Source-neutral patch-cache keys

Chose source-neutral patch-chain:<from>-<to> cache keys over repository-qualified caches because bridge dual-publishing requires byte-identical artifacts for each version pair and binpatch verifies the cached chain’s final SHA-256 before installation. Source namespacing looks safer but duplicates cache state and weakens offline reuse without adding output integrity. Offline cache hits intentionally occur before source strategy selection; misses return before network access.