"Conflicting implementations" when there are two (distinct) concrete impls, but not one

I tried this code:

trait Simple {}
trait Complex {}

impl<T: Simple> Complex for T {}
impl<T: Complex> Complex for Option<T> {}

// Not strictly necessary, just as an example.
impl Complex for u32 {}

// Comment out either of these for a successful compilation.
impl Simple for Option<u64> {}
impl Simple for Option<i64> {}

I expected this to compile without issue, as all traits are crate-local and there are in practice no overlapping implementations, and in fact it was working when I only had one impl Simple.

However, with both the compiler produces:

error[E0119]: conflicting implementations of trait `Complex` for type `Option<_>`
 --> src/lib.rs:5:1
  |
4 | impl<T: Simple> Complex for T {}
  | ----------------------------- first implementation here
5 | impl<T: Complex> Complex for Option<T> {}
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Option<_>`

It seems like either this should be forbidden when there is only one impl as well, or it should be allowed when there is more than one.

Meta

rustc --version --verbose:

rustc 1.92.0-nightly (975e6c8fe 2025-09-23)
binary: rustc
commit-hash: 975e6c8fec280816d24fbde6b8dfe19620f2efe6
commit-date: 2025-09-23
host: aarch64-apple-darwin
release: 1.92.0-nightly
LLVM version: 21.1.1

rustc 1.95.0-nightly (18d13b533 2026-02-09)
binary: rustc
commit-hash: 18d13b5332916ffca8eadb9106d54b5b434e9978
commit-date: 2026-02-09
host: aarch64-apple-darwin
release: 1.95.0-nightly
LLVM version: 22.1.0

Also checked against 1.93 stable in the playground.

Start with the minimal reproducer in src/lib.rs and compile it against the reported stable and nightly versions to confirm the inconsistent coherence behavior. Trace the compiler's trait-implementation overlap checking, then establish whether the intended result is acceptance or rejection and add a regression test covering both concrete implementations.