CLAUDE: reducers/

Purpose

• Define how Redux state changes in response to actions for the Channels webapp.
• Split between state.entities.* (server data via mattermost-redux) and state.views.* (webapp UI + persisted state).

Structure

• Root reducer composition lives in reducers/index.ts.
• Domain reducers belong under reducers/views/* for UI state or under packages/mattermost-redux for server entities.
• Keep files focused: one reducer per domain with clear initial state exports and typed actions.

Conventions

• Treat state as immutable – use spread, combineReducers, or helper functions rather than mutating.
• Persistable slices must define their keys in store/index.ts persistence config.
• Document any side-effects (e.g., clearing caches when team changes) with inline comments.

Testing & Validation

• Each reducer should have a companion *.test.ts covering happy paths, reset cases, and regression bugs.
• When updating state shape, update TypeScript definitions under channels/src/types/store/.
• Keep reducers serialization-safe; avoid storing functions, class instances, or DOM references.

References

• reducers/views/channel_sidebar.ts – example of complex UI reducer.
• reducers/index.ts – wiring pattern for new reducers.
• webapp/STYLE_GUIDE.md → Organizing Redux State, Standards Needing Refinement → Handler Placement.