Spec desktop web active-text input bridge

[warp-agent-staging]

Summary

• Define product behavior for a desktop web text-input bridge whenever a focused Warp view owns an active editable text caret.
• Specify a transparent focused <textarea> with native multiline textbox semantics and the existing sentinel input-sink model.
• Reuse WarpUI's existing cross-platform active_cursor_position contract across plain-text, code, rich-text, and raw-terminal views.
• Define single-owner routing for hardware keyboard, dictation/direct input, paste, and IME composition.
• Keep the existing mobile soft-keyboard manager and behavior unchanged.

Key decisions

• Use <textarea>, not <input> or contenteditable.
• Do not mirror surface contents or DOM selection in this scope.
• Keep the bridge focused while any editable Warp surface reports an active text caret.
• Exclude read-only, disabled, selectable-only, and hidden-caret states by tightening the existing active-caret contract.
• Support MacWhisper-class tools, macOS/browser dictation, keyboard, paste, and CJK IME; defer autofill/password managers and full screen-reader navigation.

Scope revision

The initial spec proposed a prompt-only surface gate. After requester feedback, code research showed that WarpUI already has a general focused active-caret signal used by native IME positioning. The revised spec uses that existing abstraction because it requires fewer special cases and prevents silent dictation failure in other real text fields.

Validation

Documentation-only spec PR. The tech spec requires automated event/focus tests, WASM compilation checks, Chrome and Safari MacWhisper videos across every editor family, read-only negative cases, and iOS/Android mobile regression checks during implementation.

Linear: https://linear.app/warpdotdev/issue/REMOTE-2591/warp-for-web-macwhisperdictation-tools-cannot-attach-to-prompt-input

Conversation: https://staging.warp.dev/conversation/299454b2-a3fa-4305-82e8-6d49f4eff0f7
Run: https://oz.staging.warp.dev/runs/019fdd9b-5026-7e48-b72a-9d4aa22c6d7e

Co-Authored-By: Warp Agent agent@warp.dev

This PR was generated with Oz.