fix: SSE health probe uses proper SSE protocol (GET /sse + POST /messages)

SSE-transport MCP servers (like ha-mcp) use a different protocol flow:
GET /sse to establish event stream, read endpoint event, then POST
JSON-RPC messages to /messages?session_id=... URL. Previously was
POSTing to root which returned 404.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/mcpd/src/services/health-probe.service.ts

@@ -185,24 +185,35 @@ export class HealthProbeRunner {
     const containerInfo = await this.orchestrator.inspectContainer(instance.containerId);
     const containerPort = (server.containerPort as number | null) ?? 3000;
 
-    let url: string;
+    let baseUrl: string;
     if (containerInfo.ip) {
-      url = `http://${containerInfo.ip}:${containerPort}`;
+      baseUrl = `http://${containerInfo.ip}:${containerPort}`;
     } else if (instance.port) {
-      url = `http://localhost:${instance.port}`;
+      baseUrl = `http://localhost:${instance.port}`;
     } else {
       return { healthy: false, latencyMs: 0, message: 'No container IP or port' };
     }
 
-    const start = Date.now();
+    if (server.transport === 'SSE') {
+      return this.probeSse(baseUrl, healthCheck, timeoutMs);
+    }
+    return this.probeStreamableHttp(baseUrl, healthCheck, timeoutMs);
+  }
 
-    // For HTTP servers, we need to initialize a session first, then call the tool
+  /**
+   * Probe a streamable-http MCP server (POST to root endpoint).
+   */
+  private async probeStreamableHttp(
+    baseUrl: string,
+    healthCheck: HealthCheckSpec,
+    timeoutMs: number,
+  ): Promise<ProbeResult> {
+    const start = Date.now();
     const controller = new AbortController();
     const timer = setTimeout(() => controller.abort(), timeoutMs);
 
     try {
-      // Initialize
+      const initResp = await fetch(baseUrl, {
-      const initResp = await fetch(url, {
         method: 'POST',
         headers: { 'Content-Type': 'application/json', 'Accept': 'application/json, text/event-stream' },
         body: JSON.stringify({
@@ -220,15 +231,13 @@ export class HealthProbeRunner {
       const headers: Record<string, string> = { 'Content-Type': 'application/json', 'Accept': 'application/json, text/event-stream' };
       if (sessionId) headers['Mcp-Session-Id'] = sessionId;
 
-      // Send initialized notification
+      await fetch(baseUrl, {
-      await fetch(url, {
         method: 'POST', headers,
         body: JSON.stringify({ jsonrpc: '2.0', method: 'notifications/initialized' }),
         signal: controller.signal,
       });
 
-      // Call health check tool
+      const toolResp = await fetch(baseUrl, {
-      const toolResp = await fetch(url, {
         method: 'POST', headers,
         body: JSON.stringify({
           jsonrpc: '2.0', id: 2, method: 'tools/call',
@@ -244,7 +253,6 @@ export class HealthProbeRunner {
       }
 
       const body = await toolResp.text();
-      // Check for JSON-RPC error in response
       try {
         const parsed = JSON.parse(body.includes('data: ') ? body.split('data: ')[1]!.split('\n')[0]! : body);
         if (parsed.error) {
@@ -260,6 +268,146 @@ export class HealthProbeRunner {
     }
   }
 
+  /**
+   * Probe an SSE-transport MCP server.
+   * SSE protocol: GET /sse → endpoint event → POST /messages?session_id=...
+   */
+  private async probeSse(
+    baseUrl: string,
+    healthCheck: HealthCheckSpec,
+    timeoutMs: number,
+  ): Promise<ProbeResult> {
+    const start = Date.now();
+    const controller = new AbortController();
+    const timer = setTimeout(() => controller.abort(), timeoutMs);
+
+    try {
+      // 1. Connect to SSE endpoint to get the message URL
+      const sseResp = await fetch(`${baseUrl}/sse`, {
+        method: 'GET',
+        headers: { 'Accept': 'text/event-stream' },
+        signal: controller.signal,
+      });
+
+      if (!sseResp.ok) {
+        return { healthy: false, latencyMs: Date.now() - start, message: `SSE connect HTTP ${sseResp.status}` };
+      }
+
+      // 2. Read the SSE stream to find the endpoint event
+      const reader = sseResp.body?.getReader();
+      if (!reader) {
+        return { healthy: false, latencyMs: Date.now() - start, message: 'No SSE stream body' };
+      }
+
+      const decoder = new TextDecoder();
+      let buffer = '';
+      let messagesUrl = '';
+
+      // Read until we get the endpoint event
+      while (!messagesUrl) {
+        const { done, value } = await reader.read();
+        if (done) break;
+        buffer += decoder.decode(value, { stream: true });
+
+        for (const line of buffer.split('\n')) {
+          if (line.startsWith('data: ') && buffer.includes('event: endpoint')) {
+            const endpoint = line.slice(6).trim();
+            // Endpoint may be relative (e.g., /messages?session_id=...) or absolute
+            messagesUrl = endpoint.startsWith('http') ? endpoint : `${baseUrl}${endpoint}`;
+          }
+        }
+        // Keep only the last incomplete line
+        const lines = buffer.split('\n');
+        buffer = lines[lines.length - 1] ?? '';
+      }
+
+      if (!messagesUrl) {
+        reader.cancel();
+        return { healthy: false, latencyMs: Date.now() - start, message: 'No endpoint event from SSE' };
+      }
+
+      // 3. Initialize via the messages endpoint
+      const postHeaders = { 'Content-Type': 'application/json' };
+
+      const initResp = await fetch(messagesUrl, {
+        method: 'POST', headers: postHeaders,
+        body: JSON.stringify({
+          jsonrpc: '2.0', id: 1, method: 'initialize',
+          params: { protocolVersion: '2024-11-05', capabilities: {}, clientInfo: { name: 'mcpctl-health', version: '0.1.0' } },
+        }),
+        signal: controller.signal,
+      });
+
+      if (!initResp.ok) {
+        reader.cancel();
+        return { healthy: false, latencyMs: Date.now() - start, message: `Initialize HTTP ${initResp.status}` };
+      }
+
+      // 4. Send initialized notification
+      await fetch(messagesUrl, {
+        method: 'POST', headers: postHeaders,
+        body: JSON.stringify({ jsonrpc: '2.0', method: 'notifications/initialized' }),
+        signal: controller.signal,
+      });
+
+      // 5. Call health check tool
+      const toolResp = await fetch(messagesUrl, {
+        method: 'POST', headers: postHeaders,
+        body: JSON.stringify({
+          jsonrpc: '2.0', id: 2, method: 'tools/call',
+          params: { name: healthCheck.tool, arguments: healthCheck.arguments ?? {} },
+        }),
+        signal: controller.signal,
+      });
+
+      const latencyMs = Date.now() - start;
+
+      // 6. Read tool response from SSE stream
+      // The response comes back on the SSE stream, not the POST response
+      let responseBuffer = '';
+      const readTimeout = setTimeout(() => reader.cancel(), 5000);
+
+      while (true) {
+        const { done, value } = await reader.read();
+        if (done) break;
+        responseBuffer += decoder.decode(value, { stream: true });
+
+        // Look for data lines containing our response (id: 2)
+        for (const line of responseBuffer.split('\n')) {
+          if (line.startsWith('data: ')) {
+            try {
+              const parsed = JSON.parse(line.slice(6));
+              if (parsed.id === 2) {
+                clearTimeout(readTimeout);
+                reader.cancel();
+                if (parsed.error) {
+                  return { healthy: false, latencyMs, message: parsed.error.message ?? 'Tool call error' };
+                }
+                return { healthy: true, latencyMs, message: 'ok' };
+              }
+            } catch {
+              // Not valid JSON, skip
+            }
+          }
+        }
+        const respLines = responseBuffer.split('\n');
+        responseBuffer = respLines[respLines.length - 1] ?? '';
+      }
+
+      clearTimeout(readTimeout);
+      reader.cancel();
+
+      // If POST response itself was ok (202 for SSE), consider it healthy
+      if (toolResp.ok) {
+        return { healthy: true, latencyMs, message: 'ok' };
+      }
+
+      return { healthy: false, latencyMs, message: `Tool call HTTP ${toolResp.status}` };
+    } finally {
+      clearTimeout(timer);
+    }
+  }
+
   /**
    * Probe a STDIO MCP server by running `docker exec` with a disposable Node.js
    * script that pipes JSON-RPC messages into the package binary.