refactor(subprocess): keep terminate() as the seam's only termination verb

Delete kill(signal?) from SubprocessHandle: consumers stop a process only
through terminate()'s tree-scoped SIGTERM→graceMs→SIGKILL escalation
(idempotent, also driven by the spec's abort signal, a no-op once the tree
is gone). The single-signal verb had exactly one consumer family —
lsp-local — and what it bought there was a private re-implementation of
the same escalation. The internal kill closure stays in spawn.ts as the
dispose ladder's tier primitive; terminate() now routes through it too.

lsp-local collapses onto the seam's escalation:
- LspConnection replaces its terminate()/kill() pair with one terminate()
  that delegates to handle.terminate(). Behavior change: the
  framing-failure path terminates instead of instant SIGKILL, so a
  misbehaving server now gets SIGTERM plus the killGraceMs window to
  flush before SIGKILL.
- ConnectionSpec.pipeDrainGraceMs becomes killGraceMs: one grace, the
  spawn spec's graceMs, drives both the escalation window and post-exit
  pipe draining (the provider already passed killGraceMs for it).
- LspInstance.forceTerminate() drops its hand-rolled bounded first wait
  (LSP_KILL_GRACE) and escalateProcessTree (deleted with its export and
  unit test): the seam's escalation already commits to SIGKILL after
  killGraceMs, so only the unbounded quiescence awaits stay load-bearing.

Tests: kill()-shaped spawn specs become terminate()-shaped or fold into
the terminate() suites (group-wide delivery; the settled no-op case was
already pinned by 'terminate() after the tree died'); tree-survivor
coverage is intact. A stderr-'inherit' disposition test completes the
stdout/stderr symmetry so the scoped subprocess+lsp coverage gate stands
alone instead of leaning on subagent-acp's cross-package runs.

Docs: SubprocessHandle type-equiv block, seam/impl/group READMEs, and the
consumer-migration Agent Note lose the kill(signal?) vocabulary (zh pairs
re-recorded); cordis api/services catalogs regenerated.

packages/lsp/lsp-local/tests/instance.spec.ts

@@ -1,4 +1,4 @@
-import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { afterEach, beforeEach, describe, expect, it } from 'vitest'
 import { mkdtemp, mkdir, readFile, rm, writeFile, realpath } from 'node:fs/promises'
 import { tmpdir } from 'node:os'
 import { join } from 'node:path'
@@ -6,7 +6,6 @@ import { pathToFileURL, fileURLToPath } from 'node:url'
 import { LspInstance, readHostSource } from '@deepseek-ai/dsh-lsp-local'
 import { encodeMessage } from '@deepseek-ai/dsh-lsp-local'
 import type { ConnectionWriter } from '@deepseek-ai/dsh-lsp-local/src/connection.ts'
-import { escalateProcessTree } from '@deepseek-ai/dsh-lsp-local/src/instance.ts'
 import type { InstanceSpec } from '@deepseek-ai/dsh-lsp-local/src/instance.ts'
 import type { LspProviderQuery, LspQueryResult } from '@deepseek-ai/dsh-lsp'
 import { scrubbedParentEnv } from '@deepseek-ai/dsh-subprocess'
@@ -45,7 +44,6 @@ function makeInstance(
     initializationOptions: { init: true },
     maxMessageBytes: 16_000_000,
     maxStderrBytes: 100_000,
-    pipeDrainGraceMs: 200,
     shutdownTimeoutMs: 200,
     killGraceMs: 200,
     ...overrides,
@@ -75,7 +73,6 @@ function scriptInstance(script: string, overrides: Partial<InstanceSpec> = {}):
     initializationOptions: null,
     maxMessageBytes: 16_000_000,
     maxStderrBytes: 100_000,
-    pipeDrainGraceMs: 150,
     shutdownTimeoutMs: 150,
     killGraceMs: 150,
     ...overrides,
@@ -258,14 +255,6 @@ describe('LspInstance query and abort', () => {
 })
 
 describe('LspInstance disposal', () => {
-  it('escalates only when the process tree survives its grace period', () => {
-    const forceKill = vi.fn()
-    escalateProcessTree(false, forceKill)
-    expect(forceKill).toHaveBeenCalledOnce()
-    escalateProcessTree(true, forceKill)
-    expect(forceKill).toHaveBeenCalledOnce()
-  })
-
   it('lets a server finish protocol exit before signal escalation', async () => {
     const marker = join(root, 'graceful-exit.log')
     const instance = makeInstance({