#258 mini-clos dispatch on a non-instance argument SIGSEGVs instead of no-applicable-method

Repro (asdf loaded, but any mc generic should do): (asdf/action::component-operation-time 12345) — dispatching a generic whose applicable methods specialize (operation component) with a FIXNUM second arg core-dumps the process. ANSI wants no-applicable-method → error.

Presumably mc-dispatch reads class-of/slot metadata assuming an %MC-INSTANCE% record shape and dereferences garbage for immediates/non-instances.

Context: found while chasing the asdf operate traverse blocker (2026-07-08). During (asdf:operate 'load-source-op "foo"), traverse calls the component-operation-time convenience method with a component designator whose type-of prints T (unclassifiable); somewhere past find-component the process raises "call to a name undefined at compile time" (the shared trap). Dispatch robustness on weird arguments is part of that fog: a fixnum SEGVs, the weird-T object apparently reaches the trap. Both should be no-applicable-method.

Also filed alongside: the read-all-before-eval loader keeps #. constants unevaluatable (see the asdf case-key note in cave#257 thread / north-star #205).