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)

tests/render-compaction-divider.test.tsx

@@ -0,0 +1,72 @@
+/**
+ * THE COMPACTION DIVIDERS — SSR render pins (owner round 14). Two ruled
+ * surfaces from one marker: the MOMENT divider (minimal centered small
+ * text, the retrying-message register — no rule lines) where the user
+ * is when compaction lands, and the CUT divider (the longer one —
+ * phase-divider geometry, dotted rules + a chip carrying the summarized
+ * token count) at the kept boundary. Both open the same summary dialog
+ * (the marker's full model-facing content, verbatim, scrollable).
+ *
+ * The dialog portals to document.body at z-50; SSR renders null when
+ * closed — the pins hold the open state through a jsdom-free server
+ * render (createPortal is a no-op passthrough on the server).
+ */
+
+import React from "react";
+(globalThis as Record<string, unknown>).React = React;
+
+import assert from "node:assert/strict";
+import { renderToStaticMarkup } from "react-dom/server";
+import { describe, it } from "node:test";
+import {
+	CompactionCutDivider,
+	CompactionMomentDivider,
+	CompactionSummaryBody,
+	CompactionSummaryDialog,
+	type CompactionDividerData,
+} from "../components/compaction-divider.tsx";
+
+const data: CompactionDividerData = {
+	content: "[SESSION HISTORY COMPACTED]\n\nTHE LEARNER'S UNDERSTANDING: …",
+	details: {
+		firstKeptMessageId: "kept_1",
+		tokensBefore: 152000,
+		at: "2026-10-05T00:00:00.000Z",
+	},
+};
+
+describe("CompactionMomentDivider", () => {
+	it("renders the minimal centered note — no rule lines, retrying-message register", () => {
+		const html = renderToStaticMarkup(<CompactionMomentDivider data={data} onOpen={() => {}} />);
+		assert.ok(html.includes('data-testid="compaction-divider"'));
+		assert.ok(html.includes("Context compacted"));
+		// NO horizontal rule (the owner ruling: minimal, unlike the cut)
+		assert.ok(!html.includes("border-t-2"));
+	});
+});
+
+describe("CompactionCutDivider", () => {
+	it("renders the longer seam — dotted rules + chip with the token count", () => {
+		const html = renderToStaticMarkup(<CompactionCutDivider data={data} onOpen={() => {}} />);
+		assert.ok(html.includes('data-testid="compaction-cut-divider"'));
+		assert.ok(html.includes("border-t-2 border-dotted"));
+		assert.ok(html.includes("History compacted"));
+		// 152000 → 152k tok
+		assert.ok(html.includes("152k tok"));
+	});
+});
+
+describe("CompactionSummaryDialog", () => {
+	it("renders the marker content verbatim, scrollable (the pure body — portals need document)", () => {
+		const html = renderToStaticMarkup(
+			<CompactionSummaryBody summary={data} onClose={() => {}} />,
+		);
+		assert.ok(html.includes('data-testid="compaction-summary-dialog"'));
+		assert.ok(html.includes("[SESSION HISTORY COMPACTED]"));
+		assert.ok(html.includes("overflow-y-auto"));
+		assert.ok(html.includes('data-testid="compaction-summary-close"'));
+	});
+	it("renders nothing when closed", () => {
+		assert.equal(renderToStaticMarkup(<CompactionSummaryDialog summary={null} onClose={() => {}} />), "");
+	});
+});