feat(cache-warming): per-conversation prompt-cache warming + warm() service

Backend-driven warming targeting whatever provider a conversation uses (incl. the
external Claude provider-anthropic). Core engine + on/off + last-cache-% done;
interval-as-view-control pending a ui-contract NumberField (surface-system gap).

Mechanism:
- kernel: expose HostAPI.emit (typed bus event emit; counterpart of on)
- session-orchestrator: turnStarted/turnSettled event hooks (conversationId/cwd/model);
  warm() service (cacheWarmHandle) reusing the real-turn assembly (byte-identical prefix,
  provider-agnostic), refuses mid-turn, never persists/emits, returns Usage
- cache-warming (new ext): per-conversation timers (arm on settle, cancel on start,
  in-flight invalidation), calls warm(), pct=round(clamp(cacheRead/input,0,1)*100),
  persists {enabled,intervalMs} (default on/240s), registers a controls surface
- host-bin: register cache-warming; transport-http: HostAPI stub +emit (fan-out)

Honors old-code invariants. 760 vitest + 109 bun = 869 tests; tsc -b EXIT 0; biome clean.

1 files changed, 19 insertions, 0 deletions

diff --git a/packages/cache-warming/src/index.ts b/packages/cache-warming/src/index.ts
new file mode 100644
index 0000000..8670dc5
--- /dev/null
+++ b/packages/cache-warming/src/index.ts
@@ -0,0 +1,19 @@
+export { extension, manifest } from "./extension.js";
+export {
+	type ConversationSettings,
+	type ConversationState,
+	computeCachePct,
+	DEFAULT_INTERVAL_MS,
+	isTokenCurrent,
+	MIN_INTERVAL_MS,
+	parseSettings,
+	serializeSettings,
+	settingsKey,
+	shouldWarm,
+} from "./pure.js";
+export {
+	type CacheWarmer,
+	type CacheWarmerDeps,
+	createCacheWarmer,
+	type TimerDeps,
+} from "./warmer.js";