fix: MCP proxy resilience — discovery cache, default liveness probes

Adds a per-server tools/list cache in McpRouter (positive + negative TTL)
so a slow or dead upstream only stalls the first discovery call, not every
subsequent client request. Invalidated on upstream add/remove.

Health probes now apply a default liveness spec (tools/list via the real
production path) to any RUNNING instance without an explicit healthCheck,
so synthetic and real failures converge on the same signal.

Includes supporting updates in mcpd-client, discovery, upstream/mcpd,
seeder, and fulldeploy/release scripts.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/mcplocal/tests/mcpd-upstream.test.ts

@@ -107,4 +107,38 @@ describe('McpdUpstream', () => {
     const response = await upstream.send(request);
     expect(response.error).toEqual({ code: -32601, message: 'Tool not found' });
   });
+
+  it('routes */list methods through discoveryClient when provided', async () => {
+    const mainClient = mockMcpdClient();
+    const discoveryClient = mockMcpdClient(new Map([
+      ['srv-1:tools/list', { result: { tools: [] } }],
+      ['srv-1:resources/list', { result: { resources: [] } }],
+      ['srv-1:prompts/list', { result: { prompts: [] } }],
+    ]));
+
+    const upstream = new McpdUpstream('srv-1', 'slack', mainClient as any, undefined, discoveryClient as any);
+
+    await upstream.send({ jsonrpc: '2.0', id: '1', method: 'tools/list' });
+    await upstream.send({ jsonrpc: '2.0', id: '2', method: 'resources/list' });
+    await upstream.send({ jsonrpc: '2.0', id: '3', method: 'prompts/list' });
+
+    expect(discoveryClient.post).toHaveBeenCalledTimes(3);
+    expect(mainClient.post).not.toHaveBeenCalled();
+  });
+
+  it('routes tools/call through mainClient even when discoveryClient is set', async () => {
+    const mainClient = mockMcpdClient(new Map([
+      ['srv-1:tools/call', { result: { ok: true } }],
+    ]));
+    const discoveryClient = mockMcpdClient();
+
+    const upstream = new McpdUpstream('srv-1', 'slack', mainClient as any, undefined, discoveryClient as any);
+    await upstream.send({
+      jsonrpc: '2.0', id: '1', method: 'tools/call',
+      params: { name: 'noop', arguments: {} },
+    });
+
+    expect(mainClient.post).toHaveBeenCalledTimes(1);
+    expect(discoveryClient.post).not.toHaveBeenCalled();
+  });
 });