diff --git a/docs/core-data-structures/subprocess.i18n.yaml b/docs/core-data-structures/subprocess.i18n.yaml
index b85701557b..39e7915bea 100644
--- a/docs/core-data-structures/subprocess.i18n.yaml
+++ b/docs/core-data-structures/subprocess.i18n.yaml
@@ -1,6 +1,6 @@
 # Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each
 # 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
-subprocess.md: 922e7ad0ee8b5c0dbcd0a6a4553c9d2a580f3ee2
-subprocess.zh.md: 5befdcdfc9b0e1d2a9adc825b177c90e53269def
+#   pnpm run verify-translation-pairing --write docs/core-data-structures/subprocess.md
+subprocess.md: a97e407290aa12881e7d6e847d51fec13c134135
+subprocess.zh.md: e0b6f3fc2249d7095b5e540f91a0f13b544db978
diff --git a/docs/core-data-structures/subprocess.md b/docs/core-data-structures/subprocess.md
index 922e7ad0ee..a97e407290 100644
--- a/docs/core-data-structures/subprocess.md
+++ b/docs/core-data-structures/subprocess.md
@@ -8,7 +8,7 @@ Source: [`packages/subprocess/subprocess/src/types.ts`](../../packages/subproces
 
 ## Managed environment namespace and captured output
 
-`DSH_*` variables are Harness-owned child-process facts; implementations discard ambient `DSH_*` names before the caller's explicit `env` merges, so a current fact arrives only as a deliberate entry, and each collected stream reports its truncation and spill-recovery state through `CollectedOutput`.
+`DSH_*` variables are Harness-owned child-process facts; implementations discard ambient `DSH_*` names before the caller's explicit `env` merges, so a current fact arrives only as a deliberate string entry, while an explicit `undefined` tombstone removes an ordinary ambient value. Each collected stream reports its truncation and spill-recovery state through `CollectedOutput`.
 
 ```ts type-equiv
 /** One environment key inside the managed {@link DSH_ENV_PREFIX} namespace. */
@@ -115,13 +115,12 @@ interface SubprocessSpawnSpec {
   signal?: AbortSignal | undefined
   /**
    * Explicit environment entries merged onto the implementation's scrubbed
-   * parent base (see `scrubbedParentEnv`), with no namespace validation:
-   * every entry is a deliberate caller opt-in, so a forwarded
-   * credential-shaped entry or a current `DSH_*` fact survives precisely
-   * because this layer merges after the scrub that drops its ambient
-   * namesake.
+   * parent base (see `scrubbedParentEnv`), with no namespace validation. A
+   * string is a deliberate caller opt-in, so a forwarded credential-shaped
+   * entry or current `DSH_*` fact survives the scrub; `undefined` is a
+   * tombstone that removes an ordinary ambient entry from the child.
    */
-  env?: Record<string, string> | undefined
+  env?: NodeJS.ProcessEnv | undefined
 }
 ```
 
diff --git a/docs/core-data-structures/subprocess.zh.md b/docs/core-data-structures/subprocess.zh.md
index 5befdcdfc9..e0b6f3fc22 100644
--- a/docs/core-data-structures/subprocess.zh.md
+++ b/docs/core-data-structures/subprocess.zh.md
@@ -8,7 +8,7 @@
 
 ## 受管环境命名空间与捕获的输出
 
-`DSH_*` 变量是归 Harness 所有的子进程事实；实现会在合并调用方显式 `env` 之前丢弃环境中已有的 `DSH_*` 名称，因此当前事实只会以有意提供的条目形式到达，每条被收集的流都通过 `CollectedOutput` 报告自身的截断与 spill 恢复状态。
+`DSH_*` 变量是归 Harness 所有的子进程事实；实现会在合并调用方显式 `env` 之前丢弃环境中已有的 `DSH_*` 名称，因此当前事实只会以有意提供的字符串条目形式到达，而显式的 `undefined` tombstone 会删除普通环境中已有的值。每条被收集的流都通过 `CollectedOutput` 报告自身的截断与 spill 恢复状态。
 
 ```ts type-equiv
 /** One environment key inside the managed {@link DSH_ENV_PREFIX} namespace. */
@@ -115,13 +115,12 @@ interface SubprocessSpawnSpec {
   signal?: AbortSignal | undefined
   /**
    * Explicit environment entries merged onto the implementation's scrubbed
-   * parent base (see `scrubbedParentEnv`), with no namespace validation:
-   * every entry is a deliberate caller opt-in, so a forwarded
-   * credential-shaped entry or a current `DSH_*` fact survives precisely
-   * because this layer merges after the scrub that drops its ambient
-   * namesake.
+   * parent base (see `scrubbedParentEnv`), with no namespace validation. A
+   * string is a deliberate caller opt-in, so a forwarded credential-shaped
+   * entry or current `DSH_*` fact survives the scrub; `undefined` is a
+   * tombstone that removes an ordinary ambient entry from the child.
    */
-  env?: Record<string, string> | undefined
+  env?: NodeJS.ProcessEnv | undefined
 }
 ```
 
diff --git a/packages/cordis/tool-cordis/src/api-catalog.ts b/packages/cordis/tool-cordis/src/api-catalog.ts
index 5f9af11105..2c62887faf 100644
--- a/packages/cordis/tool-cordis/src/api-catalog.ts
+++ b/packages/cordis/tool-cordis/src/api-catalog.ts
@@ -2787,7 +2787,7 @@ export const TYPE_API: readonly TypeApiEntry[] = [
   },
   {
     name: 'SubprocessSpawnSpec',
-    declaration: 'export interface SubprocessSpawnSpec {\n    argv: readonly string[];\n    cwd: string;\n    stdio: SubprocessStdio;\n    graceMs: number;\n    signal?: AbortSignal | undefined;\n    env?: Record<string, string> | undefined;\n}',
+    declaration: 'export interface SubprocessSpawnSpec {\n    argv: readonly string[];\n    cwd: string;\n    stdio: SubprocessStdio;\n    graceMs: number;\n    signal?: AbortSignal | undefined;\n    env?: NodeJS.ProcessEnv | undefined;\n}',
   },
   {
     name: 'SubprocessStdinMode',
diff --git a/packages/subagent/subagent-claude-code/src/process.ts b/packages/subagent/subagent-claude-code/src/process.ts
index e27e0a6649..32a545bf08 100644
--- a/packages/subagent/subagent-claude-code/src/process.ts
+++ b/packages/subagent/subagent-claude-code/src/process.ts
@@ -10,9 +10,10 @@ import type {
   SpawnedProcess,
   SpawnOptions,
 } from '@anthropic-ai/claude-agent-sdk'
-import type {
-  SubprocessHandle,
-  SubprocessSpawnSpec,
+import {
+  scrubbedParentEnv,
+  type SubprocessHandle,
+  type SubprocessSpawnSpec,
 } from '@deepseek-ai/dsh-subprocess'
 
 function thrown(value: unknown): Error {
@@ -21,19 +22,18 @@ function thrown(value: unknown): Error {
 }
 
 /**
- * Convert the SDK environment to the shared subprocess seam's defined-value
- * overlay without changing the effective child environment.
- * @param env - SDK-composed child environment.
- * @returns entries whose values survive Node's subprocess environment.
+ * Encode the SDK's complete child environment as a subprocess overlay.
+ * @param env - SDK-composed child environment after its removals and replacements.
+ * @returns explicit values plus tombstones for surviving ambient names the SDK removed.
  */
-export function definedEnvironment(
+export function sdkEnvironmentOverlay(
   env: SpawnOptions['env'],
-): Record<string, string> {
-  const defined: Record<string, string> = {}
-  for (const [name, value] of Object.entries(env)) {
-    if (value !== undefined) defined[name] = value
+): NodeJS.ProcessEnv {
+  const overlay: NodeJS.ProcessEnv = { ...env }
+  for (const name of Object.keys(scrubbedParentEnv())) {
+    if (!(name in env)) overlay[name] = undefined
   }
-  return defined
+  return overlay
 }
 
 /**
@@ -55,7 +55,7 @@ export function claudeSpawnSpec(
     stdio: { stdin: 'pipe', stdout: 'pipe', stderr: 'inherit' },
     graceMs,
     signal: options.signal,
-    env: definedEnvironment(options.env),
+    env: sdkEnvironmentOverlay(options.env),
   }
 }
 
diff --git a/packages/subagent/subagent-claude-code/tests/subagent-claude-code.spec.ts b/packages/subagent/subagent-claude-code/tests/subagent-claude-code.spec.ts
index 0fa781c082..3dab6ab5cd 100644
--- a/packages/subagent/subagent-claude-code/tests/subagent-claude-code.spec.ts
+++ b/packages/subagent/subagent-claude-code/tests/subagent-claude-code.spec.ts
@@ -31,8 +31,8 @@ import * as claudeCode from '../src/index.ts'
 import * as invariant from '../src/invariant.ts'
 import {
   claudeSpawnSpec,
-  definedEnvironment,
   ManagedClaudeCodeProcess,
+  sdkEnvironmentOverlay,
 } from '../src/process.ts'
 import {
   claudeQueryOptions,
@@ -386,6 +386,7 @@ describe('task admission and package contracts', () => {
 
 describe('official spawn projection', () => {
   it('forwards command, arguments, cwd, environment, and signal exactly', () => {
+    vi.stubEnv('SDK_REMOVED_AMBIENT', 'ambient-value')
     const signal = new AbortController().signal
     const options = sdkSpawnOptions({
       command: '/official/claude',
@@ -394,15 +395,26 @@ describe('official spawn projection', () => {
       env: { A: 'one', B: undefined, C: 'three' },
       signal,
     })
-    expect(definedEnvironment(options.env)).toEqual({ A: 'one', C: 'three' })
-    expect(claudeSpawnSpec(options, 321)).toEqual({
+    expect(sdkEnvironmentOverlay(options.env)).toEqual(expect.objectContaining({
+      A: 'one',
+      B: undefined,
+      C: 'three',
+      SDK_REMOVED_AMBIENT: undefined,
+    }))
+    const spawnSpec = claudeSpawnSpec(options, 321)
+    expect(spawnSpec).toMatchObject({
       argv: ['/official/claude', '--one', 'two'],
       cwd: '/parent/workspace',
       stdio: { stdin: 'pipe', stdout: 'pipe', stderr: 'inherit' },
       graceMs: 321,
       signal,
-      env: { A: 'one', C: 'three' },
     })
+    expect(spawnSpec.env).toEqual(expect.objectContaining({
+      A: 'one',
+      B: undefined,
+      C: 'three',
+      SDK_REMOVED_AMBIENT: undefined,
+    }))
     const missingCwd = sdkSpawnOptions()
     delete missingCwd.cwd
     expect(() => claudeSpawnSpec(
diff --git a/packages/subprocess/subprocess-local/src/spawn.ts b/packages/subprocess/subprocess-local/src/spawn.ts
index 932daa2c59..d3cad162fb 100644
--- a/packages/subprocess/subprocess-local/src/spawn.ts
+++ b/packages/subprocess/subprocess-local/src/spawn.ts
@@ -26,12 +26,12 @@ import type {
 
 /**
  * Build a child environment: explicit caller entries merge after the scrubbed
- * parent base, so a deliberately supplied credential or current `DSH_*` fact
- * wins over the scrub that dropped its ambient namesake.
- * @param extra - explicit caller entries, merged verbatim after the scrub.
+ * parent base. A string deliberately restores or overrides an entry; an
+ * explicit `undefined` tombstone removes an ordinary ambient entry.
+ * @param extra - explicit caller entries and tombstones, merged after the scrub.
  * @returns the environment to hand to `spawn` for the child process.
  */
-export function childEnv(extra?: Readonly<Record<string, string>>): NodeJS.ProcessEnv {
+export function childEnv(extra?: Readonly<NodeJS.ProcessEnv>): NodeJS.ProcessEnv {
   return { ...scrubbedParentEnv(), ...extra }
 }
 
diff --git a/packages/subprocess/subprocess-local/tests/spawn.spec.ts b/packages/subprocess/subprocess-local/tests/spawn.spec.ts
index ad2fc0f30a..224476b8d5 100644
--- a/packages/subprocess/subprocess-local/tests/spawn.spec.ts
+++ b/packages/subprocess/subprocess-local/tests/spawn.spec.ts
@@ -343,6 +343,19 @@ describe('stdin and extra env (set by in-process plugins)', () => {
     expect(result.stdout.text).toBe('alpha/beta\n')
   })
 
+  it('lets an explicit tombstone remove an ordinary ambient env entry', async () => {
+    process.env.SUBPROCESS_TOMBSTONE_PROBE = 'ambient-value'
+    try {
+      const result = await finish(spawnSubprocess(spec(
+        'echo "${SUBPROCESS_TOMBSTONE_PROBE:-absent}"',
+        { env: { SUBPROCESS_TOMBSTONE_PROBE: undefined } },
+      )))
+      expect(result.stdout.text).toBe('absent\n')
+    } finally {
+      delete process.env.SUBPROCESS_TOMBSTONE_PROBE
+    }
+  })
+
   it('an explicit extra env entry overrides the credential scrub', async () => {
     // EXPLICIT_OVERRIDE_PASSWORD matches the credential scrub pattern, yet an explicit
     // entry is still honored — the scrub only drops AMBIENT process.env creds.
diff --git a/packages/subprocess/subprocess/README.i18n.yaml b/packages/subprocess/subprocess/README.i18n.yaml
index 64f64d65ed..a5e47747f0 100644
--- a/packages/subprocess/subprocess/README.i18n.yaml
+++ b/packages/subprocess/subprocess/README.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 packages/subprocess/subprocess/README.md
-README.md: c360437bf2b2b95734f55f6aec46b0cecffb9260
-README.zh.md: dac459a6ed1b92c2354bf0a2cc4e0c23e824154f
+README.md: 13c634429bfae9408dc732aea69df673e5da87aa
+README.zh.md: fe7b28d3a8f256e0eb9b4cbb98093bac33816fdf
diff --git a/packages/subprocess/subprocess/README.md b/packages/subprocess/subprocess/README.md
index c360437bf2..13c634429b 100644
--- a/packages/subprocess/subprocess/README.md
+++ b/packages/subprocess/subprocess/README.md
@@ -10,7 +10,7 @@ The subprocess seam (`ctx.subprocess`). The abstract `SubprocessService` exposes
 - The spec is fully explicit — argv, cwd, per-stream stdio dispositions, grace — because deployment-varying defaults belong to the calling seam's config, not to a hidden subprocess-service default (the `dsh-bash` request/spec split is the owning template). `argv` is never shell-interpreted; a consumer that wants a shell passes `['bash', '-c', command]` itself.
 - Stdio is Node-shaped per stream: `'pipe'` hands the caller the raw stream for its own protocol framing (LSP JSON-RPC, ACP ndjson), `'inherit'` passes the parent descriptor through for diagnostics, and collect mode (`{ maxBytes, spill? }`) buffers a bounded tail with an optional full-stream spill file. Collect readers take whole-stream byte offsets and never consume, so independent readers cannot steal one another's deltas; a read whose offset slid out of the in-memory tail is `lossy` and points at the spill file when one exists. Collected output stays readable after settlement.
 - Termination is tree-scoped on every platform (POSIX detached groups with direct-child fallback; Windows `taskkill /T`): `terminate()` — the only termination verb — escalates SIGTERM→grace→SIGKILL (idempotent, driven by the spec's abort signal too, a no-op once the tree is gone), and `waitForExit(signal?)` observes whole-tree liveness so a consumer-owned teardown ladder holds each tier on real quiescence — the manager reacts but never classifies why (callers own deadlines, teardown ladders, and cause classification).
-- `scrubbedParentEnv()` / `SENSITIVE_ENV_PATTERN` are the one shared scrub definition: ambient credential-shaped and `DSH_*` names are dropped, and the spec's explicit `env` merges after the scrub with no namespace validation — a deliberately forwarded credential or a current `DSH_*` fact survives precisely because it is an explicit caller opt-in, while the stale ambient namesake never reaches the child. Spawners that cannot route through the service (node-pty backends, SDK-managed transports) import the scrub.
+- `scrubbedParentEnv()` / `SENSITIVE_ENV_PATTERN` are the one shared scrub definition: ambient credential-shaped and `DSH_*` names are dropped, and the spec's explicit `env` merges after the scrub with no namespace validation — a string deliberately forwards or overrides a value, while an `undefined` tombstone removes an ordinary ambient entry. Spawners that cannot route through the service (node-pty backends, SDK-managed transports) import the scrub.
 - Disposal of the service terminates all still-running managed processes and awaits their exit.
 
 See the [subprocess data-structure catalog](../../../docs/core-data-structures/subprocess.md) and the [seam Agent Note](../../../.agents/notes/implemented/architecture/2026-07-26-subprocess-seam.md).
diff --git a/packages/subprocess/subprocess/README.zh.md b/packages/subprocess/subprocess/README.zh.md
index dac459a6ed..fe7b28d3a8 100644
--- a/packages/subprocess/subprocess/README.zh.md
+++ b/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子进程默认值（`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 风格：`'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`）：`terminate()`（唯一的终止动词）执行 SIGTERM→宽限期→SIGKILL 升级（幂等，也由 spec 的 abort 信号驱动，进程树消亡后为空操作）；`waitForExit(signal?)` 观察整棵进程树的存活状态，使消费方自有的拆卸阶梯能在真正完全停稳后才进入下一层。管理器只响应中止，但绝不判定原因（deadline、拆卸阶梯与原因分类归调用方所有）。
-- `scrubbedParentEnv()` / `SENSITIVE_ENV_PATTERN` 是唯一一份共享的环境清理定义：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 路由到该服务的进程启动方（node-pty 后端、由 SDK 管理的传输层）改为导入环境清理函数。
+- `scrubbedParentEnv()` / `SENSITIVE_ENV_PATTERN` 是唯一一份共享的环境清理定义：环境中形似凭据的名称与 `DSH_*` 名称都会被丢弃，spec 的显式 `env` 在清理后合并且不做命名空间校验——字符串会有意转发或覆盖某个值，而 `undefined` tombstone 则会删除普通的环境条目。无法把 spawn 路由到该服务的进程启动方（node-pty 后端、由 SDK 管理的传输层）会导入该环境清理定义。
 - 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[子进程数据结构目录](../../../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)。
diff --git a/packages/subprocess/subprocess/src/types.ts b/packages/subprocess/subprocess/src/types.ts
index fdfc44b3c2..a21f6ffb0d 100644
--- a/packages/subprocess/subprocess/src/types.ts
+++ b/packages/subprocess/subprocess/src/types.ts
@@ -94,13 +94,12 @@ export interface SubprocessSpawnSpec {
   signal?: AbortSignal | undefined
   /**
    * Explicit environment entries merged onto the implementation's scrubbed
-   * parent base (see `scrubbedParentEnv`), with no namespace validation:
-   * every entry is a deliberate caller opt-in, so a forwarded
-   * credential-shaped entry or a current `DSH_*` fact survives precisely
-   * because this layer merges after the scrub that drops its ambient
-   * namesake.
+   * parent base (see `scrubbedParentEnv`), with no namespace validation. A
+   * string is a deliberate caller opt-in, so a forwarded credential-shaped
+   * entry or current `DSH_*` fact survives the scrub; `undefined` is a
+   * tombstone that removes an ordinary ambient entry from the child.
    */
-  env?: Record<string, string> | undefined
+  env?: NodeJS.ProcessEnv | undefined
 }
 
 /**