refactor: standardize on pid as canonical background execution field

Remove the dual executionId/pid fields from BackgroundExecutionData.
Use pid everywhere for consistency with existing types (ExecutingToolCall,
ExecutionHandle). A codebase-wide rename to executionId is planned as a
follow-up once all consumers are migrated.

packages/cli/src/ui/hooks/useGeminiStream.test.tsx

@@ -97,18 +97,16 @@ const MockedUserPromptEvent = vi.hoisted(() =>
 );
 const mockParseAndFormatApiError = vi.hoisted(() => vi.fn());
 const mockIsBackgroundExecutionData = vi.hoisted(
-  () => (data: unknown): data is { executionId?: number; pid?: number } => {
+  () => (data: unknown): data is { pid?: number } => {
     if (typeof data !== 'object' || data === null) {
       return false;
     }
     const value = data as {
-      executionId?: unknown;
       pid?: unknown;
       command?: unknown;
       initialOutput?: unknown;
     };
     return (
-      (value.executionId === undefined || typeof value.executionId === 'number') &&
       (value.pid === undefined || typeof value.pid === 'number') &&
       (value.command === undefined || typeof value.command === 'string') &&
       (value.initialOutput === undefined ||
@@ -116,11 +114,6 @@ const mockIsBackgroundExecutionData = vi.hoisted(
     );
   },
 );
-const mockGetBackgroundExecutionId = vi.hoisted(
-  () =>
-    (data: { executionId?: number; pid?: number }): number | undefined =>
-      data.executionId ?? data.pid,
-);
 
 const MockValidationRequiredError = vi.hoisted(
   () =>
@@ -147,7 +140,6 @@ vi.mock('@google/gemini-cli-core', async (importOriginal) => {
   return {
     ...actualCoreModule,
     isBackgroundExecutionData: mockIsBackgroundExecutionData,
-    getBackgroundExecutionId: mockGetBackgroundExecutionId,
     GitService: vi.fn(),
     GeminiClient: MockedGeminiClientClass,
     UserPromptEvent: MockedUserPromptEvent,

packages/cli/src/ui/hooks/useGeminiStream.ts

@@ -37,11 +37,9 @@ import {
   buildUserSteeringHintPrompt,
   GeminiCliOperation,
   getPlanModeExitMessage,
-  getBackgroundExecutionId,
   isBackgroundExecutionData,
 } from '@google/gemini-cli-core';
 import type {
-  BackgroundExecutionData,
   Config,
   EditorType,
   GeminiClient,
@@ -98,7 +96,7 @@ type ToolResponseWithParts = ToolCallResponseInfo & {
 };
 
 interface BackgroundedToolInfo {
-  executionId: number;
+  pid: number;
   command: string;
   initialOutput: string;
 }
@@ -123,16 +121,14 @@ function getBackgroundedToolInfo(
     return undefined;
   }
 
-  const data: BackgroundExecutionData = rawData;
-  const executionId = getBackgroundExecutionId(data);
-  if (executionId === undefined) {
+  if (rawData.pid === undefined) {
     return undefined;
   }
 
   return {
-    executionId,
-    command: data.command ?? toolCall.request.name,
-    initialOutput: data.initialOutput ?? '',
+    pid: rawData.pid,
+    command: rawData.command ?? toolCall.request.name,
+    initialOutput: rawData.initialOutput ?? '',
   };
 }
 
@@ -1676,7 +1672,7 @@ export const useGeminiStream = (
         const backgroundedTool = getBackgroundedToolInfo(toolCall);
         if (backgroundedTool) {
           registerBackgroundShell(
-            backgroundedTool.executionId,
+            backgroundedTool.pid,
             backgroundedTool.command,
             backgroundedTool.initialOutput,
           );

packages/core/src/tools/shell.ts

@@ -347,7 +347,6 @@ export class ShellToolInvocation extends BaseToolInvocation<
       } else if (this.params.is_background || result.backgrounded) {
         llmContent = `Command moved to background (PID: ${result.pid}). Output hidden. Press Ctrl+B to view.`;
         data = {
-          executionId: result.pid,
           pid: result.pid,
           command: this.params.command,
           initialOutput: result.output,

packages/core/src/tools/tools.ts

@@ -75,15 +75,13 @@ export interface ToolInvocation<
 /**
  * Structured payload used by tools to surface background execution metadata to
  * the CLI UI.
+ *
+ * NOTE: `pid` is used as the canonical identifier for now to stay consistent
+ * with existing types (ExecutingToolCall.pid, ExecutionHandle.pid, etc.).
+ * A future rename to `executionId` is planned once the codebase is fully
+ * migrated — not done in this PR to keep the diff focused on the abstraction.
  */
 export interface BackgroundExecutionData extends Record<string, unknown> {
-  /**
-   * Neutral execution identifier for background lifecycle tracking.
-   */
-  executionId?: number;
-  /**
-   * Backwards-compatible alias for executionId.
-   */
   pid?: number;
   command?: string;
   initialOutput?: string;
@@ -96,32 +94,18 @@ export function isBackgroundExecutionData(
     return false;
   }
 
-  const executionId = 'executionId' in data ? data.executionId : undefined;
   const pid = 'pid' in data ? data.pid : undefined;
   const command = 'command' in data ? data.command : undefined;
   const initialOutput =
     'initialOutput' in data ? data.initialOutput : undefined;
 
   return (
-    (executionId === undefined || typeof executionId === 'number') &&
     (pid === undefined || typeof pid === 'number') &&
     (command === undefined || typeof command === 'string') &&
     (initialOutput === undefined || typeof initialOutput === 'string')
   );
 }
 
-export function getBackgroundExecutionId(
-  data: BackgroundExecutionData,
-): number | undefined {
-  if (typeof data.executionId === 'number') {
-    return data.executionId;
-  }
-  if (typeof data.pid === 'number') {
-    return data.pid;
-  }
-  return undefined;
-}
-
 /**
  * Options for policy updates that can be customized by tool invocations.
  */