fix(tui): preserve IME text before return submit

[InphinitiZ]

Summary

• Preserve printable IME commit text when xterm delivers it in the same input burst as Return.
• Submit the pending value from the Return keypath so Dashboard/TUI sends the visible draft instead of dropping the final segment.
• Add focused regression coverage for Return-burst inputs and fix the execFileNoThrow stdio tuple typing that blocked ui-tui type-check.

Why

A browser/xterm IME flow can deliver finalized CJK text immediately followed by Return in one input burst, e.g. 会丢失内容\r. The previous Return branch submitted vRef.current before the printable prefix had gone through the ordinary input path, so the prompt visible in the UI could be longer than the submitted prompt.

This is adjacent to #39246, but covers the "IME commit text + Return in the same burst should submit the visible draft" path rather than absorbing Enter as an IME-confirmation guard. Desktop IME syncing is left to #39435.

Scope

This targets the ui-tui text input path used by the Dashboard chat's embedded TUI/xterm session. It does not touch the Electron Desktop composer (apps/desktop/...); the separate Desktop IME sync issue is covered by #39435.

Test Plan

• git diff --cached --check
• Static scan of added lines for hardcoded secrets / shell injection / eval / pickle / SQL injection patterns
• npm run test --workspace ui-tui -- src/__tests__/textInputReturnBurst.test.ts
• npm run type-check --workspace ui-tui
• npm run build --workspace ui-tui
• Independent reviewer pass: no security concerns or logic errors

[teknium1]

Thanks for the focused TUI fix. The current shared Return path still submits vRef.current without incorporating inp (ui-tui/src/components/textInput.tsx:990-999), so the reported combined IME-text-plus-Return burst remains actionable. The proposed helper reuses applyPrintableInsert, including selection handling, and applies the pending value consistently to both submit and newline paths.

Automated hermes-sweeper review.

[teknium1]

Thanks for this fix! It was salvaged into #86761 (cherry-picked onto current main with your authorship preserved in the commit history) and is now merged. Closing since the work has landed.