Brummel
47bec74b26
Adds the missing positive counterpart to the no-instance test: `show 42` with `instance Show Int` PRESENT must typecheck green. This guards against registry-keying or threading bugs that would otherwise sneak past the negative-only test (an empty registry at typecheck time, or a key shape mismatch, would silently fire no-instance even when the instance exists). Also drops the dead `let _ = ws;` and its stale comment in `check_in_workspace` — the line above already consumes `ws.registry`, so the explicit drop is redundant. The remaining comment is folded into the registry-threading comment so the "registry is the only thing threaded" rationale is preserved.