fix: multi-select Other coexistence + the malformed-assessment probe-done crash

Two live bugs from the modal-realism stress runs:

1. Multi-select ask: picking the custom 'Other…' row cleared every
   already-picked option, and picking any option cleared a typed custom
   answer — single-select displacement logic applied to both modes. The
   dock's selection is now a pure state machine in question-core
   (toggleOption/toggleOther over DockSelection, unit-tested): single
   displaces (unchanged), multi coexists — neither channel clears the
   other; the typed text always survives.

2. ProbeDoneCard crashed on a REJECTED probe_done call: the model
   stringified 'assessment' (the same double-encoding habit as the
   options bug), zod rejected the call, the model retried — but the
   card's input-preview fallback trusted the errored part's unvalidated
   input shape and died on assessment.strands.map. The preview now reads
   input only while the call is pending or streaming (guarded with
   Array.isArray); an output-error part renders a quiet
   malformed-and-retried note instead of the garbage.

Pinned: question-core.test.ts (3 dock-selection machine cases),
render-cards.test.tsx (4 probe-done card cases incl. the exact live
stringified shape, plus the multi-select ask markup pin).

Gates: tsc, lint, build, 315/315.

components/artifacts/probe-done-card.tsx

@@ -12,13 +12,27 @@ import type { ProbeDoneResult, ProbeDoneInput } from "@/src/core";
  * the prober retried on (rendered quiet and small — it is model-facing
  * bookkeeping, kept only for transcript honesty).
  *
+ * The input preview is only trustworthy while the call is pending — an
+ * input-available input cleared schema validation at the boundary, and a
+ * mid-stream partial is guarded below. An output-error part's input was
+ * REJECTED by validation and can be any shape (live crash: the model
+ * stringified `assessment`); never render it.
+ *
  * Deliberately plain v1: the proper assessment viewer design is deferred to
  * the UI wave; this card just guarantees the data is never invisible.
  */
-export function ProbeDoneCard({ part }: { part: { input?: unknown; output?: unknown } }) {
+export function ProbeDoneCard({ part }: { part: { input?: unknown; output?: unknown; state?: unknown } }) {
 	const input = part.input as ProbeDoneInput | undefined;
 	const output = part.output as ProbeDoneResult | undefined;
-	const assessment = output?.ok ? output.assessment : (input?.assessment ?? null);
+	const state = typeof part.state === "string" ? part.state : "";
+
+	const assessment =
+		output?.ok
+			? output.assessment
+			: state === "output-error"
+				? null // the rejected call — its input is unvalidated garbage
+				: (input?.assessment ?? null);
+	const strands = assessment && Array.isArray(assessment.strands) ? assessment.strands : null;
 
 	return (
 		<div data-testid="probe-done-card" className="my-3 rounded-xl border bg-card/60 p-3">
@@ -28,15 +42,19 @@ export function ProbeDoneCard({ part }: { part: { input?: unknown; output?: unkn
 			</div>
 			{output && !output.ok ? (
 				<p className="text-sm text-muted-foreground">The prober retried: {output.error}</p>
-			) : assessment ? (
+			) : state === "output-error" ? (
+				<p className="text-sm text-muted-foreground">
+					The assessment was malformed — the prober retried with a corrected one.
+				</p>
+			) : strands ? (
 				<div className="space-y-2">
-					{assessment.strands.map((s, i) => (
+					{strands.map((s, i) => (
 						<div key={i} className="rounded-lg bg-background/60 px-3 py-2">
 							<div className="text-sm font-medium">{s.strand}</div>
 							<div className="mt-0.5 text-sm text-muted-foreground">{s.assessment}</div>
 						</div>
 					))}
-					{assessment.summary && (
+					{assessment?.summary && (
 						<p className="px-1 text-sm text-muted-foreground">{assessment.summary}</p>
 					)}
 				</div>