{
  "date": "2026-07-22",
  "status": "accepted",
  "scope": "CachedBlobBackend range reads",
  "contract": {
    "range_semantics": "[start, end)",
    "production_change": "Replace end - start + 1 with end.saturating_sub(start) on cold and hot cached reads."
  },
  "baseline_correctness_probe": {
    "ranges": [
      "[0, 1)",
      "[1, 3)",
      "[3, 3)",
      "[2, EOF)"
    ],
    "expected_lengths": [
      1,
      2,
      0,
      4
    ],
    "local_backend_lengths": [
      1,
      2,
      0,
      4
    ],
    "historical_cached_backend_lengths": [
      2,
      3,
      1,
      4
    ],
    "cold_fill": {
      "remote_gets": 1,
      "remote_bytes": 6,
      "elapsed_us": 408.5
    },
    "hot_read_loop": {
      "iterations": 500,
      "local_bytes": 1000,
      "historical_cached_bytes": 1500,
      "local_average_us": 32.16,
      "historical_cached_average_us": 30.839
    },
    "outcome": "failed: the cached backend returned one extra byte whenever end was present"
  },
  "candidate_correctness": {
    "cached_backend_lengths": [
      1,
      2,
      0,
      4
    ],
    "cold_fill_remote_gets": 1,
    "cold_fill_remote_bytes": 6,
    "hot_read_loop_bytes": 1000,
    "focused_test": "cargo test --lib cached_blob_backend::tests::range_end_is_exclusive_on_cold_and_hot_cache_reads",
    "focused_test_result": "1 passed; 0 failed"
  },
  "standalone_ab": {
    "source": "tools/perf-audit/cached_range_ab.rs",
    "command": "cargo run --release --manifest-path tools/perf-audit/Cargo.toml --bin cached_range_ab",
    "environment": {
      "os": "macos",
      "arch": "aarch64"
    },
    "range": {
      "start": 1,
      "end_exclusive": 3
    },
    "warmups_per_variant": 1000,
    "iterations_per_variant": 10000,
    "historical_inclusive": {
      "bytes": 30000,
      "bytes_per_read": 3,
      "p50_us": 8.459,
      "p95_us": 28.292,
      "checksum": 2970000
    },
    "corrected_exclusive": {
      "bytes": 20000,
      "bytes_per_read": 2,
      "p50_us": 8.459,
      "p95_us": 26.917,
      "checksum": 1970000
    },
    "delta_percent": {
      "bytes": -33.333,
      "p50_latency": 0.0,
      "p95_latency": -4.86
    }
  },
  "decision": {
    "status": "accepted",
    "reason": "The candidate restores the exclusive-end contract, removes exactly one surplus byte per bounded cached range, adds no remote request or round trip, and is latency-neutral at p50 while improving this sample's p95."
  }
}