Use explicit ts specifiers for declarations

Restore explicit .ts relative specifiers in source and enable rewriteRelativeImportExtensions so emitted JS uses .js while declarations keep explicit .ts specifiers. Add a NodeNext declaration-consumer gate to prevent extensionless declaration regressions.

packages/core/session/src/index.ts

@@ -9,13 +9,13 @@
 import { Context, Service } from 'cordis'
 import { isAbsolute } from 'node:path'
 import type { ContentBlock, Message, MessageSource } from '@deepseek-ai/dsh-llm'
-import { SESSION_FORMAT_VERSION, SessionId } from './types'
-import type { CreateSessionOptions, SessionEvent, SessionEventMap, SessionEventType, SessionHeader } from './types'
-import { isJsonValue } from './json'
+import { SESSION_FORMAT_VERSION, SessionId } from './types.ts'
+import type { CreateSessionOptions, SessionEvent, SessionEventMap, SessionEventType, SessionHeader } from './types.ts'
+import { isJsonValue } from './json.ts'
 
-export * from './types'
-export { isJsonValue } from './json'
-export { interruptedTurnClosers } from './repair'
+export * from './types.ts'
+export { isJsonValue } from './json.ts'
+export { interruptedTurnClosers } from './repair.ts'
 
 declare module 'cordis' {
   interface Context {

packages/core/session/src/repair.ts

@@ -36,7 +36,7 @@
  */
 
 import type { CallId } from '@deepseek-ai/dsh-llm'
-import type { SessionEvent } from './types'
+import type { SessionEvent } from './types.ts'
 
 /**
  * Scan `events` for an open turn/step at the tail and return the synthetic