Sibling to math_parser.py — pure candidate-extraction functions that
emit list[CandidateOperation] per sentence without mutating any state.
State threading defers to P3 (per-branch graph assembly).
Topology change vs legacy:
- No first-match-wins; every verb-kind regex runs independently.
- Ambiguous verbs ('gives', 'returns') emit multiple candidates;
P1's round-trip filter + P3's decision rule resolve.
- Out-of-grammar sentences return [], NOT ParseError. Empty list
is the deterministic 'no candidate' signal.
Permissive verb tables (imported from math_roundtrip.KIND_TO_VERBS)
mean past-tense and production verbs ('bought', 'ate', 'bakes')
that the legacy parser refused are now admissible — the round-trip
filter is the safety mechanism, not regex narrowness.
P2 scope (canonical Subject-verb-Value-Unit-[to-Target] shape only):
- extract_initial_candidates(sentence) for 'X has N units'
- extract_operation_candidates(sentence) for add/subtract/transfer
Out of scope (deferred to later sub-phases):
- Pronoun resolution / unit inheritance (needs per-branch state)
- Multiply / divide / rate / comparison (same machinery, more matchers)
Regression: existing math suite 701/701 green. Zero changes to
math_parser.py, math_solver.py, math_verifier.py, math_realizer.py.
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