forceStringNoCtx error messages leaked internal string context representation (e.g. '!out!<hash>-name.drv'). Use DerivedPath syntax instead: '<store-path>^out' for built, plain path for opaque, and '<drv-path> (deep)' for deep derivation references.
The error had nothing to do with content-addressed derivations; it triggers when a supposed derivation attrset simply lacks an outPath attribute.
Improve coverage ahead of changes to get-drvs.cc and related code. Each fixture is a separate file to avoid line-number churn in error expectations.