doc: clarify that process._debugProcess() is not restricted by the Permission Model

[cybe4sent1nel]

What

Adds a documentation note to the Permission Model page clarifying that
process._debugProcess() is not restricted by the kInspector
permission scope or any other Permission Model scope.

Why

The Permission Model documentation lists "Inspector protocol" as a
restricted surface. A developer reading this reasonably expects that
--permission prevents all Inspector activation — including
cross-process activation via process._debugProcess().

The current behavior creates a silent inconsistency:

• kInspector blocks the sandboxed process from opening its own
  Inspector.
• kInspector does not block the sandboxed process from calling
  process._debugProcess(pid) to force another Node.js process to
  open its Inspector.

This gap is not documented anywhere. This note ensures developers are
not surprised by this behavior when they rely on the Permission Model
as a sandbox.

Behavior unchanged

This is a documentation-only change. No API behavior is modified.

Background

Discussed with @RafaelGSS. The behavior is consistent with the Node.js
threat model (Node.js trusts the OS environment it runs in, and
cross-process signaling is an OS-level capability). The fix here is
documentation so operators understand what responsibility falls on them
vs. the Permission Model.

Checklist

• make lint passes
• Documentation only — no tests required
• Follows the Node.js documentation style

[nodejs-github-bot]

Review requested:

• @nodejs/security-wg

[cybe4sent1nel]

Thanks for catching that — I've updated the sentence to remove the
contradiction. The paragraph now simply states that any Node.js process
running on the same host under the same OS user can be signaled,
without the conflicting parenthetical.