unexpected "dependent match elimination failed"

Prerequisites

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• Check that your issue is not already filed:
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• 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
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Description

The equation compiler gives error "dependent match elimination failed" when I expect the match to succeed

Context

inductive MyOrder : Nat × Nat × Nat → Nat × Nat × Nat → Prop
  | twice {x y n u v m : Nat} : m + 2 ≤ n → MyOrder (x, y, n) (u, v, m)
  | within {x y u v m : Nat} : x ≤ u → y ≤ v → MyOrder (x, y, m) (u, v, m)
  | next_min {x y u v m : Nat} : min x y + 1 ≤ min u v → MyOrder (x, y, m + 1) (u, v, m)

theorem antisymmetric : ∀ {x y : Nat × Nat × Nat}, MyOrder x y → MyOrder y x → x = y
  | _, _, .twice _, .twice _ => _
  | _, _, .twice _, .within _ _ => _
  | _, _, .twice _, .next_min _ => _
  | _, _, .within _ _, .twice _ => _
  | _, _, .within _ _, .within _ _ => _
  | _, _, .next_min _, .twice _ => _

Steps to Reproduce

1. Code as above

Expected behavior: Code gives errors on the six right-hand-sides to fill in the six proofs.

Actual behavior: The line | _, _, .twice _, .within _ _ => _ gives confusing error

dependent match elimination failed, inaccessible pattern found
  .(n✝)
constructor expected

Versions

Lean 4.15.0-rc1
Target: x86_64-unknown-linux-gnu

Using live.lean-lang.org on Lean nightly.

Additional Information

Discussion here: https://leanprover.zulipchat.com/#narrow/channel/270676-lean4/topic/dependent.20match.20elimination.20failed

Impact

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Start by running the minimal MyOrder and antisymmetric reproducer against the latest Lean nightly, focusing on the equation compiler's dependent match elimination. Read the linked Zulip discussion for context; done means the reported pattern no longer produces the confusing inaccessible-pattern error and behaves as expected for the six proof holes.