diff --git a/infra/fast-time/class-v3.mjs b/infra/fast-time/class-v3.mjs
index a4cb213f0..69fd8f685 100644
--- a/infra/fast-time/class-v3.mjs
+++ b/infra/fast-time/class-v3.mjs
@@ -41,12 +41,23 @@ const sleep = (ms) => new Promise(r => setTimeout(r, ms));
 for (const b of [IGNEUMD, CPU_MINER]) if (!existsSync(b)) { console.error(`missing ${b}`); process.exit(2); }
 
 rmSync(TMP, { recursive: true, force: true }); mkdirSync(TMP, { recursive: true });
-const base = JSON.parse(readFileSync(FILE, 'utf8'));
-const EPOCH = base.pow_epoch_blocks;
+// The file is merged as TEXT, never through JSON.parse: a `never` height is 18446744073709551615, which JavaScript
+// rounds to 1.8446744073709552e+19 and the node refuses ("expected u64"; the first gate run, 5 October 2026 21:30Z).
+// The merged fields are appended after the file's last field; a field already in the file is removed first.
+const baseText = readFileSync(FILE, 'utf8');
+const field = (name) => { const m = new RegExp(`"${name}":\\s*([0-9]+)`).exec(baseText); return m ? +m[1] : undefined; };
+const EPOCH = field('pow_epoch_blocks');
+const DAY_MS = field('pow_day_ms');
 const FIRST_V3_EPOCH = Math.ceil(ACTIVATION / EPOCH);
 const BOUNDARY = FIRST_V3_EPOCH * EPOCH;
 const override = `${TMP}/override.json`;
-writeFileSync(override, JSON.stringify({ ...base, genesis_bits: GENESIS_BITS, skip_proof_of_work: false, program_class_v3_activation_daa: ACTIVATION }));
+export function mergeOverrideText(text, fields) {
+  let out = text;
+  for (const k of Object.keys(fields)) out = out.replace(new RegExp(`\\s*"${k}":\\s*[^,}\\n]+,?`), '');
+  const extra = Object.entries(fields).map(([k, v]) => `"${k}": ${typeof v === 'string' ? JSON.stringify(v) : v}`).join(', ');
+  return out.replace(/,?\s*}\s*$/, `,\n  ${extra}\n}\n`);
+}
+writeFileSync(override, mergeOverrideText(baseText, { genesis_bits: GENESIS_BITS, skip_proof_of_work: false, program_class_v3_activation_daa: ACTIVATION }));
 log(`activation ${ACTIVATION} at ${EPOCH} DAA per epoch: the first v3 epoch is ${FIRST_V3_EPOCH} (DAA ${BOUNDARY}); run ${SECS} s, CPU genesis bits 0x${GENESIS_BITS.toString(16)}`);
 
 class Node {
@@ -99,7 +110,7 @@ log(`n0 PoW schedule: ${n0.grepLog(/PoW schedule from the override file/).map(l
 log(`n0 digest: ${n0.grepLog(/Consensus params digest/).map(l => l.replace(/^.*?digest: /, '').slice(0, 16)).join(' ')}`);
 
 // one real CPU miner per node, 1 thread, 2^16 expected hashes per block at genesis
-nodes.forEach((n, i) => miner(CPU_MINER, ['mine', n.grpc, String(THREADS), String(SECS), `cpu${i}`, '--engine', 'igneum-pow', '--payout-label', `cpu${i}`, '--status-secs', '30', '--no-vote'], `cpu${i}`, { IGNEUM_POW_DAY_MS: String(base.pow_day_ms) }));
+nodes.forEach((n, i) => miner(CPU_MINER, ['mine', n.grpc, String(THREADS), String(SECS), `cpu${i}`, '--engine', 'igneum-pow', '--payout-label', `cpu${i}`, '--status-secs', '30', '--no-vote'], `cpu${i}`, { IGNEUM_POW_DAY_MS: String(DAY_MS) }));
 const pay = devAddress('fast-time-v3');
 
 const epochs = new Map();       // epoch index -> { class, firstSeenDaa, at }
diff --git a/infra/fast-time/simnet.mjs b/infra/fast-time/simnet.mjs
index f70fc7d53..0f7156529 100644
--- a/infra/fast-time/simnet.mjs
+++ b/infra/fast-time/simnet.mjs
@@ -35,7 +35,9 @@ for (const b of [IGNEUMD, VMINE]) if (!existsSync(b)) { console.error(`missing $
 
 rmSync(TMP, { recursive: true, force: true }); mkdirSync(TMP, { recursive: true });
 const override = `${TMP}/override.json`;
-writeFileSync(override, JSON.stringify({ ...JSON.parse(readFileSync(FILE, 'utf8')), skip_proof_of_work: true }));
+// merged as text, not through JSON.parse: a `never` height (18446744073709551615) does not survive a JavaScript number
+// (the class-v3.mjs gate run of 5 October 2026 21:30Z: "invalid type: floating point 1.8446744073709552e+19")
+writeFileSync(override, readFileSync(FILE, 'utf8').replace(/\s*"skip_proof_of_work":\s*[^,}\n]+,?/, '').replace(/,?\s*}\s*$/, ',\n  "skip_proof_of_work": true\n}\n'));
 
 class Node {
   constructor(i, connect = []) {