`partial` defeats `#eval` guardrails

Prerequisites

Please put an X between the brackets as you perform the following steps:

• 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

partial def f (n : Nat) : Nat :=
  if n = 0 then
    #[1, 2, 3][4]'sorry
  else
    f (n - 1)

#eval f 1

causes an OOB access resulting in nonsense or crashes, even though #eval is supposed to prevent such things from happening by checking for sorrys.

Steps to Reproduce

1. Copy the code above into live.lean-lang.org

Expected behavior: Error message aborting evaluation since the expression depends on the 'sorry' axiom, which can lead to runtime instability and crashes.

Actual behavior: nonsense output or crashes

Versions

Lean 4.25.0-nightly-2025-10-13

Impact

Add 👍 to issues you consider important. If others are impacted by this issue, please ask them to add 👍 to it.

Start by running the minimal reproducer from the issue in live.lean-lang.org and examine how #eval checks for sorry dependencies when the function is marked partial. Done means the example reports the expected sorry-abort error instead of producing nonsense output or crashing.