Node-target WebSocket upgrade returns 500 due to dual-instance Symbol mismatch

[astrobot-houston]

Originally reported by @k161196 in #197.

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Describe the Bug

Node-target builds (@flue/cli) return HTTP 500 on every WebSocket upgrade request to /agents/:name/:id. The root cause is a dual-instance Symbol mismatch: @flue/cli bundles @hono/node-server into the generated dist/server.mjs, while the generated entry also imports createNodeWebSocketTransport from @flue/runtime/node (kept external), which re-imports upgradeWebSocket from a separate disk copy of @hono/node-server. The two module instances produce two distinct WAIT_FOR_WEBSOCKET_SYMBOL identities — injectWebSocket writes symbol A onto env, but upgradeWebSocket reads symbol B, finds undefined, and returns new Response(null, { status: 500 }). The same dual-copy problem applies to the ws package.

Expected Behavior

WebSocket upgrade requests to /agents/:name/:id on node-target builds should complete successfully with a 101 Switching Protocols response, allowing the SDK client to stream events over the connection.

Steps to Reproduce

1. Build a Flue project targeting Node (e.g., starting from examples/hello-world/ with the node target configured).
2. Start the built server from dist/server.mjs.
3. Attempt a WebSocket connection to /agents/:name/:id (e.g., via the SDK client or a WebSocket tool).
4. Observe that the server responds with HTTP 500 instead of upgrading the connection.

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Original implementation from #197 by @k161196