Align Flow lib defs for Node.js child_process with v24

[robhogan]

Summary:
This is an AI-assisted change to align the Flow definitions for the child_process module with the Node.js docs as at v24.

New v18+ Features:

1. AbortSignal Support (v18.0.0) - Process cancellation

   • Added signal?: AbortSignal option to all async functions (exec, execFile, fork, spawn)
   • Enables cancellation of child processes using AbortController
   • Example: const controller = new AbortController(); spawn('cmd', [], {signal: controller.signal}); controller.abort();
   • https://nodejs.org/api/child_process.html#child_processexeccommand-options-callback

2. Enhanced Process Properties (v20.x)

   • spawnargs: Array<string> - Full command-line arguments used to launch the process
   • spawnfile: string - Executable file name of the child process
   • signalCode: string | null - Signal that terminated the child process
   • https://nodejs.org/api/child_process.html#subprocessspawnargs

ChildProcess Class Updates:

3. Improved Property Types

   • stdio is now a properly typed tuple array with readonly modifier
   • channel changed from Object to mixed for better type safety

4. Enhanced Method Signatures

   • kill(signal?: string | number): boolean - Now returns boolean and accepts numeric signals
   • send() overloads properly typed with child_process$Serializable messages
   • send() accepts keepOpen option: Readonly<{keepOpen?: boolean}>
   • https://nodejs.org/api/child_process.html#subprocesskillsignal

Option Type Improvements:

6. Modern Readonly Syntax - All input options use Readonly<{...}>

   • execOpts, execFileOpts, forkOpts, spawnOpts, spawnSyncOpts, etc.
   • Allows passing readonly types safely

7. Enhanced Environment Variables

   • Changed env?: Object to env?: {[key: string]: string | void}
   • More precise typing for environment variable dictionaries

8. New Fork Options (IPC enhancements)

   • serialization?: 'json' | 'advanced' - IPC serialization format
   • killSignal and timeout options added to fork
   • https://nodejs.org/api/child_process.html#child_processforkmodulepath-args-options

9. Enhanced Spawn Options

   • Added killSignal, timeout, serialization to spawnOpts
   • Better consistency across all spawn functions

Return Type Fixes:

10. spawnRet/spawnSyncRet - Made fields properly nullable:
    • status: number | null - null if process never exited
    • signal: string | null - null if not terminated by signal
    • error: Error | void - void if no error occurred
    • Removed spread operator for exact types

Helper Types:

11. child_process$Serializable - Union type for IPC messages:

    • string | number | boolean | bigint | {...} | Array<mixed>
    • Used in send() method signatures

12. child_process$SendHandle - Type for handle passing:

    • net$Server | net$Socket
    • Used for passing server/socket handles to child processes

References:

• Node.js child_process module docs: https://nodejs.org/api/child_process.html
• AbortSignal integration: https://nodejs.org/api/child_process.html#child_processexeccommand-options-callback

Changelog: [Internal]

Generated by Confucius Code Assist (CCA)
Confucius Session, Trace

Reviewed By: vzaidman

Differential Revision: D89944331

[meta-codesync]

@robhogan has exported this pull request. If you are a Meta employee, you can view the originating Diff in D89944331.

[github-actions]

Job Summary for Gradle

Test All :: run_fantom_tests

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
react-native-github	:private:react-native-fantom:buildFantomTester	9.0.0	❌