diff --git a/docs/runs/BLOCOB_PIS_COFINS_SOURCE_V1.json b/docs/runs/BLOCOB_PIS_COFINS_SOURCE_V1.json
new file mode 100644
index 0000000..543f911
--- /dev/null
+++ b/docs/runs/BLOCOB_PIS_COFINS_SOURCE_V1.json
@@ -0,0 +1,63 @@
+{
+ "GTI": {
+  "name": "GTI",
+  "items_total": 34946,
+  "items_cst_filled": 3336,
+  "determinism_NCM": {
+   "distinct_keys": 10,
+   "items_covered": 3336,
+   "items_with_single_cst_for_key": 3336,
+   "reproduction_rate_pct": 100.0
+  },
+  "determinism_CODGRUPO": {
+   "distinct_keys": 13,
+   "items_covered": 3336,
+   "items_with_single_cst_for_key": 3336,
+   "reproduction_rate_pct": 100.0
+  },
+  "determinism_CFOP": {
+   "distinct_keys": 2,
+   "items_covered": 3336,
+   "items_with_single_cst_for_key": 3336,
+   "reproduction_rate_pct": 100.0
+  },
+  "determinism_CSOSN": {
+   "distinct_keys": 2,
+   "items_covered": 3336,
+   "items_with_single_cst_for_key": 3336,
+   "reproduction_rate_pct": 100.0
+  },
+  "determinism_GRUPO_ICMS": {
+   "distinct_keys": 1,
+   "items_covered": 3336,
+   "items_with_single_cst_for_key": 3336,
+   "reproduction_rate_pct": 100.0
+  },
+  "aliquota_filled_but_cst_blank": 1332,
+  "cst_filled_but_aliquota_null": 0
+ },
+ "CONSTRUCAO": {
+  "name": "CONSTRUCAO",
+  "items_total": 28934,
+  "items_cst_filled": 0,
+  "conclusion": "NAO_APLICAVEL_SEM_DADOS_PARA_CORRELACIONAR"
+ },
+ "MMMODAS": {
+  "name": "MMMODAS",
+  "items_total": 26067,
+  "items_cst_filled": 0,
+  "conclusion": "NAO_APLICAVEL_SEM_DADOS_PARA_CORRELACIONAR"
+ },
+ "RINCAO": {
+  "name": "RINCAO",
+  "items_total": 224355,
+  "items_cst_filled": 0,
+  "conclusion": "NAO_APLICAVEL_SEM_DADOS_PARA_CORRELACIONAR"
+ },
+ "UNIAO": {
+  "name": "UNIAO",
+  "items_total": 121266,
+  "items_cst_filled": 0,
+  "conclusion": "NAO_APLICAVEL_SEM_DADOS_PARA_CORRELACIONAR"
+ }
+}
\ No newline at end of file
diff --git a/scripts/blocoB_pis_cofins_source.py b/scripts/blocoB_pis_cofins_source.py
new file mode 100644
index 0000000..429990f
--- /dev/null
+++ b/scripts/blocoB_pis_cofins_source.py
@@ -0,0 +1,81 @@
+"""Missão 3 / Bloco B — de onde vem o CST/alíquota de PIS/COFINS emitido, somente leitura.
+Testa correlação e determinismo por NCM, CODGRUPO (via C000025), CFOP, CSOSN/CST_ICMS,
+GRUPO_ICMS. Não decide regra fiscal - só mede taxa de reprodução.
+"""
+import json
+import os
+import sys
+from pathlib import Path
+from collections import Counter, defaultdict
+
+ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(ROOT)); sys.path.insert(0, str(ROOT / "scripts")); sys.path.insert(0, str(ROOT / "agent" / "src"))
+import fdb  # noqa: E402
+import run_fiscal_decision_v1 as base  # noqa: E402
+
+DBS = {
+    "GTI": r"D:\PROJETOS\GTISISTEMAS\Banco\GTI.FDB",
+    "CONSTRUCAO": str(ROOT / "Banco" / "CONSTRUCAO.FDB"),
+    "MMMODAS": str(ROOT / "Banco" / "MMMODAS.FDB"),
+    "RINCAO": str(ROOT / "Banco" / "RINCAO.FDB"),
+    "UNIAO": str(ROOT / "Banco" / "UNIAO.FDB"),
+}
+
+
+def connect(path):
+    return fdb.connect(database=path, user=os.environ["FB_USER"], password=os.environ["FB_PASSWORD"],
+                        fb_library_name=os.environ.get("FIREBIRD_CLIENT_LIBRARY"), isolation_level=fdb.ISOLATION_LEVEL_READ_COMMITED_RO)
+
+
+def analyze(name, path):
+    conn = connect(path); cur = conn.cursor()
+    cur.execute("SELECT COUNT(*), COUNT(NULLIF(TRIM(CST_PIS_COFINS),'')) FROM NFCE_ITENS")
+    tot, filled = cur.fetchone()
+    out = {"name": name, "items_total": tot, "items_cst_filled": filled}
+    if filled == 0:
+        out["conclusion"] = "NAO_APLICAVEL_SEM_DADOS_PARA_CORRELACIONAR"
+        conn.close()
+        return out
+    # candidate determinants, only over the filled subset
+    for dim, expr in (("NCM", "i.NCM"), ("CODGRUPO", "p.CODGRUPO"), ("CFOP", "i.CFOP"), ("CSOSN", "i.CSOSN"), ("GRUPO_ICMS", "i.GRUPO_ICMS")):
+        try:
+            cur.execute(f"""
+                SELECT {expr}, TRIM(i.CST_PIS_COFINS), COUNT(*)
+                FROM NFCE_ITENS i LEFT JOIN C000025 p ON p.CODIGO = i.CODPRODUTO
+                WHERE COALESCE(TRIM(i.CST_PIS_COFINS),'') != ''
+                GROUP BY 1, 2
+            """)
+            rows = cur.fetchall()
+            by_key = defaultdict(Counter)
+            for k, cst, n in rows:
+                by_key[k][cst] += n
+            deterministic = sum(sum(c.values()) for c in by_key.values() if len(c) == 1)
+            total_filled_dim = sum(sum(c.values()) for c in by_key.values())
+            out[f"determinism_{dim}"] = {"distinct_keys": len(by_key), "items_covered": total_filled_dim,
+                                         "items_with_single_cst_for_key": deterministic,
+                                         "reproduction_rate_pct": round(100.0 * deterministic / total_filled_dim, 2) if total_filled_dim else None}
+        except Exception as e:  # noqa: BLE001
+            out[f"determinism_{dim}_error"] = str(e)[:150]
+    # aliquota_pis fill vs cst fill: same items or different?
+    cur.execute("SELECT COUNT(*) FROM NFCE_ITENS WHERE ALIQUOTA_PIS IS NOT NULL AND COALESCE(TRIM(CST_PIS_COFINS),'')=''")
+    out["aliquota_filled_but_cst_blank"] = cur.fetchone()[0]
+    cur.execute("SELECT COUNT(*) FROM NFCE_ITENS WHERE ALIQUOTA_PIS IS NULL AND COALESCE(TRIM(CST_PIS_COFINS),'')!=''")
+    out["cst_filled_but_aliquota_null"] = cur.fetchone()[0]
+    conn.close()
+    return out
+
+
+def main():
+    base.load_dotenv(ROOT / ".env")
+    results = {}
+    for name, path in DBS.items():
+        print(f"== {name}", flush=True)
+        results[name] = analyze(name, path)
+        print(json.dumps(results[name], ensure_ascii=False, indent=1, default=str), flush=True)
+    out_path = ROOT / "docs" / "runs" / "BLOCOB_PIS_COFINS_SOURCE_V1.json"
+    out_path.write_text(json.dumps(results, ensure_ascii=False, indent=1, default=str), encoding="utf-8")
+    print(f"-> {out_path}")
+
+
+if __name__ == "__main__":
+    main()