fix(#146) P3.7: coalescer carries the PEAK numeric over the window

The coalesced loop-lag summary carried an arbitrary sample's p99. Now record() tracks
the MAX (peak) over the window and the summary emits it — the peak is the number that
matters during an incident: '[loop-lag] band=critical (x47 in 30s, peak 1502ms)'. Band
CHANGES still log immediately, unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/lib/log-coalescer.js

@@ -14,22 +14,32 @@ const buf = new Map();
 let flushMs = 30000;
 let timer = null;
 
-// record(key, line, {warn}) — `key` collapses repeats; `line` is the human text to emit.
+// record(key, line, {warn, peak, peakUnit}) — `key` collapses repeats; `line` is the
+// stable human text. #146 P3.7: `peak` (a number) tracks the MAX over the window so the
+// summary carries the PEAK (the number that matters in an incident), not an arbitrary
+// sample's value.
 function record(key, line, opts = {}) {
   let e = buf.get(key);
   if (!e) {
     if (buf.size >= MAX_KEYS) flush();           // bounded: never grow past MAX_KEYS
-    e = { count: 0, sample: line, warn: !!opts.warn };
+    e = { count: 0, sample: line, warn: !!opts.warn, peak: null, peakUnit: opts.peakUnit || '' };
     buf.set(key, e);
   }
   e.count += 1;
-  e.sample = line;                                // keep the most recent detail
+  e.sample = line;                                // keep the most recent stable label
   e.warn = e.warn || !!opts.warn;
+  if (opts.peak != null) { e.peak = e.peak == null ? opts.peak : Math.max(e.peak, opts.peak); if (opts.peakUnit) e.peakUnit = opts.peakUnit; }
 }
 
 function flush() {
   for (const [, e] of buf) {
-    const line = e.count > 1 ? `${e.sample} (x${e.count} in ${Math.round(flushMs / 1000)}s)` : e.sample;
+    let line;
+    if (e.count > 1) {
+      const peak = e.peak != null ? `, peak ${e.peak}${e.peakUnit}` : '';
+      line = `${e.sample} (x${e.count} in ${Math.round(flushMs / 1000)}s${peak})`;
+    } else {
+      line = e.peak != null ? `${e.sample} (${e.peak}${e.peakUnit})` : e.sample;
+    }
     (e.warn ? console.warn : console.log)(line);
   }
   buf.clear();

server/services/loop-lag.js

@@ -83,7 +83,9 @@ function sample() {
   if (band !== prev) {
     console.log(`[loop-lag] band=${band} (was ${prev}) mean=${snap.mean_ms}ms p99=${snap.p99_ms}ms max=${snap.max_ms}ms`);
   } else if (band !== 'normal') {
-    logCoalescer.record(`loop-lag:${band}`, `[loop-lag] band=${band} p99=${snap.p99_ms}ms max=${snap.max_ms}ms`);
+    // #146 P3.7: coalesce repeats and carry the PEAK p99 over the window (not a random
+    // sample's) — the peak is the number that matters during an incident.
+    logCoalescer.record(`loop-lag:${band}`, `[loop-lag] band=${band}`, { peak: snap.p99_ms, peakUnit: 'ms' });
   }
 
   // #143 global pressure valve — log ONLY the band edge (open/close), not per shed

server/test/log-selfprotect.test.js

@@ -32,6 +32,17 @@ test('N identical lines in a window emit ONE summarized line with the count', ()
   assert.match(out[0], /band=critical/, 'keeps the sample text');
 });
 
+test('P3.7: coalesced numeric line carries the PEAK over the window, not a random sample', () => {
+  coalescer.reset();
+  coalescer.record('lag', '[loop-lag] band=critical', { peak: 300, peakUnit: 'ms' });
+  coalescer.record('lag', '[loop-lag] band=critical', { peak: 1502, peakUnit: 'ms' });
+  coalescer.record('lag', '[loop-lag] band=critical', { peak: 900, peakUnit: 'ms' });
+  const out = capture(() => coalescer.flush());
+  assert.equal(out.length, 1);
+  assert.match(out[0], /x3/);
+  assert.match(out[0], /peak 1502ms/, 'emits the MAX p99 over the window');
+});
+
 test('a single occurrence logs verbatim (no count suffix)', () => {
   coalescer.reset();
   coalescer.record('k', 'one-off line');