fix: Pass 0b batch custom_id + result handler for numeric format

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

control-pipeline/services/decomposition_pass.py

@@ -3593,9 +3593,9 @@ class DecompositionPass:
                     source_ref=obl["source_ref"],
                 )
 
-            ids_str = "+".join(o["candidate_id"] for o in batch)
+            batch_idx = i // batch_size
             requests.append({
-                "custom_id": f"p0b_{ids_str}",
+                "custom_id": f"p0b_b{batch_idx:05d}",
                 "params": {
                     "model": ANTHROPIC_MODEL,
                     "max_tokens": max(8192, len(batch) * 1500),
@@ -3778,9 +3778,40 @@ class DecompositionPass:
     async def _handle_batch_result_0b(
         self, custom_id: str, text_content: str, stats: dict,
     ) -> None:
-        """Process a single Pass 0b batch result."""
+        """Process a single Pass 0b batch result.
+
+        custom_id formats:
+          - p0b_b00001 (numeric batch index — new format)
+          - p0b_OC-CTRL-001+OC-CTRL-002 (legacy + separated candidate IDs)
+        """
         prefix = "p0b_"
-        candidate_ids = custom_id[len(prefix):].split("+") if custom_id.startswith(prefix) else []
+        suffix = custom_id[len(prefix):] if custom_id.startswith(prefix) else custom_id
+
+        # New format: p0b_b00001 — extract candidate IDs from LLM response
+        if suffix.startswith("b") and suffix[1:].isdigit():
+            results_by_id = _parse_json_object(text_content)
+            if not results_by_id:
+                # Try single object
+                parsed = _parse_json_object(text_content)
+                if parsed and "candidate_id" in parsed:
+                    cand_id = parsed["candidate_id"]
+                    obl = self._load_obligation_for_0b(cand_id)
+                    if obl:
+                        await self._process_pass0b_control(obl, parsed, stats)
+                else:
+                    stats["errors"] += 1
+                return
+
+            for cand_id, parsed in results_by_id.items():
+                if not isinstance(parsed, dict):
+                    parsed = {}
+                obl = self._load_obligation_for_0b(cand_id)
+                if obl:
+                    await self._process_pass0b_control(obl, parsed, stats)
+            return
+
+        # Legacy format: p0b_OC-CTRL-001+OC-CTRL-002
+        candidate_ids = suffix.split("+")
 
         if len(candidate_ids) == 1:
             parsed = _parse_json_object(text_content)