Resolve residual source failure-frontier mismatches after #162

[Teakowa]

Parent: #1
Evidence baseline: #158 / PR #159
Discovered by: full conformance rerun after #162 / PR #166

Goal

Resolve the remaining OPY source-language failure-frontier mismatches exposed after #160, #161, and #162 completed, before residual work is handed to compiler/canonical-WIR convergence in #157.

Context

The full offline conformance rerun from PR #166 reports 63 fixtures with 44 match, 17 divergence, and 2 inconclusive. Most remaining divergences now occur at lowering/canonical-WIR, but two cases still fail earlier in native source processing than in pinned OverPy:

• real-world/6v6-adjustments: pinned OverPy reaches an unknown-member semantic failure; native stops earlier with parser errors, first at constants/adj_constants.opy.
• synthetic/issue-29-invalid: pinned OverPy reaches the duplicate-rule-name semantic failure; native stops earlier on @Name parsing/placement.

These are not compiler/WIR residuals and must not be folded into #157 merely because the earlier stage workstreams are closed.

Scope

• Determine the root source-language capability behind each remaining earlier native failure using the existing Re-establish offline OverPy conformance with independent oracle evidence #158 oracle/provenance evidence.
• Make native parsing/source semantics reach the pinned reference frontier for the demonstrated constructs.
• Preserve diagnostic provenance and the existing stage/frontier comparison contract.
• Re-run the full offline conformance suite and confirm that no remaining divergence fails earlier than the pinned reference before lowering.
• Reclassify only genuinely later-stage residuals to Converge residual OPY compiler and canonical-WIR gaps #157 after this boundary is clean.

Non-goals

• Reopening Converge parser and source-form conformance exposed by #158 #160, Converge preprocessing and project-composition conformance exposed by #158 #161, or Converge semantic resolution and catalog-backed source conformance exposed by #158 #162 as execution vehicles.
• Fixing canonical-WIR equivalence or backend lowering residuals owned by Converge residual OPY compiler and canonical-WIR gaps #157.
• Fixture-specific parser exceptions.
• Changing Re-establish offline OverPy conformance with independent oracle evidence #158 oracle expectations or encoding current native failures as expected passes.
• Adding implementation-shaped tests without independent evidence of a missing durable language contract.

Acceptance criteria

• real-world/6v6-adjustments no longer fails natively before the pinned semantic frontier, or independent evidence demonstrates a different valid ownership classification.
• synthetic/issue-29-invalid no longer fails natively before the pinned duplicate-rule-name semantic frontier, or independent evidence demonstrates a different valid ownership classification.
• The full offline conformance rerun contains no remaining OPY-owned lexer/parser/preprocessing/source-semantic divergence that precedes a later pinned reference frontier.
• Remaining divergences are demonstrably lowering/canonical-WIR, Workshop-owned, or explicitly inconclusive with provenance.
• Existing Re-establish offline OverPy conformance with independent oracle evidence #158 oracle expectations remain independent of the implementation changes.

Dependencies / ownership

• Depends on the merged Converge parser and source-form conformance exposed by #158 #160, Converge preprocessing and project-composition conformance exposed by #158 #161, and Converge semantic resolution and catalog-backed source conformance exposed by #158 #162 work and the Re-establish offline OverPy conformance with independent oracle evidence #158 conformance contract.
• OPY source syntax/preprocessing/semantic behavior is owned by opy-rs.
• Canonical Workshop WIR/parsing/emission remains owned by workshop-rs.
• Converge residual OPY compiler and canonical-WIR gaps #157 should consume the residual classification produced after this issue completes.