No whitespace completion for `set_option`

Prerequisites

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• Check that your issue is not already filed:
  https://github.com/leanprover/lean4/issues
• Reduce the issue to a minimal, self-contained, reproducible test case.
  Avoid dependencies to Mathlib or Batteries.
• Test your test case against the latest nightly release, for example on
  https://live.lean-lang.org/#project=lean-nightly
  (You can also use the settings there to switch to “Lean nightly”)

Description

Type set_option and trigger autocompletion in an editor (VSCode and neovim tested) and no completion results are returned.
But they are properly returned for set_option t (producing all options starting with t).

Context

Reported originally here on Zulip

Steps to Reproduce

(above)

Expected behavior: [Clear and concise description of what you expect to happen]

Completion of all options if no prefix is given.

Actual behavior: [Clear and concise description of what actually happens]

No response.

Versions

[Output of #version or #eval Lean.versionString] "4.14.0"
[OS version, if not using live.lean-lang.org.] macOS 15.1 (24B83)

Additional Information

Impact

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Reproduce the issue in the VSCode or Neovim editor with Lean 4.14.0, comparing set_option with set_option t; the payload names no source file or test to start from. Done means whitespace-triggered completion returns all options while prefixed completion remains correct.