align_sections_to_v4_granularity now emits canonical sub-section ids
of the form ${section_id}-sub-${ordinal} (e.g., "04-2-sub-1"), matching
the frontend drag/drop schema. Each drilled sub-section populates
heading_number (decimal "2.1" / integer "1" / None for undecorated)
and v4_alias_keys for legacy V4 keys.
N-R5 decimal-only alias guard : v4_alias_keys is populated only when
heading_number matches re.fullmatch(r"\d+\.\d+", ...). Integer-only
H3 headings (e.g., MDX 05's "### 1", "### 2") and bare H3 headings
produce no alias to avoid sibling-parent V4 collisions (RULE 0
generalization — applies to all 32-frame MDX, not MDX 05-specific).
The drill regex is broadened from r"^###\s+(\d+\.\d+)\s+..." to
r"^###\s+(?:(\d+(?:\.\d+)?)\s+)?(.+?)$" so integer-only and bare H3
headings are now recognised as sub-sections; they previously failed
the regex and were silently kept under the parent section.
Tests : 7 new cases (MdxSection default 4-positional callers, V4 exact
passthrough, decimal drill with alias, integer-only no-alias guard,
bare H3 no-alias, no-H3 passthrough, end-to-end aligner -> resolver
round-trip with legacy V4 alias). 15/15 in test_phase_z2_subsection_schema
+ 14 override + 8 fallback baseline = 37/37 PASS.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Adds sub-section schema fields (heading_number / v4_alias_keys /
sub_sections) to MdxSection with defaults so existing 4-positional
constructions remain valid. Introduces _resolve_v4_section_key helper
that resolves a V4 mdx_sections key in exact > alias > None order with
no parent/sibling promotion (axis 7 hybrid lock).
Rewires four runtime V4 lookup sites (lookup_v4_match,
lookup_v4_match_with_fallback, lookup_v4_all_judgments,
lookup_v4_candidates) to accept an optional alias_keys kwarg and go
through the resolver. U1 callers pass empty alias lists so behaviour
is byte-identical to the previous exact-match path; U2 will populate
aliases from MDX heading_number metadata.
Closure callers in run_phase_z2 build section_alias_by_id from
MdxSection.v4_alias_keys and forward into lookup_fn /
candidates_lookup_fn / lookup_v4_all_judgments (Step 7-A trace) and
into _select_template_for_overrides single-section selector.
Step 9 candidate report (post-decision diagnostic) is marked with an
inline English exemption comment per N-R6 — runtime selection goes
through _resolve_v4_section_key, the report path stays a direct
dict-shape lookup to avoid debug_zones schema plumbing.
derive_parent_id now recognises canonical ordinal ids
("03-1-sub-2" -> "03-1") first and keeps the legacy decimal fallback
("04-2.1" -> "04-2") for V4 alias compatibility.
Tests : 8 synthetic cases in tests/test_phase_z2_subsection_schema.py
covering derive_parent_id ordinal/decimal/none and the resolver
exact/alias/no-promote/miss cases. 30/30 PASS combined with the 14
override + 8 fallback baseline.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
