th-426791: block send while a turn is in flight

[brentrager]

Problem

Sending a message while a turn was already running did not queue behind it. The daemon spawned a second concurrent turn; the two streamed back interleaved and each answer landed under the other's prompt. The agentic conversation bench (#315) reproduces it with plainly swapped responses, and it is the root cause behind the contradictory date/calendar replies.

The Stop button (#316, th-3a912a) gave a way out of a bad turn but deliberately left the footgun in place — its own PR body flagged blocking send as the follow-up. This is that follow-up.

Block, not queue

Send is refused while a turn is in flight. Queueing was considered and rejected: a queued message is composed against a conversation state the user never saw (the turn it was waiting on may have changed everything), and firing it silently later is the same "an answer arrived for a prompt I didn't mean" surprise the concurrency bug produced. Stop is the explicit, already-visible alternative, so blocking removes nothing the user can't get back with one click.

Composers covered

smooth-web (crates/smooth-web/web)

• src/turn-guard.ts — canSend({ text, attachments, disabled, turnActive }), a pure predicate with no imports. Enter and the send button both route through it, so there is one place the rule lives (the button already flipped to Stop; Enter was the hole).
• The draft is kept in the box — nothing is taken or cleared.
• Affordance: placeholder becomes Big Smooth is working — Stop to interrupt, and once there's a non-empty draft a line under the composer reads Turn in progress — Stop to interrupt, or wait; your draft is kept. It only appears when there's actually a swallowed keystroke to explain, so it isn't noise on every turn.

th code (crates/smooth-code) — it had the same free-send behaviour: Enter spawned another run_agent_streaming regardless of state.thinking.

• blocks_second_turn(input, turn_in_flight) in app.rs, checked before take_input() so the draft survives.
• Only InputKind::Normal is blocked. Slash commands and !shell run locally, so /clear, /quit, /help stay usable — th code has no interrupt, and blocking everything would leave the user with no way out at all.
• The input box titles itself ▶ Working… send paused while thinking.
• Known ceiling, marked with a ponytail: comment: an unknown /name that resolves to a skill also dispatches a turn and isn't blocked, because deciding that needs the skill registry. Corner of a corner.

Tests

• crates/smooth-web/web/src/turn-guard.test.ts — 4 tests on canSend via node --test (pnpm test in the web dir; node --experimental-strip-types, no new dependency and no test framework added). Needed allowImportingTsExtensions in tsconfig.json for the explicit .ts specifier.
• crates/smooth-code/src/app.rs — second_turn_guard_tests, 4 tests: idle passes everything, a chat message is blocked mid-turn, local commands stay live mid-turn, an empty draft isn't claimed.

Verification

• cargo test -p smooai-smooth-code — 321 passed.
• cargo clippy -p smooai-smooth-code --all-targets — clean, zero warnings.
• cargo fmt -- --check — clean.
• pnpm test (web) — 4/4 pass.
• pnpm typecheck + pnpm build (web) — clean.
• oxfmt applied to the three touched/added web files; oxlint on them reports only the pre-existing no-img-element hits on untouched lines (same three as th-3a912a: Stop button — interrupt a running Big Smooth turn #316).

Not runtime-validated against a live daemon; the guard is pure client-side state with no protocol change.

🤖 Generated with Claude Code

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Latest commit: 876b146

The changes in this PR will be included in the next version bump.

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