feat(subprocess): migrate lsp-local, subagent-acp, and the env scrubs onto the seam

Review direction (tianyicui, PR #660): in a stacked PR, change all other
process-running places to use the new service.

- lsp-local: LspConnection spawns through ctx.subprocess (piped protocol
  streams + a no-spill collected stderr tail); its private process-tree
  helpers (POSIX group signalling, Windows taskkill, liveness polling) are
  deleted in favor of the seam's handle verbs, and its buildChildEnv now
  rides scrubbedParentEnv (LSP children also stop inheriting stale DSH_*).
  The plugin injects 'subprocess'; compositions/tests mount
  dsh-subprocess-local.
- subagent-acp: the ACP child spawns through the seam (piped ndjson streams,
  inherited stderr); spawn failure surfaces through done-rejection into the
  same startup race; disposal is handle.dispose with the plugin's configured
  graces. dsh-subagent-subprocess is DELETED — its dispose ladder and scrub
  are the seam's, and the isolated-config-dir helper had no consumer.
- mcp-client, pty-local, sdk-helper: adopt scrubbedParentEnv as the one
  scrub definition (their spawns stay put by ownership: the MCP SDK and
  node-pty own those calls; the SDK wizard runs outside any composition).
- Coverage: per-file 100% over every touched src file, with each v8 ignore
  carrying a platform or contract reason; new suites cover stdio
  dispositions, the dispose ladder tiers, injected-win32 tree semantics,
  waitForExit, settled-kill/terminate no-ops, and spawn-failure disposal.
- Docs: consumer-migration Agent Note (en; zh follows in this PR), seam note
  updated in place, subprocess.md rewritten for the reshaped vocabulary
  (type-equiv re-registered), READMEs and SERVICE_ROLES updated, taskkill
  added to knip ignoreBinaries.

packages/subprocess/subprocess-local/README.md

@@ -1,14 +1,14 @@
 # @deepseek-ai/dsh-subprocess-local
 
-Local implementation of the [`@deepseek-ai/dsh-subprocess`](../subprocess/README.md) seam: `LocalSubprocessService` spawns each spec's argv as a detached process group, collects bounded output with size-limited full-stream spill files, and escalates kills SIGTERM→SIGKILL across the whole group. It has no config: every limit and directory arrives on the spawn spec, so the deployment-varying knobs stay with the calling seam's config ([`dsh-bash-local`](../../bash/bash-local/README.md) today).
+Local implementation of the [`@deepseek-ai/dsh-subprocess`](../subprocess/README.md) seam: `LocalSubprocessService` spawns each spec's argv as a detached process tree, wires the spec's per-stream stdio dispositions (raw pipes, inherit, bounded tail-keep collection with optional spill files), and signals tree-scoped with SIGTERM→SIGKILL escalation. It has no config: every disposition, limit, and directory arrives on the spawn spec, so the deployment-varying knobs stay with the calling seams' configs ([`dsh-bash-local`](../../bash/bash-local/README.md), [`dsh-lsp-local`](../../lsp/lsp-local/README.md), [`dsh-subagent-acp`](../../subagent/subagent-acp/README.md)).
 
 ## Behavior (and where it came from)
 
-- **Detached process groups with escalation** — children are spawned `detached` (own process group); kills send SIGTERM to the group, then SIGKILL after the spec's grace (OpenCode's escalation; pipelines and subshells die with the parent). After the leader exits, inherited stdout/stderr pipes receive the same bounded drain grace so a surviving descendant cannot hold the spawn open indefinitely. ESRCH is tolerated; daemons that re-parent away from the group can still survive — the same caveat as the surveyed tools.
-- **Tail-keep truncation + bounded spill files** — output beyond a stream's cap keeps the in-memory TAIL (errors and results cluster at the end — pi/OpenCode rationale) while the FULL stream is appended to a private temp file whose path is reported when available. A stream larger than the spill cap discards its now-incomplete spill and returns only the marked truncated tail; a failed final close withholds the path rather than advertising an incomplete file. Spill files are `0600` with random names under a lazily-created `0700` per-process directory.
+- **Detached process trees with platform-correct signalling** — POSIX children are spawned `detached` (own process group) and signalled by negative pgid with a direct-child fallback; Windows terminates the tree via `taskkill /PID <pid> /T /F` (injectable for tests). `terminate()` sends SIGTERM then SIGKILL after the spec's grace (OpenCode's escalation; pipelines and subshells die with the parent); `kill(signal)` sends exactly one signal and is a no-op after settlement; `dispose(graces)` runs stdin-EOF → SIGTERM → SIGKILL with caller-supplied windows and one memoized disposal per handle. After the leader exits, still-open pipes receive the same bounded drain grace so a surviving descendant cannot hold the outcome open indefinitely. ESRCH is tolerated; daemons that re-parent away from the group can still survive — the same caveat as the surveyed tools.
+- **Per-stream dispositions** — `'pipe'` hands the raw stream to the caller untouched (protocol framing stays consumer-owned); `'inherit'` passes the parent descriptor through; collect mode keeps the in-memory TAIL beyond its cap (errors and results cluster at the end — pi/OpenCode rationale) while the FULL stream is appended to a private temp file when a spill cap is configured — omitting `spill` keeps only the tail, the diagnostic shape. A stream larger than the spill cap discards its now-incomplete spill and returns only the marked truncated tail; spill fds are sealed at settlement, and a failed final close withholds the path rather than advertising an incomplete file. Spill files are `0600` with random names under a lazily-created `0700` per-process directory.
 - **Credential scrub + managed `DSH_*` merge** — `process.env` minus credential-shaped vars (`*KEY*`/`*SECRET*`/`*TOKEN*`) and all ambient `DSH_*` names; a spec's ordinary `env` merges after the scrub but rejects `DSH_*`; managed `dshEnv` rejects ordinary names and merges last, preventing stale nested-harness identity. Supplied stdin is written and closed; otherwise fd 0 is `/dev/null`. See the [stdin/env Agent Note](../../../.agents/notes/implemented/architecture/2026-06-30-bash-stdin-env-trusted-plugin-surface.md) and [managed environment Agent Note](../../../.agents/notes/implemented/feature/2026-07-10-agent-session-identity-and-log-location.md).
-- **Offset-based reads** — `SubprocessHandle` readers return deltas in whole-stream byte coordinates; the service never holds a cursor, so consumer-owned cursors (the bash background read path) and full-stream re-reads coexist.
-- **Kill-and-join disposal** — the service retains live handles only so its own disposal can kill every running group and await its exit; settled and spawn-failed handles leave the live set on settlement.
+- **Offset-based reads** — collect-mode readers return deltas in whole-stream byte coordinates; the service never holds a cursor, so consumer-owned cursors (the bash background read path) and full-stream re-reads coexist, before and after settlement.
+- **Terminate-and-join disposal** — the service retains live handles only so its own disposal can escalate every running tree and await its exit; settled and spawn-failed handles leave the live set on settlement.
 
 ## Model Experience