[Bug]: FFF panics in opencode

### Which fff frontend?

Other / multiple

### has logs
```
thread '' (466241) panicked at crates/fff-core/src/simd_path.rs:109:13:
index out of bounds: the len is 32 but the index is 32ild ·
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀
thread '' (466187) panicked at /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/neo_frizbee-0.10.2/src/one_shot/parallel.rs:181:40:
called `Result::unwrap()` on an `Err` value: Any { .. }
fatal runtime error: failed to initiate panic, error 5, aborting
```

### Description

By pressing in @ in the latest version of opencode I now get panics.
```
opencode --v
1.18.27
```

```

lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 25.04
Release: 25.04
Codename: plucky

lscpu

Model name: Intel Core Processor (Haswell, no TSX)
CPU family: 6
Model: 60
Thread(s) per core: 1
Core(s) per socket: 1
Socket(s): 6
Stepping: 1
BogoMIPS: 4788.90
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx rdtscp lm constant_tsc rep_good no
pl xtopology cpuid tsc_known_freq pni pclmulqdq vmx ssse3 fma cx16 pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c
rdrand hypervisor lahf_lm abm cpuid_fault pti tpr_shadow flexpriority ept vpid ept_ad fsgsbase bmi1 avx2 smep bmi2 erms invpcid xsaveopt arat
vnmi md_clear

```

Reproduce the crash by pressing @ in opencode 1.18.27, then inspect crates/fff-core/src/simd_path.rs around line 109 with RUST_BACKTRACE=1 enabled. Compare the failing input or index path with the Haswell/AVX2 environment described; done means the same interaction no longer panics and the relevant behavior remains covered by the repository's tests.

Written by the indexing model from the issue text.