feat(cache-warming): manual POST /chat/warm trigger endpoint

A frontend 'warm now' button (and fast tests) can trigger a warm on demand
instead of waiting for the automatic timer.
- transport-contract: WarmRequest / WarmResponse wire types
- transport-http: POST /chat/warm → cacheWarmHandle.warm(); 200 with cachePct,
  409 when the conversation is generating, 400 on missing conversationId

Live-verified vs claude haiku: seed turn cacheWrite=6799 → POST /chat/warm
returns cacheReadTokens=6799 cachePct=100 (100% hit). 760 vitest + 109 bun green.

1 files changed, 15 insertions, 2 deletions

diff --git a/packages/transport-http/src/index.ts b/packages/transport-http/src/index.ts
index 171cf6a..64929fc 100644
--- a/packages/transport-http/src/index.ts
+++ b/packages/transport-http/src/index.ts
@@ -1,16 +1,29 @@
 export type { CreateServerOptions } from "./app.js";
 export { createApp } from "./app.js";
 export { createTransportHttpExtension, manifest } from "./extension.js";
-export type { ChatCommand, ParseError, ParseResult, SinceSeqResult } from "./logic.js";
+export type {
+	ChatCommand,
+	ParseError,
+	ParseResult,
+	SinceSeqResult,
+	WarmBodyParsed,
+} from "./logic.js";
 export {
+	computeCachePct,
 	isParseError,
 	isSinceSeqError,
 	parseChatBody,
 	parseSinceSeq,
 	serializeEventLine,
 } from "./logic.js";
-export type { ConversationStore, CredentialStore, SessionOrchestrator } from "./seam.js";
+export type {
+	ConversationStore,
+	CredentialStore,
+	SessionOrchestrator,
+	WarmService,
+} from "./seam.js";
 export {
+	cacheWarmHandle,
 	conversationStoreHandle,
 	credentialStoreHandle,
 	sessionOrchestratorHandle,