timewarpengineering/timewarp-architecture/tw-slice-isolation

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

Terms

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

SliceRoot

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

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

Tiers (dependency rules)

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

Living anchors (timewarp-architecture template):

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).

1. Namespace — {RootNamespace}.Features.{SliceId} (plural segments; nested with .).

Folders rehome freely; namespaces are not renamed with folder moves.

1. Colocate page, state, actions, and slice-private components in that namespace (pages are

not shared infrastructure — no grab-bag …Pages for product UI).

1. Contracts — same plural slice path under web/features/<slice>/ with -contracts.cs

suffix (tw-web-api-contracts skill). Other assembly → free across SPA slices.

1. Wire nav / DI from Outside or platform — not from another product slice.
2. Prefer share (Components / contracts) over [CrossSliceReference].
3. 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 design system exercises the counter throw-exception pipeline.")]
partial class DesignSystemPage;

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:

• Design system → Counters: web-spa/features/design-system/pages/DesignSystemPage.razor.cs
• Auth pipeline deliberate edges: authentication code-behinds with multiple

[CrossSliceReference(...)] when needed

Limits agents must know

Good / bad examples

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

Removing a demo slice

Counter and the analytics client slice ship in every generated app. They are teaching material, not template flags — remove them by deleting code.

A slice is an independently removable vertical unit. Identity is the namespace under {RootNamespace}.Features (e.g. …Features.Counters), not the folder path. The compiler is the checklist: delete the slice folder, then fix every compile error until dev build is 0/0.

Deleting a SPA demo touches, at minimum:

1. The slice folder (web-spa/features/counter/, web-spa/features/analytics/).
2. Nothing in components/NavMenu.razor: the menu renders the generated page registry, so a

deleted page leaves the menu with it.

1. global-usings.cs / _Imports.razor — its namespace usings.
2. Tests under tests/container-apps/web/web-spa-integration-tests/ plus shared pipeline

tests that exercise its state (e.g. CloneStateBehavior uses CounterState).

1. Cross-slice opt-outs that targeted it — e.g. Design System's

[CrossSliceReference(typeof(CounterState), …)].

SPA-only demos have no EF mapping. If you remove a mapped entity (one that participates in PostgresDbContext / IEntityTypeConfiguration), delete the domain type, configuration, and DbSet, then add an EF migration that drops the unused tables. Do not hand-edit only the live database — AppHost AddEFMigrations applies committed migrations. See tw-aggregate-pattern (schema evolution).

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)
• Diagnostic catalog: AnalyzerReleases.Unshipped.md in the convention-analyzers project

(TWA0009 row). This skill is the placement rule.

• 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