Migration — Assessment Phase

Before writing any code, inventory the current state management and decide what moves to Redux.

1. Identify All Stores

Use repository searches such as find src/ -name "*.store.svelte.ts" -o -name "*.store.ts", grep -rn "writable\|readable\|derived" src/ --include="*.ts" --include="*.svelte", and grep -rn '\$state\|\$derived' src/ --include="*.store.svelte.ts". Record results as structured assessment evidence so downstream skills can consume them.

2. Classify Each Store

For each store file, determine:

1. What state does it hold? List all writable(), $state, or reactive fields
2. What derived values exist? List all derived(), $derived, getters
3. What side effects exist? localStorage, fetch, event listeners, timers, IPC
4. Who consumes it? Which components import and use this store?
5. Is it shared or local? Used by multiple components, or just one?

Decision Framework

Apply ../../../core/core-policy/SKILL.md → Setup — core rules to each field/effect, not just the file's syntax. Redux owns shared/domain state, including persisted or externally synchronized business state. Purely visual, ephemeral, instance-local fields stay local. A timer or await alone does not make UI state domain-owned; DOM-local focus, scroll, measurement, and widget lifecycle stay in the component. Record the owner, consumers, persistence needs, and cancellation lifetime before choosing a migration leaf. If that evidence is unclear, resolve the ownership question rather than defaulting every local field/effect to Redux.

Output of the Assessment

Produce a per-store table so you can order the migration (simplest / most isolated slice first — see ../SKILL.md for the recommended order and ../setup/SKILL.md for the bootstrap that must be done before the first slice):

Store file	State fields	Derived	Side effects	Consumers	Verdict
cart.store.svelte.ts	items, total	count	localStorage sync	Cart, Header, Checkout	Redux
tooltip.store.svelte.ts	open	—	—	Tooltip only	Local

Downstream skills consume this table:

• ../writable-stores/SKILL.md — for shared/domain writable / $state fields
• ../derived-stores/SKILL.md — for shared/domain derived / $derived values
• ../side-effects/SKILL.md → Effect ownership boundary — for domain effects, not DOM-local lifecycle
• ../component-migration/SKILL.md — for the migrated consumers column
• ../cleanup/SKILL.md — to confirm deletion order only after a replacement owner is verified

Examples in This Skill

• Added: assessment record type; shared writable verdict; component-local verdict; derived selector candidate; side-effect saga candidate; bad local-UI overmigration verdict.
• Retained: none (this assessment skill previously had no JS/TS examples).

Assessment Examples

1. Capture inventory as structured evidence

type StorePrimitive = "writable" | "readable" | "derived" | "$state" | "$derived" | "$effect";
type MigrationVerdict = "redux" | "local";

type StoreInventoryRecord = {
  file: string;
  primitives: StorePrimitive[];
  stateFields: string[];
  derivedValues: string[];
  sideEffects: string[];
  consumers: string[];
  verdict: MigrationVerdict;
  nextSkills: string[];
};

const cartInventory: StoreInventoryRecord = {
  file: "src/lib/stores/cart.store.svelte.ts",
  primitives: ["writable", "derived", "$effect"],
  stateFields: ["items"],
  derivedValues: ["total", "itemCount"],
  sideEffects: ["localStorage sync"],
  consumers: ["Cart.svelte", "Header.svelte", "Checkout.svelte"],
  verdict: "redux",
  nextSkills: ["writable-stores", "derived-stores", "side-effects", "component-migration"],
};

Classify shared writable state as Redux-owned

// Evidence for a verdict made using core policy, not a replacement classifier.
export const cartVerdict = {
  consumers: ["Cart.svelte", "Header.svelte"],
  persists: true,
  businessLogic: true,
  verdict: "redux",
  reason: "Shared checkout domain state persisted across navigation",
};

3. Keep ephemeral component state local

type LocalStateFinding = {
  file: string;
  field: string;
  reason: "single-component" | "ephemeral-ui";
  replacement: "component-local-state";
};

export const tooltipFinding: LocalStateFinding = {
  file: "src/lib/stores/tooltip.store.svelte.ts",
  field: "open",
  reason: "ephemeral-ui",
  replacement: "component-local-state",
};

4. Route derived values to selector migration

type DerivedFinding = {
  source: string;
  dependencies: string[];
  targetSelector: string;
  composeWithSelect: boolean;
};

export const cartTotalFinding: DerivedFinding = {
  source: "derived(items, ($items) => sumCart($items))",
  dependencies: ["items"],
  targetSelector: "selectCartTotal",
  composeWithSelect: true,
};

5. Route side effects to saga migration

type SideEffectFinding = {
  sourceFile: string;
  effect: "fetch" | "timer" | "subscription" | "storage" | "ipc";
  triggerAction: string;
  targetSaga: string;
};

export const persistenceFinding: SideEffectFinding = {
  sourceFile: "src/lib/stores/cart.store.svelte.ts",
  effect: "storage",
  triggerAction: "cart/setItems",
  targetSaga: "cartSaga",
};

6. ❌ Bad: migrate single-component UI state to Redux

// ❌ BAD: hover state belongs in the component, not in a Redux slice.
type BadAssessmentRecord = {
  file: string;
  stateFields: string[];
  consumers: string[];
  verdict: "redux" | "local";
};

export const badHoverAssessment: BadAssessmentRecord = {
  file: "src/lib/stores/card-hover.store.svelte.ts",
  stateFields: ["isHovered"],
  consumers: ["ProductCard.svelte"],
  verdict: "redux",
};

Cases Covered

Case	Example
Inventory shape for downstream skills	Capture inventory as structured evidence
Shared/persisted/business state	Classify shared writable state as Redux-owned
Local-only UI state	Keep ephemeral component state local
Derived values	Route derived values to selector migration
Effects/subscriptions/storage	Route side effects to saga migration
Incorrect overmigration	Bad: migrate single-component UI state to Redux