refactor(llm-deepseek): replace hand-rolled SSE parser with eventsource-parser

Implements the approved simplification Agent Note: sse.ts now pipes the
response body through TextDecoderStream and EventSourceParserStream
(eventsource-parser/stream) and keeps only the DeepSeek protocol shim —
yield each event's data, terminate on [DONE], throw
LlmError('STREAM_CLOSED') on EOF without the sentinel. The SSE
spec-conformance tests are deleted; sse.spec.ts pins only the
[DONE]/STREAM_CLOSED/EOF contract, including the new spec-strict verdict
that an unterminated trailing event is truncation (the old parser
flushed it — a robustness nicety no real provider shape needs).

eventsource-parser@^3.1.0 becomes llm-deepseek's second runtime
dependency (already in the lockfile transitively via the MCP SDK).

Docs: the Agent Note moves proposed/ → implemented/ and is rewritten per
the lifecycle contract; the rejected NIH roll-up note's inbound links
follow. The twin-adapters note, dsh-llm LlmAdapter JSDoc (and its
type-equiv fences), cookbook, group/package READMEs, root AGENTS.md
layout line, sdk-helper comments, and the regenerated config catalog
drop the "hand-rolled fetch + SSE" claim in both languages; all eight
touched pairs re-recorded.

docs/cookbook/adding-an-llm-adapter.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-adding-an-llm-adapter.md: f20442b8c2ce823452a3ea13409f202185d12d04
-adding-an-llm-adapter.zh.md: 2864dd1e18742c7449e24f22504a5a38976ab450
+adding-an-llm-adapter.md: c62292746f3dab4f6ee350621010349b4fbb2f64
+adding-an-llm-adapter.zh.md: 211c54ad319156b614945505f51a3f68760d64d6

docs/cookbook/adding-an-llm-adapter.md

@@ -2,7 +2,7 @@
 
 English | [中文](adding-an-llm-adapter.zh.md)
 
-How to connect a new model provider. Reference implementations: `packages/llm/llm-deepseek` (hand-rolled HTTP/SSE) and `packages/llm/llm-pi-ai` (wrapping an LLM library). Read the `StreamChunk` doc in `packages/llm/llm/src/types.ts` first — it records the protocol conventions both adapters were verified against.
+How to connect a new model provider. Reference implementations: `packages/llm/llm-deepseek` (direct HTTP, SSE framed by `eventsource-parser`) and `packages/llm/llm-pi-ai` (wrapping an LLM library). Read the `StreamChunk` doc in `packages/llm/llm/src/types.ts` first — it records the protocol conventions both adapters were verified against.
 
 ## The shape
 

docs/cookbook/adding-an-llm-adapter.zh.md

@@ -2,7 +2,7 @@
 
 [English](adding-an-llm-adapter.md) | 中文
 
-如何接入一个新的模型提供方。参考实现：`packages/llm/llm-deepseek`（手写 HTTP/SSE）与 `packages/llm/llm-pi-ai`（封装 LLM 库）。请先阅读 `packages/llm/llm/src/types.ts` 中的 `StreamChunk` 文档——它记录了两个适配器都经过验证的协议约定。
+如何接入一个新的模型提供方。参考实现：`packages/llm/llm-deepseek`（直接 HTTP，SSE 由 `eventsource-parser` 分帧）与 `packages/llm/llm-pi-ai`（封装 LLM 库）。请先阅读 `packages/llm/llm/src/types.ts` 中的 `StreamChunk` 文档——它记录了两个适配器都经过验证的协议约定。
 
 ## 基本形态