`#guard_msgs` hides error messages from commands outside of it

Prerequisites

• 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
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Description

#guard_msgs in inside other ... in commands hides error messages from the commands outside of the #guard_msgs.

Steps to Reproduce

set_option foo true in
example := True

attribute [foo] foo in
example := True

set_option foo true in
#guard_msgs in
example := True

attribute [foo] foo in
#guard_msgs in
example := True

Expected behavior: Both examples should log multiple error messages, such as Unknown option `foo`​ and Unknown attribute `[foo]`​.

Actual behavior: The first example does log multiple error messages, but the second example doesn't log anything.
Somehow the nested #guard_msgs hides the message of things outside of it.

Versions

Lean 4.36.0-nightly-2026-09-16
Target: x86_64-unknown-linux-gnu Linux

Impact

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Run the two minimal Lean reproductions against the stated nightly version and compare their diagnostics. Trace the implementation of #guard_msgs and nested ... in commands to find where message state is scoped; done means the second reproduction reports the same outside-command errors as the first.