Slice 2 wave 1: transcript reducer, wire conformance, ws chat, cache core

- core/chunks: the one pure transcript reducer (foldEvent live deltas +
  applyHistory seq-keyed reconcile + selectChunks/selectMessages); 27 tests
- core/wire: FE-side contract-conformance exhaustiveness guards + drift smoke
  tests over wire/transport-contract unions (§2.9 drift signal); 10 tests
- adapters/ws: additively multiplex chat.send/chat.delta/chat.error on the
  existing surface socket (onChat + widened send); surface API unchanged
- features/conversation-cache: pure reconcileCache/nextSinceSeq/selectEvictions
  + ConversationChunkStore port + injected createConversationCache; 26 tests

Verified green: svelte-check 0/0, vitest 169, biome clean, build ok.

1 files changed, 51 insertions, 0 deletions

diff --git a/src/core/chunks/selectors.ts b/src/core/chunks/selectors.ts
new file mode 100644
index 0000000..8fb832f
--- /dev/null
+++ b/src/core/chunks/selectors.ts
@@ -0,0 +1,51 @@
+import type { ChatMessage, Chunk } from "@dispatch/wire";
+import type { RenderedChunk, TranscriptState } from "./types";
+
+/**
+ * Select all chunks for rendering: committed first (seq order),
+ * then provisional (seq: null).
+ */
+export function selectChunks(state: TranscriptState): readonly RenderedChunk[] {
+	const result: RenderedChunk[] = [];
+	for (const c of state.committed) {
+		result.push({ seq: c.seq, role: c.role, chunk: c.chunk, provisional: false });
+	}
+	for (const p of state.provisional) {
+		result.push({ seq: null, role: p.role, chunk: p.chunk, provisional: true });
+	}
+	if (state.accumulating !== null) {
+		const chunk: Chunk =
+			state.accumulating.kind === "text"
+				? { type: "text", text: state.accumulating.text }
+				: { type: "thinking", text: state.accumulating.text };
+		result.push({ seq: null, role: "assistant", chunk, provisional: true });
+	}
+	return result;
+}
+
+/**
+ * Group consecutive same-role rendered chunks into ChatMessages.
+ */
+export function selectMessages(state: TranscriptState): readonly ChatMessage[] {
+	const rendered = selectChunks(state);
+	const first = rendered[0];
+	if (first === undefined) return [];
+
+	const messages: ChatMessage[] = [];
+	let role = first.role;
+	let chunks: Chunk[] = [first.chunk];
+
+	for (let i = 1; i < rendered.length; i++) {
+		const rc = rendered[i];
+		if (rc === undefined) continue;
+		if (rc.role === role) {
+			chunks.push(rc.chunk);
+		} else {
+			messages.push({ role, chunks });
+			role = rc.role;
+			chunks = [rc.chunk];
+		}
+	}
+	messages.push({ role, chunks });
+	return messages;
+}