBeenCalledOnce();
+    } finally {
+      warn.mockRestore();
+    }
+  });
+
+  it('encodes tools/list responses and leaves other fields intact', () => {
+    const codec = new WireNameCodec();
+    const response: JsonRpcResponse = {
+      jsonrpc: '2.0',
+      id: 1,
+      result: {
+        tools: [
+          { name: 'websearch/fetch_content', description: 'fetch', inputSchema: { type: 'object' } },
+          { name: 'begin_session', description: 'gate' },
+        ],
+      },
+    };
+    const encoded = codec.encodeToolsList(response);
+    const tools = (encoded.result as { tools: Array<{ name: string; description?: string }> }).tools;
+    expect(tools.map((t) => t.name)).toEqual(['websearch_fetch_content', 'begin_session']);
+    expect(tools[0]?.description).toBe('fetch');
+    // Original response object is not mutated.
+    const originalTools = (response.result as { tools: Array<{ name: string }> }).tools;
+    expect(originalTools[0]?.name).toBe('websearch/fetch_content');
+  });
+
+  it('returns error and non-list responses unchanged', () => {
+    const codec = new WireNameCodec();
+    const err: JsonRpcResponse = { jsonrpc: '2.0', id: 1, error: { code: -32603, message: 'boom' } };
+    expect(codec.encodeToolsList(err)).toBe(err);
+    const other: JsonRpcResponse = { jsonrpc: '2.0', id: 1, result: { content: [] } };
+    expect(codec.encodeToolsList(other)).toBe(other);
+  });
+
+  it('decodes tools/call requests for known wire names only', () => {
+    const codec = new WireNameCodec();
+    codec.encodeName('websearch/fetch_content');
+
+    const known: JsonRpcRequest = {
+      jsonrpc: '2.0',
+      id: 2,
+      method: 'tools/call',
+      params: { name: 'websearch_fetch_content', arguments: { url: 'https://x' } },
+    };
+    const decoded = codec.decodeToolCall(known);
+    expect(decoded.params?.['name']).toBe('websearch/fetch_content');
+    expect(decoded.params?.['arguments']).toEqual({ url: 'https://x' });
+    // Original request object is not mutated.
+    expect(known.params?.['name']).toBe('websearch_fetch_content');
+
+    const unknown: JsonRpcRequest = {
+      jsonrpc: '2.0',
+      id: 3,
+      method: 'tools/call',
+      params: { name: 'not_listed', arguments: {} },
+    };
+    expect(codec.decodeToolCall(unknown)).toBe(unknown);
+  });
+});
+
+describe('routeWithWireNames', () => {
+  const listResponse: JsonRpcResponse = {
+    jsonrpc: '2.0',
+    id: 1,
+    result: { tools: [{ name: 'websearch/fetch_content' }, { name: 'searxng/web_url_read' }] },
+  };
+
+  it('serves wire-safe names on tools/list and maps tools/call back', async () => {
+    const codec = new WireNameCodec();
+    const seen: JsonRpcRequest[] = [];
+    const route = async (req: JsonRpcRequest): Promise<JsonRpcResponse> => {
+      seen.push(req);
+      if (req.method === 'tools/list') return listResponse;
+      return { jsonrpc: '2.0', id: req.id, result: { content: [{ type: 'text', text: 'ok' }] } };
+    };
+
+    const listed = await routeWithWireNames(codec, route, { jsonrpc: '2.0', id: 1, method: 'tools/list' });
+    const names = (listed.result as { tools: Array<{ name: string }> }).tools.map((t) => t.name);
+    expect(names).toEqual(['websearch_fetch_content', 'searxng_web_url_read']);
+
+    // The exact scenario from the librechat incident: the model echoes the
+    // wire name; the router must receive the canonical name.
+    await routeWithWireNames(codec, route, {
+      jsonrpc: '2.0',
+      id: 2,
+      method: 'tools/call',
+      params: { name: 'websearch_fetch_content', arguments: { url: 'https://x' } },
+    });
+    expect(seen[1]?.params?.['name']).toBe('websearch/fetch_content');
+  });
+
+  it('keeps legacy slash-name calls working', async () => {
+    const codec = new WireNameCodec();
+    const seen: JsonRpcRequest[] = [];
+    const route = async (req: JsonRpcRequest): Promise<JsonRpcResponse> => {
+      seen.push(req);
+      return { jsonrpc: '2.0', id: req.id, result: {} };
+    };
+    await routeWithWireNames(codec, route, {
+      jsonrpc: '2.0',
+      id: 1,
+      method: 'tools/call',
+      params: { name: 'websearch/fetch_content', arguments: {} },
+    });
+    expect(seen[0]?.params?.['name']).toBe('websearch/fetch_content');
+  });
+
+  it('does not touch other methods', async () => {
+    const codec = new WireNameCodec();
+    const init: JsonRpcRequest = { jsonrpc: '2.0', id: 1, method: 'initialize', params: {} };
+    const response: JsonRpcResponse = { jsonrpc: '2.0', id: 1, result: { protocolVersion: '2024-11-05' } };
+    const out = await routeWithWireNames(codec, async () => response, init);
+    expect(out).toBe(response);
+  });
+});