Scala 3.8.4

Apply the Java 25 prompt first. These rules cover Scala 3.8.4 types, metaprogramming, Java interop, concurrency, parsing, processes, and artifacts.

Types and domain state

• Model trusted identities, validated input, money, paths, and authorization decisions as distinct opaque or value types.
• Use enums and sealed hierarchies for closed states and handle every case explicitly.
• Compile trust-boundary modules with -Wsafe-init, -deprecation, and -feature, plus -Werror or -Wconf rules that turn reviewed warning categories into errors. Do not use asInstanceOf or @unchecked on values that cross a trust boundary or to silence type-test and exhaustivity warnings.
• Enable the experimental -Yexplicit-nulls where dependencies allow. Java members then get flexible types that still permit member selection, so ascribe their results as T | Null or compile with -Yno-flexible-types, and narrow them with a stable null check rather than .nn or unsafeNulls.
• Import reflectiveSelectable only where the receiver's runtime class is trusted, because a structural call reflectively invokes whatever public member with that name and signature the object's class has.
• Do not expose constructors or copy paths that let callers create an invalid security-sensitive value.

Parsing and dynamic behavior

• Parse external data with schema-aware decoders and reject unknown fields, duplicates, excessive nesting, and invalid variants.
• Never compile, interpret, reflectively load, or interpolate attacker-controlled Scala source or expressions.
• Treat s, f, and raw