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bench(lbug): per-file fingerprint so the gate catches pair-file mis-routing (#2215 review)

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fingerprintEmit flattened every line of every per-pair file into one array,
sorted globally, and hashed — losing file boundaries, so a row routed to the
WRONG pair file produced an identical fingerprint. Hash a per-file digest
(filename + sha256(file bytes)) and combine the sorted entry list, so mis-routing
(and within-file row reordering) now changes the fingerprint. Baseline
regenerated; the new scheme yields a different hash on byte-identical emit,
confirming it is sensitive to file structure the old flatten ignored.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Gergo Magyar 2026-06-15 18:07:09 +00:00
parent 1eeeb816fd
commit b53e067fc0
2 changed files with 11 additions and 6 deletions
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4
gitnexus/bench/emit-persistence/baselines.json
View file

@ -1,5 +1,5 @@
{
"fingerprint": "04096714dae58fd363fa6cdbd535bcb6ba4db058b8b84d6fde504a150efaf015",
"fingerprint": "1b9dd0b783899b47067c36511d241860f291ac736e57682b0ece14148e3958ff",
"scaling_budget": 1.8,
"_note": "fingerprint = order-independent sha256 of every emitted CSV line (byte-identity gate for #2203 U2/U3). scaling_budget bounds (t_large/t_small)/(LARGE/SMALL): observed ~0.95-1.05 (linear); 1.8 tolerates disk-I/O timing noise on CI while still catching an O(n^2) re-regression (~4x). Regenerate via `node --import tsx bench/emit-persistence/measure.mjs`."
"_note": "fingerprint = sha256 over per-file digests (filename + sha256(file bytes)), entry list sorted — binds each emitted line to its file so a row routed to the WRONG pair file changes the hash, AND catches within-file row reordering (file bytes hashed as-written). Byte-identity gate for #2203 U2/U3. NOTE: a future change that legitimately reorders emit (without changing the node/edge SET) will trip --check; regenerate then. scaling_budget bounds (t_large/t_small)/(LARGE/SMALL): observed ~0.95-1.05 (linear); 1.8 tolerates disk-I/O timing noise on CI while still catching an O(n^2) re-regression (~4x). Regenerate via `node --import tsx bench/emit-persistence/measure.mjs`."
}

13
gitnexus/bench/emit-persistence/measure.mjs
View file

@ -112,13 +112,18 @@ function generateGraph(entityCount) {
* digest is a pure function of the emitted line SET (insertion-order agnostic). */
async function fingerprintEmit(graph, dir) {
await streamAllCSVsToDisk(graph, path.join(dir, 'no-such-repo'), dir);
const lines = [];
// Per-file digest bound to the filename: a row routed to the WRONG pair file
// (or a header written to the wrong file) changes the fingerprint — a global
// line-flatten could not catch that. File bytes are hashed as-written (so it
// also catches within-file row reordering); the entry list is sorted so
// readdir order doesn't matter.
const entries = [];
for (const name of fs.readdirSync(dir)) {
if (!name.endsWith('.csv')) continue;
const text = await fsp.readFile(path.join(dir, name), 'utf8');
for (const l of text.split('\n')) if (l.length > 0) lines.push(l);
const bytes = await fsp.readFile(path.join(dir, name));
entries.push(`${name}\n${crypto.createHash('sha256').update(bytes).digest('hex')}`);
}
return crypto.createHash('sha256').update(lines.sort().join('\n')).digest('hex');
return crypto.createHash('sha256').update(entries.sort().join('\n')).digest('hex');
}
// ---- timing ----