Process gets stuck attempting to create isolates in Dyalog v21.0

```
)copy isolate
C:\Program Files\Dyalog\Dyalog APL-64 21.0 Unicode\ws\isolate.dws ⍝ saved Tue Jun 23 20:34:26 2026
isos←ø¨2⊂''
```

Issuing a strong interrupt opens tracer at `[#.[LIB]] #.Conga.LIB.Clt[20]*`

```apl
[20] r←check ##.Conga.⍙CallR RootName'AClt'a 0
```

```
]version
Dyalog 21.0.54076 64-bit Unicode, BuildID 5b3e55ca
OS Windows 11 64-bit
Link 4.2.2
SALT 2.915
UCMD 2.8
.NET
WS 21.0
```

Works in v20.0

Reproduce the issue by running `)copy isolate` and `isos←ø¨2⊂''` with Dyalog APL 21.0 on Windows 11, then issue a strong interrupt and inspect `#.Conga.LIB.Clt[20]` at `#.Conga.⍙CallR`. Compare the behavior with v20.0; done means isolate creation no longer gets stuck in v21.0.

Written by the indexing model from the issue text.