diff --git a/tools/build_wave_atlas.py b/tools/build_wave_atlas.py
new file mode 100644
index 000000000..4e02f8899
--- /dev/null
+++ b/tools/build_wave_atlas.py
@@ -0,0 +1,110 @@
+#!/usr/bin/env python3
+"""Build a campaign wave from the FRONTIER ATLAS, optimized for gate throughput.
+
+Why this exists (P31, 2026-08-14): the pre-baked adapt/weak card piles are the smallest,
+best-seeded tail (12-42 ins). Drawing from them banks ~1,440 ins/wave against 635,744 open —
+0.011pp of fleet per wave. The atlas knows where the mass actually is (cousin-multi 294k ins,
+cold 183k, main-only 38k) and what lever each group needs.
+
+TWO selection principles, both measured:
+  1. GATE COST SCALES WITH (binary, TU) GROUPS, NOT DRAFTS. Each group is a whole-binary rebuild.
+     Wave C was 35 drafts over 27 groups = 1.3 drafts/rebuild, ~50 min of gate for 32 banks.
+     So: CONCENTRATE the wave in few binaries. This is free throughput.
+  2. MASS BEATS COUNT for the instruction-weighted metric — prefer bigger functions where a seed
+     exists, but keep them inside the model ladder's competence.
+
+Selection: open stubs (derived from corpus, R32/R33), not spent in a prior wave, from atlas
+groups whose lever is agent-draftable; ranked by binary concentration then instruction mass.
+
+MUST NOT run while a gate is in flight (R35 — corpus.stubs() misreports substituted drafts).
+
+Usage: build_wave_atlas.py <out.json> [N] [--max-bins K] [--min-ins M] [--levers a,b,c]
+"""
+import json, sys, collections, subprocess, argparse
+sys.path.insert(0, 'tools')
+import corpus
+
+ap = argparse.ArgumentParser()
+ap.add_argument('out')
+ap.add_argument('n', nargs='?', type=int, default=96)
+ap.add_argument('--max-bins', type=int, default=12, help='concentrate the wave in this many binaries')
+ap.add_argument('--min-ins', type=int, default=0)
+ap.add_argument('--max-ins', type=int, default=120, help='above this the bulk ladder stops being honest')
+ap.add_argument('--levers', default='head-crack,seeded-crack,redraft,len-vein,integration,family-sweep,tiny-direct',
+                help='agent-draftable levers; UNKNOWN/tell/jtbl/o0/cc1 need their own lanes')
+ap.add_argument('--atlas', default='.run/atlas.json')
+a = ap.parse_args()
+
+busy = subprocess.run(['pgrep', '-f', 'tools/(gate_stage|dedup_propagate|gate_lane)'],
+                      capture_output=True, text=True)
+if busy.returncode == 0 and busy.stdout.strip():
+    sys.exit(f"REFUSING: gate in flight (pids {busy.stdout.split()}) — corpus.stubs() would misreport (R35).")
+
+PRIORS = ['.run/wave_p31%s_cards.json' % c for c in 'abcdefghijkl']
+taken = set()
+for p in PRIORS:
+    try:
+        taken |= {c.get('fn') or c.get('name') for c in json.load(open(p))}
+    except (FileNotFoundError, json.JSONDecodeError):
+        pass
+
+levers = set(a.levers.split(','))
+atlas = json.load(open(a.atlas))
+
+_open = {}
+def is_open(binary, fn):
+    if binary not in _open:
+        # corpus.stubs() is addr -> Stub; the NAME lives on the record
+        _open[binary] = {st.symbol for st in corpus.stubs(binary).values()}
+    return fn in _open[binary]
+
+def model_for(nins):
+    if nins <= 50:  return 'haiku'
+    if nins <= 120: return 'sonnet'
+    return 'opus'
+
+cands, skipped = [], collections.Counter()
+for g in atlas['groups']:
+    if g['lever'] not in levers:
+        skipped['lever-not-in-lane'] += g['inst']; continue
+    ex = g.get('exemplar') or {}
+    seed = (g.get('seed') or {}).get('norm') or (g.get('seed') or {}).get('raw') or {}
+    for m in g.get('members', []):
+        fn, b, nins = m.get('name'), m.get('b'), m.get('nins') or 0
+        if not fn or not b:                      skipped['no-name'] += 1; continue
+        if fn in taken:                          skipped['already-waved'] += 1; continue
+        if not (a.min_ins <= nins <= a.max_ins): skipped['out-of-band'] += 1; continue
+        if not is_open(b, fn):                   skipped['already-banked'] += 1; continue
+        sub = corpus.asm_path(b, fn)
+        if not sub:                              skipped['no-asm'] += 1; continue
+        cands.append({
+            'fn': fn, 'binary': b, 'lane': 'mass', 'model': model_for(nins), 'nins': nins,
+            'addr': m.get('a'), 'sub': __import__('os').path.dirname(sub),
+            'gid': g['gid'], 'lever': g['lever'], 'confidence': g.get('confidence'),
+            'lever_alts': g.get('lever_alts', []),
+            'exemplar': {'binary': ex.get('b'), 'fn': ex.get('name'), 'nins': ex.get('nins')},
+            'seed_sim': seed.get('sim'),
+        })
+
+# principle 1: concentrate. rank binaries by how much draftable mass they hold, take the top K.
+by_bin = collections.defaultdict(list)
+for c in cands:
+    by_bin[c['binary']].append(c)
+ranked_bins = sorted(by_bin, key=lambda b: -sum(c['nins'] for c in by_bin[b]))[:a.max_bins]
+
+wave = []
+for b in ranked_bins:                       # principle 2: within a binary, mass first
+    for c in sorted(by_bin[b], key=lambda c: -c['nins']):
+        if len(wave) >= a.n: break
+        wave.append(c)
+    if len(wave) >= a.n: break
+
+json.dump(wave, open(a.out, 'w'), indent=1)
+tot = sum(c['nins'] for c in wave)
+print(f"candidates {len(cands)} in {len(by_bin)} binaries (skipped {dict(skipped)})")
+print(f"-> wave {len(wave)} drafts / {tot} ins across {len({c['binary'] for c in wave})} binaries "
+      f"= {len(wave)/max(len({c['binary'] for c in wave}),1):.1f} drafts per gate group")
+if wave:
+    print("models:", dict(collections.Counter(c['model'] for c in wave)))
+    print("levers:", dict(collections.Counter(c['lever'] for c in wave)))
+    print("nins: %d-%d (avg %.0f)" % (min(c['nins'] for c in wave), max(c['nins'] for c in wave), tot/len(wave)))
diff --git a/tools/gate_lane.py b/tools/gate_lane.py
index 8b9171aab..66b6e564a 100644
--- a/tools/gate_lane.py
+++ b/tools/gate_lane.py
@@ -21,14 +21,22 @@ def dirty(): return subprocess.run("git status --porcelain -- src/ config/",shel
 def writers(): return subprocess.run("pgrep -af 'dedup_propagate|gate_stage|harvest_verify'",
                                      shell=True,capture_output=True,text=True).stdout
 if dirty(): sys.exit("TREE DIRTY at entry — resolve before gating:\n"+dirty()[:400])
+
+# The stub's HOME .c, DERIVED from the corpus oracle (R33) rather than re-globbed. The old
+# `glob("src/<binary>/*.c")` was structurally blind to `main`, whose sources live at src/*.c —
+# every main draft grouped under src=None (R36: a consumer silently ignoring a real binary).
+# corpus.stubs() already carries the answer on each record: Stub.path.
+_HOME={}
+def _home(binary, fn):
+    if binary not in _HOME:
+        _HOME[binary]={st.symbol: st.path for st in corpus.stubs(binary).values()}
+    return _HOME[binary].get(fn)
+
 groups=collections.defaultdict(list)
 for c in cards:
     p=c.get('draft') or f"{wavedir}/{c['name']}/{c['name']}.c"   # explicit path wins (agents use per-binary dirs)
     if not os.path.isfile(p): continue
-    src=None
-    for f in sorted(glob.glob(f"src/{c['binary']}/*.c")):
-        t=open(f).read()
-        if "INCLUDE_ASM" in t and c['name'] in t: src=f; break
+    src=_home(c['binary'], c['name'])
     groups[(c['binary'],src)].append((c['name'],p))
 n_g=sum(len(v) for v in groups.values())
 missing=[c['name'] for c in cards if not os.path.isfile(c.get('draft') or f"{wavedir}/{c['name']}/{c['name']}.c")]