diff --git a/packages/effect-acp/src/_internal/stdio.test.ts b/packages/effect-acp/src/_internal/stdio.test.ts
new file mode 100644
index 00000000000..8a4171f7a8d
--- /dev/null
+++ b/packages/effect-acp/src/_internal/stdio.test.ts
@@ -0,0 +1,45 @@
+import { assert, describe, it } from "@effect/vitest";
+import * as Effect from "effect/Effect";
+import * as PlatformError from "effect/PlatformError";
+import { ChildProcessSpawner } from "effect/unstable/process";
+
+import * as AcpError from "../errors.ts";
+import { makeTerminationError } from "./stdio.ts";
+
+describe("ACP child process termination", () => {
+  it.effect("retains the process identifier with the exit code", () =>
+    Effect.gen(function* () {
+      const error = yield* makeTerminationError({
+        pid: ChildProcessSpawner.ProcessId(41),
+        exitCode: Effect.succeed(ChildProcessSpawner.ExitCode(7)),
+      });
+
+      assert.instanceOf(error, AcpError.AcpProcessExitedError);
+      assert.equal(error.pid, 41);
+      assert.equal(error.code, 7);
+      assert.equal(error.message, "ACP process exited with code 7");
+    }),
+  );
+
+  it.effect("retains the process identifier and exact exit-status cause", () =>
+    Effect.gen(function* () {
+      const rootCause = new Error("private process diagnostics");
+      const cause = PlatformError.systemError({
+        _tag: "Unknown",
+        module: "ChildProcess",
+        method: "exitCode",
+        cause: rootCause,
+      });
+      const error = yield* makeTerminationError({
+        pid: ChildProcessSpawner.ProcessId(42),
+        exitCode: Effect.fail(cause),
+      });
+
+      assert.instanceOf(error, AcpError.AcpTransportError);
+      assert.equal(error.pid, 42);
+      assert.strictEqual(error.cause, cause);
+      assert.equal(error.message, "ACP transport operation read-process-exit-status failed.");
+      assert.notInclude(error.message, rootCause.message);
+    }),
+  );
+});
diff --git a/packages/effect-acp/src/_internal/stdio.ts b/packages/effect-acp/src/_internal/stdio.ts
index 393a1c591cb..87af633637a 100644
--- a/packages/effect-acp/src/_internal/stdio.ts
+++ b/packages/effect-acp/src/_internal/stdio.ts
@@ -44,14 +44,20 @@ export const makeInMemoryStdio = Effect.fn("makeInMemoryStdio")(function* () {
   };
 });
 
+type ChildProcessTerminationHandle = Pick<
+  ChildProcessSpawner.ChildProcessHandle,
+  "exitCode" | "pid"
+>;
+
 export const makeTerminationError = (
-  handle: ChildProcessSpawner.ChildProcessHandle,
+  handle: ChildProcessTerminationHandle,
 ): Effect.Effect<AcpError.AcpError> =>
   Effect.match(handle.exitCode, {
     onFailure: (cause) =>
       new AcpError.AcpTransportError({
         operation: "read-process-exit-status",
+        pid: handle.pid,
         cause,
       }),
-    onSuccess: (code) => new AcpError.AcpProcessExitedError({ code }),
+    onSuccess: (code) => new AcpError.AcpProcessExitedError({ code, pid: handle.pid }),
   });
diff --git a/packages/effect-acp/src/errors.ts b/packages/effect-acp/src/errors.ts
index 3fe0a469001..f92568a1483 100644
--- a/packages/effect-acp/src/errors.ts
+++ b/packages/effect-acp/src/errors.ts
@@ -91,6 +91,7 @@ export class AcpProcessExitedError extends Schema.TaggedErrorClass<AcpProcessExi
   "AcpProcessExitedError",
   {
     code: Schema.optional(Schema.Number),
+    pid: Schema.optionalKey(Schema.Int),
     cause: Schema.optional(Schema.Defect()),
   },
 ) {
@@ -160,6 +161,7 @@ export class AcpTransportError extends Schema.TaggedErrorClass<AcpTransportError
     ),
     method: Schema.optional(Schema.String),
     detail: Schema.optional(Schema.String),
+    pid: Schema.optionalKey(Schema.Int),
     cause: Schema.Defect(),
   },
 ) {
diff --git a/packages/effect-codex-app-server/src/_internal/stdio.test.ts b/packages/effect-codex-app-server/src/_internal/stdio.test.ts
new file mode 100644
index 00000000000..6dbf4c857eb
--- /dev/null
+++ b/packages/effect-codex-app-server/src/_internal/stdio.test.ts
@@ -0,0 +1,48 @@
+import { assert, describe, it } from "@effect/vitest";
+import * as Effect from "effect/Effect";
+import * as PlatformError from "effect/PlatformError";
+import { ChildProcessSpawner } from "effect/unstable/process";
+
+import * as CodexError from "../errors.ts";
+import { makeTerminationError } from "./stdio.ts";
+
+describe("Codex App Server child process termination", () => {
+  it.effect("retains the process identifier with the exit code", () =>
+    Effect.gen(function* () {
+      const error = yield* makeTerminationError({
+        pid: ChildProcessSpawner.ProcessId(51),
+        exitCode: Effect.succeed(ChildProcessSpawner.ExitCode(9)),
+      });
+
+      assert.instanceOf(error, CodexError.CodexAppServerProcessExitedError);
+      assert.equal(error.pid, 51);
+      assert.equal(error.code, 9);
+      assert.equal(error.message, "Codex App Server process exited with code 9");
+    }),
+  );
+
+  it.effect("retains the process identifier and exact exit-status cause", () =>
+    Effect.gen(function* () {
+      const rootCause = new Error("private process diagnostics");
+      const cause = PlatformError.systemError({
+        _tag: "Unknown",
+        module: "ChildProcess",
+        method: "exitCode",
+        cause: rootCause,
+      });
+      const error = yield* makeTerminationError({
+        pid: ChildProcessSpawner.ProcessId(52),
+        exitCode: Effect.fail(cause),
+      });
+
+      assert.instanceOf(error, CodexError.CodexAppServerTransportError);
+      assert.equal(error.pid, 52);
+      assert.strictEqual(error.cause, cause);
+      assert.equal(
+        error.message,
+        "Codex App Server transport operation 'read-process-exit-status' failed.",
+      );
+      assert.notInclude(error.message, rootCause.message);
+    }),
+  );
+});
diff --git a/packages/effect-codex-app-server/src/_internal/stdio.ts b/packages/effect-codex-app-server/src/_internal/stdio.ts
index 9167129db5c..312022824cb 100644
--- a/packages/effect-codex-app-server/src/_internal/stdio.ts
+++ b/packages/effect-codex-app-server/src/_internal/stdio.ts
@@ -44,14 +44,20 @@ export const makeInMemoryStdio = Effect.fn("makeInMemoryStdio")(function* () {
   };
 });
 
+type ChildProcessTerminationHandle = Pick<
+  ChildProcessSpawner.ChildProcessHandle,
+  "exitCode" | "pid"
+>;
+
 export const makeTerminationError = (
-  handle: ChildProcessSpawner.ChildProcessHandle,
+  handle: ChildProcessTerminationHandle,
 ): Effect.Effect<CodexError.CodexAppServerError> =>
   Effect.match(handle.exitCode, {
     onFailure: (cause) =>
       new CodexError.CodexAppServerTransportError({
         operation: "read-process-exit-status",
+        pid: handle.pid,
         cause,
       }),
-    onSuccess: (code) => new CodexError.CodexAppServerProcessExitedError({ code }),
+    onSuccess: (code) => new CodexError.CodexAppServerProcessExitedError({ code, pid: handle.pid }),
   });
diff --git a/packages/effect-codex-app-server/src/errors.ts b/packages/effect-codex-app-server/src/errors.ts
index 3826a099229..f0e0945d352 100644
--- a/packages/effect-codex-app-server/src/errors.ts
+++ b/packages/effect-codex-app-server/src/errors.ts
@@ -146,6 +146,7 @@ export class CodexAppServerProcessExitedError extends Schema.TaggedErrorClass<Co
   "CodexAppServerProcessExitedError",
   {
     code: Schema.optional(Schema.Number),
+    pid: Schema.optionalKey(Schema.Int),
     cause: Schema.optional(Schema.Defect()),
   },
 ) {
@@ -233,6 +234,7 @@ export class CodexAppServerTransportError extends Schema.TaggedErrorClass<CodexA
   "CodexAppServerTransportError",
   {
     operation: CodexAppServerTransportOperation,
+    pid: Schema.optionalKey(Schema.Int),
     cause: Schema.Defect(),
   },
 ) {