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/llm/llm/src/assembler.ts

@@ -6,9 +6,9 @@
  * @module @deepseek-ai/dsh-llm/assembler
  */
 
-import { CallId } from './brand'
-import { assertNever } from './never'
-import type { ContentBlock, FinishReason, Message, StreamChunk, TokenUsage } from './types'
+import { CallId } from './brand.ts'
+import { assertNever } from './never.ts'
+import type { ContentBlock, FinishReason, Message, StreamChunk, TokenUsage } from './types.ts'
 
 interface PartialBlock {
   blockType: string

packages/llm/llm/src/index.ts

@@ -7,14 +7,14 @@
  */
 
 import { Context, Service } from 'cordis'
-import type { GenerateOptions, StreamChunk } from './types'
-import { HarnessError } from './error'
+import type { GenerateOptions, StreamChunk } from './types.ts'
+import { HarnessError } from './error.ts'
 
-export * from './brand'
-export * from './never'
-export * from './error'
-export * from './types'
-export { BlockAssembler } from './assembler'
+export * from './brand.ts'
+export * from './never.ts'
+export * from './error.ts'
+export * from './types.ts'
+export { BlockAssembler } from './assembler.ts'
 
 declare module 'cordis' {
   interface Context {

packages/llm/llm/src/types.ts

@@ -19,7 +19,7 @@
  * ```
  */
 
-import type { CallId } from './brand'
+import type { CallId } from './brand.ts'
 
 /** Cache hint attached to a content block (provider-interpreted). */
 export type CacheHint = 'ephemeral'