fix(acp): accept baseline resource links and release a failed prompt slot

ACP v1 requires every agent to accept text AND resource_link prompt
content; the automation rewrite dropped the resource_link half of that
baseline. Restore the old bracketed-reference flattening in the codec,
reject only beyond-baseline blocks, and update the package contract and
Agent Note.

Also release the per-session prompt slot when agent.send() throws
synchronously (an agent disposed outside the bridge would otherwise
wedge the session into permanent 'already in flight' rejections),
drop the tautological version-negotiation branch, prove the scenario
env layer reaches the snapshot subprocess, pin bridge-side fail-closed
permission errors, and correct two overpromising test names.

.agents/notes/implemented/simplification/2026-07-23-acp-automation-only-protocol.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
-2026-07-23-acp-automation-only-protocol.md: 5faeae49d8730c12995c80057437350af68cf962
-2026-07-23-acp-automation-only-protocol.zh.md: e464ca023a56eb5cb5b997c12a14cafb1f93ac23
+2026-07-23-acp-automation-only-protocol.md: 2a92f306065b348764f35e1e63f0d7750a636372
+2026-07-23-acp-automation-only-protocol.zh.md: 5889d668310e3bd63f3934a39d4e5250f83f063d

.agents/notes/implemented/simplification/2026-07-23-acp-automation-only-protocol.md

@@ -14,7 +14,7 @@ The snapshot suite complicates removal. Most ACP scenarios exercise the assemble
 
 ## Decision
 
-`@deepseek-ai/dsh-acp` is an automation transport under [`packages/acp/acp`](../../../../packages/acp/acp/README.md), outside the `ui` package group. Its public protocol is intentionally small: version negotiation, fresh text sessions with one in-flight prompt each, committed assistant text updates, per-session cancellation, concurrent sessions, and connection-owned teardown. The bridge rejects additional directories, MCP servers, non-text prompts, empty prompts, unknown sessions, and overlapping prompts.
+`@deepseek-ai/dsh-acp` is an automation transport under [`packages/acp/acp`](../../../../packages/acp/acp/README.md), outside the `ui` package group. Its public protocol is intentionally small: version negotiation, fresh text sessions with one in-flight prompt each, committed assistant text updates, per-session cancellation, concurrent sessions, and connection-owned teardown. Prompts carry the spec-required baseline only — text plus resource links flattened to bracketed textual references; the bridge rejects additional directories, MCP servers, beyond-baseline prompt content (image, audio, embedded resources), empty prompts, unknown sessions, and overlapping prompts.
 
 The bridge emits only committed `assistant/message` text. Reasoning, raw chunks, tool activity, todos, plans, titles, retry markers, terminal metadata, diffs, locations, and resource links remain in the durable session log or in UI-specific transports. It does not provide session load/list/delete, commands, modes, configuration selectors, model switching, plan review, or human elicitation.
 

.agents/notes/implemented/simplification/2026-07-23-acp-automation-only-protocol.zh.md

@@ -14,7 +14,7 @@ ACP 仍有一个有用的职责：另一个 agent（智能体）或自动化控
 
 ## 决策
 
-`@deepseek-ai/dsh-acp` 是位于 [`packages/acp/acp`](../../../../packages/acp/acp/README.md) 下、独立于 `ui` 包组的自动化传输层。其公开协议特意保持精简：版本协商、全新文本会话（每个会话最多允许一个进行中的提示词）、已提交的助手文本更新、按会话取消、并发会话，以及由连接负责的资源清理。桥接层会拒绝附加目录、MCP 服务器、非文本提示词、空提示词、未知会话和重叠提示词。
+`@deepseek-ai/dsh-acp` 是位于 [`packages/acp/acp`](../../../../packages/acp/acp/README.md) 下、独立于 `ui` 包组的自动化传输层。其公开协议特意保持精简：版本协商、全新文本会话（每个会话最多允许一个进行中的提示词）、已提交的助手文本更新、按会话取消、并发会话，以及由连接负责的资源清理。提示词只承载规范要求的基线内容——文本，加上被展平为方括号文本引用的资源链接；桥接层会拒绝附加目录、MCP 服务器、超出基线的提示词内容（图片、音频、内嵌资源）、空提示词、未知会话和重叠提示词。
 
 桥接层只发出已提交的 `assistant/message` 文本。推理、原始分片、工具活动、待办事项、计划、标题、重试标记、终端元数据、diff、位置和资源链接仍保留在持久会话日志或 UI 专用传输层中。它不提供会话加载、列出与删除、命令、模式、配置选择器、模型切换、plan 评审或面向人类的询问。