Store ordinary task returns in HIR

[OttoApocalypse69]

What changed

• store one closed ordinary-task return-form record in HIR for explicit, implicit-block, and arrow tasks
• carry explicit declared return surface text and exact span through HIR snapshot v5
• make TY consume explicit ordinary-task returns through HIR while preserving isolated arrow and nonordinary fallbacks
• add transitive anti-token-scraping guards with a helper-indirection mutation self-test
• add snapshot validation/atomic restore and return-only HIR/TY/MIR/Meiya/editor invalidation coverage

Ownership boundary

This is a bounded No Syntax Past HIR slice. HIR owns the normalized declared return fact; TY owns canonicalization and inference; MIR/Meiya/editor continue consuming TY APIs. Impl/doctrine/extern returns, arrow-expression inference, and implicit block inference remain explicit follow-up families.

Local validation

• independent exact-head review of 47c77abaeebfdf28e4e10c41d5f4665398fce838...a6e7de0060967e920a0fbfb7dcf3d65f225d49b3: APPROVE, no P0-P3
• python -u -m py_compile freakc/auditor.py src/compiler/v4/check_v4.py
• python -u -m freakc audit-conformance
• focused task return semantic boundary smoke under Global\FreakCheckV4
• python -u src/compiler/v4/check_v4.py --fast: all 249 fixtures passed; 3,697 flattened statements; 40.7 MB peak retained
• git diff --check

Pending remote evidence

• current-head GitHub CI and automated review
• cross-platform runtime execution remains CI-owned

Conservative boundaries

• ordinary top-level task declarations only
• no new return inference or language semantics
• impl, doctrine, extern, closure, and function-type return syntax remain follow-up slices
• TY snapshot stays v1; HIR snapshot v5 is validation-before-restore atomic

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