composer steering: the general steering machinery (owner arc 2026-10-03)

STEERING, NOT FOLLOW-UPS — pi-agent-core's two rails, used deliberately:
agent.steer() injects at the next response boundary INSIDE the live run
(one logical turn, the model changes course); followUp() would only extend
an ended run — not built. The same rail job markers already ride
(steeringMode 'all', the 2026-09-26 doctrine).

- POST /api/chats/[id]/steer: 404/400 honest guards; no live turn → 409
  and the client silently falls back to a plain text send (the settle
  race); live → steerLiveChat hands the message to the live agent's
  steering queue AND parks it in the userSteers registry — the stranding
  safety net. A steer stranded behind a question termination or abort
  stays parked and rides the chat's NEXT run (handOffEligible), the same
  deliver-or-requeue lifecycle as job markers. Reconciliation at settle:
  delivered ids drop (reconcileUserSteers).
- Client: steer(text) queues + POSTs without flipping any turn state;
  the drain's verbatim message events upsert the real user card by the
  client-minted id (steer_<localid>) and the indicator fold drops the
  line. canSend no longer gates on turnInFlight — Enter mid-turn steers;
  Enter with an empty composer still stops; the square button stays Stop.
- The queued-steer indicator (owner spec): quiet one-liners above the
  composer shell — right-aligned to where its corner rounding starts,
  truncated with an ellipsis, fixed max width, ~half opacity, no
  background, no container. Tunable later.
- Verified from pi-agent-core source: steering drains per completed turn
  inside the loop; injected messages emit message_start/end verbatim;
  finishTurn {action:'end'} (our question stopper) exits BEFORE the
  steering poll — hence the registry.

tests/render-queued-steers.test.tsx

@@ -0,0 +1,51 @@
+/**
+ * The queued-steer indicator's pins (composer steering, owner arc
+ * 2026-10-03): the quiet one-liners above the composer shell, and the
+ * visibleQueuedSteers fold that decides which queued steers still show.
+ */
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { renderToStaticMarkup } from "react-dom/server";
+import { QueuedSteersBody } from "../components/queued-steers.tsx";
+import { visibleQueuedSteers } from "../components/session-core.ts";
+
+describe("QueuedSteersBody (the quiet queue above the composer)", () => {
+	it("renders one truncated right-aligned line per queued steer — no background, no container chrome", () => {
+		const html = renderToStaticMarkup(
+			<QueuedSteersBody
+				steers={[
+					{ id: "steer_a", text: "also cover Venus while you are at it, please and thank you" },
+					{ id: "steer_b", text: "short one" },
+				]}
+			/>,
+		);
+		assert.match(html, /data-testid="queued-steers"/);
+		assert.equal(html.match(/<span/g)?.length, 2, "one span per steer");
+		assert.match(html, /truncate/, "single-line truncation with ellipsis");
+		assert.match(html, /items-end/, "right-aligned stack");
+		assert.match(html, /max-w-\[240px\]/, "fixed-width stash");
+		assert.match(html, /muted-foreground\/60/, "quiet, roughly half opacity");
+		assert.doesNotMatch(html, /bg-|border|rounded/, "no background, no container");
+		assert.match(html, /also cover Venus/, "the text rides the line");
+	});
+
+	it("empty queue renders nothing", () => {
+		assert.equal(renderToStaticMarkup(<QueuedSteersBody steers={[]} />), "");
+	});
+});
+
+describe("visibleQueuedSteers (the fold: a line dies when its card lands)", () => {
+	it("a queued steer stays visible until its id lands in the messages", () => {
+		const queue = [
+			{ id: "steer_a", text: "a" },
+			{ id: "steer_b", text: "b" },
+		];
+		const before = visibleQueuedSteers(queue, [{ id: "msg_1" } as never]);
+		assert.equal(before.length, 2, "nothing landed yet — both lines show");
+		const after = visibleQueuedSteers(queue, [
+			{ id: "msg_1" } as never,
+			{ id: "steer_a", role: "user", content: "a" } as never,
+		]);
+		assert.deepEqual(after.map((s) => s.id), ["steer_b"], "the drained steer's line dropped");
+	});
+});