diff --git a/packages/chord/test/next/examples/60-session-sync/main.ts b/packages/chord/test/next/examples/60-session-sync/main.ts
new file mode 100644
index 000000000..04c922d8f
--- /dev/null
+++ b/packages/chord/test/next/examples/60-session-sync/main.ts
@@ -0,0 +1,180 @@
+// Session sync as decided (decisions S3, S5, S7, W9, "The outbox is optional, internal and versioned", "p3 meeting,
+// 2026-11-02"), played with Chord's real pieces: a laptop store with an outbox, `store.outbox.read`/`trim`,
+// `store.export` with `encodeJsonl`, `importStore`, and batch apply, `applyBatch` (internal: exported from
+// `chord/next` marked internal, imported here from `src/next/store/apply-batch.ts`; it takes the `ChordStore` behind
+// `openStore`'s `Store`). Radius and the laptop's sync client are stand-ins written for this example (`radius.ts`,
+// `sync.ts`), not Chord APIs: the sync layer is not built yet (slices.md, "The sync layer").
+// Steps: 1. a session on the laptop; 2. the handshake and a first upload; 3. a second sync moves only the tail;
+// 4. a bootstrap from an archive for a session whose outbox was turned on late; 5. "continue on Radius" and the epoch
+// fence (the split), then the same without the fence (silent divergence); 6. back to the laptop with a pull.
+// Run from packages/chord:
+//   node --conditions=source --experimental-strip-types test/next/examples/60-session-sync/main.ts
+import { mkdtemp, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { Readable } from "node:stream";
+import { BACKGROUND_CONTEXT as context } from "../../../../src/context/index.ts";
+import { decodeJsonl, importStore, openStore, type Store, sqliteBackend } from "../../../../src/next/store/index.ts";
+import { openNodeSqliteDatabase } from "../../../../src/sqlite/node.ts";
+import { RadiusStandIn } from "./radius.ts";
+import { describe, withSession } from "./session.ts";
+import { archiveOf, type LocalSession, pull, push, type Synced, sync } from "./sync.ts";
+
+const radius = new RadiusStandIn();
+const directory = await mkdtemp(join(tmpdir(), "chord-sync-"));
+
+/** One sync's result as a line. */
+function shown(result: Synced): string {
+	switch (result.kind) {
+		case "uploaded":
+			return `uploaded ${result.from}..${result.to}, Radius at ${result.lastSeq}, trimmed through it`;
+		case "nothing":
+			return `nothing to send, Radius at ${result.lastSeq}`;
+		case "bootstrapped":
+			return `archive uploaded (${result.bytes} bytes), Radius imported it at ${result.lastSeq}`;
+		case "behind":
+			return `Radius is ahead at ${result.lastSeq}`;
+		case "split":
+			return `refused for an old epoch: this copy is now ${result.session.id}`;
+		case "refused":
+			return `refused: ${result.message}`;
+	}
+}
+
+/** A new in-memory store (outbox on) imported from archive bytes. */
+async function copyOf(bytes: Uint8Array): Promise<Store> {
+	const backend = sqliteBackend(await openNodeSqliteDatabase(":memory:"));
+	return importStore(backend, decodeJsonl(Readable.from([bytes])), context, { outbox: true });
+}
+
+/** Radius's view of a session as a line. */
+function atRadius(id: string): string {
+	const known = radius.handshake()[id]!;
+	return `Radius ${id}: lastSeq ${known.lastSeq}, log ${radius.logRange(id)}, epoch ${known.epoch} (${known.driver})`;
+}
+
+try {
+	// 1. The laptop: SQLite in memory with the outbox on from its first commit; one session, a few commits.
+	const store = await openStore(sqliteBackend(await openNodeSqliteDatabase(":memory:")), context, { outbox: true });
+	const s1: LocalSession = { id: "s1", store, epoch: 1, acked: 0 };
+	await withSession(store, async (session) => {
+		await session.rename("Fix the parser", context);
+		await session.say({ role: "user", text: "the parser drops comments" }, context);
+		await session.say({ role: "assistant", text: "found it in lexer.ts" }, context);
+	});
+	console.log("1. laptop s1: lastSeq", store.lastSeq, "outbox floor", store.outbox!.floor);
+
+	// 2. The handshake: Radius has no s1 (lastSeq 0), so the whole outbox goes, 1..lastSeq; then trimmed.
+	console.log("2. sync:", shown(await sync(s1, radius)));
+	console.log("  ", atRadius("s1"), "- laptop outbox floor", store.outbox!.floor);
+
+	// 3. Two more commits; the next sync sends only them.
+	await withSession(store, async (session) => {
+		await session.say({ role: "user", text: "and strings too" }, context);
+		await session.say({ role: "assistant", text: "fixed both" }, context);
+	});
+	console.log("3. laptop s1: lastSeq", store.lastSeq, "- sync:", shown(await sync(s1, radius)));
+	console.log("  ", atRadius("s1"));
+	console.log("   laptop:", await describe(store));
+	console.log("   Radius:", await describe(radius.replica("s1")));
+
+	// 4. Session s2 ran without an outbox (a file here, since it is reopened), then sync was turned on: the outbox starts
+	// after its lastSeq, so Radius, which has nothing, needs an archive first; batches go on from there.
+	const path = join(directory, "s2.sqlite");
+	const before = await openStore(sqliteBackend(await openNodeSqliteDatabase(path)), context);
+	await withSession(before, async (session) => {
+		await session.rename("Release notes", context);
+		await session.say({ role: "user", text: "draft the notes for 1.4" }, context);
+	});
+	await before.close(context);
+	const store2 = await openStore(sqliteBackend(await openNodeSqliteDatabase(path)), context, { outbox: true });
+	const s2: LocalSession = { id: "s2", store: store2, epoch: 1, acked: 0 };
+	console.log(
+		"4. laptop s2: lastSeq",
+		store2.lastSeq,
+		"outbox floor",
+		store2.outbox!.floor,
+		"- sync:",
+		shown(await sync(s2, radius)),
+	);
+	await withSession(store2, async (session) => {
+		await session.say({ role: "assistant", text: "here is a draft" }, context);
+	});
+	console.log("   laptop s2: lastSeq", store2.lastSeq, "- sync:", shown(await sync(s2, radius)));
+	console.log("  ", atRadius("s2"));
+	console.log("   Radius:", await describe(radius.replica("s2")));
+	await store2.close(context);
+
+	// 5. "Continue on Radius": the laptop uploads its tail (nothing left here), Radius bumps the epoch and drives,
+	// writing a commit on its replica. The laptop keeps its copy as a replica and writes nothing.
+	const handoff = await archiveOf(store);
+	console.log(
+		"5. laptop s1 sync:",
+		shown(await sync(s1, radius)),
+		"- Radius takes over, epoch",
+		radius.takeOver("s1"),
+	);
+	await radius.drive("s1", (replica) =>
+		withSession(replica, async (session) => {
+			await session.say({ role: "assistant", text: "(on Radius) added a test" }, context);
+		}),
+	);
+	console.log("  ", atRadius("s1"));
+	// A laptop process that missed the handoff (here a copy of the laptop's store at it, so the laptop itself can take
+	// the session back in step 6) writes at epoch 1 and uploads the new commit after its last acknowledgement.
+	const stale: LocalSession = { id: "s1", store: await copyOf(handoff), epoch: 1, acked: 6 };
+	await withSession(stale.store, async (session) => {
+		await session.say({ role: "assistant", text: "(stale laptop) added a different test" }, context);
+	});
+	const fenced = await push(stale, radius);
+	console.log("   stale laptop: lastSeq", stale.store.lastSeq, "- push:", shown(fenced));
+	// The split (S7): no rollback; the copy is a new session with its origin, synced on its own from an archive.
+	if (fenced.kind === "split") {
+		const split = fenced.session;
+		console.log(
+			"   split",
+			split.id,
+			"origin",
+			JSON.stringify(split.origin),
+			"- sync:",
+			shown(await sync(split, radius)),
+		);
+		console.log("  ", atRadius(split.id));
+	}
+	await stale.store.close(context);
+
+	// 5b. The same without the epoch fence: the stale upload of seq 7 does not follow Radius's 7 and is refused, so far
+	// so good; but the next handshake finds both at 7, sends nothing and trims the laptop's commit 7 as acknowledged.
+	radius.checkEpochs = false;
+	const unfenced: LocalSession = { id: "s1", store: await copyOf(handoff), epoch: 1, acked: 6 };
+	await withSession(unfenced.store, async (session) => {
+		await session.say({ role: "assistant", text: "(stale laptop) added a different test" }, context);
+	});
+	console.log("5b. no epoch check - stale push:", shown(await push(unfenced, radius)));
+	console.log("   stale sync:", shown(await sync(unfenced, radius)), "- outbox floor", unfenced.store.outbox!.floor);
+	console.log("   stale: ", await describe(unfenced.store));
+	console.log("   Radius:", await describe(radius.replica("s1")));
+	await unfenced.store.close(context);
+	radius.checkEpochs = true;
+
+	// 6. Back to the laptop: it takes the epoch (Radius stops driving), pulls Radius's commits after its lastSeq
+	// (batch apply on the laptop's store; no host open on it), and drives again.
+	s1.epoch = radius.handBack("s1", "laptop");
+	const pulled = await pull(s1, radius);
+	console.log(`6. laptop takes epoch ${s1.epoch}, pulls ${pulled.from}..${pulled.to}: lastSeq ${store.lastSeq}`);
+	const [laptopView, radiusView] = [await describe(store), await describe(radius.replica("s1"))];
+	console.log("   laptop:", laptopView);
+	console.log("   Radius:", radiusView);
+	console.log("   same values:", laptopView === radiusView);
+	await withSession(store, async (session) => {
+		await session.rename("Fix the parser (done)", context);
+	});
+	console.log("   laptop writes, sync:", shown(await sync(s1, radius)));
+	console.log("  ", atRadius("s1"));
+	console.log("   same values:", (await describe(store)) === (await describe(radius.replica("s1"))));
+
+	await store.close(context);
+} finally {
+	await radius.close();
+	await rm(directory, { recursive: true, force: true });
+}
diff --git a/packages/chord/test/next/examples/60-session-sync/radius.ts b/packages/chord/test/next/examples/60-session-sync/radius.ts
new file mode 100644
index 000000000..177ca5cf9
--- /dev/null
+++ b/packages/chord/test/next/examples/60-session-sync/radius.ts
@@ -0,0 +1,159 @@
+// STAND-IN for Radius, not a Chord API: what example 60 needs of the server side of session sync, in memory. Per
+// session id it keeps a replica store (SQLite in memory, as a Durable Object's SQLite would be), the commit log (what
+// R2 would hold; the replica's outbox is moved into it and trimmed after every change), the driver and its epoch.
+// Batches and archives cross a "wire" as JSON and JSONL bytes, so the replica checks them as a trust boundary.
+// `checkEpochs = false` turns the epoch fence off, to show what the gap analysis warned about.
+import { Readable } from "node:stream";
+import { BACKGROUND_CONTEXT as context } from "../../../../src/context/index.ts";
+import { ChordError } from "../../../../src/next/data/index.ts";
+// Internal: the sync layer's batch apply (exported from `chord/next` marked internal) takes the `ChordStore` that
+// `openStore` returns behind the app-facing `Store` type.
+import { applyBatch } from "../../../../src/next/store/apply-batch.ts";
+import {
+	decodeJsonl,
+	importStore,
+	type OutboxCommit,
+	openStore,
+	type Store,
+	sqliteBackend,
+} from "../../../../src/next/store/index.ts";
+import type { ChordStore } from "../../../../src/next/store/store.ts";
+import { openNodeSqliteDatabase } from "../../../../src/sqlite/node.ts";
+
+/** What the handshake reports per session: Radius's applied head, the epoch and who drives. */
+export type Known = { readonly lastSeq: number; readonly epoch: number; readonly driver: string };
+
+/** A batch as it travels: the commits `from..to` and the uploader's epoch (S5: every batch carries `from` and `to`). */
+export type Batch = {
+	readonly from: number;
+	readonly to: number;
+	readonly epoch: number;
+	readonly commits: readonly OutboxCommit[];
+};
+
+/** An upload's answer: applied (the new head is the acknowledgement) or refused, for an old epoch or by the replica. */
+export type Uploaded =
+	| { readonly kind: "applied"; readonly lastSeq: number; readonly epoch: number }
+	| { readonly kind: "refused"; readonly reason: "epoch"; readonly epoch: number }
+	| { readonly kind: "refused"; readonly reason: "batch"; readonly message: string };
+
+type Entry = {
+	readonly replica: Store;
+	/** The commit log (R2's part): every commit after `logFloor` (the seq it was bootstrapped at). */
+	readonly log: OutboxCommit[];
+	readonly logFloor: number;
+	epoch: number;
+	driver: string;
+};
+
+/** The stand-in: sessions by id, for one owner. */
+export class RadiusStandIn {
+	/** The epoch fence (S7); off only to show the divergence without it. */
+	checkEpochs = true;
+	readonly #sessions = new Map<string, Entry>();
+
+	/** The handshake: every session Radius has, with its `lastSeq`, epoch and driver. */
+	handshake(): Record<string, Known> {
+		const known: Record<string, Known> = {};
+		for (const [id, { replica, epoch, driver }] of this.#sessions)
+			known[id] = { lastSeq: replica.lastSeq, epoch, driver };
+		return known;
+	}
+
+	/** Applies an uploaded batch (JSON) to the session's replica; a first batch from seq 1 makes the session. */
+	async upload(id: string, driver: string, wire: string): Promise<Uploaded> {
+		const batch = JSON.parse(wire) as Batch;
+		let entry = this.#sessions.get(id);
+		if (entry === undefined && batch.from === 1) entry = this.#create(id, driver, await openReplica());
+		if (entry === undefined) return { kind: "refused", reason: "batch", message: "unknown session: bootstrap first" };
+		if (this.checkEpochs && batch.epoch !== entry.epoch)
+			return { kind: "refused", reason: "epoch", epoch: entry.epoch };
+		try {
+			await applyBatch(entry.replica as ChordStore, batch.commits, context);
+		} catch (error) {
+			if (!(error instanceof ChordError)) throw error;
+			return { kind: "refused", reason: "batch", message: error.message };
+		}
+		await this.#moveToLog(entry);
+		return { kind: "applied", lastSeq: entry.replica.lastSeq, epoch: entry.epoch };
+	}
+
+	/** Makes the session from an archive (JSONL bytes): its replica imported, the log starting at its `lastSeq`. */
+	async bootstrap(id: string, driver: string, bytes: Uint8Array): Promise<Known> {
+		const backend = sqliteBackend(await openNodeSqliteDatabase(":memory:"));
+		const replica = await importStore(backend, decodeJsonl(Readable.from([bytes])), context, { outbox: true });
+		const entry = this.#create(id, driver, replica);
+		return { lastSeq: replica.lastSeq, epoch: entry.epoch, driver };
+	}
+
+	/** "Continue on Radius": a new epoch, Radius drives; an upload at the old epoch is refused from now on. */
+	takeOver(id: string): number {
+		const entry = this.#entry(id);
+		entry.epoch += 1;
+		entry.driver = "radius";
+		return entry.epoch;
+	}
+
+	/** Radius as the driver: `work` writes on the replica (a host on it, closed again), its commits go to the log. */
+	async drive(id: string, work: (replica: Store) => Promise<void>): Promise<void> {
+		const entry = this.#entry(id);
+		if (entry.driver !== "radius") throw new Error(`radius: ${id} is driven by ${entry.driver}`);
+		await work(entry.replica);
+		await this.#moveToLog(entry);
+	}
+
+	/** "Back to the laptop": a new epoch for `driver`; Radius stops writing. */
+	handBack(id: string, driver: string): number {
+		const entry = this.#entry(id);
+		entry.epoch += 1;
+		entry.driver = driver;
+		return entry.epoch;
+	}
+
+	/** The log's commits after `afterSeq` (JSON), for a pull. */
+	pull(id: string, afterSeq: number): string {
+		const entry = this.#entry(id);
+		if (afterSeq < entry.logFloor) throw new Error(`radius: ${id}'s log starts after ${entry.logFloor}`);
+		return JSON.stringify(entry.log.filter((commit) => commit.seq > afterSeq));
+	}
+
+	/** The session's replica, to read it in the example. */
+	replica(id: string): Store {
+		return this.#entry(id).replica;
+	}
+
+	/** The seqs the log holds, as `from..to`. */
+	logRange(id: string): string {
+		const { log, logFloor } = this.#entry(id);
+		return log.length === 0 ? `empty after ${logFloor}` : `${log[0]!.seq}..${log.at(-1)!.seq}`;
+	}
+
+	/** Closes every replica. */
+	async close(): Promise<void> {
+		for (const { replica } of this.#sessions.values()) await replica.close(context);
+	}
+
+	#create(id: string, driver: string, replica: Store): Entry {
+		const entry: Entry = { replica, log: [], logFloor: replica.lastSeq, epoch: 1, driver };
+		this.#sessions.set(id, entry);
+		return entry;
+	}
+
+	#entry(id: string): Entry {
+		const entry = this.#sessions.get(id);
+		if (entry === undefined) throw new Error(`radius: no session ${id}`);
+		return entry;
+	}
+
+	/** The replica's new commits into the log (the DO writing its commit log to R2), then trimmed from its outbox. */
+	async #moveToLog(entry: Entry): Promise<void> {
+		const outbox = entry.replica.outbox!;
+		entry.log.push(...(await outbox.read(outbox.floor, 10_000, context)));
+		await outbox.trim(entry.replica.lastSeq, context);
+	}
+}
+
+/** A replica as Radius makes it for a session uploaded from seq 1: empty, its outbox on. */
+async function openReplica(): Promise<Store> {
+	return openStore(sqliteBackend(await openNodeSqliteDatabase(":memory:")), context, { outbox: true });
+}
diff --git a/packages/chord/test/next/examples/60-session-sync/session.ts b/packages/chord/test/next/examples/60-session-sync/session.ts
new file mode 100644
index 000000000..b1d4c9e30
--- /dev/null
+++ b/packages/chord/test/next/examples/60-session-sync/session.ts
@@ -0,0 +1,83 @@
+// The session example 60 syncs: one object per host with a persisted title document and a `messages` table, and a
+// helper running a host on a store for the length of some work (one open host per store; a closed host holds no
+// claims, so a batch may apply to its store afterwards).
+import { BACKGROUND_CONTEXT as context } from "../../../../src/context/index.ts";
+import { arr, int, local, method, obj, str } from "../../../../src/next/contracts/index.ts";
+import { defineState } from "../../../../src/next/documents/index.ts";
+import { createHost, defineFacet, type Reference } from "../../../../src/next/host/index.ts";
+import { defineTable, query, type Store } from "../../../../src/next/store/index.ts";
+
+const Messages = defineTable("messages", {
+	version: 1,
+	columns: { n: int(), role: str(), text: str() },
+	key: ["n"],
+});
+
+const Title = defineState("title", {
+	schema: obj({ text: str() }),
+	version: 1,
+	initial: () => ({ text: "untitled" }),
+	persist: true,
+	checkpointWhen: () => false,
+});
+
+/** The session's contract: its title, a message (one commit each), a rename (one commit) and the transcript. */
+export const Session = local("example.session", {
+	version: 1,
+	params: {},
+	members: {
+		title: obj({ text: str() }),
+		say: method(obj({ role: str(), text: str() }), int()),
+		rename: method(str()),
+		transcript: method(obj({}), arr(str())),
+	},
+});
+
+const facet = defineFacet((host) => {
+	host.serve(Session, (_, self) => {
+		const messages = self.table(Messages);
+		const title = self.state(Title);
+		const all = query(Messages).orderBy((m) => m.n, "asc");
+		return {
+			title,
+			say: async ({ role, text }, ctx) => {
+				const n = (await messages.count(all, ctx)) + 1;
+				await self.tx(async (tx) => tx.put(messages, { n, role, text }), ctx);
+				return n;
+			},
+			rename: async (text, ctx) => {
+				await title.change((draft) => {
+					draft.text = text;
+				}, ctx);
+				return null;
+			},
+			transcript: async (_, ctx) => {
+				const lines: string[] = [];
+				for await (const m of messages.rows(all, ctx)) lines.push(`${m.n} ${m.role}: ${m.text}`);
+				return lines;
+			},
+		};
+	});
+});
+
+/** Runs a host serving the session on `store` until `work` is done, then closes the host (the store stays open). */
+export async function withSession<T>(
+	store: Store,
+	work: (session: Reference<typeof Session>) => Promise<T>,
+): Promise<T> {
+	const host = createHost({ store, onError: (error) => console.error("background error:", error) });
+	try {
+		await host.load([{ name: "@example/session", facet }], context);
+		return await work(await host.get(Session, {}, context));
+	} finally {
+		await host.close(context);
+	}
+}
+
+/** The session as one line: its title and its messages. */
+export function describe(store: Store): Promise<string> {
+	return withSession(store, async (session) => {
+		const lines = await session.transcript({}, context);
+		return `"${session.title.value.text}" [${lines.join(" | ")}]`;
+	});
+}
diff --git a/packages/chord/test/next/examples/60-session-sync/sync.ts b/packages/chord/test/next/examples/60-session-sync/sync.ts
new file mode 100644
index 000000000..e88c7e0b9
--- /dev/null
+++ b/packages/chord/test/next/examples/60-session-sync/sync.ts
@@ -0,0 +1,101 @@
+// STAND-IN for the laptop's sync layer, not a Chord API: the decided handshake (ask Radius for `lastSeq`, send the
+// outbox from `lastSeq + 1`, trim through the answer), the bootstrap from an archive, the eager upload of new commits
+// after the last acknowledgement (S5), the split on an old epoch (S7) and the pull of Radius's commits. Built on
+// Chord's real pieces: `store.outbox.read`/`trim`, `store.export`, `encodeJsonl`, and `applyBatch` (internal).
+import { BACKGROUND_CONTEXT as context } from "../../../../src/context/index.ts";
+import { applyBatch } from "../../../../src/next/store/apply-batch.ts";
+import { encodeJsonl, type OutboxCommit, type Store } from "../../../../src/next/store/index.ts";
+import type { ChordStore } from "../../../../src/next/store/store.ts";
+import type { Batch, RadiusStandIn } from "./radius.ts";
+
+/** A session on the laptop: its id, store, the epoch it drives in (a new session: 1) and the `lastSeq` Radius last acknowledged. */
+export type LocalSession = {
+	readonly id: string;
+	readonly store: Store;
+	epoch: number;
+	acked: number;
+	/** A split-off copy's origin: the session it was and the last seq they share (S7). */
+	readonly origin?: { readonly id: string; readonly seq: number };
+};
+
+/** What a sync or a push did. */
+export type Synced =
+	| { readonly kind: "uploaded"; readonly from: number; readonly to: number; readonly lastSeq: number }
+	| { readonly kind: "nothing"; readonly lastSeq: number }
+	| { readonly kind: "bootstrapped"; readonly lastSeq: number; readonly bytes: number }
+	| { readonly kind: "behind"; readonly lastSeq: number }
+	| { readonly kind: "split"; readonly session: LocalSession }
+	| { readonly kind: "refused"; readonly message: string };
+
+const DRIVER = "laptop";
+
+/** The handshake, then the outbox from Radius's `lastSeq + 1`; an archive when Radius has less than the outbox. */
+export async function sync(session: LocalSession, radius: RadiusStandIn): Promise<Synced> {
+	const { store } = session;
+	const outbox = store.outbox!;
+	const known = radius.handshake()[session.id];
+	if (known === undefined && outbox.floor > 0) return bootstrap(session, radius);
+	if (known !== undefined && known.lastSeq < outbox.floor) return bootstrap(session, radius);
+	// Radius ahead: a pull-back (S3, same epoch) or a split (S7); step 6 pulls explicitly.
+	if (known !== undefined && known.lastSeq > store.lastSeq) return { kind: "behind", lastSeq: known.lastSeq };
+	session.acked = known?.lastSeq ?? 0;
+	await outbox.trim(session.acked, context);
+	return push(session, radius);
+}
+
+/** Uploads the outbox after the last acknowledgement, without asking first (an eager or resubmitted upload, S5). */
+export async function push(session: LocalSession, radius: RadiusStandIn): Promise<Synced> {
+	const { store } = session;
+	const commits = await store.outbox!.read(session.acked, 10_000, context);
+	if (commits.length === 0) return { kind: "nothing", lastSeq: session.acked };
+	const batch: Batch = { from: commits[0]!.seq, to: commits.at(-1)!.seq, epoch: session.epoch, commits };
+	const answer = await radius.upload(session.id, DRIVER, JSON.stringify(batch));
+	switch (answer.kind) {
+		case "applied":
+			session.acked = answer.lastSeq;
+			session.epoch = answer.epoch;
+			await store.outbox!.trim(answer.lastSeq, context);
+			return { kind: "uploaded", from: batch.from, to: batch.to, lastSeq: answer.lastSeq };
+		case "refused":
+			if (answer.reason === "batch") return { kind: "refused", message: answer.message };
+			// S7: no rollback; this copy goes on as a new session that shares the old one's commits through `acked`.
+			return {
+				kind: "split",
+				session: {
+					id: `${session.id}~split@${session.acked}`,
+					store,
+					epoch: 1,
+					acked: 0,
+					origin: { id: session.id, seq: session.acked },
+				},
+			};
+	}
+}
+
+/** Uploads the store's archive; Radius imports it and batches go on from its `lastSeq`. */
+async function bootstrap(session: LocalSession, radius: RadiusStandIn): Promise<Synced> {
+	const bytes = await archiveOf(session.store);
+	const known = await radius.bootstrap(session.id, DRIVER, bytes);
+	session.acked = known.lastSeq;
+	session.epoch = known.epoch;
+	await session.store.outbox!.trim(known.lastSeq, context);
+	return { kind: "bootstrapped", lastSeq: known.lastSeq, bytes: bytes.length };
+}
+
+/** Applies Radius's commits after the local `lastSeq` (no host may be open on the store: its claims refuse a batch). */
+export async function pull(session: LocalSession, radius: RadiusStandIn): Promise<{ from: number; to: number }> {
+	const commits = JSON.parse(radius.pull(session.id, session.store.lastSeq)) as OutboxCommit[];
+	const from = session.store.lastSeq + 1;
+	await applyBatch(session.store as ChordStore, commits, context);
+	// Batch apply writes the commits to this store's outbox too; Radius has them, so they are acknowledged.
+	session.acked = session.store.lastSeq;
+	await session.store.outbox!.trim(session.acked, context);
+	return { from, to: session.store.lastSeq };
+}
+
+/** The store's archive as JSONL bytes (the commit queue held while it is read). */
+export async function archiveOf(store: Store): Promise<Uint8Array> {
+	const parts: Uint8Array[] = [];
+	for await (const part of encodeJsonl(store.export(context))) parts.push(part);
+	return Buffer.concat(parts);
+}