nx_http_cache.nx

nx_http_cache.nx -- HTTP caching primitives (ETag + 304). Standard nginx/apache behavior: substrate emits ETag header on every cacheable response; client sends back If-None-Match on the next request; substrate compares + emits 304 Not Modified if content unchanged. Saves bandwidth on repeated dashboard loads: a 14 KB response becomes a 113-byte 304 header. Per cardinal feedback-no-third-party-trust-native-or-nothing: substrate's own ETag computation. No external hash library. ETag algorithm: FNV-1a 64-bit hash of response body bytes emitted as 16-char lowercase hex. Weak-equivalent per RFC 7232 §2.1 (the weak prefix `W/` is not emitted; substrate uses strong equivalence -- byte-equal response = byte-equal ETag). FNV-1a was chosen because: 1. No crypto-dep transitive imports (works under any syscall ABI) 2. ~1 GB/s single-thread on modern hardware (no perf hit) 3. Adequate collision resistance for HTTP caching (not security) 4. ~30 LOC; auditable nx_capability_claims: needs: [sealed_enum, byte_ops, http_header_search] provides: [etag_compute_fnv1a_hex, cache_control_emit, 304_not_modified_emit, if_none_match_parse] safety: [no_unchecked_deref, no_floating_point, no_syscall, bounded_iteration, bit_equal_reproducible] verdict: [sealed_enum_4_state] license: ORIGINAL kind: racing_crew_specialist layer: L3 (algorithm: HTTP cache decision)