feat(surfaces): NumberField + per-conversation surface scoping; cache-warming controls

Extend the surface framework so cache-warming exposes per-conversation controls:
- ui-contract: add NumberField (settable free-value numeric) to SurfaceField;
  add optional conversationId to subscribe/unsubscribe/invoke + surface/update
- surface-registry: SurfaceContext { conversationId? } on getSpec/invoke (backward-compatible)
- transport-ws: thread conversationId; key subscriptions by (surfaceId, conversationId);
  tag surface/update replies with conversationId
- cache-warming: per-conversation surface — Toggle(enabled) + Number(interval seconds,
  cache-warming/set-interval) + Stat(last cache %); drop the currentConversationId closure

Global surfaces (surface-loaded-extensions) unchanged. 784 vitest + 109 bun = 893 tests;
tsc -b EXIT 0; biome clean.

1 files changed, 5 insertions, 0 deletions

diff --git a/packages/cache-warming/src/index.ts b/packages/cache-warming/src/index.ts
index 8670dc5..d77f4ec 100644
--- a/packages/cache-warming/src/index.ts
+++ b/packages/cache-warming/src/index.ts
@@ -1,12 +1,17 @@
 export { extension, manifest } from "./extension.js";
 export {
+	buildConversationSpec,
+	buildDefaultSpec,
 	type ConversationSettings,
 	type ConversationState,
 	computeCachePct,
 	DEFAULT_INTERVAL_MS,
 	isTokenCurrent,
 	MIN_INTERVAL_MS,
+	msToSeconds,
+	parseIntervalPayload,
 	parseSettings,
+	secondsToMs,
 	serializeSettings,
 	settingsKey,
 	shouldWarm,