[Facet] already had AllowMultiple = true but the generator silently ignored every attribute after the first — ModelBuilder always read context.Attributes[0], and even when the pipeline produced duplicate models they were deduplicated away.

What changed

Generator pipeline

• ModelBuilder: added BuildModels() that iterates all context.Attributes, one model per [Facet]; BuildModel now delegates to a shared private BuildModelForAttribute.
• FacetGenerator: switched from .Select(BuildModel) → .SelectMany(BuildModels); groups models by target FullName before emitting; facetLookup uses first-wins instead of ToDictionary (which would throw on duplicate keys).

Code generation for multi-source targets

• CodeBuilder.GenerateCombined: emits a single .g.cs with the union of all source members (deduped by name, first-wins), then generates per-source artefacts:
  • Constructors / FromSource overloads — no naming change needed (naturally overloaded by parameter type).
  • ProjectionFrom{SourceSimpleName} static property per source (avoids static-property name collision).
  • To{SourceSimpleName}() instance method per source (can't overload on return type); BackTo alias suppressed for multi-source.
• Shared artefacts (parameterless ctor, copy ctor, equality) are generated once from the primary model.
• MemberGenerator.GenerateMembers accepts an optional membersOverride list for the union-member pass.
• ProjectionGenerator / ToSourceGenerator accept optional name parameters; single-source output is fully backward-compatible (Projection, ToSource(), BackTo() unchanged).

Documentation

• docs/06_AdvancedScenarios.md: new "Multiple Source Types to One Target" section covering motivation, generated API, union-of-members behaviour, per-source GenerateToSource, and a behaviour reference table.
• docs/README.md and README.md: updated table of contents and features list to reference multi-source mapping.

CI — Preview NuGet publishing

• New .github/workflows/preview.yml: triggers on every PR push (opened, synchronize, reopened) targeting main/master/develop.
  • Computes a pre-release version: {base_version}-preview.pr{PR_NUMBER}.{RUN_NUMBER} (e.g. 6.1.4-preview.pr42.7).
  • Builds, packs, and publishes all packages to NuGet.org using the same per-package API key routing as release.yml.
  • Posts (and updates) a single bot comment on the PR with the exact version and dotnet add package install command.
  • concurrency: cancel-in-progress per PR prevents stale publishes when multiple commits land quickly.

Usage

[Facet(typeof(UnitEntity), Include = [nameof(UnitEntity.Name)])]
[Facet(typeof(UnitDto),    Include = [nameof(UnitDto.Name)])]
public partial class UnitDropDownDto;

// Generated:
var a = new UnitDropDownDto(unitEntity);          // constructor overload
var b = new UnitDropDownDto(unitDto);
var c = UnitDropDownDto.FromSource(unitEntity);   // factory overload
var d = UnitDropDownDto.FromSource(unitDto);

// Projection per source (multi-source naming)
IQueryable<UnitDropDownDto> q1 = dbContext.Units.Select(UnitDropDownDto.ProjectionFromUnitEntity);
IQueryable<UnitDropDownDto> q2 = dtos.AsQueryable().Select(UnitDropDownDto.ProjectionFromUnitDto);