Evidence-based map of the comprehension coverage wall (the C decision). GSM8K
diagnostic: 4/0/46, no single barrier >10%, ~24 fragmented primary barriers with
heavy multi-barrier co-occurrence (compound+comparative+fraction+coreference stack
on the same cases). Capability lanes are narrow curated-gold conformance
(combined-rate: 6 solvable shapes, 19/19 oracle). Single-shape recognizers are
proven metric-inert (4th confirmation). Diagnosis: shape-recognizers don't COMPOSE
within compound statements / across coreference. Leverage: Tier 1 recognizer
additions ~+5 cases then cap; Tier 2 compositional reading is the only real lever
(architectural, must stay wrong=0). Recommendation: don't add isolated recognizers;
design a compositional reader.
