docs: record source-model DataLinks runtime evidence

Plant3D2026/P_Rec_Annot/docs/ortho-source-mapping.md

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+# Ortho source-model mapping
+
+## Confirmed Plant 3D 2026 read path
+
+```text
+Active Ortho document
+→ OrthoProject.DwgSheetDefinitions
+→ IDwgSheetDef.DwgViewDefs
+→ IDwgViewDef.DwgQuery.ModelFiles[].ModelFileName
+→ PipingProject.GetPnPDrawingFiles()
+→ exact normalized-path match to PnPProjectDrawing
+→ PnPProjectDrawing.Id
+→ DataLinksManager.SelectAcPpRowIds(int dwgid)
+→ GetObjectClassname / GetAllProperties
+→ independent PlantObjectSnapshot
+→ AnnotationPlanBuilder
+```
+
+`PlantOrthoViewportReader.ReadViewports` reads the typed DwgQuery contract and
+creates an Ortho viewport snapshot. `PlantObjectReader.ReadObjects` resolves
+the resulting model-file reference through the Piping project drawing list and
+reads DataLinks by project drawing ID. The active Ortho database is not a
+Piping-row source.
+
+All calls are read-only. The adapter opens no write transaction and does not
+save a drawing, DCF, or project metadata.
+
+## Diagnostics
+
+The source reader returns stable telemetry diagnostics rather than suppressing
+the result of a failed query: `ORTHO_SOURCE_DRAWING_NOT_RESOLVED`,
+`ORTHO_SOURCE_DRAWING_NOT_IN_PROJECT`, `ORTHO_SOURCE_DRAWING_AMBIGUOUS`,
+`PIPING_PROJECT_PART_NOT_FOUND`, `SOURCE_DATALINKS_UNAVAILABLE`,
+`SOURCE_DATALINKS_NO_ROWS`, `SOURCE_DATABASE_READ_FAILED`,
+`SOURCE_PIPE_ROWS_NOT_FOUND`, or `SOURCE_DATALINKS_READ`.
+
+Exact membership of a source object in a particular Ortho viewport is not yet
+implemented. A source-level DryRun plan must not be presented as proof of
+viewport membership.