fix(align): stream JSONL + support sensing_update format (#641)

Two blockers discovered while running ADR-079 P7→P8 end-to-end against
a 30-minute paired session (39,088 GT frames + 45,625 CSI frames):

1. `readFileSync(_, 'utf8').split('\n')` hit Node's `String.MaxLength`
   (~512 MB) on the 750 MB CSI recording. Result:
       Error: Cannot create a string longer than 0x1fffffe8 characters
   Replaced loadJsonl with a 1 MiB byte-buffer streaming reader that
   decodes line-by-line, so memory use stays bounded by the largest
   single record.

2. The sensing-server has long since switched from the legacy `raw_csi`
   / `feature` typed records to a single `sensing_update` record per
   tick (with nodes[].amplitude and top-level features). The aligner
   filtered on the old types and produced 0 frames every time. Added a
   `sensing_update` branch that projects each tick into rawCsi/features
   entries the existing windowing code can consume, and updated
   extractCsiMatrix to use already-extracted amplitudes when iqHex is
   absent. timestamp is now accepted as either ISO string (legacy) or
   numeric float-seconds (current).

End-to-end verified: produces 1,077 paired samples at
`--min-confidence 0.3 --window-frames 20` from the full 30-min
recording; downstream `train-wiflow-supervised.js` runs to completion.
See follow-up #640 for the PCK gap (data + GPU needed) — those are
training concerns, not aligner concerns.

scripts/align-ground-truth.js

@@ -136,18 +136,42 @@ function extractAmplitude(iqBytes, nSubcarriers) {
 
 /**
  * Load and parse a JSONL file, skipping blank/malformed lines.
+ *
+ * Reads byte-by-byte into Buffer slices to avoid Node's
+ * `String.MaxLength` (~512 MB) cap that `readFileSync(_, 'utf8')` hits
+ * on 30-min CSI recordings. Each line is decoded individually, so
+ * memory use stays bounded by the largest single record.
  */
 function loadJsonl(filePath) {
-  const lines = fs.readFileSync(filePath, 'utf8').split('\n');
   const records = [];
-  for (const line of lines) {
-    const trimmed = line.trim();
-    if (!trimmed) continue;
-    try {
-      records.push(JSON.parse(trimmed));
-    } catch {
-      // skip malformed lines
+  const fd = fs.openSync(filePath, 'r');
+  try {
+    const bufSize = 1 << 20; // 1 MiB
+    const buf = Buffer.alloc(bufSize);
+    let leftover = '';
+    let bytesRead;
+    do {
+      bytesRead = fs.readSync(fd, buf, 0, bufSize, null);
+      if (bytesRead > 0) {
+        const chunk = leftover + buf.toString('utf8', 0, bytesRead);
+        const lines = chunk.split('\n');
+        leftover = lines.pop(); // last fragment may be incomplete
+        for (const line of lines) {
+          const trimmed = line.trim();
+          if (!trimmed) continue;
+          try {
+            records.push(JSON.parse(trimmed));
+          } catch {
+            // skip malformed lines
+          }
+        }
+      }
+    } while (bytesRead === bufSize);
+    if (leftover.trim()) {
+      try { records.push(JSON.parse(leftover.trim())); } catch {}
     }
+  } finally {
+    fs.closeSync(fd);
   }
   return records;
 }
@@ -184,8 +208,12 @@ function loadCsi(filePath) {
   const features = [];
 
   for (const r of raw) {
-    if (!r.timestamp) continue;
-    const tsMs = isoToMs(r.timestamp);
+    if (r.timestamp == null) continue;
+    // Two timestamp formats: ISO string (legacy raw_csi/feature) or
+    // numeric float-seconds (current sensing_update from the Rust server).
+    const tsMs = typeof r.timestamp === 'number'
+      ? r.timestamp * 1000
+      : isoToMs(r.timestamp);
     if (isNaN(tsMs)) continue;
 
     if (r.type === 'raw_csi') {
@@ -205,6 +233,33 @@ function loadCsi(filePath) {
         rssi: r.rssi,
         seq: r.seq,
       });
+    } else if (r.type === 'sensing_update') {
+      // Current sensing-server schema: one record per tick contains
+      // already-extracted amplitudes per node plus a server-computed
+      // feature vector. Project each into rawCsi/features so downstream
+      // windowing/matrix extraction can reuse its existing paths.
+      if (Array.isArray(r.nodes)) {
+        for (const node of r.nodes) {
+          if (!Array.isArray(node.amplitude) || node.amplitude.length === 0) continue;
+          rawCsi.push({
+            tsMs,
+            nodeId: node.node_id,
+            subcarriers: node.amplitude.length,
+            amplitude: node.amplitude, // pre-extracted, no iq_hex needed
+            rssi: node.rssi_dbm,
+            seq: r.tick,
+          });
+        }
+      }
+      if (Array.isArray(r.features) && r.features.length > 0) {
+        features.push({
+          tsMs,
+          nodeId: 0,
+          features: r.features,
+          rssi: null,
+          seq: r.tick,
+        });
+      }
     }
   }
 
@@ -297,7 +352,11 @@ function extractCsiMatrix(window) {
 
   for (let f = 0; f < nFrames; f++) {
     const frame = window[f];
-    if (frame.iqHex) {
+    if (frame.amplitude && frame.amplitude.length > 0) {
+      // Already-extracted amplitudes from sensing_update — copy directly.
+      const n = Math.min(nSc, frame.amplitude.length);
+      for (let s = 0; s < n; s++) matrix[f * nSc + s] = frame.amplitude[s];
+    } else if (frame.iqHex) {
       const iq = parseIqHex(frame.iqHex);
       const amp = extractAmplitude(iq, nSc);
       matrix.set(amp, f * nSc);