experiment: kORE/iDRegEx vs CRX on flat bags (Round 15)

Key finding: iDRegEx/kORE return None on genuinely diverse groups (flat bags).
CRX is the only algorithm that produces anything for these groups.
For structured groups, CRX already captures ordering well.

Conclusion: kORE/iDRegEx are not better fallbacks for flat bags.
The pipeline's existing filtering (min_structure, split_mixed) is the right approach.

experiments/EXPERIMENT_LOG.md

@@ -621,3 +621,67 @@ the real problem. Clean symbols → clean grammars.
 
 **Decision:** Keep `code_bytes = code.encode()` pattern permanently. Remove
 `sanitize_symbol()` (dead code). Remove `call_only` parameter (no longer needed).
+
+---
+
+## Round 15: kORE/iDRegEx vs CRX on Flat Bags
+
+**Question:** Would kORE or iDRegEx produce tighter grammars for the groups where
+CRX over-approximates (flat bags with structure < 0.3)?
+
+**Method:** Hand-crafted sequences mimicking real RAGSAK patterns. Tested CRX,
+iDRegEx (k=2, N=3), and kORE (k=2, N=3) on two example types.
+
+**Example 1: Structured sequences (clear branching)**
+```
+Input: 6 methods with session.use.{run/execute}.{parameters/query}.{single/list}.{get/map/filter}
+CRX:     session.use.execute?.run?.query?.parameters?.list?.single?.filter?.map?.get?.count?.(toLong+toString)?.(asLong+asString)?
+         → Flat optional chain. All symbols listed, no real structure.
+         
+iDRegEx: session.use.(run.parameters|execute.query).(single.get.(asLong|asString)|list.(filter.count|map.(toLong|toString)))
+         → Nested disjunctions. Shows actual branching: run vs execute, single vs list.
+         
+kORE:    Same as iDRegEx.
+```
+**Verdict:** iDRegEx/kORE produce MORE informative grammars. Nested disjunctions
+show the actual code paths. CRX flattens everything into optional chains.
+
+**Example 2: Flat bag (diverse patterns)**
+```
+Input: 6 methods with different call patterns (request/response/error paths)
+CRX:     return.error?.(request+response)?.message?.json?.data?.status?.ok?
+         → Partial structure, some optional paths.
+         
+iDRegEx: None
+kORE:    None
+```
+**Verdict:** When there's genuinely no structure, iDRegEx/kORE return None. CRX
+is the only one that produces anything.
+
+**Real-world RAGSAK test (6 methods, health check package):**
+```
+CRX:     (HealthCheckReply+`when`+collectionExistsAsync+...)+ → flat bag, score 0.126
+iDRegEx: None (at k=2,3)
+kORE:    None
+```
+Both iDRegEx and kORE return None on real flat bags because the sequences are
+too diverse.
+
+**Key insight:** CRX and iDRegEx/kORE operate on different principles:
+- **CRX**: Deterministic, always produces something, but over-approximates on diverse groups
+- **iDRegEx/kORE**: Probabilistic, need repeating patterns to infer, return None when patterns are too diverse
+
+**Recommendation:** The flat bags (structure < 0.2) are genuinely diverse groups —
+no algorithm can find meaningful structure. The fix is:
+1. **Split further** (recursive split already does this)
+2. **Filter by structure** (min_structure ≥ 0.3 drops flat bags)
+3. **Accept that some groups are noise** and skip them
+
+Using kORE/iDRegEx as fallback for low-structure groups would just return None
+more often. CRX is the right default — it's fast and always produces something.
+For the structured groups, CRX already captures the ordering well (score ≥ 0.5).
+
+**Decision:** Keep CRX as default. kORE/iDRegEx are not better for flat bags
+(they return None) and not needed for structured groups (CRX already works).
+The pipeline's existing filtering (min_structure, split_mixed) is the right
+approach to handle diversity.