[TypeScript SDK] Expose hardened execution controls for automation

What feature would you like to see?

Please expose a lower-level hardened execution surface in @openai/codex-sdk, or first-class thread options that provide these equivalent controls before codex exec starts:

• ignore ambient user configuration and exec-policy rules, equivalent to --ignore-user-config and --ignore-rules;
• bound each stdout JSONL record and retained stderr output, while reporting when bytes or records were discarded; and
• expose the spawned child/process-group lifecycle so an aborting automation host can terminate and await the complete descendant process tree.

The separate ephemeral-session gap is already tracked in #34760.

Config overrides and a controlled environment are useful but do not replace the first requirement: they cannot stop ambient files from being loaded before overrides apply. Likewise, an AbortSignal that kills only the direct child does not guarantee cleanup when tool commands have spawned descendants.

A possible API could be one of:

1. explicit ThreadOptions for the isolation flags plus bounded diagnostic callbacks and a process-tree-aware abort contract; or
2. a documented low-level execution hook that receives the fully constructed invocation and child handle while the SDK continues to own protocol compatibility.

Why is this useful?

Long-running CI and agent-harness services need stronger guarantees than an interactive client:

• host config or approval rules must not silently change a supposedly pinned run;
• a hostile or accidental multi-megabyte JSONL/stderr record must not grow memory without limit;
• telemetry consumers must be able to mark results incomplete when stream data was dropped instead of guessing; and
• timeout, cancellation, and shutdown must not leave tool subprocesses running after the SDK call ends.

Without these hooks, automation either accepts weaker isolation/resource guarantees or maintains a parallel CLI/protocol/process wrapper. The SDK already covers typed events, output schemas, controlled environments, config overrides, and custom executable selection; these lifecycle controls are the remaining gap for adopting it as the sole invocation boundary.

Additional context

Re-evaluated against @openai/codex-sdk 0.145.0 on 2026-07-22. A migration contract can be validated with tests that assert ambient config/rules are bypassed, oversized diagnostic records are bounded and observable, and aborting the SDK invocation kills a spawned grandchild process.