tw-slice-isolation

name	tw-slice-isolation
description	**TIMEWARP SKILL** — product slice placement and TWA0009 isolation (SliceRoot, namespaces, platform Applications, Components/contracts sharing, CrossSliceReference opt-out). Invoke before scaffolding a new feature/slice/page or when fixing TWA0009 / cross-slice references. WHEN: Add a new clients feature page, Where does this state live?, TWA0009 slice references another product slice, CrossSliceReference, new product area under features/, greenfield slice scaffolding.
when-to-use	slice, slice isolation, TWA0009, CrossSliceReference, SliceRoot, TimeWarpSliceRoot, product feature folder, features/, Applications platform, cross-slice, where page/state live

Slice isolation (TWA0009)

Slices are independently removable vertical units. Folders organize humans; the namespace under SliceRoot is the law. Analyzer TWA0009 is the reactive safety net; this skill is for correct first placement so greenfield work does not couple product areas by accident.

Enforcement ships in TimeWarp.Architecture.Analyzers (and monorepo ProjectReference). Do not re-interpret rules here — mirror the analyzer.

Detection — when to invoke

Signal	How to find it
Product area under features/	SPA: web-spa/features/…; server product code: web/features/<slice>/ (axis-1 cohesive tree; layer projects glob *-{layer}.cs)
Namespace under SliceRoot	…Features.<Id> (or nested …Features.Admin.Roles)
TWA0009 / CrossSliceReference	diagnostic text or attribute on a type
“Where does this page/state live?”	any new product capability before scaffolding

Terms

Term	Meaning
Slice	Removable vertical capability; the isolation unit
Feature	Informal product language only — not the analyzer’s unit name
Module	IModule / host DI composition — not a product slice

Prefer saying slice in diagnostics, opt-outs, and agent prose. Namespace path may still use …Features.* (familiar VSA / contracts layout).

SliceRoot

Setting	Value
Default	{RootNamespace}.Features (from MSBuild RootNamespace)
Override	MSBuild property TimeWarpSliceRoot (must be CompilerVisibleProperty)

Slice id = path under SliceRoot after stripping structural suffixes Pages, Components, Application. Nested ids are the full path:

Namespace	Slice id / tier
…Features	Substrate (bare root)
…Features.Applications	Platform id Applications
…Features.Counters	Product id Counters
…Features.Counters.Pages	Product id Counters (suffix stripped)
…Features.Admin.Roles	Product id Admin.Roles
…Components, layouts, app root types	Outside SliceRoot

Folders usually mirror slices (features/counter/ ↔ …Features.Counters) but moving a file does not change legal dependencies — only the namespace does.

Tiers (dependency rules)

Tier	Example	May reference
Outside	…Components, shell, layouts	Anything (composition free)
Substrate	bare …Features (BaseComponent, shared base types)	Outside, substrate, platform — not product without opt-out
Platform	…Features.Applications	Outside, substrate, platform — not product without opt-out
Product	…Features.Counters, …Features.Admin.Roles	Outside, substrate, platform, own product id, contracts (other assembly). Not another product id without opt-out

Forbidden without opt-out (TWA0009):

• product A → product B (A ≠ B)
• platform → product
• substrate → product

Free by design:

• product → platform (Applications) — e.g. CounterPage → ApplicationState
• any code → other assemblies (contracts are sharing-by-design)
• Outside → product (nav shell, shared components)

Placement matrix

Artifact	Where
Page, state, actions, slice-local UI	Inside the product slice namespace
App chrome / shell / empty MainLayout	Outside SliceRoot (e.g. …Components) — see tw-blazor-layout
Shared UI used by multiple slices	components/ → namespace outside SliceRoot
Shared API shapes	Contracts project (other assembly; free under TWA0009)
Host-wide modal / menu / branding state	Platform Applications

Living anchors (timewarp-architecture template):

Role	Path	Namespace
Product	web-spa/features/counter/	…Features.Counters
Nested product	web-spa/features/admin/roles/	…Features.Admin.Roles
Platform	web-spa/features/application/	…Features.Applications
Substrate	web-spa/features/base/base-component.cs	…Features
Outside shell	web-spa/components/TimeWarpPage.razor	…Components

Greenfield scaffold workflow

1. Name the slice — plural, domain-oriented (Clients, Admin.Roles).
2. Folder — kebab path under the project’s features/ tree (match sibling casing).
   • SPA UI stays under web-spa/features/<slice>/ (conventional; not rehomed by axis-1).
   • Contracts / application / server product files live in the cohesive tree web/features/<slice>/ with filename grammar <name>[-<function>]-<layer>.cs (see tw-feature-placement for the full grammar and registry).
3. Namespace — {RootNamespace}.Features.{SliceId} (plural segments; nested with .). Folders rehome freely; namespaces are not renamed with folder moves.
4. Colocate page, state, actions, and slice-private components in that namespace (pages are not shared infrastructure — no grab-bag …Pages for product UI).
5. Contracts — same plural slice path under web/features/<slice>/ with -contracts.cs suffix (tw-web-api-contracts skill). Other assembly → free across SPA slices.
6. Wire nav / DI from Outside or platform — not from another product slice.
7. Prefer share (Components / contracts) over [CrossSliceReference].
8. Build — fix TWA0009 by relocating code first; mute only for deliberate demo/integration edges.

Share vs opt-out

Prefer share

• Promote shared controls to …Components.
• Share API shapes via contracts assembly.
• Depend product → platform without attributes when the dependency is real host state.

Opt-out — deliberate edges only

using TimeWarp.Foundation.Features;

[CrossSliceReference(typeof(CounterState), "Living style guide exercises the counter throw-exception pipeline.")]
partial class StyleGuidePage;

Rules:

• Attribute on the referencing type (AllowMultiple = true for multiple foreign slices).
• typeof(T) maps to the target product slice; only edges into that slice are suppressed.
• Reason must be non-empty (human paperwork).
• Partial-safe (semantic attributes).
• Type: TimeWarp.Foundation.Features.CrossSliceReferenceAttribute (package TimeWarp.Foundation.Contracts / monorepo foundation-contracts).

Living examples:

• Style guide → Counters: web-spa/features/style-guide/pages/StyleGuidePage.razor.cs
• Auth pipeline deliberate edges: authentication code-behinds with multiple [CrossSliceReference(...)] when needed

Limits agents must know

Limit	Implication
Same assembly only	Contracts / NuGet metadata types never trip TWA0009
Hand-written C#	GeneratedCodeAnalysisFlags.None — pure .razor without .razor.cs is not scanned; put deliberate edges on code-behind
Folders can lie	Namespace still owns the type
Structural suffixes	…Counters.Pages is still product id Counters

Good / bad examples

Bad	Why	Fix
…Features.Counters type uses WeatherForecastsState	product → product	Share via Components/contracts, or reasoned [CrossSliceReference]
Product page in grab-bag …Pages outside any slice	not removable with the capability	Namespace under …Features.<Id>
Platform type reaches into Counters	platform ↛ product	Invert dependency (product → platform) or rare opt-out on platform type
Mute TWA0009 globally / without reason	hides real coupling	Relocate or scoped opt-out

Good	Why
CounterPage uses ApplicationState	product → platform free
TimeWarpPage in …Components	Outside composition free
Admin.Roles only uses own types + contracts + platform	nested product isolation

Agent checklist

• New capability has a slice id and matching {Root}.Features.{Id} namespace
• Page, state, and actions live in that namespace
• Shell/layout stay outside SliceRoot (or platform only when truly host state)
• Cross-slice data via Components or contracts first
• Any remaining edge has [CrossSliceReference(typeof(T), "reason")]
• No silent coupling or unexplained suppressions

Related skills and pointers

• tw-feature-placement — filename grammar and layer membership once you know which slice a file belongs to (<name>[-<function>]-<layer>.cs, TWA0015/TWA0016, membership guard)
• tw-web-api-contracts — contract placement; contracts assemblies are free under TWA0009; still use plural …Features.* aligned with SPA product slices
• tw-blazor-layout — empty layout + shell; chrome outside SliceRoot
• tw-blazor-css-strategy — shell/component styling only
• tw-agent-context-regions — Purpose/Design on new files (TWA0004)
• AGENTS.md — TWA diagnostic table (row TWA0009)
• how-to-remove-demo-features.md — delete Counter/EventStream demo slices
• Analyzer (source of truth): source/analyzers/timewarp-architecture-convention-analyzers/slice-isolation-analyzer.cs
• Opt-out attribute: source/foundation/foundation-contracts/base/cross-slice-reference-attribute.cs