typed loads: the reverse member→snake_case rule has three copies (TypedLoadContract.ToSnakeCase, STJ SnakeCaseLower, YamlDotNet UnderscoredNamingConvention) and Core has no reverse of NameMangling.ToPascalCase

[antonsynd]

Found by /verify-implementation plan-0ca7b7 (2026-09-26), measured @ 61bf20f with the built sharpyc; pre-existing at BASE acd1d40 unless noted.

R-CG (#2040) made NameMangling.ToPascalCase the single forward rule (snake → emitted member). 516bd7d routed toml's copy through it. The typed json/yaml doors map in the other direction, and there are three separate copies of that mapping:

• TypedLoadContract.ToSnakeCase, which recovers the missing-field name from the CLR member;
• Json.cs JsonNamingPolicy.SnakeCaseLower;
• Yaml.cs UnderscoredNamingConvention.

These are the libraries' snake rules, not the inverse of R-CG. The affixed names that forced 516bd7d (x_ → X_, _x → _X) are the cells to probe: a field x_ loaded from {"x_": 4} must bind x_ and report x_ when missing. Needs a design: either a Core reverse rule, or the python-name channel stamped on the member ([SharpyName], R-CF) read by a custom naming policy.

[antonsynd]

Batching 2026-09-30 @ db8e05b — charter .claude/plans/remediation-round-2026-09-20-batching.md §3.27, P32 — typed-load doors (order N21, after P11g).

Ruling R-DE (owner, 2026-09-30): [SharpyName] stamped on members whose mangled name differs from the source name (R-CF's attribute-when-different rule at member level — the same stamp R-DG puts on methods), read by ONE custom naming policy shared by the three doors; a missing-field message reports the stamped name; affixed names (x_, _x) round-trip losslessly. Rejected: a Core ToSnakeCase inverse (lossy for affixed names). Contract: the typed json/yaml/toml doors share ONE naming rule (source ↔ member) and ONE message channel (python-spelled type names, python-shaped errors), and accept the same target shapes. Fidelity-scope: type names in messages are COMPARED (R-CF); message text beyond the name is DEVIATION (R-CI) — cells assert the type name and the exception TYPE, not library prose. After P11g. Lane / reach: silent-wrong · probe. This issue is the class tracker. No seam hypothesis — the plan measures the seam.