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.

1 files changed, 24 insertions, 3 deletions

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();