Meter coaching: flag lines that break the stanza's pattern

When >=60% of a stanza's lines share a syllable count (+-1), outliers
get a wavy underline and the readout names the target count.

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

app.py

@@ -540,13 +540,31 @@ def analyze(draft: Draft):
          "slant": t["slant"] or groups_out[t["gid"]]["slant"]}
         for t in [*tokens, *phrases] if t["gid"] is not None
     ]
-    meter = []
+    meter, meter_by_line = [], {}
     for i, line in enumerate(lines):
         if sids[i] is None:
             continue
         m = line_meter(line)
         if m:
-            meter.append({"l": i, **m})
+            entry = {"l": i, **m, "off": False}
+            meter.append(entry)
+            meter_by_line[i] = entry
+
+    # meter coaching: when a stanza has a clear syllable pattern, flag
+    # the lines that break it
+    for s, lns in stanza_lines.items():
+        entries = [meter_by_line[i] for i in lns if i in meter_by_line]
+        if len(entries) < 3:
+            continue
+        counts = [e["syl"] for e in entries]
+        # mode with +-1 tolerance: the count that covers the most lines
+        mode = max(set(counts), key=lambda c: sum(abs(v - c) <= 1 for v in counts))
+        covered = sum(abs(v - mode) <= 1 for v in counts)
+        if covered / len(entries) >= 0.6:
+            for e in entries:
+                e["off"] = abs(e["syl"] - mode) > 1
+            for e in entries:
+                e["target"] = mode
 
     return {"lines": lines, "tokens": toks_out,
             "groups": groups_out, "stanzas": stanzas, "meter": meter}

static/index.html

@@ -124,6 +124,11 @@
   .rh.slant.end {
     box-shadow: inset 0 -2px 0 0 color-mix(in srgb, var(--c) 45%, transparent);
   }
+  .offbeat {
+    text-decoration: underline wavy color-mix(in srgb, var(--r6) 45%, transparent);
+    text-decoration-skip-ink: none;
+    text-underline-offset: 7px;
+  }
   .toolbar {
     display: flex; align-items: center; gap: 10px; flex-wrap: wrap;
   }
@@ -494,7 +499,8 @@ function render(){
       pos = t.e;
     });
     h += esc(line.slice(pos));
-    html += h + '\n';
+    const m = fresh && analysis.meter ? analysis.meter.find(x=>x.l===i) : null;
+    html += (m && m.off ? `<span class="offbeat">${h}</span>` : h) + '\n';
   });
   highlight.innerHTML = html;
   highlight.scrollTop = editor.scrollTop;
@@ -522,7 +528,11 @@ function buildReadout(){
   const parts = [];
   const ln = caretLine();
   const m = analysis && analysis.meter ? analysis.meter.find(x=>x.l===ln) : null;
-  if(m) parts.push(`${m.syl} syl` + (m.label ? ` · ${m.label}` : ''));
+  if(m){
+    let p = `${m.syl} syl` + (m.label ? ` · ${m.label}` : '');
+    if(m.off) p += ` <span class="offline">· breaks stanza meter (~${m.target} syl)</span>`;
+    parts.push(p);
+  }
   const st = caretStanza();
   if(st && st.scheme) parts.push(`scheme <b>${st.scheme.toUpperCase().split('').join(' ')}</b>`);
   schemeReadout.innerHTML = parts.join(' &nbsp;&nbsp; ');

tests/test_rhymes.py

@@ -222,3 +222,20 @@ def test_trailing_schwa_trimmed_militia_commissioner():
     text = ("Swagger down pat, call my shit Patricia\n"
             "Young Money militia, and I am the commissioner")
     group_with(text, "patricia", "militia", "commissioner")
+
+
+def test_meter_coaching_flags_outlier_line():
+    text = ("I walk the lonely road tonight\n"
+            "I hold the heavy stone of light\n"
+            "I call the fading stars to fight\n"
+            "and everybody wonders where the time has gone")
+    res = analyze(Draft(text=text))
+    flagged = [m["l"] for m in res["meter"] if m["off"]]
+    assert flagged == [3]
+    assert res["meter"][3]["target"] == 8
+
+
+def test_meter_coaching_needs_a_pattern_to_break():
+    # two lines of wildly different lengths: no dominant pattern, no flags
+    res = analyze(Draft(text="short line here\na very much longer line that runs on and on"))
+    assert not any(m["off"] for m in res["meter"])