feat(rust): add WebSocket (WSS) support with typed channel clients

[iamnamananand996]

Description

Refs #12338

POC for WebSocket/WSS support in the Rust SDK generator. Adds a tokio-tungstenite-based runtime and a code generator that reads ir.websocketChannels to emit typed per-channel Rust client structs with send/receive methods.

Link to Devin run: https://app.devin.ai/sessions/9a2809fa93d24d13be0c3c338e042e91
Requested by: @iamnamananand996

Changes Made

Runtime (websocket.rs — new as-is file)

• WebSocketClient struct with async connect, send_json, send_raw, close
• WebSocketOptions (headers, query params, reconnection config)
• WebSocketState enum and parse_websocket_message<T> helper
• Feature-gated behind #[cfg(feature = "websocket")], matching the SSE pattern

Generator (WebSocketChannelGenerator.ts — new)

• Reads ir.websocketChannels and emits one Rust file per channel under src/api/websocket/
• Generates typed ServerMessage enum (serde-tagged), client struct, connect, per-message send_*, recv, and close methods
• Generates mod.rs with re-exports

Integration (modified files)

• AbstractRustGeneratorContext.ts — hasWebSocketChannels(), optional deps (tokio-tungstenite, urlencoding), websocket Cargo feature
• SdkGeneratorCli.ts — wires generator into pipeline, adds websocket module to API mod file
• SdkGeneratorContext.ts — conditionally includes websocket.rs in core as-is files
• ErrorGenerator.ts — adds WebSocketError variant
• AsIs.ts / mod.rs — registers and exports the new as-is file

⚠️ Important Review Notes

This is a proof-of-concept — the following items are intentionally incomplete or need scrutiny:

1. read_loop is stubbed: The read half of the split WebSocket stream is never stored or consumed. incoming_rx will never yield messages. The receive path is non-functional — this needs a real implementation before shipping.

2. No seed fixtures: The generated Rust code has not been validated to compile or run against a real IR with WebSocket channels. Recommend adding a WebSocket test case to the exhaustive seed fixture.

3. String-based code generation: WebSocketChannelGenerator builds Rust via string templates. Typos or incorrect type references won't be caught until Rust compile time. Needs validation.

4. Path expression building: buildPathExpression uses IR property names directly in format strings — verify these match the snake_case parameter names in the generated connect() method.

5. Channel wiring confusion: Two unbounded channels are created in connect() but only one is used. The outgoing_tx is stored but never consumed. The read half from ws_stream.split() is also unused.

6. Missing explicit http crate dependency: websocket.rs references http::uri::InvalidUri but http isn't explicitly listed (may come transitively via tokio-tungstenite).

Human Review Checklist

• Verify read half of split stream and channel wiring make sense before shipping
• Confirm http crate is available transitively or add explicit dep
• Validate generated Rust compiles with a real WebSocket channel IR fixture
• Review buildPathExpression output against generated connect() parameter names

Updates since last revision

• Updated 9 ErrorGenerator test snapshots to include the new WebSocketError variant (all tests now pass)

Testing

• Lint checks pass (pnpm run check)
• ErrorGenerator snapshots updated for WebSocketError variant
• Seed test fixtures added — None added (POC)
• Manual testing completed — Not tested (POC)

Next steps before production-ready:

• Implement actual read_loop to consume WebSocket messages
• Add seed test fixture with WebSocket channel definition
• Verify generated code compiles and runs
• Fix channel wiring and unused variables

[devin-ai-integration]

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