Expose canonical Workshop action layout for relative Skip lowering

[Teakowa]

Goal

Expose a minimal workshop-rs-owned canonical action-layout capability so consumers can lower native Workshop relative Skip semantics without duplicating emitter expansion rules.

Context

wrightkit/opy-rs#61 lowers OverPy control-flow sugar such as switch and do ... while into native Workshop primitives. switch, case/default, do-while placement, fallthrough, break policy, and source-language labels remain entirely OPY-owned semantics.

The actual cross-repository gap is lower-level: workshop-rs WIR is structured (If, While, For, etc.), while native Workshop Skip(n) distances are measured in the emitted Workshop action stream. A single structured WIR node may emit multiple native actions/markers. opy-rs currently mirrors those expansion rules locally to compute distances, which duplicates Workshop-owned emitter/layout semantics and can drift when canonical emission changes.

This issue is therefore about canonical Workshop action layout only, not a generic control-flow target system.

Scope

• Provide a source-language-neutral public way to determine the native Workshop action span/width produced by canonical WIR actions or action sequences.
• Cover nested structured actions whose emission expands into multiple native Workshop actions, including If/Else/End, While, and For forms.
• Ensure the layout query and canonical emitter share one authoritative expansion model rather than maintaining duplicate width tables inside workshop-rs.
• Keep validation/error handling explicit for malformed or unsupported WIR.
• Add focused tests proving layout results remain consistent with deterministic canonical emission.

Non-goals

• No Switch, Case, Default, DoWhile, OPY/DEL label, goto, CFG, or source-language control-flow node in WIR.
• No source-language fallthrough, break, continue, or placement semantics in workshop-rs.
• No generic symbolic relocation/target system unless future independent consumers provide concrete evidence that action-span queries are insufficient.
• No reproduction of OverPy/OSTW compiler internals or output-text identity.
• No broad WIR redesign unrelated to native action layout.

Acceptance Criteria

• A documented public workshop-rs contract can report canonical native Workshop action span/width for validated WIR actions/sequences.
• Nested If, While, ForGlobalVariable, and ForPlayerVariable structures have executable coverage.
• The contract and emitter derive layout from the same authoritative implementation/source of truth; there is no second manually synchronized emitter-width table.
• Invalid WIR/layout requests fail explicitly.
• opy-rs#61 can delete its local normalized_action_width() model and consume the released Workshop-owned capability while retaining all OPY-specific switch/do-while semantics locally.
• No source-language-specific semantic ownership is introduced into workshop-rs.

Dependencies

• Blocks the durable relative-Skip lowering path in wrightkit/opy-rs#61 / wrightkit/opy-rs#47.
• Consumer flow: implement and test the authoritative contract here -> publish a workshop-rs release -> update opy-rs#61 to consume it.