Bug 1: ELSE IF breaks IF false_seq parsing (core.py)
- _parse_if checked self.clean() == 'ELSE' which fails on 'ELSE IF ...'
- Fix: use startswith('ELSE'), reinsert IF portion for recursive parse
- Impact: ALL ELSE IF chains were silently dropped (huge branch loss)
Bug 2: READ skip loop greedily consumes subsequent statements (core.py)
- READ's AT END / NOT AT END skip loop used bare advance() with no
statement boundary detection
- Fix: add _stmt_boundary regex that stops on IF/PERFORM/READ/etc.
- Impact: everything after first READ was consumed as 'AT END' lines
Bug 3: _walk() in extract_structure doesn't descend into BrPerform (__init__.py)
- Branch counting _walk() only handled BrIf/BrEval/BrSeq
- IF statements inside PERFORM bodies were never counted
- Fix: add BrPerform.body_seq and BrSearch descent
Combined impact: matching programs (MT01-33) now correctly report
their branches instead of 0. Full regression: 749 passed (unchanged).
NB-076
hangshuo652