ADR-0074: Frontend module boundaries are enforced with eslint-plugin-boundaries

• Status: accepted
• Date: 2026-09-13
• Deciders: Mahdi Amirabdollahi
• Depends on: ADR-0069, ADR-0070

Context

The frontend has no import restrictions. There are eight feature-to-feature imports today; clusters/ and topology/ import each other. The shell imports feature internals, and the API and stream modules import app-level helpers. Feature-first folders (ADR-0069) and slots (ADR-0070) only stay meaningful if something fails when a feature reaches into another feature or the kernel reaches into a feature.

Decision

web/eslint.config.js uses eslint-plugin-boundaries (7.2.0, boundaries/dependencies, default: "disallow") over these elements:

• kernel = src/kernel/**
• ui = src/ui/**
• feature = src/features/*, capturing the id
• app = src/app/**, the composition root
• test = src/test/**

Policies:

• ui imports nothing app-specific except the generated DTO types in kernel/api/schema.d.ts.
• kernel imports ui.
• A feature imports kernel, ui and its own files.
• A feature may import another feature only through that feature's index.ts, and only for the edges listed in the change design:
  • rr → queues
  • sql → messages, queues
  • brokerconfig → messages
  • audit → security, apitokens → security
  • any feature → clusters
• app imports everything.
• Tests follow the rules of the element they test, and may also use the shared harness in test/.

The rule starts at warn while the tree is being moved and becomes error once every folder lives in its element. npm run lint in CI then fails on a violation.

Consequences

• Cross-feature needs become explicit: either a slot (ADR-0070) or a named public export on an allowed edge.
• The allowed feature edges are listed twice: in package-info.java (backend) and in the eslint policy (frontend). A new edge is added to both deliberately.
• Lint gets somewhat slower, since the plugin resolves imports.

Alternatives considered

• no-restricted-imports patterns. Cannot express "a feature may import itself but not its siblings" without one pattern per feature.
• eslint-plugin-import no-restricted-paths. Workable, but zones must be listed pairwise and there are no captured element ids.
• TypeScript project references per feature. Compiler-enforced, but multiplies tsconfig files and slows builds for a single SPA.
• Nx or another monorepo tool. A build system adopted for one lint rule.