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, 100 insertions, 0 deletions

diff --git a/src/core/wire/conformance.ts b/src/core/wire/conformance.ts
new file mode 100644
index 0000000..5d75a60
--- /dev/null
+++ b/src/core/wire/conformance.ts
@@ -0,0 +1,100 @@
+import type { WsClientMessage, WsServerMessage } from "@dispatch/transport-contract";
+import type { AgentEvent, Chunk } from "@dispatch/wire";
+
+/**
+ * Compile-time exhaustiveness guard for `AgentEvent.type`.
+ * If a variant is added/removed/renamed in `@dispatch/wire`, this function's
+ * default branch becomes reachable → TypeScript error at build time.
+ */
+export function assertAgentEventExhaustive(event: AgentEvent): string {
+	switch (event.type) {
+		case "status":
+			return "status";
+		case "turn-start":
+			return "turn-start";
+		case "text-delta":
+			return "text-delta";
+		case "reasoning-delta":
+			return "reasoning-delta";
+		case "tool-call":
+			return "tool-call";
+		case "tool-result":
+			return "tool-result";
+		case "tool-output":
+			return "tool-output";
+		case "usage":
+			return "usage";
+		case "error":
+			return "error";
+		case "done":
+			return "done";
+		case "turn-sealed":
+			return "turn-sealed";
+		default:
+			return event satisfies never;
+	}
+}
+
+/**
+ * Compile-time exhaustiveness guard for `Chunk.type`.
+ */
+export function assertChunkExhaustive(chunk: Chunk): string {
+	switch (chunk.type) {
+		case "text":
+			return "text";
+		case "thinking":
+			return "thinking";
+		case "tool-call":
+			return "tool-call";
+		case "tool-result":
+			return "tool-result";
+		case "error":
+			return "error";
+		case "system":
+			return "system";
+		default:
+			return chunk satisfies never;
+	}
+}
+
+/**
+ * Compile-time exhaustiveness guard for `WsServerMessage.type`.
+ * Covers both surface ops and chat ops.
+ */
+export function assertWsServerMessageExhaustive(msg: WsServerMessage): string {
+	switch (msg.type) {
+		case "catalog":
+			return "catalog";
+		case "surface":
+			return "surface";
+		case "update":
+			return "update";
+		case "error":
+			return "error";
+		case "chat.delta":
+			return "chat.delta";
+		case "chat.error":
+			return "chat.error";
+		default:
+			return msg satisfies never;
+	}
+}
+
+/**
+ * Compile-time exhaustiveness guard for `WsClientMessage.type`.
+ * Covers both surface ops and chat ops.
+ */
+export function assertWsClientMessageExhaustive(msg: WsClientMessage): string {
+	switch (msg.type) {
+		case "subscribe":
+			return "subscribe";
+		case "unsubscribe":
+			return "unsubscribe";
+		case "invoke":
+			return "invoke";
+		case "chat.send":
+			return "chat.send";
+		default:
+			return msg satisfies never;
+	}
+}