Reports that the catalog entry for `controlId` omits a `requiredField`.

Builds a `ControlDiagnostic` from an explicit `code`, `severity`, and `message`, optionally scoped to a `controlId` and `kind`.

Reports that a control `kind` declares a non-standard `extensionName` outside the standard contract.

Reports that `packageId` exposes a transitive `dependencyPath` that should not leak across the package boundary.

Reports that attribute `name` was supplied more than once on a control of `kind`.

Reports that `runtimeName` is defined more than once, the duplicate residing at `path`.

Reports that the same `key` identifies two sibling controls, a `ControlId` collision.

Reports that a control of `kind` lacks the accessibility metadata it requires.

Reports that a control of `kind` is missing a required attribute `name`.

Reports that standard control `kind` omits a required standard attribute `name`.

Feature 113 (Phase 5) — the stability-diagnostic report (report-only, NOT an enforced gate). Given TWO builds of the SAME logical control (sub)tree (`first`/`second` — the same model run through `View` twice), walk them in parallel and return one `UnstableReuseInput` finding per attribute/event that compared UNEQUAL despite no semantic change: a rebuilt `UntypedValue`, a per-frame event closure (reference-fresh each build), or an unstable key. Each finding names the control (`ControlId` + `ControlKind`) and the offending attribute/event name. An empty list ⇒ the tree's inputs are stable across builds (the case memoization can exploit). Stable structural values (`TextValue`, `StringListValue`, …) and reference-shared event handlers do not flag. Pure, total, deterministic; never compares a function with `=` (uses reference identity for closures).

Reports that an `eventKind` binding targets a `controlId` that no longer exists in the tree.

Reports a `packageId` reference at `path` that no longer resolves to a current package.

Reports that a control of `kind` requested a `capability` the host environment does not support.

Reports that `scopeName` owned by `owner` cannot be expanded as requested.

Reports that standard control `kind` does not support the standard attribute `name`.

Reports that standard control `kind` does not raise the standard event `eventKind`.