node:child_process largely stubbed — 52 radar tests fail with 'value is not a function'

[proggeramlug]

Summary

node:child_process is largely stubbed — 52 of ~74 judged tests fail at runtime with value is not a function (Perry resolves a child_process method to a non-callable stub, then the test calls it).

Examples: test-child-process-default-options.js, test-child-process-destroy.js, test-child-process-advanced-serialization-*.js.

What to do

Audit the child_process surface (spawn/exec/execFile/fork/spawnSync/...) — the 52 failures indicate most entry points return stubs rather than working implementations. File sub-tickets per method family once the surface is mapped, or implement the core spawn/exec path first (most tests bottom out there).

Note: some child_process tests are also in the feature-link-artifact bucket (#1778) — confirm linkage before attributing a failure to a missing impl.

Context: full #800 radar sweep (1300 judged), perry 0.5.1028.

[proggeramlug]

Partial fix in #1827 (PR), plus scope mapping:

Fixed: child_process.exec(cmd[, options], callback) — js_child_process_exec was a null stub and the codegen lowered the callback then discarded it, so exec(cmd, cb) never fired its callback. exec now runs the command (shell, like execSync) and invokes the callback with (err, stdout, stderr) (immediate-callback model, same as the async fs wrappers). The callback is located whether it sits in the options slot (exec(cmd, cb)) or the third slot (exec(cmd, options, cb)); non-zero exit yields an Error; the no-callback form still returns the stdout string. execSync / spawnSync already worked.

Still open — the larger part of this ticket: the dominant node-core child_process pattern is the streaming API:

const child = spawn(cmd, args);
child.stdout.on('data', d => …);   // child.stdout is currently a string → "(string).on is not a function"
child.on('exit'|'close'|'error', …);

js_child_process_spawn / exec (the streaming forms) are explicit null-returning stubs ("needs event loop integration"). A real ChildProcess object — stdout/stderr as Readable streams, stdin Writable, EventEmitter (spawn/exit/close/error/message), pid/kill(), and IPC for fork — is a sizeable feature requiring subprocess + event-loop integration. Most of the 52 radar fails bottom out there. Suggest splitting that into its own ticket (spawn-with-streams) and keeping this for the audit.