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/lsp/lsp-local/src/connection.ts

@@ -11,7 +11,6 @@
  */
 
 import type { Writable } from 'node:stream'
-import { splitEnvChannels } from '@deepseek-ai/dsh-subprocess'
 import type { SubprocessHandle, SubprocessSpawnSpec } from '@deepseek-ai/dsh-subprocess'
 import { encodeMessage, MessageDecoder } from './framing.ts'
 
@@ -99,9 +98,10 @@ export class LspConnection {
         stderr: { maxBytes: spec.maxStderrBytes },
       },
       graceMs: spec.pipeDrainGraceMs,
-      // spec.env mixes the scrubbed base with explicit config entries; a
-      // configured DSH_* fact takes the managed channel the seam reserves.
-      ...splitEnvChannels(spec.env),
+      // spec.env mixes the scrubbed base with explicit config entries; the
+      // seam merges the whole map after its own ambient scrub, so a
+      // configured DSH_* fact reaches the child.
+      env: spec.env,
     })
     /* v8 ignore start -- 'pipe' dispositions expose both streams by the seam contract; defensive. */
     if (this.handle.stdin === undefined || this.handle.stdout === undefined) {