Emit typed SectionedResume from cascade + retire skillsSectionText side-channel (proof PR)

[s-annam]

Follow-up from the #127 segmentation spike (docs/segmentation-spike.md), under epic #109. PR 1 of the sequence — the provably-inert proof.

Goal

Promote the section structure the cascade already computes (PdfSection[] in buildHeuristicResult, openresume.ts:166) into a typed SectionedResume field on CascadeResult, and use it to retire the skillsSectionText side-channel end to end.

Why

The scorer can't answer "is this line a skill?" so the cascade hands it a hand-serialized slice (skillsSectionLines → skillsSectionText → buildSkillsExclusion). That slice is a fragment of the section structure the cascade already had and threw away. Promote the structure; delete the side-channel. This is the smallest end-to-end proof that the model works (spike §3).

Scope (Option A, minimal slice — see spike §3)

• Add SectionedResume type ({ byName: ReadonlyMap<SectionName|"profile", string[]>, accomplishmentSections, source }) + a toSectionedResume(sections, source) builder.
• buildHeuristicResult returns sections on HeuristicResult; cascade carries it onto both CascadeResult builders (cascade.ts:198, :408).
• computeAnonymousAtsScore derives the skills-exclusion set from input.sections.byName.get("skills") instead of skillsSectionText.
• Delete CascadeResult.skillsSectionText (types.ts:189), AnonymousAtsScoreInput.skillsSectionText (score.ts:532), HeuristicResult.skillsSectionLines build (openresume.ts:294), and the two cascade spreads.
• Update consumers: App.tsx:52, useResumeAnalysis.ts:99, corpus.test.ts:108; reshape score.test.ts Skills section scored with experience-bullet rules (action verb / metric / length) #30 tests (:503-:520, :542).

Acceptance

• skillsSectionText no longer exists in the codebase.
• Corpus goldens (24 .expected.json) are UNCHANGED — this is behavior-preserving. Regenerating goldens would mask a regression; a clean diff is the pass condition.
• typecheck + corpus suite green.

Notes

• Targets post-Refactor: split extract-fields.ts god-module (1060 LOC) into per-field modules #126 module paths (extract-fields.ts is being split into extract/*.ts). Rebase onto / sequence after Refactor: split extract-fields.ts god-module (1060 LOC) into per-field modules #126.
• Do NOT scope the bullet pool in this PR — that is the next issue (deliberate score change, algo bump). Keep this one inert.

Refs #127, #109.

[s-annam]

Implementation Complete — d09fca2 (PR #138)

Acceptance Criteria

• skillsSectionText no longer exists in the codebase — field removed from CascadeResult, AnonymousAtsScoreInput, and the HeuristicResult.skillsSectionLines build; only doc-comment references remain.
• Corpus goldens (24 .expected.json) UNCHANGED — behavior-preserving; goldens NOT regenerated, diff is clean (the pass condition).
• typecheck + corpus suite green — 616/616 tests, typecheck + lint clean.

Additional Changes

• Added SectionedResume type + toSectionedResume(sections, source) builder in src/lib/heuristics/sections.ts; sections now required on HeuristicResult and CascadeResult (3 no-Tier-1 paths given inert empty views).
• Scorer derives skills-exclusion from input.sections.byName.get("skills") instead of the side-channel.
• accomplishmentSections populated but not yet consumed — deferred to Pool anon scorer bullets from accomplishment sections (retire rawText walk + buildSkillsExclusion) #133 (deliberate score change).
• One out-of-scope type-only touch: confidence.test.ts (its mkHeuristic literal now needs sections).