diff --git a/crates/fission-signatures/src/fpk.rs b/crates/fission-signatures/src/fpk.rs
index 9b35c712f..da80b74bb 100644
--- a/crates/fission-signatures/src/fpk.rs
+++ b/crates/fission-signatures/src/fpk.rs
@@ -29,7 +29,7 @@ use std::collections::HashMap;
 use std::fs::File;
 use std::io::Read;
 use std::path::Path;
-use std::sync::{Arc, Mutex};
+use std::sync::{Arc, Mutex, OnceLock};
 
 const MAGIC: &[u8; 4] = b"FPK1";
 const HEADER_LEN: usize = 72;
@@ -86,6 +86,41 @@ struct BlockRef {
     raw_len: usize,
 }
 
+/// One immutable decoded payload, with optional random row access. Ordinary
+/// block consumers keep their shared String without building the row index.
+struct CachedPayloadBlock {
+    text: Arc<String>,
+    rows: OnceLock<Vec<std::ops::Range<usize>>>,
+}
+
+impl CachedPayloadBlock {
+    fn new(text: String) -> Self {
+        Self {
+            text: Arc::new(text),
+            rows: OnceLock::new(),
+        }
+    }
+
+    fn line_at(&self, row: usize) -> Option<&str> {
+        let rows = self.rows.get_or_init(|| {
+            let mut offset = 0usize;
+            self.text
+                .split_inclusive('\n')
+                .map(|raw| {
+                    let content = raw
+                        .strip_suffix('\n')
+                        .map(|line| line.strip_suffix('\r').unwrap_or(line))
+                        .unwrap_or(raw);
+                    let range = offset..offset + content.len();
+                    offset += raw.len();
+                    range
+                })
+                .collect()
+        });
+        self.text.get(rows.get(row)?.clone())
+    }
+}
+
 pub struct FpkReader {
     map: Mmap,
     blocks: Vec<BlockRef>,
@@ -95,7 +130,7 @@ pub struct FpkReader {
     /// resolve names that sort near each other, so the same block answers many
     /// of them. Without this a lazy database pays a decompress per lookup
     /// instead of per block.
-    cache: Mutex<HashMap<usize, Arc<String>>>,
+    cache: Mutex<HashMap<usize, Arc<CachedPayloadBlock>>>,
 }
 
 fn u16_at(b: &[u8], at: usize) -> u16 {
@@ -237,16 +272,23 @@ impl FpkReader {
 
     /// Decompressed block `index`, from the cache when it is already there.
     pub fn block_at(&self, index: usize) -> Result<Arc<String>, FpkError> {
+        self.cached_block_at(index)
+            .map(|block| Arc::clone(&block.text))
+    }
+
+    fn cached_block_at(&self, index: usize) -> Result<Arc<CachedPayloadBlock>, FpkError> {
         if let Ok(cache) = self.cache.lock()
             && let Some(hit) = cache.get(&index)
         {
             return Ok(Arc::clone(hit));
         }
-        let text = Arc::new(self.decompress(&self.blocks[index])?);
+        let block = Arc::new(CachedPayloadBlock::new(
+            self.decompress(&self.blocks[index])?,
+        ));
         if let Ok(mut cache) = self.cache.lock() {
-            cache.insert(index, Arc::clone(&text));
+            cache.insert(index, Arc::clone(&block));
         }
-        Ok(text)
+        Ok(block)
     }
 
     /// The index directory, or `None` when the file has none.
@@ -347,8 +389,8 @@ impl FpkReader {
                         self.blocks.len()
                     )));
                 }
-                let text = self.block_at(block)?;
-                match text.lines().nth(row) {
+                let text = self.cached_block_at(block)?;
+                match text.line_at(row) {
                     Some(line) => out.push(line.to_owned()),
                     None => {
                         return Err(FpkError::Corrupt(format!(
@@ -995,6 +1037,105 @@ mod tests {
         std::fs::remove_file(&path).ok();
     }
 
+    #[test]
+    fn cached_payload_rows_match_str_lines() {
+        for text in [
+            "",
+            "\n",
+            "\n\n",
+            "\r",
+            "\r\n",
+            "a",
+            "a\n",
+            "a\r",
+            "a\r\n",
+            "a\n\nb",
+            "a\r\n\r\nb\n",
+            "\nlast",
+            "a\r\rb\n",
+            "값\r\n다음\n끝",
+            "a\u{2028}b\u{0085}c",
+        ] {
+            let block = CachedPayloadBlock::new(text.to_owned());
+            assert!(block.rows.get().is_none());
+            let expected: Vec<_> = text.lines().collect();
+            for row in 0..expected.len() + 3 {
+                assert_eq!(
+                    block.line_at(row),
+                    expected.get(row).copied(),
+                    "{text:?} row={row}"
+                );
+            }
+            assert_eq!(block.line_at(usize::MAX), None);
+        }
+    }
+
+    #[test]
+    fn hash_rows_share_the_existing_payload_and_preserve_order_under_concurrency() {
+        let records: Vec<_> = (0..80).map(|i| format!("key|row{i:04}|payload")).collect();
+        let (mut image, locators) = pack_with_locators(&records, 1, CODEC_ZLIB, 1, 64 * 1024);
+        append_hash_index(
+            &mut image,
+            locators
+                .iter()
+                .map(|l| HashEntry {
+                    key: 42,
+                    block: l.block,
+                    row: l.row,
+                })
+                .collect(),
+        );
+        let path = write_temp(&image);
+        let reader = FpkReader::open(&path).unwrap();
+        assert_eq!(reader.block_count(), 1);
+        let public = reader.block_at(0).unwrap();
+        let cached = reader.cached_block_at(0).unwrap();
+        assert!(
+            cached.rows.get().is_none(),
+            "ordinary reads must not index lines"
+        );
+        std::thread::scope(|scope| {
+            let handles: Vec<_> = (0..8)
+                .map(|_| {
+                    scope.spawn(|| {
+                        for _ in 0..20 {
+                            assert_eq!(reader.records_by_key(42).unwrap(), records);
+                            assert!(reader.records_by_key(43).unwrap().is_empty());
+                        }
+                    })
+                })
+                .collect();
+            for handle in handles {
+                handle.join().unwrap();
+            }
+        });
+        assert_eq!(cached.rows.get().unwrap().len(), records.len());
+        assert!(Arc::ptr_eq(&public, &reader.block_at(0).unwrap()));
+        assert!(Arc::ptr_eq(&cached, &reader.cached_block_at(0).unwrap()));
+        std::fs::remove_file(path).ok();
+    }
+
+    #[test]
+    fn indexed_payload_keeps_invalid_locator_errors() {
+        let records = vec!["key|one".to_owned()];
+        let (mut image, _) = pack_with_locators(&records, 1, CODEC_ZLIB, 1, 4096);
+        append_hash_index(
+            &mut image,
+            vec![HashEntry {
+                key: 7,
+                block: 0,
+                row: 100,
+            }],
+        );
+        let path = write_temp(&image);
+        let reader = FpkReader::open(&path).unwrap();
+        assert_eq!(
+            reader.records_by_key(7).unwrap_err().to_string(),
+            "fpk corrupt: hash index points at row 100 of block 0"
+        );
+        std::fs::remove_file(path).ok();
+    }
+
     #[test]
     fn a_file_without_a_hash_index_says_so() {
         let path = write_temp(&pack(&["a|1", "b|2"]));
diff --git a/docs/proposals/2026-10-15-fid-row-access.md b/docs/proposals/2026-10-15-fid-row-access.md
new file mode 100644
index 000000000..31d6aacb8
--- /dev/null
+++ b/docs/proposals/2026-10-15-fid-row-access.md
@@ -0,0 +1,27 @@
+# Indexed access to immutable FPK payload rows
+
+Mechanical performance follow-up to PR #205; no quality, FID-admission, naming, ordering, cache-key, runtime-dependency, or worker-policy change.
+
+## Measured anchor and owner
+
+Pinned qualification revision 07dd95dbe6214b8a78fc1e4a55961ab515986489. PR #205's measured release candidate (SHA256 4c0485b7da200135afbc2e0bfbdbb9de8a7058549a1f9a1d6af3e91c9c6dc320) is the new control: selected small medians 2.224/1.171/1.380 s and large control 103.820 s. A symbolized candidate diagnostic at 65 s shows FID matching in FpkReader::records_by_key line 351, text.lines().nth(row), with 1337 samples at that line in a representative worker stack. The 35 s diagnostic still shows native decode, so this is a distinct later phase. Native samples are diagnostics, not timing or output-parity runs; they are retained under benchmark/artifacts/performance/2026-10-14-kuna/startup-large-profile-*.txt.
+
+The FPK reader already caches immutable decompressed payload blocks. Each hash locator names a row in such a block. Starting String::lines from the beginning for every locator repeats the same prefix scan. The previous rejected index-chunk experiment avoided decompression; it did not avoid this row scan. Keep that experiment excluded.
+
+## Invariant and implementation boundary
+
+Extend the existing per-reader payload cache entry with a lazily initialized line-range index. Construct ranges from newline-delimited chunks, removing exactly the same LF/optional CRLF terminators as str::lines. Empty input, empty interior lines, trailing newline, bare CR, Unicode and unterminated final rows must match str::lines exactly. Read one row by a bounds-checked string slice. Keep public block_at/block_for returning the original shared Arc<String>; direct block consumers need not build the row index.
+
+Keep index-directory searches, decompression/validation, locator checks, matched record order, duplicate handling, full/specific hashes, FID thresholds and error messages unchanged. The row index is built synchronously from the already validated immutable string and does not call Rayon, I/O or the reader cache. Retain it only with that existing cached payload, with two usize offsets per line plus vector capacity overhead; do not add a parallel program-fact map, hidden runtime dependency or global cache. Preserve cold-cache publication behavior and do not cache failures.
+
+## Verification and acceptance
+
+- Compare indexed rows with str::lines across empty/LF/CRLF/bare-CR/Unicode/repeated rows and out-of-range indices.
+- Assert public Arc ownership/warm identity remains unchanged; ordinary block reads leave line indexes uninitialized; repeated/concurrent hash reads return identical ordered records.
+- Retain existing cross-chunk duplicate-key, payload format, malformed input and block-boundary tests. Run focused signatures nextest then signatures/static/decompiler/CLI suites, checks, release CLI and workspace formatting.
+- Freeze a separate candidate binary. Measure five alternating small pairs and a sequential large control against PR #205's immutable measured binary. Fresh full 250-function stripped replay must preserve every non-time output field; no score or ranking change is claimed.
+- Keep only an observed practical gain with output parity. Report the added row-index memory and any timing regression. The remaining Kuna gap is not assumed closed.
+
+## Accepted local evidence
+
+15 focused FPK tests and 398 related tests passed (one skipped), with crate checks, release CLI and workspace formatting passing. Five-pair small controls are unchanged on Linux/macOS and improve Windows 1.1763 -> 0.9614 s. The fresh sequential large control improves 112.924 -> 42.235 s (CPU 1044.333 -> 233.619 s), with unchanged six outputs and similar observed maximum RSS (3.624/3.598 GiB). Fresh 250-function replay changes no non-time records. Details and all limits are recorded in docs/validation/fid-row-access-performance.md and its compact JSON. The 22-function pinned Kuna comparison remains 4.17–15.47 times slower; Kuna-level performance is not achieved.
diff --git a/docs/validation/fid-row-access-performance.json b/docs/validation/fid-row-access-performance.json
new file mode 100644
index 000000000..335be5940
--- /dev/null
+++ b/docs/validation/fid-row-access-performance.json
@@ -0,0 +1,1474 @@
+{
+  "measurement_context": "PR #204 source plus PR #205 production patch; candidate additionally applies this FPK change",
+  "independent_main_base": "b33e4e125dd151501c20d2e81bac3f3238c4bb0d",
+  "binaries": {
+    "baseline": "4c0485b7da200135afbc2e0bfbdbb9de8a7058549a1f9a1d6af3e91c9c6dc320",
+    "candidate": "28ec116dcb4966fa53546dcbf2e76977efcfb7a4b6bec380ba14174b2df14aba"
+  },
+  "population_reference": "decompiler-startup-performance.json:population",
+  "dataset_revision": "07dd95dbe6214b8a78fc1e4a55961ab515986489",
+  "timing_keys_excluded": [
+    "build_duration_ms",
+    "decomp_sec",
+    "normalize_duration_ms",
+    "postprocess_sec",
+    "render_duration_ms",
+    "structuring_duration_ms",
+    "total_time_ms"
+  ],
+  "incremental_paired": [
+    {
+      "cell": "03",
+      "baseline": 2.2162096250103787,
+      "baseline_deterministic": true,
+      "candidate": 2.210409125080332,
+      "candidate_deterministic": true,
+      "speedup": 1.0026241748028595
+    },
+    {
+      "cell": "27",
+      "baseline": 1.1763345000799745,
+      "baseline_deterministic": true,
+      "candidate": 0.9613626659847796,
+      "candidate_deterministic": true,
+      "speedup": 1.223611589779167
+    },
+    {
+      "cell": "40",
+      "baseline": 1.3782720419112593,
+      "baseline_deterministic": true,
+      "candidate": 1.371471417020075,
+      "candidate_deterministic": true,
+      "speedup": 1.0049586340676064
+    }
+  ],
+  "incremental_raw_timings": [
+    {
+      "cell": "03",
+      "tag": "paired-03-baseline-0",
+      "seconds": 2.2895658750785515,
+      "cpu_seconds": 3.591924,
+      "exit": 0,
+      "timeout": false,
+      "returned": 6,
+      "sha": "2c243fef3e4e8640e9bc0d613f9505778900aa281195acd55b208fff68b9de24"
+    },
+    {
+      "cell": "03",
+      "tag": "paired-03-candidate-0",
+      "seconds": 2.7855617500608787,
+      "cpu_seconds": 3.61283,
+      "exit": 0,
+      "timeout": false,
+      "returned": 6,
+      "sha": "2c243fef3e4e8640e9bc0d613f9505778900aa281195acd55b208fff68b9de24"
+    },
+    {
+      "cell": "03",
+      "tag": "paired-03-candidate-1",
+      "seconds": 2.2102583330124617,
+      "cpu_seconds": 3.5897819999999987,
+      "exit": 0,
+      "timeout": false,
+      "returned": 6,
+      "sha": "2c243fef3e4e8640e9bc0d613f9505778900aa281195acd55b208fff68b9de24"
+    },
+    {
+      "cell": "03",
+      "tag": "paired-03-baseline-1",
+      "seconds": 2.2162096250103787,
+      "cpu_seconds": 3.5796209999999995,
+      "exit": 0,
+      "timeout": false,
+      "returned": 6,
+      "sha": "2c243fef3e4e8640e9bc0d613f9505778900aa281195acd55b208fff68b9de24"
+    },
+    {
+      "cell": "03",
+      "tag": "paired-03-baseline-2",
+      "seconds": 2.2099199580261484,
+      "cpu_seconds": 3.6183950000000005,
+      "exit": 0,
+      "timeout": false,
+      "returned": 6,
+      "sha": "2c243fef3e4e8640e9bc0d613f9505778900aa281195acd55b208fff68b9de24"
+    },
+    {
+      "cell": "03",
+      "tag": "paired-03-candidate-2",
+      "seconds": 2.2084731669165194,
+      "cpu_seconds": 3.5699300000000003,
+      "exit": 0,
+      "timeout": false,
+      "returned": 6,
+      "sha": "2c243fef3e4e8640e9bc0d613f9505778900aa281195acd55b208fff68b9de24"
+    },
+    {
+      "cell": "03",
+      "tag": "paired-03-candidate-3",
+      "seconds": 2.210409125080332,
+      "cpu_seconds": 3.571881000000001,
+      "exit": 0,
+      "timeout": false,
+      "returned": 6,
+      "sha": "2c243fef3e4e8640e9bc0d613f9505778900aa281195acd55b208fff68b9de24"
+    },
+    {
+      "cell": "03",
+      "tag": "paired-03-baseline-3",
+      "seconds": 2.211886875098571,
+      "cpu_seconds": 3.6173439999999983,
+      "exit": 0,
+      "timeout": false,
+      "returned": 6,
+      "sha": "2c243fef3e4e8640e9bc0d613f9505778900aa281195acd55b208fff68b9de24"
+    },
+    {
+      "cell": "03",
+      "tag": "paired-03-baseline-4",
+      "seconds": 2.2166683330433443,
+      "cpu_seconds": 3.6007709999999986,
+      "exit": 0,
+      "timeout": false,
+      "returned": 6,
+      "sha": "2c243fef3e4e8640e9bc0d613f9505778900aa281195acd55b208fff68b9de24"
+    },
+    {
+      "cell": "03",
+      "tag": "paired-03-candidate-4",
+      "seconds": 2.217003667028621,
+      "cpu_seconds": 3.6050730000000017,
+      "exit": 0,
+      "timeout": false,
+      "returned": 6,
+      "sha": "2c243fef3e4e8640e9bc0d613f9505778900aa281195acd55b208fff68b9de24"
+    },
+    {
+      "cell": "27",
+      "tag": "paired-27-baseline-0",
+      "seconds": 1.2056539169279858,
+      "cpu_seconds": 1.7234799999999955,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "561a5e1e1dad723fefa2f2fa5f515becc6989cfa614a12e5bc6d7bf481f02e64"
+    },
+    {
+      "cell": "27",
+      "tag": "paired-27-candidate-0",
+      "seconds": 0.9571909579681233,
+      "cpu_seconds": 1.444932000000001,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "561a5e1e1dad723fefa2f2fa5f515becc6989cfa614a12e5bc6d7bf481f02e64"
+    },
+    {
+      "cell": "27",
+      "tag": "paired-27-candidate-1",
+      "seconds": 0.9539643339812756,
+      "cpu_seconds": 1.4494729999999951,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "561a5e1e1dad723fefa2f2fa5f515becc6989cfa614a12e5bc6d7bf481f02e64"
+    },
+    {
+      "cell": "27",
+      "tag": "paired-27-baseline-1",
+      "seconds": 1.1763345000799745,
+      "cpu_seconds": 1.7238680000000006,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "561a5e1e1dad723fefa2f2fa5f515becc6989cfa614a12e5bc6d7bf481f02e64"
+    },
+    {
+      "cell": "27",
+      "tag": "paired-27-baseline-2",
+      "seconds": 1.1700560830067843,
+      "cpu_seconds": 1.708376999999999,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "561a5e1e1dad723fefa2f2fa5f515becc6989cfa614a12e5bc6d7bf481f02e64"
+    },
+    {
+      "cell": "27",
+      "tag": "paired-27-candidate-2",
+      "seconds": 0.9613996249390766,
+      "cpu_seconds": 1.452781000000003,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "561a5e1e1dad723fefa2f2fa5f515becc6989cfa614a12e5bc6d7bf481f02e64"
+    },
+    {
+      "cell": "27",
+      "tag": "paired-27-candidate-3",
+      "seconds": 0.9650211250409484,
+      "cpu_seconds": 1.4586270000000003,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "561a5e1e1dad723fefa2f2fa5f515becc6989cfa614a12e5bc6d7bf481f02e64"
+    },
+    {
+      "cell": "27",
+      "tag": "paired-27-baseline-3",
+      "seconds": 1.173958458006382,
+      "cpu_seconds": 1.7325210000000013,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "561a5e1e1dad723fefa2f2fa5f515becc6989cfa614a12e5bc6d7bf481f02e64"
+    },
+    {
+      "cell": "27",
+      "tag": "paired-27-baseline-4",
+      "seconds": 1.1826912079704925,
+      "cpu_seconds": 1.7198909999999978,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "561a5e1e1dad723fefa2f2fa5f515becc6989cfa614a12e5bc6d7bf481f02e64"
+    },
+    {
+      "cell": "27",
+      "tag": "paired-27-candidate-4",
+      "seconds": 0.9613626659847796,
+      "cpu_seconds": 1.4580710000000006,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "561a5e1e1dad723fefa2f2fa5f515becc6989cfa614a12e5bc6d7bf481f02e64"
+    },
+    {
+      "cell": "40",
+      "tag": "paired-40-baseline-0",
+      "seconds": 1.394614625023678,
+      "cpu_seconds": 3.105412000000001,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "33923701a75d02dc01d24981e80bd53e4902d5ee45dddcde046ac42447f325a4"
+    },
+    {
+      "cell": "40",
+      "tag": "paired-40-candidate-0",
+      "seconds": 1.3698977080639452,
+      "cpu_seconds": 3.0940629999999962,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "33923701a75d02dc01d24981e80bd53e4902d5ee45dddcde046ac42447f325a4"
+    },
+    {
+      "cell": "40",
+      "tag": "paired-40-candidate-1",
+      "seconds": 1.371471417020075,
+      "cpu_seconds": 3.109605000000002,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "33923701a75d02dc01d24981e80bd53e4902d5ee45dddcde046ac42447f325a4"
+    },
+    {
+      "cell": "40",
+      "tag": "paired-40-baseline-1",
+      "seconds": 1.3749173330143094,
+      "cpu_seconds": 3.171002000000011,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "33923701a75d02dc01d24981e80bd53e4902d5ee45dddcde046ac42447f325a4"
+    },
+    {
+      "cell": "40",
+      "tag": "paired-40-baseline-2",
+      "seconds": 1.3782720419112593,
+      "cpu_seconds": 3.142907,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "33923701a75d02dc01d24981e80bd53e4902d5ee45dddcde046ac42447f325a4"
+    },
+    {
+      "cell": "40",
+      "tag": "paired-40-candidate-2",
+      "seconds": 1.365558375022374,
+      "cpu_seconds": 3.1134309999999963,
+      "exit": 0,
+      "timeout": false,
+      "returned": 5,
+      "sha": "33923701a75d02dc01d24981e80bd53e4902d5ee45dddcde046ac42447f325a4"
+    },
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+}
diff --git a/docs/validation/fid-row-access-performance.md b/docs/validation/fid-row-access-performance.md
new file mode 100644
index 000000000..e9104b161
--- /dev/null
+++ b/docs/validation/fid-row-access-performance.md
@@ -0,0 +1,67 @@
+# FID payload row access — 2026-10-15
+
+Mechanical follow-up to [PR #205](https://github.com/fission-systems/Fission/pull/205). This is a measured producer-performance change, not a semantic/readability, execution-parity or ranking claim. FID admission, hashes, record order, errors, analysis/worker policies and output schemas are unchanged.
+
+## Owner and representation
+
+`FpkReader::records_by_key` already knows the payload block and row from the hash locator. Previously, `text.lines().nth(row)` scanned the same immutable prefix for every lookup. The existing payload-cache entry now retains an optional line-range index, initialized synchronously once from its immutable text. Row access uses a checked string slice.
+
+Public `block_at`/`block_for` still return the shared `Arc<String>`; ordinary block reads do not initialize line ranges. LF, CRLF, bare CR, empty lines, Unicode and final unterminated rows match `str::lines`. Directory searches, decompression/validation, locator bounds, duplicate handling and record ordering retain their original behavior. Failed decompression is not cached. No new dependency, program-fact map or global cache was added.
+
+The added retained storage is two `usize` offsets per indexed line, plus vector spare capacity and the small lazy-cache header. It lives with the existing decoded payload and is not a second text copy. The earlier rejected compressed-index cache remains excluded. See [the proposal](../proposals/2026-10-15-fid-row-access.md).
+
+## Fixed source and population
+
+Baseline CLI SHA256: `4c0485b7da200135afbc2e0bfbdbb9de8a7058549a1f9a1d6af3e91c9c6dc320` (the PR #205 measured candidate). Candidate: `28ec116dcb4966fa53546dcbf2e76977efcfb7a4b6bec380ba14174b2df14aba`.
+
+As in [the preceding report](decompiler-startup-performance.md), native measurements retain the PR #203/#204 context: PR #204 head `efe35ee69`, then PR #205 production changes, then this FPK patch. The FPK preimage is identical on independent main `b33e4e125`; this PR therefore needs no draft prerequisite. Native performance on main without those drafts is not inferred from these measurements. CI validates that independent source separately.
+
+Same Apple M4 Pro / 14 CPUs / 24 GiB / rustc 1.97.0 / native arm64 release profile, fixed resources/cwd, stripped inputs, addresses and CLI options. No task-owned builds, tests or profiler overlap timing. OS caches were not flushed and desktop scheduling remains uncontrolled.
+
+Frozen [qualification revision](https://huggingface.co/datasets/sjkim1127/decbench-cpp-qualification/tree/07dd95dbe6214b8a78fc1e4a55961ab515986489). All 45 input hashes were rechecked before replay. The complete population is in [the preceding compact evidence](decompiler-startup-performance.json); [this compact evidence](fid-row-access-performance.json) records raw times, hashes and output digests.
+
+## Five-pair small controls
+
+Alternating fresh processes, one requested-function worker, existing FID Rayon policy. All paired non-time function records match; repeated timed records are deterministic.
+
+| Batch | Baseline median, s | Candidate median, s | Interpretation |
+|---|---:|---:|---|
+| Linux AArch64 / Snappy O0, 6 functions | 2.2162 | 2.2104 | Essentially unchanged |
+| Windows x86-64 / Snappy O2, 5 functions | 1.1763 | 0.9614 | 18.27% lower wall time |
+| macOS arm64 / Ninja O2, 5 functions | 1.3783 | 1.3715 | Essentially unchanged |
+
+A separate direct five-pair comparison against the original PR #204 binary (`63e11b25...`) measures both patches together: Linux 2.3214/2.2082 s, Windows 1.2544/0.9609 s, macOS 1.4802/1.3693 s. These are selected-batch results, not a corpus-wide estimate.
+
+## Large control and memory
+
+One sequential candidate-first/baseline-second Tracy O0 pair, six requests, default requested-function worker policy. Both complete outputs match the frozen reference. `/usr/bin/time -l` wraps both commands to record process maximum RSS. CPU is child user + system time across threads. CLI timeout is 30,000 ms per function; external process cap is 600 seconds.
+
+| Build | Wall, s | CPU, s | Maximum RSS, GiB |
+|---|---:|---:|---:|
+| Baseline | 112.924 | 1044.333 | 3.624 |
+| Candidate | 42.235 | 233.619 | 3.598 |
+
+This pair reduces wall time by 62.60% and CPU by 77.63%. Peak RSS is similar in this one control; it does not establish reduced memory usage. The lazy row index adds retained metadata as described above. This is not a statistically robust or whole-corpus speed claim. The earlier unwrapped baseline control was 103.820 s; use the fresh wrapped pair for the incremental percentage.
+
+## Pinned Kuna comparison
+
+Three alternating fresh-process runs per tool, one requested-function worker/job, exact requested entry sets and successful returned counts checked. Output evidence is deterministic within each tool; cross-tool semantic equivalence is not claimed. The six large Fission records also match across all three runs after excluding only duration fields.
+
+| Batch | Fission median, s | Kuna 1.808 median, s | Fission / Kuna |
+|---|---:|---:|---:|
+| Linux Snappy O0 | 2.220 | 0.189 | 11.73× |
+| Windows Tracy O0 | 44.355 | 2.868 | 15.47× |
+| Windows Snappy O2 | 0.957 | 0.111 | 8.62× |
+| macOS Ninja O2 | 1.376 | 0.330 | 4.17× |
+
+Fission has not reached Kuna-level speed. The remaining whole-program decode/preparation cost needs further investigation; this patch does not bypass it.
+
+## Validation and reproduction
+
+Fresh stripped replay returned **250/250 functions across 45 binaries with zero changed non-time function records** against the frozen reference already verified for the preceding candidate. All code layers, variables/types, direct PCs, scoped maps, errors/fallbacks, evidence and non-time counters were compared. Only the seven duration keys in the compact evidence were excluded. Replay uses default requested-function workers and two binary processes as a regression check; no concurrent speed claim follows. Timed subset repetitions are deterministic, but repeated generation of all 250 is not claimed.
+
+- Focused FPK: **15 passed**; related signatures/static/decompiler/CLI: **398 passed / 1 skipped** on the measured source.
+- Crate checks, release CLI and workspace formatting passed. Coverage includes line-iterator equivalence, lazy public ownership, repeated/concurrent ordered hash lookups, invalid row errors and existing cross-block/chunk duplicate cases.
+- Remote independent-main CI is a separate gate.
+
+Raw artifacts remain in `benchmark/artifacts/performance/2026-10-14-kuna/`: `rows-only`, `cumulative-final`, `rows-large`, `rows-vs-kuna`, `rows-replay`, frozen binaries, profiles and build/test logs. Reuse the exact producer invocation and duration exclusions in the preceding report. For measured-source reproduction, apply this PR's `crates/` diff on the PR #205 measured context; for independent-main CI reproduction, build this PR directly. No corpus executable runs and no quality metric or denominator changes.