feat: add an optional effect map to createStore (RD-05)

createStore now takes a third, optional StoreEffects map. Each key is a
Model tag. The store runs that tag's handler after update() returns, and
only when the store enters the tag: the previous tag differs from the new
tag, and the message is not Seed (the mount/restore message in every
machine that has one).

This closes the gap where a component had to call dispatch(msg) and then
a private runIfSubmitting() by hand, or state got silently stuck. No call
site changes here. RD-06 and RD-08 migrate the 5 components that
duplicate that pattern today.

The effect map is a conditional type, not a generic constraint, so a
tagless Model (store.spec.ts's plain number store) still resolves it to
never and needs no third argument. Both tag checks use a typeof/in guard
for the same reason.

Regenerated libs/shared/docs/behaviour-spec.mdx for the 5 new spec titles.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/project/readable-codebase/RD-05-store-effect-map.md

@@ -0,0 +1,182 @@
+# RD-05 — `createStore` gains an effect map
+
+Status: done
+Source: PLAN.md 1a
+
+## Why
+
+`runIfSubmitting` is not shared. It is a `private async` method copy-pasted into 5 components
+under 2 names, and it must be called by hand immediately after `dispatch`:
+
+```ts
+this.dispatch({ tag: 'Submit' }); // the reducer decides
+this.runIfSubmitting(); // then re-read state() and re-check the tag it hoped for
+```
+
+**Forgetting the second line fails silently.** This ticket makes that impossible by moving the
+effect into the one sanctioned wiring idiom, so entering a state runs its effect by
+construction.
+
+This ticket is **behaviour-neutral**: it changes no call site. RD-06 and RD-08 migrate them.
+Landing the mechanism alone keeps the risk isolated to one reviewable commit.
+
+## Read first
+
+- `libs/shared/src/application/store.ts` — all 33 lines. The comment at lines 27-30 is the
+  specification for the invocation order below.
+- `libs/shared/src/application/store.spec.ts` — both existing tests. **Neither may be
+  deleted or weakened.**
+- `PLAN.md` 1a, including the two rejected alternatives.
+- `libs/shared/src/application/submit.ts` — `runResult`, `runSubmit`, `SUBMIT_FAILED`.
+
+## Decisions (pre-made, don't relitigate)
+
+1. **The API.** In `libs/shared/src/application/store.ts`:
+
+   ```ts
+   export type StoreEffects<Model, Msg> = Model extends { tag: string }
+     ? {
+         [K in Model['tag']]?: (
+           state: Extract<Model, { tag: K }>,
+           store: Store<Model, Msg>,
+         ) => unknown;
+       }
+     : never;
+
+   export function createStore<Model, Msg>(
+     init: Model,
+     update: (model: Model, msg: Msg) => Model,
+     effects?: StoreEffects<Model, Msg>,
+   ): Store<Model, Msg>;
+   ```
+
+2. **A conditional type, NOT a `Model extends { tag: string }` constraint.** This is not
+   stylistic. `store.spec.ts:8` calls `createStore(0, (n: number, m: number) => n + m)`, where
+   `Model = number` and has no `tag`. A constraint breaks that existing spec. With the
+   conditional, `Model = number` resolves `StoreEffects` to `never`, so passing effects there
+   is a compile error while omitting them stays legal.
+
+3. **Keys are `Model['tag']`**, so a renamed or misspelled state tag is a compile error. This
+   buys the typo half of exhaustiveness. The completeness half (a full Elm `[state, Cmd]`) is
+   knowingly not bought — see PLAN.md 1a for why.
+
+4. **The narrowed state is argument one.** This is what deletes the
+   `const s = this.state(); if (s.tag !== 'Submitting') return;` preamble at all 8 call sites
+   in RD-06/RD-08. The body cannot run in the wrong state, so it cannot re-guess it.
+
+5. **The store is argument two.** The effect needs `dispatch`, but `createStore(...)` runs in
+   a field initializer before `this.store` is assigned. Build the store object, then close
+   over it, so the effect is independent of field-declaration order.
+
+6. **The trigger rule.** Run `effects[next.tag]` when **both** hold:
+   - `prev.tag !== next.tag` — the store _entered_ the tag. A `Submit` that fails validation
+     is `Editing → Editing`: no fire. A second `Submit` while `Submitting` is a reducer
+     no-op: no fire, so **double-submit protection falls out of the rule**. `Retry` is
+     `Failed → Submitting`: fires, so `onRetry` needs no special case anywhere.
+   - **the msg tag is not `Seed`.** Without this, the five components that mount a
+     `Submitting` state in Storybook via `Seed` fire real network calls (see Risks), and
+     `draftSync.onResume` re-submits a resumed draft. Document it on `StoreEffects` as the
+     convention it already is: `Seed` is the mount/restore message in all 7 machines that
+     have one.
+
+7. **Invocation order.** Capture `prev` and `next` inside the `model.update(...)` callback
+   into locals, and invoke the effect **after** `update` returns. Do **not** read `model()`
+   inside `dispatch`, and do **not** invoke the effect inside the updater (a signal write
+   nested in an updater). `store.ts:27-30` explains why: a tracked read there makes an
+   effect depend on its own write and livelocks the main thread. It already crashed the
+   upload wizards once.
+
+8. **The tag check must be safe on a non-object `Msg`.** Same reason as decision 2 —
+   `store.spec.ts:8` dispatches plain numbers. Guard with
+   `typeof msg === 'object' && msg !== null && 'tag' in msg`, never a bare `msg.tag`. The
+   same applies to reading `prev.tag`/`next.tag` when `Model` is not an object.
+
+9. **`dispatch` stays `void`-returning.** The effect's promise is floated, exactly as
+   `this.runIfSubmitting();` is floated today. Every effect body ends in a `Result` from
+   `runSubmit`/`runResult`, so it cannot throw — state that as the effect contract in the doc
+   comment rather than adding a try/catch.
+
+10. **No call site changes in this ticket.** Do not migrate any component. Do not touch the
+    5 components or any `*.machine.ts`.
+
+## Files
+
+- `libs/shared/src/application/store.ts` — the type, the third parameter, the trigger rule,
+  and a doc comment covering the effect contract and the `Seed` convention.
+- `libs/shared/src/application/store.spec.ts` — 5 new cases, both existing cases untouched.
+
+## Steps
+
+1. Add `StoreEffects<Model, Msg>` per decision 1.
+2. Add the optional third parameter and implement the trigger rule per decisions 6-8.
+3. Extend the doc comment: what the effect slot is for, the "never throws, returns a
+   `Result`" contract, and why `Seed` is exempt.
+4. Add the 5 spec cases from Acceptance below.
+5. Run `npm run gen:behaviour-spec` — **new `it()` titles mean the drift check fails without
+   it** (see Risks).
+6. Update this ticket's `Status:` to `done` and the README's RD-05 row to `done`.
+7. Commit all of it together.
+
+## Acceptance criteria
+
+Five new plain-function spec cases, no TestBed:
+
+```
+- fires the effect when the store enters the tag
+- does not fire when the tag is unchanged
+- does not fire for a Seed message
+- a dispatch from inside the effect lands
+- the narrowed state is passed to the effect
+```
+
+Both existing cases still present and passing — in particular
+`dispatch from inside an effect does not self-loop`, which is the regression guard for
+decision 7.
+
+```bash
+npm test        # exits 0
+npm run ci      # exits 0
+```
+
+Type-level proof that decision 2 holds, i.e. the old call shape still compiles:
+
+```bash
+npm run typecheck   # exits 0 — store.spec.ts:8's createStore(0, ...) must still type-check
+```
+
+## Verification
+
+`npm run ci`. This ticket touches no story, no `.mdx`, and no component, so `--full` is not
+required.
+
+## Out of scope
+
+- Migrating any call site. RD-06 (the 2 single-step forms, which is also a bug fix) and RD-08
+  (the 3 wizards).
+- Adding a `Primary` message to any machine. That is RD-07.
+- The full Elm `reduce -> [state, Cmd]` refactor. Rejected in PLAN.md 1a, with reasons;
+  recorded there as the documented upgrade path if effects ever need asserting inside a domain
+  spec.
+- `upload.machine.ts`'s `type:` discriminant. That is optional RD-35.
+
+## Risks
+
+- **The Storybook trap.** All 5 components mount their `Submitting`/`Indienen` state via
+  `Seed` in stories that use a real `provideHttpClient()` with **no request mocking**
+  (`besluit-form.stories.ts:33`, `herregistratie-wizard.stories.ts:70`,
+  `intake-wizard.stories.ts:38`, `change-request-form.stories.ts:34`,
+  `registratie-wizard.stories.ts:88`). The `Seed` exemption is what stops them firing real
+  calls and reddening `storybook-a11y`. Nothing migrates in this ticket, so the trap does not
+  fire yet — but the exemption must be implemented and documented **here**, because RD-06 is
+  where it would otherwise bite.
+- **Two dispatch sites live inside Angular `effect()`s** — `intake-wizard.component.ts:363`
+  (`SetPolicy`) and `registratie-wizard.component.ts` (`PrefillAdres`). Both land on an
+  unchanged tag, so nothing fires, and both are already `untracked`. **Never key an effect on
+  an editing tag** — that is the livelock.
+- **`behaviour-spec.mdx` drift.** `scripts/ci-local.sh` regenerates
+  `libs/shared/docs/behaviour-spec.mdx` from a path-sorted walk of spec titles and fails on
+  drift. New `it()` titles must be accompanied by `npm run gen:behaviour-spec` in the same
+  commit.
+- **`snippets.generated.ts` drift.** Verified: `store.ts` carries **no** `// #region showcase:`
+  marker, so this ticket cannot cause snippet drift. (`remote-data.ts:30` has
+  `showcase:fold`, which RD-11 and RD-17 must respect — not this ticket.)

docs/project/readable-codebase/README.md

@@ -99,7 +99,7 @@ two. Note that RD-15 exists because 22 abandoned agent worktrees are still on di
 | RD-02 | `max-lines` rule + `reportUnusedDisableDirectives` + 7 disables              | 01         |           | done   |
 | RD-03 | `overzicht` context: page + 2 nav sections, boundary edge, admin-links token | 02         | yes       | done   |
 | RD-04 | Story titles to `Domein/<Context>/<Name>`; add the missing stories           | 03         | yes       | todo   |
-| RD-05 | `createStore` gains the effect map + specs                                   | 02         |           | todo   |
+| RD-05 | `createStore` gains the effect map + specs                                   | 02         |           | done   |
 | RD-06 | **Bug fix:** 2 single-step forms to the effect map + retry affordance        | 05         | yes       | todo   |
 | RD-07 | Add `Primary` to the 3 wizard machines + specs                               | 05         |           | todo   |
 | RD-08 | Migrate the 3 wizards to the effect map + `Primary`                          | 07         | yes       | todo   |

libs/shared/docs/behaviour-spec.mdx

@@ -20,7 +20,7 @@ tested where._
 
 Every bullet below is a real test name from the suite — an `it()` title (frontend) or a test
 method name (backend), read as a sentence. Nothing here is hand-written prose: this page
-**is** the suite, reshaped for a business reader. 505 frontend behaviours across
+**is** the suite, reshaped for a business reader. 510 frontend behaviours across
 9 contexts; 261 backend behaviours across 42 test
 classes.
 
@@ -752,6 +752,11 @@ classes.
 
 - applies the pure update on dispatch
 - dispatch from inside an effect does not self-loop
+- fires the effect when the store enters the tag
+- does not fire when the tag is unchanged
+- does not fire for a Seed message
+- a dispatch from inside the effect lands
+- the narrowed state is passed to the effect
 
 #### currentRole (dev mechanism)
 

libs/shared/src/application/store.spec.ts

@@ -29,4 +29,75 @@ describe('createStore', () => {
     expect(runs).toBe(1); // effect ran once; its own dispatch did not retrigger it
     expect(store.model()).toBe(1);
   });
+
+  type ToggleModel = { tag: 'Off' } | { tag: 'On' };
+  type ToggleMsg = { tag: 'Seed' } | { tag: 'Flip' } | { tag: 'Stay' };
+
+  function reduceToggle(model: ToggleModel, msg: ToggleMsg): ToggleModel {
+    switch (msg.tag) {
+      case 'Flip':
+        return model.tag === 'Off' ? { tag: 'On' } : { tag: 'Off' };
+      case 'Seed':
+        return { tag: 'On' }; // mounts straight into 'On', e.g. restoring a draft
+      case 'Stay':
+        return model;
+    }
+  }
+
+  it('fires the effect when the store enters the tag', () => {
+    let fired = false;
+    const store = createStore<ToggleModel, ToggleMsg>({ tag: 'Off' }, reduceToggle, {
+      On: () => (fired = true),
+    });
+
+    store.dispatch({ tag: 'Flip' });
+
+    expect(fired).toBe(true);
+  });
+
+  it('does not fire when the tag is unchanged', () => {
+    let fired = false;
+    const store = createStore<ToggleModel, ToggleMsg>({ tag: 'Off' }, reduceToggle, {
+      Off: () => (fired = true),
+    });
+
+    store.dispatch({ tag: 'Stay' }); // Off -> Off, no tag change
+
+    expect(fired).toBe(false);
+  });
+
+  it('does not fire for a Seed message', () => {
+    let fired = false;
+    // Off -> On is a real tag change, but Seed is the mount/restore message
+    // (e.g. a Storybook story or a resumed draft) and must stay exempt.
+    const store = createStore<ToggleModel, ToggleMsg>({ tag: 'Off' }, reduceToggle, {
+      On: () => (fired = true),
+    });
+
+    store.dispatch({ tag: 'Seed' }); // Off -> On
+
+    expect(store.model()).toEqual({ tag: 'On' });
+    expect(fired).toBe(false);
+  });
+
+  it('a dispatch from inside the effect lands', () => {
+    const store = createStore<ToggleModel, ToggleMsg>({ tag: 'Off' }, reduceToggle, {
+      On: (_s, s) => s.dispatch({ tag: 'Flip' }), // On -> Off, from inside the effect
+    });
+
+    store.dispatch({ tag: 'Flip' }); // Off -> On, fires the effect above
+
+    expect(store.model()).toEqual({ tag: 'Off' });
+  });
+
+  it('the narrowed state is passed to the effect', () => {
+    let seen: ToggleModel | undefined;
+    const store = createStore<ToggleModel, ToggleMsg>({ tag: 'Off' }, reduceToggle, {
+      On: (state) => (seen = state),
+    });
+
+    store.dispatch({ tag: 'Flip' });
+
+    expect(seen).toEqual({ tag: 'On' });
+  });
 });

libs/shared/src/application/store.ts

@@ -17,17 +17,62 @@ export interface Store<Model, Msg> {
   dispatch(msg: Msg): void;
 }
 
+/**
+ * The effect map: one optional handler per state tag, run when the store
+ * enters that tag (see the trigger rule on `createStore` below). Resolves to
+ * `never` for a tagless `Model` (e.g. `Model = number` in `store.spec.ts`), so
+ * a plain-value store still compiles without ever supplying effects.
+ *
+ * An effect body must never throw: end it in a `Result` from
+ * `runSubmit`/`runResult` (`submit.ts`) and let the failure travel as a
+ * dispatched message, not an exception. `dispatch` floats the effect's
+ * promise, exactly as the `runIfSubmitting()` call it replaces did.
+ */
+export type StoreEffects<Model, Msg> = Model extends { tag: string }
+  ? {
+      [K in Model['tag']]?: (
+        state: Extract<Model, { tag: K }>,
+        store: Store<Model, Msg>,
+      ) => unknown;
+    }
+  : never;
+
+function hasTag(value: unknown): value is { tag: unknown } {
+  return typeof value === 'object' && value !== null && 'tag' in value;
+}
+
 export function createStore<Model, Msg>(
   init: Model,
   update: (model: Model, msg: Msg) => Model,
+  effects?: StoreEffects<Model, Msg>,
 ): Store<Model, Msg> {
   const model = signal(init);
-  return {
+  const store: Store<Model, Msg> = {
     model: model.asReadonly(),
+    dispatch: (msg) => {
+      let prev!: Model;
+      let next!: Model;
       // Use `.update` (raw current value, no tracked read) not `set(update(model(), …))`:
       // dispatch is a command and must never subscribe its caller to `model`. Reading
       // `model()` here inside an effect that also dispatches makes the effect depend on
       // its own write and livelock the main thread (crashed the upload wizards).
-    dispatch: (msg) => model.update((m) => update(m, msg)),
+      model.update((m) => {
+        prev = m;
+        next = update(m, msg);
+        return next;
+      });
+
+      // Fire the entered tag's effect, but only when the store actually entered it
+      // (prev.tag !== next.tag) and the message is not `Seed` — the mount/restore
+      // message in every machine that has one. Without the `Seed` exemption, a
+      // component that mounts straight into `Submitting` (Storybook, a resumed
+      // draft) would fire the effect on load, not on user action.
+      if (!hasTag(next) || !hasTag(prev) || prev.tag === next.tag) return;
+      if (hasTag(msg) && msg.tag === 'Seed') return;
+      const handler = (effects as Record<string, unknown> | undefined)?.[String(next.tag)] as
+        ((state: Model, store: Store<Model, Msg>) => unknown) | undefined;
+      handler?.(next, store);
+    },
   };
+  return store;
 }