TypeScript, in layers, with a strict linter

The client was one main.js, one preload.js, three files in lib/ and one renderer
script. It is now a typed application whose imports point inward: domain (models,
ports, errors) knows nothing about Electron, Node or Python; application orchestrates
it through those ports; infrastructure holds the adapters — the Python CLI, HTTP, the
filesystem, Electron itself — and main, preload and renderer sit on top as hosts.

STRUCTURE.md is the map, and the deliverable as much as the code is: every layer, every
pattern in use (ports and adapters, repository vs gateway, service, DTO and mapper,
composition root, controller and router, single flight, observer streams, state store
with unidirectional flow, passive view, coded error hierarchy, frozen constant tables,
untrusted-data readers) and the naming rules — files, classes, and a verb vocabulary
for methods where find/require/read/list/apply/render/handle each state a contract.

Two properties fell out of the move, and they are why it was worth doing:

  - The catalog can be driven with no window and no Electron at all. The smoke test
    assembles the same services against the same ports in a plain Node process; it used
    to be a script that reimplemented the bridge.
  - The window never receives a filesystem path. A title crosses the bridge without
    one, and launching is asked for by name, resolved in the main process from the
    store's own state. Verified with a fake launcher: an unknown name answers false, a
    native title resolves to its menu entry, a hosted one to its catalog URL.

Types are mandatory, including where inference would manage: explicit return,
parameter and property types, strict plus noUncheckedIndexedAccess,
exactOptionalPropertyTypes, noImplicitOverride and noPropertyAccessFromIndexSignature,
typescript-eslint strictTypeChecked and stylisticTypeChecked, exhaustive switches, no
any, no non-null assertions, and no casts on foreign data — engine stdout and the
registry go through readers that turn unknown into typed values. naming-convention
enforces the patterns rather than trusting them.

Two rule conflicts had to be decided rather than papered over. typedef and
no-inferrable-types disagree about `fallback: string = ''`: the annotation wins, since a
signature states its types. erasableSyntaxOnly is off, because it forbids constructor
parameter properties, which are how dependencies are declared here.

The preload and the renderer are bundled by esbuild into one file each: a sandboxed
preload may not require its own modules, and a module script over file:// is blocked by
the page's own origin rules. tsc compiles the rest. The package ships build/** and
package.json — 111 entries, no sources, no toolchain.

New targets: build, typecheck, lint, lint-fix, and check — typecheck, lint, then both
test suites, cheapest failure first. Every script that runs the app builds first, so a
stale bundle cannot be tested.

Nothing about the window changed: same side menu, same categories, same switcher, same
two languages. make check is clean, both test suites pass with one store and with two,
the packaged 1.3.0 bundle drives the real store, and the window was photographed before
and after — the two are the same picture.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/renderer/views/GateView.ts

@@ -0,0 +1,91 @@
+import type { RegistryStoreDto } from '../../shared/contracts/dto/RegistryStoreDto'
+import { createElement, requireElement, setHidden, setText } from '../dom/Dom'
+import type { MessageBundle } from '../../shared/i18n/MessageBundle'
+
+/** A button on the gate, and what choosing it does. */
+export interface GateAction {
+  readonly label: string
+  readonly perform: (chosen: RegistryStoreDto | null) => void
+}
+
+export interface GateLink {
+  readonly label: string
+  readonly url: string
+}
+
+export interface GatePresentation {
+  readonly title: string
+  readonly body: string
+  readonly action?: GateAction
+  readonly link?: GateLink
+  readonly choices?: readonly RegistryStoreDto[]
+}
+
+/**
+ * The screen shown instead of the grid when there is nothing to drive: no Python, no
+ * store yet, an engine too old, or a registry that cannot be reached.
+ */
+export class GateView {
+  private readonly section = requireElement('gate', HTMLElement)
+  private readonly title = requireElement('gate-title', HTMLElement)
+  private readonly body = requireElement('gate-body', HTMLElement)
+  private readonly choice = requireElement('gate-choice', HTMLElement)
+  private readonly choiceLabel = requireElement('gate-choice-label', HTMLElement)
+  private readonly select = requireElement('gate-select', HTMLSelectElement)
+  private readonly button = requireElement('gate-action', HTMLButtonElement)
+  private readonly link = requireElement('gate-link', HTMLAnchorElement)
+
+  public constructor (private readonly onOpenUrl: (url: string) => void) {}
+
+  public show (presentation: GatePresentation, messages: MessageBundle): void {
+    setHidden(this.section, false)
+    setText(this.title, presentation.title)
+    setText(this.body, presentation.body)
+    this.renderChoices(presentation.choices ?? [], messages)
+    this.renderAction(presentation)
+    this.renderLink(presentation.link ?? null)
+  }
+
+  public hide (): void {
+    setHidden(this.section, true)
+  }
+
+  public get visible (): boolean {
+    return !this.section.hidden
+  }
+
+  /** Only shown when the registry offers more than one store; with a single one there is nothing to decide. */
+  private renderChoices (choices: readonly RegistryStoreDto[], messages: MessageBundle): void {
+    setHidden(this.choice, choices.length < 2)
+    if (choices.length < 2) return
+    setText(this.choiceLabel, messages.setupChoose)
+    this.select.replaceChildren(...choices.map((store: RegistryStoreDto, index: number): HTMLOptionElement => {
+      const option = createElement('option', undefined, store.name)
+      option.value = String(index)
+      return option
+    }))
+  }
+
+  private renderAction (presentation: GatePresentation): void {
+    const action = presentation.action
+    setHidden(this.button, action === undefined)
+    this.button.disabled = false
+    if (action === undefined) return
+    setText(this.button, action.label)
+    this.button.onclick = (): void => {
+      const choices = presentation.choices ?? []
+      const index = Number(this.select.value)
+      action.perform(choices[Number.isFinite(index) ? index : 0] ?? choices[0] ?? null)
+    }
+  }
+
+  private renderLink (link: GateLink | null): void {
+    setHidden(this.link, link === null)
+    if (link === null) return
+    setText(this.link, link.label)
+    this.link.onclick = (event: MouseEvent): void => {
+      event.preventDefault()
+      this.onOpenUrl(link.url)
+    }
+  }
+}