feat(transport-http): GET /conversations/:id?sinceSeq= read-side history endpoint

Incremental rehydration endpoint for long-lived clients. Returns
ConversationHistoryResponse { chunks: StoredChunk[], latestSeq } — the RAW,
append-order, seq-filtered slice from conversation-store.loadSince, NOT
reconciled (reconcile conflicts with the per-chunk seq cursor, so it stays on
the turn path; the read path is a pure sync primitive).

- transport-contract: add ConversationHistoryResponse + StoredChunk re-export.
- transport-http: GET /conversations/:id route reaching the log directly via
  conversationStoreHandle (dependsOn conversation-store); pure parseSinceSeq
  (absent->0, invalid->400).
- build wiring: conversation-store dep + project ref.

FE Slice 2 backend prereq (read-side). typecheck clean, 481 vitest, biome clean.

7 files changed, 232 insertions, 14 deletions

diff --git a/packages/transport-http/src/app.test.ts b/packages/transport-http/src/app.test.ts
index 38089e4..f4707bc 100644
--- a/packages/transport-http/src/app.test.ts
+++ b/packages/transport-http/src/app.test.ts
@@ -1,7 +1,23 @@
-import type { AgentEvent } from "@dispatch/kernel";
+import type { AgentEvent, StoredChunk } from "@dispatch/kernel";
 import { describe, expect, it } from "vitest";
 import { createApp } from "./app.js";
-import type { CredentialStore, SessionOrchestrator } from "./seam.js";
+import type { ConversationStore, CredentialStore, SessionOrchestrator } from "./seam.js";
+
+function createFakeConversationStore(
+	store: Map<string, StoredChunk[]> = new Map(),
+): ConversationStore {
+	return {
+		async append() {},
+		async load() {
+			return [];
+		},
+		async loadSince(conversationId, sinceSeq) {
+			const chunks = store.get(conversationId) ?? [];
+			const minSeq = sinceSeq ?? 0;
+			return chunks.filter((c) => c.seq > minSeq);
+		},
+	};
+}
 
 function createFakeOrchestrator(events: AgentEvent[]): SessionOrchestrator {
 	return {
@@ -62,6 +78,7 @@ function createThrowingCredentialStore(error: Error): CredentialStore {
 describe("GET /health", () => {
 	it("returns ok", async () => {
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createFakeOrchestrator([]),
 			credentialStore: createFakeCredentialStore([]),
 		});
@@ -75,6 +92,7 @@ describe("GET /health", () => {
 describe("GET /models", () => {
 	it("returns model catalog", async () => {
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createFakeOrchestrator([]),
 			credentialStore: createFakeCredentialStore(["opencode/m1", "openai/gpt-4"]),
 		});
@@ -86,6 +104,7 @@ describe("GET /models", () => {
 
 	it("returns empty array when no models", async () => {
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createFakeOrchestrator([]),
 			credentialStore: createFakeCredentialStore([]),
 		});
@@ -97,6 +116,7 @@ describe("GET /models", () => {
 
 	it("returns 502 when listCatalog throws", async () => {
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createFakeOrchestrator([]),
 			credentialStore: createThrowingCredentialStore(new Error("db down")),
 		});
@@ -110,6 +130,7 @@ describe("GET /models", () => {
 describe("POST /chat", () => {
 	it("returns 400 for invalid JSON", async () => {
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createFakeOrchestrator([]),
 			credentialStore: createFakeCredentialStore([]),
 		});
@@ -123,6 +144,7 @@ describe("POST /chat", () => {
 
 	it("returns 400 for missing message", async () => {
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createFakeOrchestrator([]),
 			credentialStore: createFakeCredentialStore([]),
 		});
@@ -138,6 +160,7 @@ describe("POST /chat", () => {
 
 	it("returns 400 for empty message", async () => {
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createFakeOrchestrator([]),
 			credentialStore: createFakeCredentialStore([]),
 		});
@@ -157,6 +180,7 @@ describe("POST /chat", () => {
 			{ type: "done", conversationId: "tab1", turnId: "turn1", reason: "stop" },
 		];
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createFakeOrchestrator(events),
 			credentialStore: createFakeCredentialStore([]),
 		});
@@ -185,6 +209,7 @@ describe("POST /chat", () => {
 
 	it("generates conversationId when not provided", async () => {
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createFakeOrchestrator([
 				{ type: "done", conversationId: "tab1", turnId: "turn1", reason: "stop" },
 			]),
@@ -204,6 +229,7 @@ describe("POST /chat", () => {
 
 	it("emits error event when orchestrator throws", async () => {
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createThrowingOrchestrator(new Error("provider unavailable")),
 			credentialStore: createFakeCredentialStore([]),
 		});
@@ -230,6 +256,7 @@ describe("POST /chat", () => {
 
 	it("handles empty event list", async () => {
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: createFakeOrchestrator([]),
 			credentialStore: createFakeCredentialStore([]),
 		});
@@ -248,6 +275,7 @@ describe("POST /chat", () => {
 	it("forwards modelName and cwd to orchestrator", async () => {
 		const cap = createCapturingOrchestrator();
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: cap,
 			credentialStore: createFakeCredentialStore([]),
 		});
@@ -274,6 +302,7 @@ describe("POST /chat", () => {
 	it("omits modelName and cwd when not provided", async () => {
 		const cap = createCapturingOrchestrator();
 		const app = createApp({
+			conversationStore: createFakeConversationStore(),
 			orchestrator: cap,
 			credentialStore: createFakeCredentialStore([]),
 		});
@@ -290,3 +319,99 @@ describe("POST /chat", () => {
 		expect(cap.received?.cwd).toBeUndefined();
 	});
 });
+
+describe("GET /conversations/:id", () => {
+	const sampleChunks: StoredChunk[] = [
+		{ seq: 1, role: "user", chunk: { type: "text", text: "hello" } },
+		{ seq: 2, role: "assistant", chunk: { type: "text", text: "hi there" } },
+		{ seq: 3, role: "user", chunk: { type: "text", text: "how are you?" } },
+		{ seq: 4, role: "assistant", chunk: { type: "text", text: "I'm good!" } },
+	];
+
+	it("returns the full seq-ordered StoredChunk history", async () => {
+		const store = new Map<string, StoredChunk[]>([["conv1", sampleChunks]]);
+		const app = createApp({
+			conversationStore: createFakeConversationStore(store),
+			orchestrator: createFakeOrchestrator([]),
+			credentialStore: createFakeCredentialStore([]),
+		});
+
+		const res = await app.request("/conversations/conv1");
+		expect(res.status).toBe(200);
+		const body = (await res.json()) as { chunks: readonly StoredChunk[]; latestSeq: number };
+		expect(body.chunks).toHaveLength(4);
+		expect(body.chunks[0]?.seq).toBe(1);
+		expect(body.chunks[3]?.seq).toBe(4);
+		expect(body.latestSeq).toBe(4);
+	});
+
+	it("returns only chunks with seq > N and latestSeq = last seq", async () => {
+		const store = new Map<string, StoredChunk[]>([["conv1", sampleChunks]]);
+		const app = createApp({
+			conversationStore: createFakeConversationStore(store),
+			orchestrator: createFakeOrchestrator([]),
+			credentialStore: createFakeCredentialStore([]),
+		});
+
+		const res = await app.request("/conversations/conv1?sinceSeq=2");
+		expect(res.status).toBe(200);
+		const body = (await res.json()) as { chunks: readonly StoredChunk[]; latestSeq: number };
+		expect(body.chunks).toHaveLength(2);
+		expect(body.chunks[0]?.seq).toBe(3);
+		expect(body.chunks[1]?.seq).toBe(4);
+		expect(body.latestSeq).toBe(4);
+	});
+
+	it("returns empty chunks and latestSeq === sinceSeq when caught up", async () => {
+		const store = new Map<string, StoredChunk[]>([["conv1", sampleChunks]]);
+		const app = createApp({
+			conversationStore: createFakeConversationStore(store),
+			orchestrator: createFakeOrchestrator([]),
+			credentialStore: createFakeCredentialStore([]),
+		});
+
+		const res = await app.request("/conversations/conv1?sinceSeq=4");
+		expect(res.status).toBe(200);
+		const body = (await res.json()) as { chunks: readonly StoredChunk[]; latestSeq: number };
+		expect(body.chunks).toHaveLength(0);
+		expect(body.latestSeq).toBe(4);
+	});
+
+	it("returns empty chunks and latestSeq 0 for unknown conversation", async () => {
+		const app = createApp({
+			conversationStore: createFakeConversationStore(),
+			orchestrator: createFakeOrchestrator([]),
+			credentialStore: createFakeCredentialStore([]),
+		});
+
+		const res = await app.request("/conversations/unknown");
+		expect(res.status).toBe(200);
+		const body = (await res.json()) as { chunks: readonly StoredChunk[]; latestSeq: number };
+		expect(body.chunks).toHaveLength(0);
+		expect(body.latestSeq).toBe(0);
+	});
+
+	it("returns 400 for invalid sinceSeq", async () => {
+		const app = createApp({
+			conversationStore: createFakeConversationStore(),
+			orchestrator: createFakeOrchestrator([]),
+			credentialStore: createFakeCredentialStore([]),
+		});
+
+		const res = await app.request("/conversations/conv1?sinceSeq=abc");
+		expect(res.status).toBe(400);
+		const body = (await res.json()) as { error: string };
+		expect(body.error).toContain("sinceSeq");
+	});
+
+	it("returns 400 for negative sinceSeq", async () => {
+		const app = createApp({
+			conversationStore: createFakeConversationStore(),
+			orchestrator: createFakeOrchestrator([]),
+			credentialStore: createFakeCredentialStore([]),
+		});
+
+		const res = await app.request("/conversations/conv1?sinceSeq=-1");
+		expect(res.status).toBe(400);
+	});
+});
diff --git a/packages/transport-http/src/app.ts b/packages/transport-http/src/app.ts
index d5492ce..5f63683 100644
--- a/packages/transport-http/src/app.ts
+++ b/packages/transport-http/src/app.ts
@@ -1,10 +1,17 @@
 import type { AgentEvent } from "@dispatch/kernel";
-import type { ModelsResponse } from "@dispatch/transport-contract";
+import type { ConversationHistoryResponse, ModelsResponse } from "@dispatch/transport-contract";
 import { Hono } from "hono";
-import { isParseError, parseChatBody, serializeEventLine } from "./logic.js";
-import type { CredentialStore, SessionOrchestrator } from "./seam.js";
+import {
+	isParseError,
+	isSinceSeqError,
+	parseChatBody,
+	parseSinceSeq,
+	serializeEventLine,
+} from "./logic.js";
+import type { ConversationStore, CredentialStore, SessionOrchestrator } from "./seam.js";
 
 export interface CreateServerOptions {
+	readonly conversationStore: ConversationStore;
 	readonly orchestrator: SessionOrchestrator;
 	readonly credentialStore: CredentialStore;
 	readonly generateId?: () => string;
@@ -16,6 +23,20 @@ export function createApp(opts: CreateServerOptions): Hono {
 
 	app.get("/health", (c) => c.json({ ok: true }));
 
+	app.get("/conversations/:id", async (c) => {
+		const conversationId = c.req.param("id");
+		const sinceSeqResult = parseSinceSeq(c.req.query("sinceSeq"));
+		if (isSinceSeqError(sinceSeqResult)) {
+			return c.json({ error: sinceSeqResult.error }, 400);
+		}
+
+		const chunks = await opts.conversationStore.loadSince(conversationId, sinceSeqResult);
+		const latestSeq =
+			chunks.length > 0 ? (chunks[chunks.length - 1]?.seq ?? sinceSeqResult) : sinceSeqResult;
+		const body: ConversationHistoryResponse = { chunks, latestSeq };
+		return c.json(body, 200);
+	});
+
 	app.get("/models", async (c) => {
 		try {
 			const models = await opts.credentialStore.listCatalog();
diff --git a/packages/transport-http/src/extension.ts b/packages/transport-http/src/extension.ts
index e9613c5..ba45f9d 100644
--- a/packages/transport-http/src/extension.ts
+++ b/packages/transport-http/src/extension.ts
@@ -1,7 +1,11 @@
 import type { Extension, HostAPI, Manifest } from "@dispatch/kernel";
 import type { Hono } from "hono";
 import { createApp } from "./app.js";
-import { credentialStoreHandle, sessionOrchestratorHandle } from "./seam.js";
+import {
+	conversationStoreHandle,
+	credentialStoreHandle,
+	sessionOrchestratorHandle,
+} from "./seam.js";
 
 export const manifest: Manifest = {
 	id: "transport-http",
@@ -9,9 +13,9 @@ export const manifest: Manifest = {
 	version: "0.0.0",
 	apiVersion: "^0.1.0",
 	trust: "bundled",
-	dependsOn: ["credential-store", "session-orchestrator"],
+	dependsOn: ["conversation-store", "credential-store", "session-orchestrator"],
 	capabilities: { network: true },
-	contributes: { routes: ["/chat", "/health", "/models"] },
+	contributes: { routes: ["/chat", "/conversations/:id", "/health", "/models"] },
 	activation: "eager",
 };
 
@@ -20,9 +24,10 @@ export interface CreateServerOptions {
 }
 
 export function createServer(host: HostAPI, _opts?: CreateServerOptions): Hono {
+	const conversationStore = host.getService(conversationStoreHandle);
 	const orchestrator = host.getService(sessionOrchestratorHandle);
 	const credentialStore = host.getService(credentialStoreHandle);
-	return createApp({ orchestrator, credentialStore });
+	return createApp({ conversationStore, orchestrator, credentialStore });
 }
 
 export const extension: Extension = {
diff --git a/packages/transport-http/src/index.ts b/packages/transport-http/src/index.ts
index d91f9ad..d92319c 100644
--- a/packages/transport-http/src/index.ts
+++ b/packages/transport-http/src/index.ts
@@ -1,7 +1,17 @@
 export type { CreateServerOptions } from "./app.js";
 export { createApp } from "./app.js";
 export { createServer, extension, manifest } from "./extension.js";
-export type { ChatCommand, ParseError, ParseResult } from "./logic.js";
-export { isParseError, parseChatBody, serializeEventLine } from "./logic.js";
-export type { CredentialStore, SessionOrchestrator } from "./seam.js";
-export { credentialStoreHandle, sessionOrchestratorHandle } from "./seam.js";
+export type { ChatCommand, ParseError, ParseResult, SinceSeqResult } from "./logic.js";
+export {
+	isParseError,
+	isSinceSeqError,
+	parseChatBody,
+	parseSinceSeq,
+	serializeEventLine,
+} from "./logic.js";
+export type { ConversationStore, CredentialStore, SessionOrchestrator } from "./seam.js";
+export {
+	conversationStoreHandle,
+	credentialStoreHandle,
+	sessionOrchestratorHandle,
+} from "./seam.js";
diff --git a/packages/transport-http/src/logic.test.ts b/packages/transport-http/src/logic.test.ts
index 141549f..1e33f40 100644
--- a/packages/transport-http/src/logic.test.ts
+++ b/packages/transport-http/src/logic.test.ts
@@ -1,6 +1,12 @@
 import type { AgentEvent } from "@dispatch/kernel";
 import { describe, expect, it } from "vitest";
-import { isParseError, parseChatBody, serializeEventLine } from "./logic.js";
+import {
+	isParseError,
+	isSinceSeqError,
+	parseChatBody,
+	parseSinceSeq,
+	serializeEventLine,
+} from "./logic.js";
 
 describe("parseChatBody", () => {
 	const fakeId = () => "test-uuid";
@@ -132,6 +138,40 @@ describe("parseChatBody", () => {
 	});
 });
 
+describe("parseSinceSeq", () => {
+	it("returns 0 when undefined", () => {
+		expect(parseSinceSeq(undefined)).toBe(0);
+	});
+
+	it("returns 0 when empty string", () => {
+		expect(parseSinceSeq("")).toBe(0);
+	});
+
+	it("parses valid non-negative integer", () => {
+		expect(parseSinceSeq("0")).toBe(0);
+		expect(parseSinceSeq("5")).toBe(5);
+		expect(parseSinceSeq("42")).toBe(42);
+	});
+
+	it("returns ParseError for non-integer string", () => {
+		const result = parseSinceSeq("abc");
+		expect(isSinceSeqError(result)).toBe(true);
+		if (isSinceSeqError(result)) {
+			expect(result.error).toContain("sinceSeq");
+		}
+	});
+
+	it("returns ParseError for float", () => {
+		const result = parseSinceSeq("3.14");
+		expect(isSinceSeqError(result)).toBe(true);
+	});
+
+	it("returns ParseError for negative integer", () => {
+		const result = parseSinceSeq("-1");
+		expect(isSinceSeqError(result)).toBe(true);
+	});
+});
+
 describe("serializeEventLine", () => {
 	it("serializes an event as JSON followed by newline", () => {
 		const event: AgentEvent = {
diff --git a/packages/transport-http/src/logic.ts b/packages/transport-http/src/logic.ts
index 11133a5..f1d5b8c 100644
--- a/packages/transport-http/src/logic.ts
+++ b/packages/transport-http/src/logic.ts
@@ -13,6 +13,8 @@ export interface ParseError {
 
 export type ParseResult = ChatCommand | ParseError;
 
+export type SinceSeqResult = number | ParseError;
+
 export function parseChatBody(body: unknown, generateId: () => string): ParseResult {
 	if (body === null || typeof body !== "object") {
 		return { error: "Request body must be a JSON object" };
@@ -56,3 +58,16 @@ export function isParseError(result: ParseResult): result is ParseError {
 export function serializeEventLine(event: AgentEvent): string {
 	return `${JSON.stringify(event)}\n`;
 }
+
+export function parseSinceSeq(raw: string | undefined): SinceSeqResult {
+	if (raw === undefined || raw === "") return 0;
+	const n = Number(raw);
+	if (!Number.isInteger(n) || n < 0) {
+		return { error: "sinceSeq must be a non-negative integer" };
+	}
+	return n;
+}
+
+export function isSinceSeqError(result: SinceSeqResult): result is ParseError {
+	return typeof result === "object";
+}
diff --git a/packages/transport-http/src/seam.ts b/packages/transport-http/src/seam.ts
index 297fb22..c7bfb74 100644
--- a/packages/transport-http/src/seam.ts
+++ b/packages/transport-http/src/seam.ts
@@ -1,3 +1,5 @@
+export type { ConversationStore } from "@dispatch/conversation-store";
+export { conversationStoreHandle } from "@dispatch/conversation-store";
 export type { CredentialStore } from "@dispatch/credential-store";
 export { credentialStoreHandle } from "@dispatch/credential-store";
 export type { SessionOrchestrator } from "@dispatch/session-orchestrator";