fix(pi): render input dialogs as free-text questions#33494

Pi extension input dialogs displayed their placeholder as the question and offered a fake “Submit empty value” option. They now use the existing free-text/editor card: a generic header, the unchanged title as the question, no preset options, and the composer for the answer.

Reuse initialAnswer: "" so both clients preserve exact text and accept an intentionally empty answer. Web and mobile use “Type your answer” for this existing literal-answer flow. Select behavior and editor prefill remain covered by the existing tests.

Validation:

• Test-first adapter proof: the input mapping assertion failed on upstream main; the literal-answer assertion failed before the second fix. All 120 Pi adapter tests pass, including whitespace, empty string, cancellation, select values and editor prefill. Another 20 shared answer/draft tests pass.
• pnpm exec vp run check:changed passes all nine tasks. No full suite was run.
• A credential-free real Pi 1.5 extension called ctx.ui.input in an isolated web client. The extension received {"value":" SQLite","cancelled":false} and {"value":"","cancelled":false}. The slash command made no model request.

This implements selected Paper A. Pi-specific placeholder hints remain deferred: there is no placeholder wire field, and the question is not rewritten to include the hint. Literal newlines remain intact in the adapter; their visual presentation is separate #33353, whose patch is not included. Extension-specific structured select recovery is outside this change.

Web was exercised; desktop shares that component. Mobile's draft seeding, exact/empty answer handling, input field and placeholder were audited in source. Native mobile keyboard/layout, the Electron shell, and a live cancellation roundtrip were not separately verified; cancellation is covered at the adapter boundary.

Small change: 36 production lines changed, no new state or interface. Separate trim and proof-auditor runs skipped under the small-change rule. Local cubic flagged the deferred placeholder hint; appending it would violate the selected unchanged-question design. Its earlier mobile-copy finding was fixed; its multiline-input concern follows the explicitly selected existing editor behavior. Optional review nits on comment wording and the blank-placeholder case were retained. Design-lens follow-up: if future providers combine initialAnswer with options, revisit the hint condition; today Pi only emits it for optionless questions.

Council review

No blocker or should finding remains. Round 2 includes the mobile hint correction. The final commit only adds model credits.

Created with GPT 6.1 Sol (implementation and review) through Codex, Claude Opus 5.5 (review) through Claude, and Grok 4.7 (Grok) (review and evidence) through Grok, in T3 Code.

Closes #23494