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Chat composer send/interrupt morph: disable Send + one-tap interrupt while working

ADR-0016 shipped the embedded chat with a composer that stayed sendable while the agent worked — a mid-turn reply was delivered as a bracketed paste and the agent's own TUI queued it, with the UI showing a subtle "queued" hint — and put Interrupt behind a two-step confirm tap, distinct from the run Stop. ADR-0019 then made the composer Send an icon-only paper-plane. In practice the queue affordance misleads (the reply vanishes into the TUI with no in-lab echo, and "queued" reads as a promise lab can't show being kept) and the confirm tap adds friction to the one intervention an operator reaches for most — interrupting a turn that has gone the wrong way. The Claude app models this better: while the agent is working, Send is replaced by a single interrupt control.

This ADR records that change. It is a pure frontend/CSS diff within the existing design language — no colour/type/radius/shadow redesign, and no backend/API/SSE/message-schema/provider/migration change — the same class of change as ADR-0019. It evolves ADR-0016, superseding two of its pinned bullets (the queue hint and the confirm-tap interrupt); the rest of ADR-0016 stands.

The decisions, pinned (settled with the maintainer 2026-07-07 via /frontend-design + /grill-me — do not re-litigate):

  • One morphing composer button replaces the [Send + separate Interrupt] pair. Same slot; the glyph, action, and accessible name swap on the conversational state. idle / needs_input → a send paper-plane, accessible name "Send", disabled when the input is empty or a send is in flight, click replies through the existing replyRun flow (unchanged). working → a square, accessible name "Interrupt", always enabled, one tap calls interruptRun (the tmux Escape), showing a busy "…" while the request is in flight.

  • Strict swap — queueing is dropped from the UI (supersedes ADR-0016). There is no Send affordance while the agent works and the "your reply will be queued" hint is removed. The textarea stays editable while working (compose-ahead), but nothing can be sent until the agent returns to idle/needs_input. The backend Reply (tmux bracketed-paste + Enter) is unchanged — it is simply no longer reachable from the UI mid-turn. This supersedes ADR-0016's "a mid-turn agent queues it … the UI shows a subtle 'queued' hint."

  • One-tap interrupt — no confirm (supersedes ADR-0016). The working-state square interrupts immediately. Interrupt is non-destructive — the agent survives, idles, and is re-promptable — and it is the primary intervention affordance, so a confirm tap is pure friction. This supersedes ADR-0016's "Interrupt is an explicit Escape behind a confirm tap."

  • Consistency — the same one-tap square everywhere it appears in the composer. The two-step InterruptButton is replaced by the identical one-tap square in all three composer sites: the working-state morph, the question-without-structured-dialog locked state, and the DialogPanel escape hatch. Accessible name "Interrupt" in every case.

  • Lexicon and separation from the header Stop. The accessible name is "Interrupt", never "Abort/Cancel/Stop" (CONTEXT.md forbids cancel/abort/ kill on the Neutral Stop concept, and ADR-0016 already names this action "Interrupt"; the maintainer said "abort" colloquially, but the UI stays "Interrupt"). The square glyph is shared with the header Stop but the two stay distinct: header Stop = danger-red, two-step verbal confirm, destructive teardown (ADR-0019, unchanged); composer Interrupt = accent, one-tap, non-destructive. ADR-0019's "icon-only never applies to a destructive confirmation" still holds — the destructive one (Stop) keeps its verbal confirm; the non-destructive one (Interrupt) is icon-only and one-tap.

  • An honest working cue. The removed "queued" hint is replaced by a calm line — "The agent is working — tap to interrupt." — that describes what the square does rather than promising a queued send.

  • Composer polish, all within the design language. (a) Cmd/Ctrl+Enter sends in the idle/needs_input state only — never bare Enter, so a phone's return key inserts a newline instead of firing a send [overturned on fine-pointer devices by ADR-0031, 2026-07-09 — bare Enter now sends there; touch devices are unaffected]; the shortcut is inert while working (no keyboard interrupt — the square is the only interrupt). (b) The textarea auto-grows from one row to a capped height then scrolls, replacing the fixed rows={1} + resize: vertical. (c) The working-state square carries a subtle pulse, gated by @media (prefers-reduced-motion: reduce).

Status

Superseded by ADR-0029 (issue #61): the working-state morph and its send-block are reversed — Send is always available and Interrupt lives in the chat header. ADR-0022's supersessions of ADR-0016 (no queued hint; one-tap interrupt) remain in force via ADR-0029.

[This ADR's bare-Enter-stays-a-newline clause, and the corresponding rejected option below, are additionally superseded/overturned by ADR-0031 (issue #70, 2026-07-09): bare Enter now sends on fine-pointer devices. Touch devices keep the original return-as-newline behaviour.]

Accepted. A pure SPA diff: web/src/routes/RunChat.tsx, web/src/base.css, and web/src/routes/RunChat.test.tsx, plus this ADR and the two compat.md notes below. No Go, API, SSE, message-schema, provider, or migration change. A future Codex/Gemini provider inherits the composer behaviour for free — it is provider-agnostic.

Considered options

  • Keep the queue-while-working composer (ADR-0016 status quo). Rejected: the reply disappears into the agent's TUI with no in-lab echo, and the "queued" copy reads as a promise lab cannot visibly keep. Compose-ahead (an editable textarea whose send is gated until the agent idles) gives the same "type now, send soon" without the misleading affordance.
  • Keep the two-step confirm on Interrupt. Rejected: interrupt is non-destructive and re-promptable, and it is the affordance an operator reaches for most when a turn goes wrong — a confirm tap is friction on the hot path. The confirm stays only on the genuinely destructive header Stop.
  • Bare Enter sends (with Shift+Enter for a newline). Rejected: the composer is phone-first (ADR-0005) and a mobile keyboard's return key must insert a newline, not submit. Cmd/Ctrl+Enter is the explicit send; bare Enter is always a newline. [Rejected then, overturned for fine-pointer devices by ADR-0031, 2026-07-09 — phones and other touch-only devices keep this rejection in force; the reversal applies only where a fine pointer is present.]
  • Style the composer Interrupt like the header Stop (danger-red). Rejected: danger colour signals destructive teardown; a non-destructive interrupt in the accent colour, occupying the same slot Send just vacated, makes the morph read as one control changing mode rather than two different buttons.
  • A JS-measured max-rows textarea vs CSS-only. The auto-grow sets an exact inline height from scrollHeight (reset to one row first) and lets CSS max-height + overflow-y: auto do the cap and scroll — the smallest change that grows-then-scrolls. jsdom performs no layout (scrollHeight is 0), so the grow is an inert no-op under test and the unit suite still asserts behaviour by role/accessible name.

Consequences

  • internal/compat/compat.md is kept accurate: §6 (Reply send-keys) notes the recipe is retained at the backend but no longer surfaced in the UI mid-turn, and §8 (Interrupt keystroke) drops "behind a confirm tap" for the one-tap UI. The keystroke recipes themselves are unchanged.
  • Component tests select the composer controls by accessible name — Send and Interrupt (ADR-0019's pattern for icon-only controls) — and assert the morph, the one-tap interrupt (no confirm), the Cmd/Ctrl+Enter vs bare-Enter split [bare-Enter side overturned on fine-pointer devices by ADR-0031], and the absence of any "queued" copy.
  • The pulse adds one keyframe behind a prefers-reduced-motion guard, matching the existing reduced-motion discipline (pulse-fade, progress-slide); the button is fully usable with motion disabled.