fix(tui): honor display.busy_input_mode in TUI v2 (#17110)

* fix(tui): honor display.busy_input_mode in TUI v2

The TUI v2 frontend hard-coded `composerActions.enqueue(full)` whenever
`ui.busy` was true. The classic CLI and gateway adapters honor the
`display.busy_input_mode` config key (`interrupt` | `queue` | `steer`),
but Ink ignored it — sending a message during a long-running turn always
landed in the queue regardless of config. The config default is already
`interrupt` (hermes_cli/config.py), so users who explicitly opted into
that experience were silently stuck on the legacy queue path.

This wires the value through the existing config-sync surface:

* `applyDisplay` now reads `display.busy_input_mode`, defaults to
  `interrupt` (matching `_load_busy_input_mode` in tui_gateway), and
  drops it into a new `UiState.busyInputMode` field.
* `dispatchSubmission` and the queue-edit fall-through call a shared
  `handleBusyInput` helper that branches on the mode:
    * `queue`     — legacy behavior, append to the queue.
    * `steer`     — call `session.steer`; on rejection, fall back to
                    queue with a sys note.
    * `interrupt` — `turnController.interruptTurn(...)` then `send()`,
                    so the new prompt actually moves.
* Mtime polling in `useConfigSync` already re-applies `config.full`, so
  flipping `display.busy_input_mode` in `~/.hermes/config.yaml` takes
  effect on the next 5s tick without restarting the TUI.

Tests:
* `applyDisplay → busy_input_mode` covers normalization + UiState fan-out.
* `normalizeBusyInputMode` mirrors the Python side's allow-list.

Validation:
* `npm run type-check` (in `ui-tui/`) — clean.
* `npm test --run` (in `ui-tui/`) — 394/394.

* review(copilot): narrow busy_input_mode type, preserve queue order on steer fallback

* review(copilot): clarify handleBusyInput comment (option, not return value)

* fix(tui): default busy_input_mode to queue in TUI (CLI keeps interrupt)

In a full-screen TUI users typically author the next prompt while the
agent is still streaming, so an unintended interrupt loses in-flight
typing.  TUI fallback now defaults to `queue`; CLI / messaging
adapters keep `interrupt` as the framework default.

Override per-config via `display.busy_input_mode: interrupt` (or
`steer`) — the normalize/wire path is unchanged, only the missing-
value branch differs from the Python default.

uiStore initial value also flipped to `queue` so first-frame render
before `config.full` lands matches the eventual normalized value.

ui-tui/src/app/interfaces.ts

@@ -27,6 +27,8 @@ export interface StateSetter<T> {
 
 export type StatusBarMode = 'bottom' | 'off' | 'top'
 
+export type BusyInputMode = 'interrupt' | 'queue' | 'steer'
+
 export interface SelectionApi {
   captureScrolledRows: (firstRow: number, lastRow: number, side: 'above' | 'below') => void
   clearSelection: () => void
@@ -85,6 +87,7 @@ export interface TranscriptRow {
 export interface UiState {
   bgTasks: Set<string>
   busy: boolean
+  busyInputMode: BusyInputMode
   compact: boolean
   detailsMode: DetailsMode
   detailsModeCommandOverride: boolean

ui-tui/src/app/uiStore.ts

@@ -9,6 +9,7 @@ import type { UiState } from './interfaces.js'
 const buildUiState = (): UiState => ({
   bgTasks: new Set(),
   busy: false,
+  busyInputMode: 'queue',
   compact: false,
   detailsMode: 'collapsed',
   detailsModeCommandOverride: false,

ui-tui/src/app/useConfigSync.ts

@@ -10,7 +10,7 @@ import type {
 } from '../gatewayTypes.js'
 import { asRpcResult } from '../lib/rpc.js'
 
-import type { StatusBarMode } from './interfaces.js'
+import type { BusyInputMode, StatusBarMode } from './interfaces.js'
 import { turnController } from './turnController.js'
 import { patchUiState } from './uiStore.js'
 
@@ -24,6 +24,27 @@ const STATUSBAR_ALIAS: Record<string, StatusBarMode> = {
 export const normalizeStatusBar = (raw: unknown): StatusBarMode =>
   raw === false ? 'off' : typeof raw === 'string' ? (STATUSBAR_ALIAS[raw.trim().toLowerCase()] ?? 'top') : 'top'
 
+const BUSY_MODES = new Set<BusyInputMode>(['interrupt', 'queue', 'steer'])
+
+// TUI defaults to `queue` even though the framework default
+// (`hermes_cli/config.py`) is `interrupt`.  Rationale: in a full-screen
+// TUI you're typically authoring the next prompt while the agent is
+// still streaming, and an unintended interrupt loses work.  Set
+// `display.busy_input_mode: interrupt` (or `steer`) explicitly to
+// opt out per-config; CLI / messaging adapters keep their `interrupt`
+// default unchanged.
+const TUI_BUSY_DEFAULT: BusyInputMode = 'queue'
+
+export const normalizeBusyInputMode = (raw: unknown): BusyInputMode => {
+  if (typeof raw !== 'string') {
+    return TUI_BUSY_DEFAULT
+  }
+
+  const v = raw.trim().toLowerCase() as BusyInputMode
+
+  return BUSY_MODES.has(v) ? v : TUI_BUSY_DEFAULT
+}
+
 const MTIME_POLL_MS = 5000
 
 const quietRpc = async <T extends Record<string, any> = Record<string, any>>(
@@ -43,6 +64,7 @@ export const applyDisplay = (cfg: ConfigFullResponse | null, setBell: (v: boolea
 
   setBell(!!d.bell_on_complete)
   patchUiState({
+    busyInputMode: normalizeBusyInputMode(d.busy_input_mode),
     compact: !!d.tui_compact,
     detailsMode: resolveDetailsMode(d),
     detailsModeCommandOverride: false,

ui-tui/src/app/useSubmission.ts

@@ -4,7 +4,12 @@ import { TYPING_IDLE_MS } from '../config/timing.js'
 import { attachedImageNotice } from '../domain/messages.js'
 import { looksLikeSlashCommand } from '../domain/slash.js'
 import type { GatewayClient } from '../gatewayClient.js'
-import type { InputDetectDropResponse, PromptSubmitResponse, ShellExecResponse } from '../gatewayTypes.js'
+import type {
+  InputDetectDropResponse,
+  PromptSubmitResponse,
+  SessionSteerResponse,
+  ShellExecResponse
+} from '../gatewayTypes.js'
 import { asRpcResult } from '../lib/rpc.js'
 import { hasInterpolation, INTERPOLATION_RE } from '../protocol/interpolation.js'
 import { PASTE_SNIPPET_RE } from '../protocol/paste.js'
@@ -207,6 +212,70 @@ export function useSubmission(opts: UseSubmissionOptions) {
     [interpolate, send, shellExec]
   )
 
+  // Honors `display.busy_input_mode` from config.yaml (CLI parity):
+  //   - 'queue'     (legacy): append to queueRef; drains on busy → false
+  //   - 'steer'     : inject into the current turn via session.steer; falls
+  //                   back to queue when steer is rejected (no agent / no
+  //                   tool window).
+  //   - 'interrupt' (default): cancel the in-flight turn, then send the
+  //                   new text as a fresh prompt so it actually moves.
+  //
+  // `opts.fallbackToFront` controls whether a steer fallback re-inserts
+  // at the front of the queue (used by the queue-edit path to preserve
+  // a picked item's position); the mainline submit path always appends.
+  const handleBusyInput = useCallback(
+    (full: string, opts: { fallbackToFront?: boolean } = {}) => {
+      const live = getUiState()
+      const mode = live.busyInputMode
+      const fallback = (note: string) => {
+        if (opts.fallbackToFront) {
+          composerRefs.queueRef.current.unshift(full)
+          composerActions.syncQueue()
+        } else {
+          composerActions.enqueue(full)
+        }
+        sys(note)
+      }
+
+      if (mode === 'queue') {
+        return composerActions.enqueue(full)
+      }
+
+      if (mode === 'steer' && live.sid) {
+        gw.request<SessionSteerResponse>('session.steer', { session_id: live.sid, text: full })
+          .then(raw => {
+            const r = asRpcResult<SessionSteerResponse>(raw)
+
+            if (r?.status !== 'queued') {
+              fallback('steer rejected — message queued for next turn')
+            }
+          })
+          .catch(() => fallback('steer failed — message queued for next turn'))
+
+        return
+      }
+
+      // 'interrupt' (default): tear down the current turn, then send.
+      // `interruptTurn` fires `session.interrupt` without awaiting; if
+      // the gateway is still mid-response when `prompt.submit` lands,
+      // `send()`'s catch path re-queues with a "queued: ..." sys note
+      // (`isSessionBusyError`) — so a lost race degrades to queue
+      // semantics, not a dropped message.
+      if (live.sid) {
+        turnController.interruptTurn({ appendMessage, gw, sid: live.sid, sys })
+      }
+
+      if (hasInterpolation(full)) {
+        patchUiState({ busy: true })
+
+        return interpolate(full, send)
+      }
+
+      send(full)
+    },
+    [appendMessage, composerActions, composerRefs, gw, interpolate, send, sys]
+  )
+
   const dispatchSubmission = useCallback(
     (full: string) => {
       if (!full.trim()) {
@@ -252,9 +321,16 @@ export function useSubmission(opts: UseSubmissionOptions) {
         }
 
         if (getUiState().busy) {
-          composerRefs.queueRef.current.unshift(picked)
+          // 'interrupt' / 'steer' should reach the live turn instead of
+          // silently going back to the queue.  handleBusyInput resolves
+          // mode-specific behavior (interrupt-and-send, steer, or queue).
+          if (getUiState().busyInputMode === 'queue') {
+            composerRefs.queueRef.current.unshift(picked)
 
-          return composerActions.syncQueue()
+            return composerActions.syncQueue()
+          }
+
+          return handleBusyInput(picked, { fallbackToFront: true })
         }
 
         return sendQueued(picked)
@@ -263,7 +339,7 @@ export function useSubmission(opts: UseSubmissionOptions) {
       composerActions.pushHistory(full)
 
       if (getUiState().busy) {
-        return composerActions.enqueue(full)
+        return handleBusyInput(full)
       }
 
       if (hasInterpolation(full)) {
@@ -274,7 +350,17 @@ export function useSubmission(opts: UseSubmissionOptions) {
 
       send(full)
     },
-    [appendMessage, composerActions, composerRefs, interpolate, send, sendQueued, shellExec, slashRef]
+    [
+      appendMessage,
+      composerActions,
+      composerRefs,
+      handleBusyInput,
+      interpolate,
+      send,
+      sendQueued,
+      shellExec,
+      slashRef
+    ]
   )
 
   const submit = useCallback(