suffixes of hygienic goal names

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

some tactics (e.g. apply) introduce hygienized goal names; later on the "case tag" tactic checks if tag is a suffix of the hygienized goal name, failing. This is also very confusing because the hygienic part of the goal name is hidden to the users

Context

[Broader context that the issue occured in. If there was any prior discussion on the Lean Zulip, link it here as well.]

https://leanprover.zulipchat.com/#narrow/stream/239415-metaprogramming-.2F-tactics/topic/suffixes.20of.20hygienic.20goals.20name

Steps to Reproduce

axiom set: Type
axiom mem: set → set → Prop

infix:50 (priority := high) " ∈ " => mem

axiom ax_extensionality: ∀A, (∀Z, Z ∈ A → Z ∈ A) → A=A

axiom union: set → set → set
infix:70 (priority := high) " ∪ " => union
axiom K1 : Prop
axiom K2 : Prop
axiom ax_union1: ∀A B, ∀Z, (Z ∈ A ∪ B → K1 ∨ K2)

theorem union_symmetric: ∀A: set, A∪A=A∪A := by
 intros A
 apply ax_extensionality
 intro Z
 intro U
 have H : K1 ∨ K2 := ax_union1 A A Z U
 cases H
 . case inl => sorry  --- error here: inl is not a suffix because the goal name is really a.inl._@.VerboseMatita.Bug._hyg.1269
 . sorry

1. enter the code above
2. the error is in the line with the comment; the comment explains why the error occurs; Sebastian explained on Zulip that the hygienized name is actually due to the only "apply" tactic

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

"case inl" should match the goal

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

but it does not

Versions

4.9.0-rc3

Reproduce the provided Lean snippet on the latest nightly release and confirm that case inl fails because of the hygienic goal-name suffix. Then inspect the case tag tactic and the goal-name hygiene handling. Done means case inl matches the user-visible goal while preserving hygienic naming behavior.