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)

src/core/settings.ts

@@ -575,8 +575,9 @@ function sanitizeGraph(raw: Record<string, unknown>): GraphSettings {
 
 /** clamp-never-reject (the sanitizer's discipline): a finite positive
  *  number floors to COMPACTION_THRESHOLD_FLOOR, anything else drops (the
- *  factory default resolves at read time). */
-const COMPACTION_THRESHOLD_FLOOR = 32_000;
+ *  factory default resolves at read time). Exported for the PUT parser's
+ *  reject-with-rationale (the graph chunk-budget precedent). */
+export const COMPACTION_THRESHOLD_FLOOR = 32_000;
 
 function sanitizeCompaction(raw: Record<string, unknown>): CompactionSettings {
 	const out: CompactionSettings = {};

src/core/view.ts

@@ -35,6 +35,7 @@
 import type { AssistantMessage, ToolResultMessage } from "@earendil-works/pi-ai";
 import type { LhMarkerMessage, LhMessage } from "./native-messages.ts";
 import { modelSolutionForConclude, PRACTICE_CONCLUDE_TOOL } from "./native-messages.ts";
+import { activeCompactionOf, type CompactionDetails } from "./compaction.ts";
 import { QUESTION_TOOLS } from "./pending.ts";
 import type { SubagentArtifactData, SubagentResultMeta } from "./contracts/jobs.ts";
 import type { PlanBlockData } from "./contracts/chat.ts";
@@ -145,9 +146,30 @@ export function projectView(messages: readonly LhMessage[], live?: LiveTurnState
 		return undefined;
 	};
 
+	// The active compaction (owner round 14): the fold emits the CUT
+	// DIVIDER — the longer, at-the-seam marker — immediately BEFORE the
+	// first kept message, so the transcript shows exactly where history
+	// was summarized away. Everything before it stays visible to the
+	// user (full history is never hidden); only the MODEL's context jumps.
+	const compaction = activeCompactionOf(messages);
+
 	for (const m of messages) {
 		const role = (m as { role?: string }).role;
 
+		if (compaction && m.id === compaction.details.firstKeptMessageId) {
+			out.push({
+				id: `cut_${compaction.id}`,
+				role: "user",
+				parts: [
+					{
+						type: "data-compaction-cut",
+						id: `cc_${compaction.id}`,
+						data: { content: compaction.content, details: compaction.details },
+					},
+				],
+			});
+		}
+
 		if (role === "user") {
 			const content = m.content as string | Array<{ type: string; text?: string }>;
 			const texts =
@@ -383,6 +405,25 @@ function projectMarker(marker: LhMarkerMessage, out: LhViewMessage[]): void {
 			// UI-only (the ask-style dismissal): the synthesized conclude
 			// pair — which rides the NEXT input — carries the record's face.
 			return;
+		case "compaction": {
+			// THE MOMENT DIVIDER (owner round 14): minimal centered small
+			// text at the compaction moment — where the user currently is
+			// (the marker appends at the record's tail). Clicking opens the
+			// full summary. The cut divider is emitted by the fold loop at
+			// the kept boundary (see projectView).
+			out.push({
+				id: marker.id,
+				role: "user",
+				parts: [
+					{
+					type: "data-compaction",
+					id: `cm_${marker.id}`,
+					data: { content: marker.content, details: marker.details as CompactionDetails },
+				},
+				],
+			});
+			return;
+		}
 		case "plan-block": {
 			// No message of its own: splice into the preceding assistant
 			// group, IN FLOW after the last successful plan_init call.

src/server/settings-body.ts

@@ -17,12 +17,13 @@ import type {
 	AgentSettings,
 	AppearanceSettings,
 	BackgroundModelRole,
+	CompactionSettings,
 	GeneralSettings,
 	GraphSettings,
 	ModelsSettings,
 	RoleModelOverride,
 } from "../core/settings.ts";
-import { BACKGROUND_MODEL_ROLES, EXTRACTION_CHUNK_TOKENS_FLOOR, MODEL_SLOTS } from "../core/settings.ts";
+import { BACKGROUND_MODEL_ROLES, COMPACTION_THRESHOLD_FLOOR, EXTRACTION_CHUNK_TOKENS_FLOOR, MODEL_SLOTS } from "../core/settings.ts";
 import { WRITABLE_TOOL_KEYS } from "../core/pending.ts";
 
 /** Parsed-or-rejected — `ok: false` carries the 400's error message. */
@@ -342,6 +343,34 @@ export function parseModelsSettingsBody(body: unknown): SettingsBodyResult<Model
 	return { ok: true, settings };
 }
 
+/** compaction (owner round 14): the context-compaction threshold — the
+ *  projected-token budget over which a session summarizes its own history
+ *  into the compaction marker. Strict write side: a present
+ *  thresholdTokens must be a number at or above the floor (the floor is
+ *  anti-churn: each compaction keeps a ~20k-token recent tail, so a
+ *  smaller threshold would re-summarize the tail it just wrote). Absent =
+ *  factory default 150k at resolution. Replace-whole, like every
+ *  section. */
+export function parseCompactionSettingsBody(body: unknown): SettingsBodyResult<CompactionSettings> {
+	const raw = asRecord(body);
+	if (!raw) return { ok: false, error: "Invalid JSON body" };
+	const settings: CompactionSettings = {};
+	if (raw.thresholdTokens !== undefined) {
+		if (typeof raw.thresholdTokens !== "number" || !Number.isFinite(raw.thresholdTokens)) {
+			return { ok: false, error: "thresholdTokens must be a number" };
+		}
+		const floored = Math.floor(raw.thresholdTokens);
+		if (floored < COMPACTION_THRESHOLD_FLOOR) {
+			return {
+				ok: false,
+				error: `thresholdTokens must be at least ${COMPACTION_THRESHOLD_FLOOR} (compaction keeps a ~20k-token recent tail — smaller budgets would churn it)`,
+			};
+		}
+		settings.thresholdTokens = floored;
+	}
+	return { ok: true, settings };
+}
+
 /** The section→parser map for PUT /api/settings/[section] (the route also
  *  carries the special prompts sub-resource). */
 export const SETTINGS_SECTIONS = {
@@ -350,6 +379,7 @@ export const SETTINGS_SECTIONS = {
 	agent: parseAgentSettingsBody,
 	appearance: parseAppearanceSettingsBody,
 	graph: parseGraphSettingsBody,
+	compaction: parseCompactionSettingsBody,
 	models: parseModelsSettingsBody,
 } as const;