[M13 acceptance] Integrate reverse source conversion and verify Workshop-centered interoperability

[Teakowa]

Parent: #90
Depends on: #124, #125

Goal

Integrate the accepted Workshop -> OPY and Workshop -> OSTW reconstructors into Wright's shared driver/tool surface and independently verify the M13 interoperability contract with Workshop as the canonical hub.

Context

#124 and #125 own language-specific canonical source reconstruction from validated Workshop WIR. This issue owns only the shared orchestration, public conversion contract, and final cross-format acceptance.

Scope

• Add one shared driver/session conversion operation over validated Workshop input with explicit target selection (opy or ostw).
• Expose the operation through a thin CLI/API contract without duplicating frontend/emitter semantics in the CLI layer.
• Preserve structured diagnostics and unsupported-surface reporting from the language-owned reconstructors.
• Validate the supported loops:
  • Workshop -> OPY -> Workshop;
  • Workshop -> OSTW -> Workshop;
  • existing OPY -> Workshop;
  • existing OSTW -> Workshop.
• Use semantic/normalized equivalence and declared round-trip contracts, not source-text identity.
• Add cross-format fixtures and machine-readable result coverage suitable for CI/embedding/agent consumers.
• Update the ecosystem compatibility/support documentation with the exact supported directions and reconstruction limits.
• Reassess whether direct OPY <-> OSTW conversion adds value after composition through Workshop is proven; explicitly defer it if no concrete product need exists.

Non-goals

• A generic transpiler matrix abstraction.
• Direct OPY <-> OSTW conversion merely for symmetry.
• Recovering lost comments/formatting/macros/source abstractions.
• Using whole-source reconstruction as the default agent-edit workflow.
• Expanding either source language just to increase conversion coverage.

Acceptance criteria

• Users/library consumers can request canonical OPY or OSTW reconstruction from a supported raw Workshop input through the shared Wright contract.
• Both reconstructed sources recompile through Wright's native frontends to semantically equivalent Workshop for the declared reconstruction surface.
• Structured unsupported diagnostics identify non-representable constructs rather than silently changing semantics.
• Forward OPY/OSTW and reverse Workshop directions all converge on the same Wright-owned Workshop/WIR semantics.
• No upstream language runtime is required in supported production conversion workflows.
• Documentation accurately distinguishes semantic reconstruction from original-source recovery.
• Current tooling, compatibility, and CI gates are green.
• PM records the post-M13 roadmap reassessment before expanding language compatibility further.

Relationships

• Final reverse-interoperability/acceptance child of [M13] Source-language interoperability and OSTW compatibility #90.
• Starts after [M13 reverse] Reconstruct the declared Workshop surface as valid OPY source #124 and [M13 reverse] Reconstruct the declared Workshop surface as valid OSTW source #125 are accepted.
• Direct OPY <-> OSTW remains optional and should be deferred unless this acceptance work produces concrete evidence for it.

[Teakowa]

PM acceptance — M13 reverse integration verified

Verified current main at 25f21e6c0a5f3b313fc58938fd61007aa11c706c rather than relying on the auto-close.

Acceptance evidence:

• CompilerSession::convert is the single shared orchestration contract for raw Workshop input and delegates reconstruction to the language-owned wright_opy / wright_ostw reconstructors; the driver does not contain a transpiler matrix or duplicate emitter semantics.
• wright convert --target opy|ostw is a thin CLI surface over that driver contract.
• Reconstructor failures retain structured stable diagnostics, produce no partial source, and map recognized unsupported conversion to exit code 3; non-Workshop conversion input is rejected explicitly.
• The committed cross-format suite exercises Workshop -> OPY -> native OPY -> Workshop and Workshop -> OSTW -> native OSTW -> Workshop, using semantic/normalized equivalence rather than source-text identity; existing forward OPY/OSTW -> Workshop paths remain the same shared Workshop/WIR boundary.
• Production conversion has no upstream OverPy/OSTW runtime dependency.
• Documentation records reconstruction as canonical semantic reconstruction, not original-source recovery, and explicitly defers direct OPY <-> OSTW conversion.
• GitHub Actions on 25f21e6 executed 11 checks with no failures, including stable/MSRV Rust quality, compatibility/reference/differential gates, OSTW forward differential, v1 gates, and all distribution platforms.

#126 is accepted as complete.