[0] un-named cross param_space():
    sma_cross.sma.length : I64
    sma_cross.sma.length : I64
    exposure.scale : F64
[1] un-named cross bootstrap is_err: true
    -> diagnostic the author sees: UnknownKnob("sma_cross.length")
[1a] bind the real emitted (duplicate) name -> Some(AmbiguousKnob("sma_cross.sma.length"))

[1b] un-named cross compile_with_params err: Some(IndistinguishableFanIn { node: 2 })
    -> IndistinguishableFanIn at interior node index 2 (the Sub that fans in both un-named SMAs)

[2] named cross bootstrap ok: true
[2] named run recorded 12 rows

OK: un-named fan-in rejected, naming the legs is the single recovering act.