Increment 2 for ADR-0252 Track B. Extends Increment 1's structure-mapping
slice with pure-family canonicals S2–S4, overlapping-waves selector, and a
structure-mapping-owned pure-S1 text extract that recovers four real
holdout cases the serving reader misses (0148, 0228, 0234, 0441).
Bar results (command-backed via scripts/measure_trackb_inc2.py):
- generalization ratio S1 = 9.0 (9 holdout cases / 1 template)
- coverage gain organ 5 → trackb 9, wrong=0
- selector routes S1/S2/S3; refuses empty; surface≠structure
Off-serving: no organ retirement, serving reader untouched. S2–S4 holdout
ratios are 0 (parser frontier). S3/S4 emit refuses at multi-register scope
without weakening the three-gate wrong=0 path.
[Verification]: Smoke suite passed locally (~132s, 176 passed);
trackb unit tests 35 passed; measure_trackb_inc2 all modes green.
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