feat(runtime): bridge user-input events and API to external GUI clients

[gaord]

Summary

The TUI engine already emits EngineEvent::UserInputRequired and the Engine handle exposes submit_user_input / cancel_user_input, but the runtime API layer (used by external GUI clients like VSCode extensions) was missing the plumbing to propagate these events or accept responses. This meant request_user_input tool calls would hang indefinitely in GUI mode with no dialog appearing.

Changes

1. approval.rs — Timeout protection for await_user_input

• Added a 5-minute timeout (USER_INPUT_TIMEOUT) around the rx_user_input.recv() call
• On timeout, the engine emits a Status event and returns a ToolError
• Prevents a disconnected GUI from stalling the agent loop forever

2. runtime_threads.rs — Event forwarding + manager methods + interrupt fix

• Event forwarding: Handle EngineEvent::UserInputRequired in the event loop, emitting a "user_input.required" SSE event with the input ID and full request payload (questions, options)
• Manager methods: Added submit_user_input() and cancel_user_input() on RuntimeThreadManager that delegate to the Engine handle
• Interrupt fix: interrupt_turn() now immediately clears active_turn and emits "turn.completed" so the thread accepts new messages after /interrupt — this prevents persistent 409 "Thread already has an active turn" errors

3. runtime_api.rs — REST endpoint for user input submission

• Added POST /v1/user-input/{thread_id}/{input_id} endpoint
• Accepts { "answers": [{ "id": "...", "label": "...", "value": "..." }] }
• Delivers responses to the engine via RuntimeThreadManager::submit_user_input()

Flow

Tool calls request_user_input
  → approval.rs sends Event::UserInputRequired
  → runtime_threads.rs forwards as SSE "user_input.required"
  → GUI displays dialog with option buttons
  → GUI calls POST /v1/user-input/{thread_id}/{input_id}
  → runtime_api.rs delivers to engine via channel
  → approval.rs receives answer, returns to tool

Testing

• cargo check -p codewhale-tui passes
• cargo clippy -p codewhale-tui --all-targets passes (no new warnings)
• Verified end-to-end with VSCode extension (CodeWhale VSCode) that user input dialogs appear and responses are correctly delivered

Related

• Mirrors the existing approval flow (approval.required SSE + POST /v1/approvals/{id}) that already works for tool authorization dialogs

[gemini-code-assist]

Code Review

This pull request introduces a 300-second timeout for user input requests and adds a new API endpoint for submitting user input. It also updates the runtime thread manager to handle user input events and modifies turn interruption logic. Feedback suggests improving error handling consistency by using standard error mapping for missing threads and removing redundant turn finalization code that could cause duplicate events and data loss.