GUIDE — Java + Spring under the Discipline, v0.1 (overlay)

§0 additions — baseline

• 04Boot BOM pinned; starters are audited dependencies, not magic: every starter admitted to the build is listed with the auto-configurations it activates (one-time inventory, then diffed). spring-boot-properties-migrator class tooling at upgrades.
• ArchUnit ring rule (the overlay's load-bearing check): ..cells.. may not depend on org.springframework.. — committed as a test, failing red the day someone "just adds @Component".

§1' — cells

05Inherited, plus: no Spring types in cells, period. No stereotypes (@Component/@Service), no @Autowired, no ApplicationContext awareness, no Spring events, no @Value. A cell is constructed by new, in a @Bean method, with everything it needs — which is precisely why it tests in microseconds without a context (§7').

§2' — seams

06Inherited, plus: no Spring types in seam signatures — no ResponseEntity, no Spring Data Page/Pageable, no MultipartFile. Where pagination or streaming is part of the domain contract, the seams module defines its own small records (Slice, PageRequest); boundary adapters translate. A seam that leaks a framework type has annexed the cell into the second language.

§3' — registry and flags

07The trunk's hand-written registry is idiomatic Spring, written the way Spring's own documentation recommends for libraries:

@Configuration(proxyBeanMethods = false)
public class SolverConfig {

    @Bean
    @ConditionalOnProperty(name = "app.solver", havingValue = "sat")
    DepSolver satDepSolver(DepProvider p, Clock clock) {     // R-001: the flag, at the seam
        return new SatDepSolver(p, clock);
    }

    @Bean
    @ConditionalOnMissingBean(DepSolver.class)
    DepSolver naiveDepSolver(DepProvider p) {
        return new NaiveDepSolver(p);
    }
}

• 09Explicit @Bean methods are the registry; component scanning is confined to boundary packages and never reaches cells — wiring stays readable as code, not discoverable as folklore. proxyBeanMethods = false keeps the configuration class itself proxy-free.
• @ConditionalOnProperty is the literal R-001 binding — the flag is read by the container, at the seam, once, with provenance supplied by Spring's property-source ordering (cli > env > file > default), which maps one-to-one onto the Discipline's provenance chain.
• Runtime tier: @ConfigurationProperties records with constructor binding, validated at startup — the config object the trunk's §3 demanded, container-built. No @Value scatter; no Environment lookups outside the boundary.
• Constructor injection only. Field injection is banned (it is reflection-through-the-back-door and makes the framework-free test impossible); single-constructor classes need no annotation at all. A circular dependency is a design failure to fix, not a @Lazy/setter workaround to apply.

§4' — errors and proxies

10Inherited (sealed results at seams), plus the overlay's two honesty paragraphs:

• 11Exception translation is boundary work: Spring's unchecked hierarchies (DataAccessException and kin) are translated into seam error types in adapters; framework exceptions never cross inward.
• Proxy honesty: @Transactional, @Cacheable, @Async, @Retryable are dynamic proxies — self-invocation silently skips them, final methods defeat them, and they constitute hidden control flow (R-021) if sprinkled into domain logic. They are legal only on boundary/use-case orchestration classes; transaction boundaries live where use-cases are composed, never inside cells — which is where the DDD mainstream puts them anyway. A cell that needs "a transaction" actually needs a unit-of-work capability on its seam.

§7' — replacement and tests

12Inherited, plus the test pyramid binding: cell tests are plain JUnit — no context, no @SpringBootTest, no Mockito (trunk rule), constructor + injected fakes, microseconds. Boundary slices use @WebMvcTest/@DataJpaTest-class slices; full @SpringBootTest contexts are few and live at the top — each one is counted, because context startup is the test suite's wish-ratio. Testcontainers (MIT) for real-infrastructure boundary tests. A cell test that needs the container running is a misplaced boundary test — move it, don't speed it up.

§8' — additional risk rows

14Overlay note. Everything this overlay forbids has a sanctioned home one ring out; the discipline is placement, not abstinence. The framework-free-core test (cells compile without Spring) is the overlay's single most valuable artifact — cheap, binary, and brutally honest.