V2-PHASE1-P2: Export record-shaped PMI (datum, diameter) to AP242 with tolerance support

[yuechen-li-dev]

Motivation

• Wire the V2 Phase1 record-shaped pmi authoring flow into real AP242 export so datum and diameter PMI authored over existing InlineStep models produce semantic AP242 evidence.
• Preserve toleranced let dimensions for diameter PMI and make unsupported PMI kinds explicit (deferred) rather than silently dropped.
• Surface export evidence in CLI JSON output and integrate with the existing V2 validation/reporting flow.

Description

• Bridge bound V2 record-shaped PMI into the legacy Step242SemanticPmi pipeline by enhancing BuildV2SemanticPmi to include diameter tolerances from bound PMI and datum mappings.
• Emit AP242 semantic tolerance evidence for diameter PMI in Step242Exporter as diameter_tolerance:<featureId> with tolerance_plus and tolerance_minus MEASURE_REPRESENTATION_ITEMs.
• Add deterministic export validation ValidateV2PmiExportSupport that rejects build/export when export-deferred PMI records (distance, flatness, parallel, perpendicular, coplanar) are present.
• Report PMI export evidence in CLI build JSON by adding pmiExportEvidence to CliRunner and add parser/binder + export regression tests and fixtures under fixtures/FirmamentV2/InlineStep (valid primary fixture and two invalid fixtures).
• Add implementation documentation at docs/implementation/v2-phase1-p2-record-pmi-ap242-export.md and update docs/v2/aetheris-v2-phase1-scope-contract.md status note.

Testing

• Ran full .NET restore/build: dotnet restore Aetheris.slnx and dotnet build Aetheris.slnx -f net10.0 --no-restore /m:1 — build succeeded (pre-existing warnings).
• Ran targeted unit tests: dotnet test Aetheris.Kernel.Firmament.Tests/... --filter "RecordPmi|PMI|Pmi|Datum|Diameter|InlineStep|AP242|FirmamentV2" --no-build — tests passed (192 tests matched).
• Exercised CLI end-to-end on the primary fixture: aetheris validate <fixture> --json, aetheris build <fixture> --out <tmp>.step --json, and aetheris analyze <tmp>.step --json — validation, build, export and reimport checks completed and expected AP242 evidence strings were present.
• New tests cover binding toleranced dimension: lets, AP242 emission/reimport evidence, rejection of diameter without tolerance, and deterministic failure/reporting for export-deferred flatness records.

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Codex Task