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, 8 insertions, 0 deletions

diff --git a/src/features/conversation-cache/index.ts b/src/features/conversation-cache/index.ts
new file mode 100644
index 0000000..ba3f69a
--- /dev/null
+++ b/src/features/conversation-cache/index.ts
@@ -0,0 +1,8 @@
+export type { ConversationCache, ConversationCacheOptions } from "./cache";
+export { createConversationCache } from "./cache";
+export { nextSinceSeq, reconcileCache, selectEvictions } from "./logic";
+export type {
+	ConversationCacheIndexEntry,
+	ConversationChunkStore,
+	ReconcileResult,
+} from "./types";