fix(dev): forward custom headers from web UI proxy to local agent

The Agent Inspector web UI proxy (handleInvocations) constructs new
headers when proxying to the local Python/TS agent but never reads
or forwards req.headers from the incoming request. This causes all
x-amzn-bedrock-agentcore-runtime-custom-* headers to be silently
dropped.

The direct CLI invoke path already does this correctly via
...customHeaders spread — this patch brings the web UI proxy path
to parity.

Also applies the same fix to handleAguiInvocation which has the
same issue.

Reproduction:
1. agentcore create --name Test --framework Strands --model-provider Bedrock --protocol HTTP
2. agentcore dev (launches Inspector on 8081, agent on 8082)
3. curl -X POST http://localhost:8081/invocations -H 'X-Agentcore-Local: true' -H 'X-Amzn-Bedrock-AgentCore-Runtime-Custom-MyHeader: test-value' -H 'Content-Type: application/json' -d '{"prompt":"Hello"}'
4. Observe: custom header is NOT received by the Python agent
5. After fix: custom header IS received

Tested on CLI v0.25.0, Node.js 23.11.0, macOS ARM64.

Author: lavaraja

src/cli/operations/dev/web-ui/handlers/invocations.ts

@@ -11,6 +11,21 @@ import { type IncomingMessage, type ServerResponse, request as httpRequest } fro
 
 let a2aRequestId = 1;
 
+/**
+ * Forward allowlisted custom headers from the incoming request.
+ * Currently forwards all `x-amzn-bedrock-agentcore-runtime-custom-*` headers
+ * which are the documented custom header prefix for AgentCore Runtime.
+ */
+function forwardCustomHeaders(req: IncomingMessage, headers: Record<string, string>): void {
+  if (req.headers) {
+    for (const [key, value] of Object.entries(req.headers)) {
+      if (key.startsWith('x-amzn-bedrock-agentcore-runtime-custom-') && typeof value === 'string') {
+        headers[key] = value;
+      }
+    }
+  }
+}
+
 /**
  * POST /invocations — proxy to the selected agent.
  * Body must include agentName to route to the correct running agent.
@@ -84,7 +99,7 @@ export async function handleInvocations(
 
   // AGUI agents need RunAgentInput body; SSE response is passed through raw
   if (agentProtocol === 'AGUI') {
-    return handleAguiInvocation(ctx, res, body, agentPort, sessionId, userId, origin);
+    return handleAguiInvocation(ctx, req, res, body, agentPort, sessionId, userId, origin);
   }
 
   return new Promise<void>((resolve, reject) => {
@@ -96,6 +111,8 @@ export async function handleInvocations(
     if (userId) {
       headers['x-amzn-bedrock-agentcore-runtime-user-id'] = userId;
     }
+    // Forward custom headers from the incoming request
+    forwardCustomHeaders(req, headers);
 
     const proxyReq = httpRequest(
       {
@@ -277,6 +294,7 @@ async function handleA2AInvocation(
  */
 async function handleAguiInvocation(
   ctx: RouteContext,
+  req: IncomingMessage,
   res: ServerResponse,
   rawBody: string,
   agentPort: number,
@@ -314,6 +332,8 @@ async function handleAguiInvocation(
     if (userId) {
       headers['x-amzn-bedrock-agentcore-runtime-user-id'] = userId;
     }
+    // Forward custom headers from the incoming request
+    forwardCustomHeaders(req, headers);
 
     const proxyReq = httpRequest(
       {