compaction: the surface — settings row, two ruled dividers, summary dialog, send gate (round 14 slice 3)

- settings: compaction.thresholdTokens row on the Agent tab (owner pick)
  in a Context group — CommitInput mirroring the graph budget row, hint
  resolved through the SAME core resolver the trigger reads; PUT rejects
  below the 32k floor with the anti-churn rationale; own section
  (compaction) in SETTINGS_SECTIONS + the settings-signal union
- view fold: one marker → two dividers — the minimal MOMENT divider at
  the marker (retrying-message register, no rule lines) and the longer
  CUT divider emitted immediately before the first kept message
  (phase-divider geometry, chip carries '· Nk tok'); both carry the full
  summary payload; full history stays visible to the user
- components/compaction-divider.tsx: the dividers + summary dialog
  (pure exported body for SSR pins, the delete-dialog pattern; Esc +
  Close dismiss, backdrop does not)
- chat.tsx: compaction-changed SSE flips the running state — composer
  canSend, onSend/doSend/doSteerOrSend, and both docks' submit + hint
  ('compacting session…') gate on it (the server's registry mutex is the
  structural gate; this is the affordance); dialog mounts beside the
  abort dialog
- pins: settings-body (4), view fold (2), divider SSR (4)

components/practice-dock.tsx

@@ -41,9 +41,14 @@ export interface PracticeDockProps {
 	onSubmit: (text: string) => void;
 	/** Escape in the thinking field stops dictation (threaded from the page). */
 	onEscape?: () => void;
+	/** Compaction is running for this chat (owner round 14): the thinking
+	 *  POST would block on the server's compaction gate — disable submit
+	 *  and say so in the hint row. The server registry is the real gate;
+	 *  this is the affordance. */
+	compactionRunning?: boolean;
 }
 
-export function PracticeDock({ problemCallId, input, expanded, onExpand, onSubmit, onEscape }: PracticeDockProps) {
+export function PracticeDock({ problemCallId, input, expanded, onExpand, onSubmit, onEscape, compactionRunning = false }: PracticeDockProps) {
 	const [thinking, setThinking] = useState("");
 	// Ref MIRRORS the field ("nothing gets lost", the question-dock
 	// discipline): a submit resuming after `await finishDictation()` reads
@@ -63,6 +68,7 @@ export function PracticeDock({ problemCallId, input, expanded, onExpand, onSubmi
 	);
 
 	const submit = () => {
+		if (compactionRunning) return;
 		const text = thinkingRef.current.trim();
 		if (text.length === 0) return;
 		thinkingRef.current = "";
@@ -149,12 +155,12 @@ export function PracticeDock({ problemCallId, input, expanded, onExpand, onSubmi
 				    field 10 − p-1 (4) = button 6. */}
 				<div className="flex items-center justify-between gap-2 p-1">
 					<span aria-hidden className="pl-1.5 text-xs text-muted-foreground">
-						↵ submits · ⇧↵ newline
+						{compactionRunning ? "compacting session…" : "↵ submits · ⇧↵ newline"}
 					</span>
 					<Button
 						type="button"
 						data-testid="practice-send"
-						disabled={thinking.trim().length === 0}
+						disabled={thinking.trim().length === 0 || compactionRunning}
 						onClick={() => submit()}
 						className="ml-auto h-9 rounded-[6px] px-3.5 text-sm font-medium"
 					>