subprocess: one explicit env channel on the spawn spec

Drop SubprocessSpawnSpec.dshEnv and splitEnvChannels(); childEnv() is now
scrubbed-base + explicit entries with no namespace validation. The invariant
dropped is the reserved-namespace check on explicit entries (DSH_* rejected
from env, non-DSH_* rejected from dshEnv). Explicit-entry trust already
covers it: an explicit credential-shaped entry has always merged after the
scrub as a deliberate caller opt-in, and an explicit DSH_* entry is the same
deliberate act — the staleness invariant lives entirely in scrubbedParentEnv
dropping AMBIENT credential-shaped and DSH_* names, which stays. The
validation's only observed effect was rejecting legitimate explicit entries:
both recent CI breakages (DSH_GATE_CONCURRENCY exported into every job
crashing lsp specs, DSH_PERMISSION_MODE in acp config.env crashing the
child spawn) were this check firing on values a caller meant to pass, each
fixed by routing around the bureaucracy the seam itself imposed.

The bash seam keeps its own request/spec dshEnv field: that is bash-owned
trusted-plugin vocabulary (the ctx.bashEnv collected overlay) whose merge-last
position guarantees a caller env entry cannot displace a managed fact;
bash-local now flattens ENV_OVERRIDES -> spec.env -> spec.dshEnv into the
seam's one env map. subagent-acp and lsp-local pass their single config env
map straight through. DshEnvironment/DshEnvironmentKey/DSH_ENV_PREFIX stay on
the subprocess seam as the namespace vocabulary (bash re-exports them;
scrubbedParentEnv filters on the prefix).

Tests: the two channel-rejection specs and the splitEnvChannels partition
spec are deleted; one spawn spec now proves an explicit DSH_* env entry
reaches the child while an ambient one is scrubbed; the acp/lsp forwarding
specs keep their MOCK_ECHO_ENV / LSP_FAKE_ECHO_ENV assertions with the split
comments rewritten to merge-after-scrub. Docs (en+zh, re-recorded) and the
owning Agent Notes updated; cordis api/services catalogs regenerated.

packages/subprocess/subprocess/README.zh.md

@@ -10,7 +10,7 @@
 - spec 完全显式（argv、cwd、按流划分的 stdio 处置方式（disposition）、宽限期），因为随部署变化的默认值属于调用方 seam 的配置，而不属于某个隐藏的进程管理器默认值（`dsh-bash` 的 request/spec 拆分是这条规则的所属模板）。`argv` 绝不经过 shell 解释；需要 shell 的消费方自行传入 `['bash', '-c', command]`。
 - stdio 按流采用 Node 形状：`'pipe'` 把原始流交给调用方做自己的协议分帧（LSP 的 JSON-RPC、ACP（Agent Client Protocol）的 ndjson），`'inherit'` 直通父进程描述符以承载诊断输出，收集模式（collect）`{ maxBytes, spill? }` 则缓冲一段有界尾部，外加可选的完整流 spill 文件。收集模式的读取器接受全流字节偏移量且从不消费，因此独立的读取器不会抢走彼此的增量；偏移量滑出内存尾部窗口的读取标记为 `lossy`，并在 spill 文件存在时指向它。收集到的输出在结算后仍可读取。
 - 终止在每个平台上都以进程树为范围（POSIX 用 detached 进程组并以直接子进程回退；Windows 用 `taskkill /T`）：`kill(signal)` 以 Node 风格只发送一个信号，结算后为空操作；`terminate()`（以及 spec 的 abort 信号）执行 SIGTERM→宽限期→SIGKILL 升级；`waitForExit()` 观察整棵进程树；`dispose(graces)` 运行进程外子进程所需的协作式 stdin EOF→SIGTERM→SIGKILL 阶梯。管理器只响应中止，但绝不判定原因（deadline 与原因分类归调用方所有）。
-- `scrubbedParentEnv()` / `SENSITIVE_ENV_PATTERN` 是唯一一份共享的凭据清除定义：环境中形似凭据的名称与 `DSH_*` 名称都会被丢弃，显式 `env` 在清除之后合并（有意转发的键会保留下来），`dshEnv` 则经由自身带校验的通道携带当前 harness 事实；`splitEnvChannels()` 把消费方配置中单一的混合 env 映射按这两条通道切分（lsp-local 的服务器配置与 ACP 后端只暴露一个映射，而配置的 `DSH_*` 事实必须走受管通道，普通通道会拒绝它）。无法把 spawn 路由到该服务的调用点（node-pty 后端、由 SDK 管理的传输层）改为导入凭据清除函数。
+- `scrubbedParentEnv()` / `SENSITIVE_ENV_PATTERN` 是唯一一份共享的凭据清除定义：环境中形似凭据的名称与 `DSH_*` 名称都会被丢弃，spec 的显式 `env` 在清除之后合并且不做命名空间校验——有意转发的凭据或当前 `DSH_*` 事实之所以能保留下来，正因为它是调用方的显式选择，而陈旧的同名环境值永远到不了子进程。无法把 spawn 路由到该服务的调用点（node-pty 后端、由 SDK 管理的传输层）改为导入凭据清除函数。
 - 服务自身的 dispose（资源释放）会终止所有仍在运行的受管进程并等待其退出。
 
 参见[进程管理器数据结构目录](../../../docs/core-data-structures/subprocess.md)与 [seam Agent Note（agent 决策记录）](../../../.agents/notes/implemented/architecture/2026-07-26-subprocess-seam.md)。