ADR 0012 — V3 monolith-retirement closeout

Status: Accepted Date: 2026-06-02 Feature: 053-v3-monolith-retirement (V3 programme Stage 5 — final stage) Supersedes/closes: the V3 modular-distribution programme (ADRs 0007–0011)

Context

The V3 modular-distribution programme split the broad FS.Skia.UI monolith into nine focused packages across Stages 0–4 (features 048/050/051/052): the Vulkan/Skia host was relocated into FS.Skia.UI.SkiaViewer (ADR 0007), the duplicate scene vocabulary was collapsed to a single source in FS.Skia.UI.Scene (ADR 0008), the AgentValidation surface moved into FS.Skia.UI.Build (ADR 0009), the legacy sample policy was settled (ADR 0010), and the parity oracle method was fixed (ADR 0011). After Stage 4 the only remaining build-consumer of src/Lib was tests/Package.Tests, and the monolith held just the Parity evidence helper.

Decision

Complete the retirement:

1. Delete src/Lib. Library.fs(i) + InternalsVisibleTo.fs + Lib.fsproj are git rm'd; the project is removed from FS-Skia-UI.sln, from packProjects, and from the packable enumerations. The Parity helper + its ParityReport/ParityStatus/ EvidenceType/ParityEvidenceItem types retire with it.
2. Stop publishing FS.Skia.UI. It is dropped from packProjects/the pack flow and from docs/reports/dependencies.md (monolith row + the historical SkiaViewer → FS.Skia.UI leak note removed). No CPM or template pin ever named it (verify-only).
3. Decouple the last consumer. tests/Package.Tests is rewritten against the split-package pack shape and drops its conditional Lib.fsproj reference; the aggregate FS.Skia.UI surface baseline is removed.
4. Enforce the per-package surface gate. PerPackageSurfaceDiff is added to the package-surface routing rule's RequiredGates and to the knownGates allowlist, and rendered into validation.contract.yml — so a public src/**/*.fsi change Route-selects the per-package DiffPlex check and an unrecorded .fsi edit fails the gate (FR-007).
5. Assert generated-app cleanliness. GeneratedProductCheck gains a cleanliness gate asserting a generated app/governed profile carries no samples/, framework docs/reports/ set, historical specs/, or framework root-README copy, and references the split packages rather than copying framework projects (FR-008).
6. Publish closeout artifacts. The V2→V3 migration guide (docs/migration/v2-to-v3.md), this ADR, and the after-measurement baseline (docs/reports/_baselines/2026-06-02-v3-after.md) mirroring the Stage-0 before-baseline.

No runtime src/** code moved this stage — all runtime moved and was parity-proven in Stages 1–4. This stage is deletion + governance/enforcement only; the deterministic scene-output oracle (ADR 0011) is preserved and authoritative.

Consequences

• The package set is the nine split packages (FS.Skia.UI.Scene, .SkiaViewer, .Elmish, .KeyboardInput, .Input, .Layout, .Controls, .Controls.Elmish, .Testing) plus the FS.Skia.UI.Build governance engine. The broad FS.Skia.UI identity no longer exists.
• The package dependency graph is acyclic and FS.Skia.UI.Scene stays FSharp.Core-only.
• A repo-wide no-consumer grep over src samples tests template build *.sln returns zero hits for the monolith identity (SC-001).
• The V3 programme is closed. Remaining roadmap items (a first-class Charts/DataGrid package split, additional template profiles) are explicitly future work, not a further V3 stage.

Links

• Programme ADRs: 0007 (host ownership), 0008 (scene vocabulary single source), 0009 (AgentValidation placement), 0010 (legacy sample policy), 0011 (parity oracle method).
• Before/after baselines: docs/reports/_baselines/2026-06-02-v3-before.md / 2026-06-02-v3-after.md.
• Migration guide: docs/migration/v2-to-v3.md.