Motivation

• Strengthen property-based coverage around the core factory cache to catch regressions where determinism could accidentally depend on insertion order, cache state, or request ordering.
• Exercise a broader space of artifact identities (domain, label, spec, variant) in proptest traces to increase confidence that cache and derivation invariants hold under arbitrary operation sequences.

Description

• Add a CacheOp model and cache_op_strategy() to generate arbitrary cache operation traces varying domain, label, spec, and variant in crates/uselesskey-core/tests/core_prop.rs.
• Add a reusable materialize_ops(seed, ops) helper that drives a deterministic Factory through a sequence of CacheOps and records the observed derived bytes in a BTreeMap.
• Add a new trace-level proptest prop_arbitrary_cache_traces_are_order_and_cache_independent that validates outputs are stable across duplicate requests, cache clears, fresh factories, and canonical replay ordering.
• Import BTreeMap and wire the new helpers into the existing core_prop.rs proptest suite without changing existing assertions.

Testing

• Ran cargo test -p uselesskey-core --test core_prop and all tests passed (17 passed; 0 failed).
• The new property (prop_arbitrary_cache_traces_are_order_and_cache_independent) executes as part of core_prop and succeeded in the test run.

Codex Task