feat(wire,conversation-store): per-chunk seq sync cursor (StoredChunk)

Add StoredChunk { seq, role, chunk } to @dispatch/wire (re-exported via the
kernel contract shims). Keeps Chunk pure (provider-facing, no cursor); the
sync cursor lives only on the envelope.

conversation-store: rekey conv:<id>:msg:<seq> -> conv:<id>:chunk:<seq>;
append explodes messages into role-tagged seq'd chunks (1-based, gap-free,
monotonic) with internal boundary metadata so load() round-trips ChatMessage[]
losslessly and still reconciles; new loadSince(id, sinceSeq?) raw sync stream.
session-orchestrator test fake conforms to the widened interface.

FE Slice 2 backend prereq (per-chunk seq). typecheck clean, 469 vitest, biome clean.

1 files changed, 15 insertions, 0 deletions

diff --git a/packages/session-orchestrator/src/orchestrator.test.ts b/packages/session-orchestrator/src/orchestrator.test.ts
index d381d6c..39c95d5 100644
--- a/packages/session-orchestrator/src/orchestrator.test.ts
+++ b/packages/session-orchestrator/src/orchestrator.test.ts
@@ -6,6 +6,7 @@ import type {
 	ProviderEvent,
 	RunTurnInput,
 	RunTurnResult,
+	StoredChunk,
 } from "@dispatch/kernel";
 import { runTurn } from "@dispatch/kernel";
 import { describe, expect, it } from "vitest";
@@ -24,6 +25,20 @@ function createInMemoryStore(): ConversationStore & {
 		async load(conversationId) {
 			return [...(data.get(conversationId) ?? [])];
 		},
+		async loadSince(conversationId, sinceSeq) {
+			const messages = data.get(conversationId) ?? [];
+			const result: StoredChunk[] = [];
+			let seq = 1;
+			for (const msg of messages) {
+				for (const chunk of msg.chunks) {
+					if (sinceSeq === undefined || seq > sinceSeq) {
+						result.push({ seq, role: msg.role, chunk });
+					}
+					seq++;
+				}
+			}
+			return result;
+		},
 	};
 }