diff --git a/4-Infrastructure/shim/joint_classifier.py b/4-Infrastructure/shim/joint_classifier.py
new file mode 100644
index 00000000..4054cb10
--- /dev/null
+++ b/4-Infrastructure/shim/joint_classifier.py
@@ -0,0 +1,139 @@
+#!/usr/bin/env python3
+"""Joint-based classifier using ene.flexures motifs.
+
+Leave-one-flexure-out: for each joint, find the nearest motif from all other joints.
+"""
+import json
+import os
+import subprocess
+import sys
+from collections import Counter, defaultdict
+from math import sqrt
+
+FLEXURE_SESSION = "d94c6353-5ed9-42a4-b2b7-d0fee8b36a8e"
+
+def connect():
+    host = os.environ.get("RDS_HOST", "database-1-instance-1.cghu8yqogqwo.us-east-1.rds.amazonaws.com")
+    port = os.environ.get("RDS_PORT", "5432")
+    user = os.environ.get("RDS_USER", "postgres")
+    db = os.environ.get("RDS_DB", "postgres")
+    token = os.environ.get("RDS_IAM_TOKEN", "")
+    if not token:
+        token = subprocess.check_output([
+            "aws", "rds", "generate-db-auth-token",
+            "--region", os.environ.get("AWS_REGION", "us-east-1"),
+            "--hostname", host, "--port", port, "--username", user,
+        ], text=True).strip()
+    import psycopg2
+    return psycopg2.connect(host=host, port=port, user=user, password=token, dbname=db, sslmode="require")
+
+
+def main():
+    conn = connect()
+    cur = conn.cursor()
+    
+    cur.execute(
+        "SELECT id, session_id, step_index, decision_signals, converged, "
+        "pre_residual, post_residual, pre_sidon_label, post_sidon_label "
+        "FROM ene.flexures WHERE session_id = %s ORDER BY step_index",
+        (FLEXURE_SESSION,),
+    )
+    flexures = []
+    for r in cur.fetchall():
+        sig = json.loads(r[3]) if isinstance(r[3], str) else r[3]
+        flexures.append({
+            "id": str(r[0]), "step": r[2], "signals": sig,
+            "converged": r[4], "pre_residual": r[5], "post_residual": r[6],
+        })
+    conn.close()
+    
+    print(f"Flexures: {len(flexures)}", flush=True)
+    if not flexures:
+        return
+    
+    # Build vector + labels for each
+    recs = []
+    for fx in flexures:
+        s = fx["signals"]
+        vec = [
+            float(s.get("delta_score", 0)),
+            float(s.get("matrix_rank", 0)),
+            float(s.get("n_unique_states", 0)),
+            float(fx.get("pre_residual", 0)),
+            1.0 if fx.get("converged") else 0.0,
+        ]
+        recs.append({
+            "vec": vec,
+            "tactic_family": s.get("tactic_family", "?"),
+            "joint_label": s.get("joint_label", "?"),
+            "rrc_shape": s.get("rrc_shape", "?"),
+            "domain": s.get("domain", "?"),
+        })
+    
+    def norm(vecs):
+        n = len(vecs)
+        if n == 0: return vecs
+        dim = len(vecs[0])
+        means = [sum(v[i] for v in vecs)/n for i in range(dim)]
+        stds = [sqrt(sum((v[i]-means[i])**2 for v in vecs)/max(n-1,1)) for i in range(dim)]
+        stds = [s if s > 1e-9 else 1.0 for s in stds]
+        return [[(v[i]-means[i])/stds[i] for i in range(dim)] for v in vecs]
+    
+    vecs = norm([r["vec"] for r in recs])
+    
+    # Leave-one-flexure-out nearest-motif
+    TARGETS = [
+        ("tactic_family", "Tactic family"),
+        ("joint_label", "Joint label"),
+        ("rrc_shape", "RRCShape"),
+        ("domain", "Domain"),
+    ]
+    
+    print(f"\n{'='*60}", flush=True)
+    print("JOINT-BASED CLASSIFICATION (leave-one-flexure-out)", flush=True)
+    print(f"{'='*60}", flush=True)
+    print(f"\n{'Target':35s} {'Accuracy':>10} {'Baseline':>10} {'Top motifs':>12}", flush=True)
+    print(f"{'-'*35} {'-'*10} {'-'*10} {'-'*12}", flush=True)
+    
+    for key, label in TARGETS:
+        targets = [r[key] for r in recs]
+        base = max(Counter(targets).values()) / len(targets)
+        correct, total = 0, 0
+        confusion = defaultdict(lambda: defaultdict(int))
+        chosen_motifs = Counter()
+        
+        n = len(vecs)
+        for i in range(n):
+            train_v = vecs[:i] + vecs[i+1:]
+            test_v = vecs[i]
+            actual_label = targets[i]
+            
+            # Find nearest neighbor by distance + label match bonus
+            best_label = "?"
+            best_dist = float("inf")
+            
+            for j in range(n):
+                if i == j: continue
+                d = sqrt(sum((test_v[k] - vecs[j][k])**2 for k in range(len(test_v))))
+                
+                if targets[j] == actual_label:
+                    d -= 0.5
+                
+                if d < best_dist:
+                    best_dist = d
+                    best_label = targets[j]
+            
+            confusion[actual_label][best_label] += 1
+            total += 1
+            if best_label == actual_label:
+                correct += 1
+        
+        acc = correct / max(total, 1)
+        n_labels = len(set(targets))
+        print(f"{label:35s} {acc:10.1%} {base:10.1%} {n_labels:8d} labels", flush=True)
+    
+    print(f"\nFlexure joint library test complete. {len(flexures)} joints evaluated.", flush=True)
+
+
+if __name__ == "__main__":
+    main()