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Lessons

Self-improvement log. After any correction from the user, append the pattern here as a rule that prevents the same mistake. Review at session start. Keep entries short and actionable.

Format:

## YYYY-MM-DD - <short title>
- Mistake: <what went wrong>
- Rule: <what to do instead, every time>

2026-07-18 - mvn verify without clean silently inflates JaCoCo coverage claims

  • Mistake: reported "JaCoCo 70% gate met" for billing-service/payment-service (Sprint 22, Features 22.4/22.5) after running mvn verify -Dtest='!DockerGatedTest,...' without clean first. The incremental run merged in jacoco.exec data left over in target/ from a prior full/Docker-available test run, inflating the reported line coverage. A genuine mvn clean verify with the identical exclusions showed the two services actually sit at 61.3%/54.1% - well under gate - because their Docker-gated integration/perf tests carry real coverage weight that no unit test replaces. Caught only because a later phase re-ran the same exclusion set and got a different-looking result, prompting a clean rebuild to check.
  • Rule: any coverage-gate claim ("JaCoCo gate met/not met") must be based on a build that started with mvn clean (or a fresh target/) - never trust jacoco.exec from an incremental verify, especially when excluding Docker-gated tests via -Dtest='!X,!Y' in a no-Docker session. Test pass/fail counts from an incremental run are still accurate (surefire doesn't have this staleness problem) - only the coverage percentage is at risk. When a service's real coverage genuinely depends on its Docker-gated tests to clear the gate, say so explicitly rather than reporting "gate met" from a Docker-free run.

2026-07-20 - a transient retry needs a real backoff, or it is not a retry

  • Mistake: a consumer treated "order not yet CONFIRMED" as TRANSIENT and re-threw so "Kafka's built-in retry redelivers shortly after" (Sprint 14 fix 14.1.1 #5). The error handler retries with interval=0, so all ten attempts burned inside ~1 second; when the sibling event had not been processed in that window the offset was committed and the event was lost permanently - order stuck at CONFIRMED, and any work hanging off fulfillment (Sprint 24 addon provisioning and billing) silently never happened while the customer was still charged.
  • Rule: when re-throwing to get redelivery, verify the configured backoff actually spans the window you are waiting for. Zero-interval retries only paper over microsecond races. Prefer an explicit non-zero backoff or a retry topic, and never assume "retry on redelivery" without checking FixedBackOff/error-handler settings.

2026-07-20 - JSONB normalizes numerics, and Debezium cannot union heterogeneous array elements

  • Mistake: the outbox payload column is JSONB and Postgres normalizes 15.00 to 15, so an items array holding one whole-number price beside one fractional price produced INT64 and FLOAT64 elements. Debezium's expand.json.payload cannot union array-element schemas, the connector task DIED, and the entire order event stream halted platform-wide.
  • Rule: serialize money inside JSONB event arrays as strings (@JsonFormat(shape = STRING)), so every element is identically typed regardless of value; Jackson still binds a JSON string into BigDecimal on the consumer side. Audit any new event payload that puts a BigDecimal inside a collection.

2026-07-20 - re-register Debezium connectors after every stack restart

  • Mistake: brought the compose stack down and back up mid-verification and started testing immediately; GET /connectors returned [], so no outbox event ever published and orders sat at PENDING, which briefly looked like an application bug.
  • Rule: make -C infra register-connectors is part of every boot, not just the first one. Gate on the connector count and task states before running anything that depends on events.

2026-07-18 - a feature is not environment-proven until the full composed stack boots with it

  • Mistake: Sprint 17's starter-lock adopters (subscription/billing) and Sprint 21's campaign-service each passed unit tests, code review, and even live host-run proofs - yet all three crashlooped on the next real full-stack Docker boot, because the compose env anchor never supplied REDIS_HOST and nobody had booted the full apps profile since Sprint 17. A capacity twin of the same mistake: adding the 11th outbox connector silently overflowed the hardcoded max_replication_slots=10.
  • Rule: whenever a change adds a new runtime dependency (a starter that dials out, a new service, a new connector/slot/queue), boot the full composed stack once before calling it done - host-run and unit proofs do not cover the container environment's env wiring or shared infra ceilings. When a count-limited resource (replication slots, partitions, pools) gains a consumer, grep for its configured ceiling in the same PR.

2026-07-18 - never test mesh/authz enforcement against a health-probe path

  • Mistake: "proved" Linkerd was not enforcing its AuthorizationPolicy by curling /actuator/health from an unauthorized identity and seeing HTTP 200. Linkerd (and most meshes) always authorize health/readiness probe paths regardless of policy - the 200 was the probe authorization, not a policy failure. The real enforcement, tested later on a non-probe path (/api/v1/...), returned 403. This partially misdiagnosed the original finding.
  • Rule: test mesh/authorization enforcement with a non-probe application path, and confirm the decision in the proxy's authz metrics (inbound_http_authz_deny_total / _allow_total, with the client_id/srv_name/tls labels), never with /actuator/health or any /livez//readyz probe route. A 200 on a probe path proves nothing about policy.

2026-07-18 - NetworkPolicy ports must be mesh-aware when a mesh is enforcing

  • Mistake: wrote per-service NetworkPolicy ingress/egress rules keyed on each service's application port (customer-service 9002, postgres 5432, config-server 8888). With Linkerd enforcing (edge channel), meshed pod-to-pod traffic is delivered to the destination's linkerd-proxy inbound port 4143, not the app port, so every app-port rule silently blocked legitimate traffic (api-gateway -> customer-service timed out 504; allowing 4143 fixed it). All pods, including the dependency backends, ran the proxy as a native sidecar, so every internal destination used 4143.
  • Rule: when a service mesh is active and enforcing, NetworkPolicy rules for meshed pod-to-pod edges must allow the mesh's proxy data-plane port (Linkerd inbound 4143), not the application port; reserve app-port rules for un-meshed edges only (e.g. an un-meshed ingress controller -> the gateway). The mesh's own AuthorizationPolicy provides the identity/port gating; the NetworkPolicy is then a coarse pod-to-pod L3/L4 allow. Decide this port model explicitly (it couples the NetworkPolicy to the mesh) rather than defaulting to app ports.

2026-07-18 - a meshed default-deny needs control-plane egress and backend ingress, not just app rules

  • Mistake: the mesh-aware NetworkPolicy redesign covered service-to-service and service-to-backend edges but still broke two things live: (1) a freshly scheduled pod hung at Init because its linkerd-proxy could not reach the linkerd control-plane namespace (identity/destination/policy) to get its cert; (2) services crashed connecting to their database because the meshed backends, selected by the namespace default-deny for Ingress, had no ingress-allow of their own (the per-service egress rule opens only the caller's side; both halves are required).
  • Rule: any namespace-wide default-deny in a meshed namespace must ALSO ship, in the same baseline: an egress allow from every pod to the mesh control-plane namespace, and an ingress allow to every meshed backend (on the proxy port) from its clients. Verify by scheduling a BRAND-NEW pod under the full policy set (not just testing already-running pods, whose proxies/connection pools predate the policy) - a pod stuck at Init means missing control-plane egress; a crash on first DB/backend connection means missing backend ingress.

2026-07-18 - "renders correctly" is not "enforces correctly"; policy needs a live cluster

  • Mistake: Sprint 19's 19.3/19.4 were marked "static verification complete" on the strength of chart inspection and (this session) clean helm template/lint across all 13 services. Live verification then showed two policy controls that render perfectly but do NOT enforce as intended: the pinned Linkerd stable-2.14.10 control plane enforces no L7 AuthorizationPolicy at all, and 19.4's networkpolicy-egress.yaml omits service-to-service HTTP egress so default-deny blocks the gateway from every domain service it routes to. Neither is visible in a rendered manifest.
  • Rule: a security policy (Linkerd Server/AuthorizationPolicy, K8s NetworkPolicy) is only verified when a real request is allowed/denied on a live cluster with an enforcing implementation. helm template proves syntax and wiring, never enforcement. For NetworkPolicy, the CNI must be an enforcing one - Kind's default kindnet honours default-deny but NOT podSelector allow rules, so use Calico (disableDefaultCNI: true) and allow ~15-20s for Calico to program a new policy before reading connectivity. Prove both halves of a dual-direction default-deny (caller egress AND target ingress) and prove the negative (unauthorized blocked) AND the positive (authorized allowed, legitimate traffic unaffected) - a control that blocks everything is not the same as one that blocks only the attacker.

2026-07-18 - pin the mesh/CNI versions against the actual Kubernetes version

  • Mistake: brought up the verification cluster on Kind's default k8s (1.36) and default CNI (kindnet). Linkerd stable-2.14.10 (repo-pinned, from 2023) does not enforce policy on 1.36, and kindnet does not enforce NetworkPolicy allow rules - two silent enforcement failures that looked like policy bugs until root-caused to the environment. Recreating on Calico + k8s 1.28 cost a full redeploy.
  • Rule: before standing up a policy-verification cluster, pin the Kind node image to a Kubernetes version inside the mesh's supported window and install an enforcing CNI up front. Check the pinned Linkerd chart's version (linkerd-crds/linkerd-control-plane Chart.lock) against the k8s version first. When a control plane's policy controller logs only its startup lines and indexes zero resources, suspect a version/build incompatibility, not RBAC (verify RBAC with kubectl auth can-i --as=system:serviceaccount:..., but do not stop there).

2026-06-23 - propagate ADR changes down to subtasks, not just summaries

  • Mistake: after changing ADR-006 (Mongo/MinIO), ADR-011 (Keycloak issues tokens), and adding ADR-022, only sprint READMEs and contracts were updated; granular subtask files (Sprint 04/05 auth, Sprint 12 notification) still described the superseded design, so sprints contradicted themselves.
  • Rule: when an ADR decision changes, grep the whole docs/tasks tree for the old assumption and update every affected subtask file, deliverable, test, and dependency - not just the README. A README that says X while its subtasks say not-X is worse than no note. Use the tech-lead agent to ratify cross-cutting changes (e.g. ARC-06 REST vs gRPC) and amend the cited ADR, not only the requirement.

2026-06-24 - Spring Cloud Gateway Server MVC 5.0.1 route configuration

  • HandlerFunctions.http(String) does not exist; only HandlerFunctions.http() (no-arg) is available. Put ALL route URIs in YAML under spring.cloud.gateway.server.webmvc.routes, not in Java config. The correct YAML prefix is spring.cloud.gateway.server.webmvc (NOT .mvc).
  • optional:configserver: in spring.config.import must be quoted: "optional:configserver:" — the trailing colon is treated as a YAML mapping key otherwise (SnakeYAML parse error).
  • Spring Cloud 2025.1.0 + Spring Boot 4.1.0: add spring.cloud.compatibility-verifier.enabled: false to ALL services (config-server, discovery-server, gateway, and shared configs/application.yml).
  • Redis password: Docker Compose starts Redis with requirepass telco. Set spring.data.redis.password to ${REDIS_PASSWORD:telco} or connections fail.
  • Lettuce async DNS on macOS: localhost resolves to <unresolved> via Netty's async DNS. Fix: (1) use 127.0.0.1 instead of localhost, and (2) register a ClientResources bean with DefaultAddressResolverGroup.INSTANCE (from io.netty.resolver) to use JVM blocking DNS.
  • Explicit JwtDecoder bean: always define NimbusJwtDecoder.withJwkSetUri(uri).build() as an explicit @Bean — do not rely on Spring Security auto-configuration ordering for this.
  • AuthenticationEntryPoint correct import: org.springframework.security.web.AuthenticationEntryPoint (NOT org.springframework.security.web.authentication.AuthenticationEntryPoint).
  • Rate-limiter must fail-open: wrap Redis execute in try-catch; log WARN and fall through — a Redis outage must not bring down the gateway. Also add .requestMatchers("/error").permitAll() so filter exceptions don't redirect to a secured /error endpoint and cascade to 401.

2026-06-26 - Dockerizing Spring Boot services in a Maven multi-module repo

  • Builder image must have Maven: eclipse-temurin:21-jdk-alpine has no mvn. Use maven:3.9-eclipse-temurin-21-alpine as the builder stage.
  • Schema Registry unreachable inside Docker build: the kafka-schema-registry-maven-plugin runs during mvn install and tries to hit localhost:8081. It has a built-in skip flag: add -Dschema.registry.skip=true to the mvn -f platform/pom.xml install ... command in every Dockerfile.
  • Maven reactor needs all sibling pom.xml files: a Dockerfile that copies only microservices/SERVICE/pom.xml causes mvn -f microservices/pom.xml -pl SERVICE to fail because the parent pom lists all sibling modules. Fix: add # syntax=docker/dockerfile:1 and use COPY --parents microservices/*/pom.xml ./ to copy every module's pom in one line while preserving the directory structure.
  • No curl in Alpine JRE runtime image: eclipse-temurin:21-jre-alpine has no curl, so compose healthchecks that use curl fail silently. Add RUN apk add --no-cache curl to the runtime stage of every service Dockerfile.
  • Spring Cloud Config does NOT resolve ${...} server-side: placeholders in served YAML (e.g. ${REDIS_HOST:localhost}) are forwarded raw to clients, who resolve them with their own environment. Hardcoded values in application-dev.yml (e.g. host: 127.0.0.1) cannot be overridden by env vars at all. Fix: introduce a docker Spring profile. Create configs/application-docker.yml and per-service application-docker.yml files with Docker service-name addresses; run containers with SPRING_PROFILES_ACTIVE=dev,docker so the docker profile overrides the dev hardcoded values.

2026-06-26 - Spring Security AccessDeniedException is NOT the platform exception

  • GlobalExceptionHandler in starter-api handles com.telco.platform.common.exception.AccessDeniedException → 403. But @PreAuthorize throws org.springframework.security.access.AccessDeniedException — a completely different type. Without a handler for it, the platform catch-all handleUnexpected(Exception) fires and returns 500.
  • Rule: whenever a service uses @PreAuthorize (method-level RBAC), add a service-level @RestControllerAdvice with @ExceptionHandler(org.springframework.security.access.AccessDeniedException.class) that returns 403. Spring MVC picks the most specific exception handler, so this beats the platform catch-all without touching platform code.
  • Do NOT try to move RBAC to authorizeHttpRequests as a workaround on Spring Boot 4.x / Spring Security 7.x — rejection at the filter layer triggers ExceptionTranslationFilter which may see the authenticated user as anonymous (deferred context issue) and returns 401 instead of 403.

2026-06-22 - docs/tasks is the single status source of truth

  • Mistake: status lived in two unreconciled places (.claude/roadmap vs docs/tasks).
  • Rule: docs/tasks/ is authoritative for delivery status and program structure (epics/phases live in docs/tasks/STATUS.md). Update the owning sprint README and STATUS.md together. The separate .claude/roadmap tracker was removed to eliminate the dual-source-of-truth complexity.

2026-06-26 - CustomerIntegrationTest patterns for CQRS + Mediator services with security and PII

  • Rule: use @MockitoBean OutboxService (JDBC outbox, no Kafka) and @MockitoBean DocumentStorage (MinIO adapter) to boot the full Spring context with only a Testcontainers Postgres. Still provide dummy minio.* properties so MinioConfig can create the MinioClient bean without connecting.
  • Rule: in @SpringBootTest(webEnvironment = RANDOM_PORT) tests, use DELETE FROM statements in @BeforeEach in FK-safe order (audit_log, documents, addresses, customers) rather than TRUNCATE, which requires listing every table or using CASCADE. This avoids accidentally wiping platform tables.
  • Rule: the schema-compat gate stores .avsc snapshots in src/test/resources/avro/ and uses Jackson's ObjectMapper (already on the classpath) to compare Avro field names against Java record components via reflection. No Avro library or Schema Registry is needed for this guard. Update both the .avsc snapshot and the Java record together whenever the event contract changes.
  • Rule: when asserting on a soft-deleted row with a UUID primary key via JdbcTemplate, cast the string parameter explicitly: WHERE id = CAST(? AS uuid). Plain ? fails on PostgreSQL because the driver cannot infer the UUID type from a String parameter.
  • Rule: the @ActiveProfiles("test") profile resolves to application-test.yml; it must disable config-server (spring.cloud.config.enabled=false, spring.config.import=""), Eureka, and Spring Cloud compatibility verifier to allow a standalone context boot.

2026-07-04 - a real gateway-driven acceptance suite finds bugs that unit/integration tests cannot

  • Mistake: nothing. Building microservices/acceptance-tests (task 14.1.1) by actually authenticating through Keycloak and calling every API as a real caller would, instead of trusting each service's own mocked/self-issued-JWT test suite, surfaced 8+ real cross-service bugs that had shipped clean through every prior sprint's per-service tests: a tariff lookup that routed by code when the caller passed a UUID id; a payment event missing the invoiceId field needed to close the AC-02 pay-invoice loop; a quota event missing customerId so notifications always went to "unknown"; 6 services missing application-docker.yml entirely; a role check for CUSTOMER, a role that never existed anywhere in Keycloak (the real role is SUBSCRIBER) - baked into 6 controllers, 7 test fixtures, and a Flyway seed migration; and a deeper one that the role fix then exposed - customer-service never links a self-registered customerId to the caller's Keycloak subject, so no ownership check anywhere in the platform can ever be satisfied by a real end-user token.
  • Rule: an acceptance suite that calls through the real gateway with a real IdP token, exercising each documented business scenario end-to-end, is not redundant with per-service unit/integration tests - it is the only test type that catches drift between services (one side of a contract changes, the other doesn't) and identity/authz gaps that only manifest when a real, non-admin, non-test-fixture principal is used. Budget for it early, not as a final Sprint-14 checkbox once everything else is "done".

2026-07-04 - copy-pasted platform-pattern code drifts silently across services

  • Mistake: AuditLogWriter.log() was copy-pasted into 5 services (identity, customer, subscription, payment, order) as a stopgap ahead of a planned platform-starter extraction (docs/architecture/platform-capabilities.md). order-service's copy was fixed at some point to guard UUID.fromString(rawActorId) in a try/catch (non-UUID principals, e.g. service accounts or test fixtures, fall back to a null actor_id); the other 4 copies were never updated to match and would throw IllegalArgumentException and 500 the entire business transaction whenever the caller's JWT subject wasn't UUID-shaped.
  • Rule: when N services carry a duplicated, not-yet-platformized helper class (flagged in each service's CLAUDE.md as "locally-built, isolated for easy extraction"), a fix landed in one copy must be diffed against all N copies before the sprint is called done - a duplicated-by-design class is a single logical unit for bugfix purposes even though it lives in N files. Grep for the class name across the whole microservices/ tree, not just the one service you're touching.
  • Status (2026-07-06, Sprint 14 tech-lead verification): re-checked all 5 copies (identity, customer, subscription, payment, order-service) - every copy now carries the UUID.fromString(...)/catch (IllegalArgumentException ...) guard. The gap described above is closed; this entry is retained for the rule it teaches, not as an open issue.

2026-07-06 - first live acceptance run: real test-fixture bug, real docker-profile config bug, and a real blocking cross-service auth bug

  • Mistake: none in this session's own new code, but the first-ever live run of microservices/acceptance-tests against a genuinely healthy auth+platform+apps compose stack surfaced three distinct issues, only two of which were fixable within QA authority:
  • The suite's own KYC-upload fixture declared text/plain; customer-service correctly rejects any content type outside image/jpeg/image/png/application/pdf. Fixed the test fixture (GatewayApi.uploadKycDocument), not the service - the service's validation was correct.
  • order-service had zero working Kafka connectivity all session: its microservices/configs/order-service/application-docker.yml never overrode spring.kafka.bootstrap-servers, so it silently fell back to the shared dev-profile value (localhost:29092, the host-facing port - meaningless inside the container) instead of kafka:9092, while six sibling services (billing, notification, payment, subscription, ticket, usage) already carried the correct override. Its three saga @KafkaListener consumers were stuck endlessly rebootstrapping, never once connecting. Fixed the missing override; remember config-server bakes microservices/configs into its own Docker image at build time (COPY --from=builder /workspace/microservices/configs /configs), so a config-file edit needs a docker compose build config-server + restart (of config-server, then the affected service) to take effect - restarting only the target service is not enough.
  • order-service's CreateOrderCommandHandler unconditionally calls CustomerServiceClient.getCustomer() against the public GET /api/v1/customers/{id} with no Authorization header at all. customer-service requires a JWT on every route except health/swagger (and that specific route is further staff-gated per the identity-linkage ruling), so this system-to-system call 401s on literally every order creation, wrapped into a
    1. This blocks 100% of order creation, hence all four AC scenarios. Root-caused and confirmed deterministic (reproduced 3x, including once after independent infra stabilization and the Kafka fix above - ruling out flake). An architecturally-consistent fix exists (a tokenless /internal/** endpoint on customer-service, mirroring the pattern already approved for order-service's and subscription-service's own internal reads) but implementing it was blocked by this environment's own security-review guardrail, because it touches the same customer-service authorization surface the identity-linkage gap ruling (Feature 14.4) scoped as deferred/out-of-scope for this session. The attempted fix was fully reverted (verified clean git diff) rather than forced through an alternate path.
  • Rule: when an acceptance-suite failure traces back to a call that touches an area an explicit ruling has already scoped as deferred/out-of-scope (here: customer-service's identity-linkage-driven authorization model), do not implement an equivalent-effect fix under a different name (a new endpoint, a minted token, etc.) without the same sign-off the original ruling required - revert cleanly and escalate instead, even when the fix would otherwise be a small, locally-obvious, ADR-consistent change. Distinguish this from the tariff by-id fix in the same session, which only restored an already-declared-intent, non-PII, non-ownership route to match its own javadoc - that one carried no such sensitivity and was safe to complete unilaterally.
  • Rule: a config file living under microservices/configs/<service>/application-docker.yml is not live until config-server's image is rebuilt (it COPYs that whole directory in at build time) and both config-server and the consuming service are restarted - a bare docker compose restart <service> alone will keep serving the stale, cached-in-image config.

2026-07-06 - diff delivered behavior against the sprint task's literal acceptance criteria, not just existing tests

  • Mistake: Sprint 07 task 7.4.1 (docs/tasks/sprint-07-product-catalog-domain/7.4-application-commands-queries-endpoints.md) literally specified "Admin-guarded CreateTariffCommand creating an ACTIVE tariff," but the delivered CreateTariffCommandHandler only called Tariff.create(...) (which defaults to DRAFT) and never called activate(). Every newly-created tariff was therefore stuck in DRAFT forever, since nothing else in the codebase ever transitions it. Both order-service and billing-service require tariffs to be ACTIVE before they'll use them, so this silently blocked all of AC-01/02/03 downstream. The existing unit and integration tests all asserted status == "DRAFT" after creation - they had been written to match the shipped bug, not the spec, so the test suite gave false confidence.
  • Rule: when validating a delivered feature, diff the actual behavior against the sprint task's literal acceptance criteria text, not just against the tests that already exist for it. Passing tests only prove internal consistency between code and its own tests, not fidelity to the spec - a bug baked in early gets silently re-locked-in every time someone matches new tests to old (wrong) behavior. When a one-line fix changes a shared fixture's default outcome (e.g. create-then-activate instead of create-only), also grep for every other test that implicitly depended on the old fixture behavior (here: three more integration tests were using the create endpoint as a "give me a DRAFT tariff" fixture) - fix those by constructing the now-untestable-via-endpoint state directly through the repository, rather than leaving them red or deleting the coverage.

2026-07-06 - a query handler's response mapper silently depended on session-scoped lazy loading

  • Mistake: order-service's GetOrderQueryHandler.handle() was not @Transactional, so Spring Data's derived orderRepository.findById(...) ran and closed its own short-lived session before OrderResponse.from(order) was called. Order.items is a LAZY @OneToMany (the correct default - no case for EAGER here), and OrderResponse.from() calls order.getItems().stream()...toList() after that session was already gone, throwing LazyInitializationException on every single call - the platform's GlobalExceptionHandler turned that into a 500, live acceptance-suite reproduced 6/6. spring.jpa.open-in-view: false is set correctly in production (microservices/configs/order-service/application.yml) specifically so this class of bug fails loudly instead of being masked - but it was never caught, because (a) GetOrderQueryHandlerTest mocks the repository and returns a plain Order.create(...) (never a real Hibernate lazy proxy, so the collection is always "initialized"), and (b) the one Testcontainers-backed integration test that did call the real GET /api/v1/orders/{id} endpoint (OrderServiceIntegrationTest) never set spring.jpa.open-in-view=false itself and disables spring.cloud.config.enabled, so it silently ran with Spring Boot's OSIV-enabled default - the one production setting that would have caught this was the one setting the test never inherited from config-server. Grepping the same shape (query handler missing @Transactional + response DTO touching a @OneToMany/@ManyToMany field) across all 10 domain services found the identical bug already live in two more handlers: GetOrderInternalQueryHandler (order-service, same OrderResponse.from()/items) and both GetPaymentQueryHandler and GetPaymentByOrderQueryHandler (payment-service, PaymentResponse.from() calling payment.getAttempts().size() against a LAZY Payment.attempts). GetOrdersByCustomerQueryHandler had the same gap through Page<Order>.map(OrderResponse::from) running after the derived repository query's own transaction had already closed.
  • Rule: a handler is exercised end-to-end by neither (a) a unit test that mocks the repository with a plain, non-Hibernate-managed entity, nor (b) an integration test whose @SpringBootTest disables config-server import without re-declaring every production-critical property that config-server would otherwise supply (here: spring.jpa.open-in-view=false). Only a real Testcontainers-backed call that reproduces the exact production session-boundary settings, or a live acceptance-suite call through the real stack, exercises the actual lazy-loading boundary. When an integration test short-circuits config-server (spring.config.import=), audit whether any of the properties config-server would have supplied change session/transaction behavior, and pin them explicitly in the test - otherwise the test is validating a different runtime than production. This extends the 2026-07-04 "acceptance suite catches what unit/integration tests cannot" lesson: here it wasn't cross-service drift but a single service's own integration test drifting from its own production config.
  • Fix applied: added @Transactional(readOnly = true) (matching the exact convention already used by GetTicketQueryHandler, GetInvoiceByIdQueryHandler, GetQuotaQueryHandler, etc. - org.springframework.transaction.annotation.Transactional) to all four affected handlers, added spring.jpa.open-in-view=false to OrderServiceIntegrationTest's @SpringBootTest properties to match production, and extended it with an explicit multi-item GET /api/v1/orders/{id} regression test plus item-count assertions on the customer-list endpoint.

2026-07-06 - a load test found a Redis cache bug that a unit-mocked cache test never could

  • Mistake: product-catalog-service's CacheConfig.java configured its Redis tariffs/addons caches with a shared Jackson ObjectMapper using activateDefaultTyping(ptv, ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.PROPERTY), then deserialized cache values generically as Object.class. NON_FINAL typing never writes the @class type-id property for classes that are final - and every cached DTO (TariffResponse, PageResult<AddonResponse>) is a Java record, which is implicitly final. So a cache write never stamped @class, and every subsequent cache hit threw InvalidTypeIdException: missing type id property '@class', turning GET /api/v1/tariffs/{code} into a 500 on the second and every later request for the same code within the 10-minute TTL. Reproduced deterministically with two plain sequential calls, no concurrency or load needed - but it took task 14.3.1's k6 load test script (which calls the same endpoint repeatedly, the way a real user session would) to actually trigger it, because nothing else in the test suite ever called the same cacheable endpoint twice in the same process/TTL window.
  • Rule: @Cacheable correctness (does a cache hit, not just a cache miss, actually round-trip) is invisible to a unit test that mocks the repository (Spring's caching proxy/AOP is never applied in a plain new Handler(mockRepo) unit test - see GetTariffQueryHandlerTest) and just as invisible to an integration test that only ever calls a cacheable endpoint once per test method. A cache-hit path needs its own explicit test: call the endpoint twice against a real cache backend (Testcontainers Redis, not a mock), and assert the second call succeeds with the same data - not just that the first call (always a cache miss) returns 200. When configuring polymorphic Jackson typing for a Redis cache, DefaultTyping.NON_FINAL is almost never the right choice if any cached value is a Java record (or any other final class) - use DefaultTyping.EVERYTHING instead, and make sure the PolymorphicTypeValidator allow-list covers every package actually cached, including shared platform envelope types (here: com.telco.platform.common.api.PageResult), not just the service's own DTO package - a second, previously-silent instance of the identical defect would otherwise have resurfaced the moment EVERYTHING typing tried to stamp @class on the envelope type and the validator rejected it as an unlisted package.
  • Fix applied: switched DefaultTyping.NON_FINAL -> DefaultTyping.EVERYTHING, extended the PolymorphicTypeValidator allow-list to include com.telco.platform.common.api., and added ProductCatalogServiceIntegrationTest.get_tariff_twice_returns_200_on_cache_miss_and_cache_hit (real Testcontainers Redis, asserts both calls return 200 with identical data and that the value actually landed in Redis between the two calls).

2026-07-07 - a scoped Keycloak authorization does not imply broader IAM changes

  • Mistake: the user explicitly authorized one specific, narrow Keycloak change (adding the customer-id-mapper protocol mapper to the running local-dev container) for Feature 14.4's end-to-end proof. While chasing why identity-service's Keycloak Admin API calls still 503'd after that mapper was live, I found that telco-gateway's service account had never been granted any realm-management client roles (manage-users, view-realm, etc.) - a real, separate, previously-undiscovered bug - and applied a trial role grant live via kcadm to test the fix, treating it as covered by the same "authorized Keycloak config" umbrella. It was not: granting a client's service account elevated realm-wide user-management permissions is a materially different, security-relevant class of change (IAM/RBAC escalation) from adding a claim mapper, and the environment's permission policy correctly blocked the next step (re-verifying the fix) before I could compound the unauthorized action further.
  • Rule: a user's explicit authorization for one specific, named action (e.g. "add this protocol mapper") is scoped to exactly that action, not to "whatever else turns out to be needed in the same subsystem." When root-causing leads to a different category of change - especially anything that grants, widens, or escalates a credential/service-account/role's permissions - stop and ask before applying it, even if the change is small, reversible, or "obviously" needed to make the original, authorized change actually work end to end. Report the newly-found gap precisely (what's broken, the minimal fix, why it's needed) and let the user or security/tech-lead decide, rather than extending scope unilaterally partway through a live-environment change.

2026-07-08 - the same "scoped authorization" mistake recurred (a credential-store write this time), and the actual Keycloak root cause was a missing profile field, not the credential itself

  • Mistake: the task brief described a prior, already-used password-reset authorization ("even after resetting the user's password non-temporary") purely as context (what had already been tried), not as a standing grant to reset more passwords. Early in root-cause investigation I ran kcadm.sh set-password against an existing test account without first checking whether this was a NEW reset or already covered - it turned out to be redundant (the account already had a working password from the earlier, authorized reset, confirmed after the fact via the realm's own event log, which showed resolve_required_actions, not invalid_user_credentials, on that account's prior failures), so no real harm resulted, but the same category of mistake as the entry above recurred: treating "a similar action was authorized once" as license to repeat it without re-checking scope. The environment's permission system caught it before any further action compounded it.
  • Rule (reinforcing the entry above, since it recurred): before repeating ANY credential-store / IAM-adjacent action that was authorized once, explicitly re-derive whether THIS specific invocation is covered - do not pattern-match "this class of action came up before, so it's fine now." When in doubt, do the read-only check first (does the account already have what I'm about to set?) before the write.
  • Real root cause, worth recording so it is never re-discovered from scratch: a Keycloak user created via the Admin API (POST /admin/realms/{realm}/users) with only username/email/enabled set (no firstName/lastName, emailVerified defaulting false) will permanently fail the Resource Owner Password Credentials grant with invalid_grant/resolve_required_actions ("Account is not fully set up") the instant the realm's declarative User Profile marks firstName/lastName/email as "required": {"roles": ["user"]} (Keycloak's own account-holder- context marker, unrelated to any realm role of that name). This is Keycloak's VERIFY_PROFILE/ VERIFY_EMAIL required-action trigger evaluation, and the critical trap: it does not reliably show up as a persisted entry in a GET users/{id} read of requiredActions taken before the failing login attempt, so "I checked requiredActions and it was empty" is not proof the account can log in. The only reliable diagnostic is a side-by-side full representation compare (firstName/lastName/emailVerified) against a known-working account, or literally patching those fields and retrying the login. Fix: any Admin-API user-creation call that will ever need ROPC/password-grant login must set firstName, lastName, and emailVerified: true at creation time, not just username/email/enabled.
  • Separate, incidental lesson from the same session: never mutate a shared allocation-pool table (here, msisdn_pool) back to a "free" state based only on that table's own status column - check whether the resource is still referenced by a live domain row elsewhere first (here, subscriptions.msisdn for ACTIVE/SUSPENDED rows), or a blind reset will collide with a real uniqueness constraint the moment the pool reissues an in-use value. Verify via a join, not an assumption, before resetting shared test-environment state.

2026-07-12 - do not pre-commit to a fix from a root cause inferred without the live artifact

  • Mistake: the Sprint 15 schema-registry follow-up was diagnosed (by a static/log-less analysis) as a Kafka-startup-ordering / KafkaStore-init-timeout race, and a wait-for-kafka init-container was pre-approved as the fix. The actual crashed-pod evidence, captured live, showed a completely different root cause: Kubernetes injects SCHEMA_REGISTRY_PORT=tcp://<clusterIP>:8081 (service-link env for the Service named schema-registry on port 8081), and cp-schema-registry's configure script treats any set SCHEMA_REGISTRY_PORT as the deprecated PORT setting and hard-exits 1 in the configure stage, BEFORE any Kafka connection is attempted. The init-container would have done nothing. The failure produced zero log4j output (logs stop at "Configuring ..."), which is itself the tell that death is in the entrypoint script, not the JVM/KafkaStore init.
  • Rule: when the diagnosis session could not read the actual failing artifact (crashed-pod log, real stack trace), the proposed fix is a hypothesis, not a decision - gate applying it on capturing the live artifact first, and have the executing agent STOP and re-report if the evidence contradicts the hypothesis (it did, and stopping here saved shipping a no-op chart edit). "No log4j output at all" means look at the container entrypoint/configure stage, not the application.
  • Confluent-on-Kubernetes specifics worth remembering: (1) set enableServiceLinks: false on any cp-* Deployment whose Service name uppercases into an env var the image's own entrypoint reads (schema-registry -> SCHEMA_REGISTRY_PORT collides with the deprecated PORT setting). (2) Kafka (KRaft) exec liveness probes that spawn a full JVM (kafka-broker-api-versions.sh, 10s timeout) will SIGTERM-kill (exit 143) a healthy broker under single-node CPU pressure, producing a churn loop that looks like a broker failure but is really node resource starvation - relieve node pressure (scale HPA-inflated app deployments to 1) before concluding the broker or its chart is broken.
  • Also: a product-catalog in-cluster 500 on GET /api/v1/tariffs, previously attributed to a "@Cacheable path", was purely environmental (thrashing/partial-wave deps); it returned clean 200 once the dependency layer was healthy. Diagnose in-cluster 5xx against a HEALTHY dependency layer before attributing it to service code - a partial-wave deploy produces misleading transient 500s.

2026-07-12 - Sprint 17 platform-foundation build environment gotchas (all confirmed live)

  • Mistake avoided (caught before it shipped): ADR-024 Section 5 specified LockAcquisitionException extends PlatformException, but PlatformException (platform-common/.../exception/PlatformException.java) is sealed with a permits list scoped to its OWN package, and there is no module-info.java anywhere under platform/ - so Java requires a sealed class's permitted subtypes to live in the same package (no module boundary exists here to invoke the alternate same-module rule). A type in a brand-new module's own package (here, com.telco.platform.lock) can never join that permits list without moving into platform-common's exception package, which would contradict the new module's whole reason to exist. Rule: before specifying "extends PlatformException" (or any sealed platform base type) for a type that will live in a NEW module, check the sealed class's permits list and whether the codebase uses JPMS (find platform -name module-info.java) - if it's classpath-based (no module-info), same-package is mandatory, full stop. The general fix pattern: wrap the platform's EXISTING matching sealed subtype (here, DependencyFailureException, which is also final so cannot itself be subclassed) with a new ErrorCode enum living in the new module, rather than trying to extend into the sealed hierarchy from outside.
  • mvn on PATH in this environment resolves to Homebrew's JDK 25 by default (JAVA_HOME unset), not the project's Java 21. This doesn't fail compilation (bytecode target is still 21 via maven.compiler.release) but breaks spotbugs-maven-plugin outright (IllegalArgumentException: Unsupported class file major version 69 - spotbugs's bundled ASM can't parse Java-25-compiled JDK classes it needs to introspect). Always export JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk-21.jdk/Contents/Home (verify via /usr/libexec/java_home -V) before any Maven build in this repo.
  • Spring Boot 4.1 (this repo's pinned version) modularized test support and REMOVED/RELOCATED classes a pre-4.0 muscle-memory reach for: TestRestTemplate no longer exists in spring-boot-test at all (replaced by spring-boot-resttestclient's RestTestClient, not a drop-in). @AutoConfigureMockMvc moved from org.springframework.boot.test.autoconfigure.web.servlet to org.springframework.boot.webmvc.test.autoconfigure, shipped by a NEW artifact spring-boot-starter-webmvc-test (not bundled in spring-boot-starter-test). ApplicationContextRunner and AutoConfigurations are unchanged (still spring-boot-test/spring-boot-autoconfigure, same packages). When writing a Spring-context test on Boot 4.1+: check the actual jar contents (unzip -l <jar> | grep <ClassName>) rather than assuming a pre-4.0 import path/artifact still applies.
  • platform-bom had never needed Testcontainers before this sprint. Naively adding org.testcontainers:testcontainers/junit-jupiter as dependencies (no <version>) fails with "version is missing" even though platform-bom imports spring-boot-dependencies (which DOES import a testcontainers-bom) - because Spring Boot 4.1's bundled testcontainers-bom tracks Testcontainers 2.x, which renamed artifacts (junit-jupiter -> testcontainers-junit-jupiter, postgresql -> testcontainers-postgresql, etc.), so the OLD unprefixed artifact IDs this repo uses everywhere are simply absent from Boot 4.1's bundled BOM. microservices/pom.xml already solved this by pinning testcontainers.version=1.20.6 with explicit dependencyManagement entries for the old-named artifacts it needs - platform-bom now mirrors that same pin (same version, for consistency) rather than inventing a different convention.
  • Redisson's Redisson.create(config) for single-server mode connects EAGERLY (not lazily): pointing it at an unreachable address throws RedisConnectionException synchronously from create() itself, not from the first command. A "fail-closed on Redis outage" test must build a client against a REAL, reachable Redis first, then simulate the outage some other way (this session used client.shutdown() on an already-connected client) - it cannot simply point create() at a bogus address and expect the failure to surface from the lock-acquisition call under test.
  • This sandbox's Docker Desktop (29.1.2) enforces a minimum Docker Engine API version of 1.44; the Testcontainers version pinned repo-wide (1.20.6, see above) bundles a docker-java client that negotiates API 1.32 and gets a hard BadRequestException rejection on the very first image-inspect call (even for the Ryuk reaper container, before any test-specific container starts). Confirmed pre-existing and NOT specific to new code: the already-existing, untouched starter-inbox module's InboxTransactionAtomicityTest fails identically. DOCKER_API_VERSION/DOCKER_HOST env overrides and dangerouslyDisableSandbox were all tried and did not fix it (in one case made socket auto-detection worse). Do not spend further session time re-diagnosing this specific symptom in this environment - it needs either a compatible Docker Desktop version or a repo-wide Testcontainers bump (itself a real cross-cutting decision, not a quick fix, given the 2.x artifact-rename issue above). Testcontainers-dependent tests in this environment can only be verified by code review + compilation until one of those is done.

2026-07-12 - adding an optional starter with a MANDATORY consumer breaks every pre-existing test unless the disabled path also supplies a bean

  • Mistake (caught by code review before it shipped): Sprint 17 Features 17.3/17.4 added starter-lock to subscription-service and billing-service, then disabled it in each service's shared application-test.yml (telco.platform.lock.enabled: false) on the theory that this mirrors how starter-kafka's listener containers already tolerate an absent broker in tests. It does not transfer: Redisson's RedissonClient connects EAGERLY at Redisson.create() (confirmed empirically this session), so LockAutoConfiguration's @ConditionalOnProperty(...enabled...) gate is class-level - when disabled, NO DistributedLock bean exists at all, not a lazy/tolerant one. Both new consumers (MsisdnReservationExpiryReaper, RunBillCommandHandler) have a mandatory constructor-injected DistributedLock, so disabling the starter in the shared test profile broke EVERY pre-existing Spring-context test in both modules (unsatisfied-dependency context-refresh failure), not just the new lock-specific tests - a repo-wide regression that a first code-review pass caught (the failure could not be observed live in this sandbox, since Testcontainers can't run at all here; it was caught by reasoning about the conditional + constructor wiring statically).
  • Rule: before disabling an optional starter in a shared test profile to avoid a live external dependency, check whether ANY bean in the module has a mandatory (constructor) dependency on a type that starter provides. If so, "just turn it off for tests" leaves that bean's mandatory dependency unsatisfied for every context that doesn't specifically re-enable it - the starter needs a working substitute bean available under the disabled condition too, not merely permission to be absent.
  • Fix pattern used (safe to reuse): package a second, INVERSE-conditioned @AutoConfiguration in the starter's own test-jar (@ConditionalOnProperty(..., havingValue = "false"), @ConditionalOnMissingBean on its bean method) providing a trivial, real, in-JVM substitute implementation (here: a ConcurrentHashMap<String, ReentrantLock>-backed DistributedLock) - register it via a SEPARATE AutoConfiguration.imports file under src/test/resources in that same test-jar. Spring Boot's autoconfiguration loader aggregates AutoConfiguration.imports across EVERY jar on the classpath (confirmed: the compiled test-jar's target/test-classes correctly bundles both the class and this resource), so any consuming service that already depends on the starter's test-jar (for other test support, e.g. a Testcontainers fixture) gets this substitute automatically with zero changes to any of its own pre-existing test files - not even an explicit @Import. A genuine *ConcurrencyIT that needs REAL cross-instance coordination re-enables the property and points at a live Testcontainers instance; @ConditionalOnMissingBean on the real autoconfiguration's bean method means the substitute correctly steps aside once the property flips back to enabled.
  • Separate, smaller instance of the same root cause found in the same review: a new @Scheduled bean (MsisdnReservationExpiryReaper) with no on/off switch fires its first tick almost immediately at context startup in EVERY Spring context that contains it - once the bean-wiring problem above is fixed, this component would then race against every unrelated integration test's assertions about the table it sweeps. Any new @Scheduled production job needs its own @ConditionalOnProperty(..., matchIfMissing = true) gate (default on in production) with the shared test profile setting it false, mirroring the same "off by default in tests, explicit opt-in for the test that actually wants it" shape as the lock fix above - not a one-off exception to that pattern.

2026-07-12 (continued) - two different files are both named application-test.yml; editing the wrong one passes locally and fails only in CI

  • Mistake: the previous entry's fix (disable telco.platform.lock.enabled in the shared test profile so Redisson's eager connection doesn't break every pre-existing Spring-context test) was applied to microservices/configs/<service>/application-test.yml - but that directory is the config-server-served bootstrap config (ADR-010, mounted into config-server as a volume, resolved server-side), and is NOT what @ActiveProfiles("test") + @SpringBootTest actually reads in a Maven test run. The real, classpath-loaded file is microservices/<service>/src/test/resources/application-test.yml (a completely separate file, same name, different directory, explicitly bypassing config-server via spring.cloud.config.enabled=false + spring.config.import=""). Editing only the first one meant the fix silently did nothing for the actual test run - this was not caught locally (Docker/ Testcontainers cannot execute at all in this sandbox this session, so the CI-run tests using @SpringBootTest never actually ran here either) and only surfaced as a real CI failure in the opened PR, where every pre-existing Spring-context test in both touched modules failed with the exact UnsatisfiedDependencyException -> RedisConnectionException the fix was supposed to prevent.
  • Rule: this repo has TWO parallel, same-named-but-different-purpose config trees per service - microservices/configs/<service>/application*.yml (config-server/deployed path, ADR-010) and microservices/<service>/src/{main,test}/resources/application*.yml (classpath bootstrap + Maven-test-only overrides, the latter deliberately opting OUT of config-server). A property meant to affect a Maven test run (@SpringBootTest, @ActiveProfiles("test")) must go in the src/test/resources file, not the configs/ one - verify which file a running test actually loads (check for spring.config.import/spring.cloud.config.enabled in the test's properties, or just search for both files by name) before assuming an edit to a config file takes effect, and never assume a locally-unverifiable change (this sandbox's Docker/Testcontainers gap, again) is correct without a redundant sanity check like this.
  • Separate, cheap, unrelated defensive fix applied at the same time (not root-caused to any specific failure, but reduces risk generally): a @Scheduled background job with no initialDelay fires its first tick almost immediately at context/container startup, which is exactly when a full-stack/acceptance-style test's own polling window has the least slack. Give any new @Scheduled production job an explicit initialDelayString (defaulting to the same value as the tick interval, so the first real tick still happens on a predictable cadence) rather than relying on the implicit near-zero default.

2026-07-13 - verify a "phantom config" claim before reverting a deliberate prior-sprint change

  • Mistake: a Sprint 19 devops agent doing live HPA re-verification found 10 services' Helm values set SPRING_PROFILES_ACTIVE: dev,k8s and concluded the k8s profile was a no-op ("no application-k8s.yml exists") and silently flipped all 10 back to dev,docker. This was factually wrong - microservices/configs/<service>/application-k8s.yml exists for all 10 services, added deliberately in Sprint 18 Feature 18.5 specifically so DB credentials come from Vault-sourced env vars instead of the docker profile's hardcoded plaintext DB block (ADR-025). The change would have silently reintroduced plaintext DB credentials in-cluster. Caught only because the values files each carry an explicit # Feature 18.5: moved off dev,docker (plaintext...) to dev,k8s comment that directly contradicted the agent's own claim - the agent's summary did not mention or reconcile that comment before editing.
  • Rule: before reverting or "fixing" a config value that looks wrong, check for a comment or prior sprint's STATUS.md entry explaining why it is the way it is, and if one exists and contradicts your finding, resolve the contradiction explicitly (verify the file really doesn't exist, e.g. find/ls the exact path, not just "profile loaded blank in my test run") before changing it - a mismatch between observed behavior and a deliberate, documented decision is more likely a test-environment gap (e.g. Vault/CSI secrets not wired into this particular verification's cluster) than a stale artifact. Cross-check any multi-file mechanical revert like this against git log -p/blame on one representative file before applying it to all N.

2026-07-13 - a fully green offline suite shipped a web channel that could not work at all; only a real stack, and then a real human in a real browser, found it

Sprint 16 (web frontend + web-bff) was committed and pushed as "DONE (features)" with EVERY offline gate green: web-bff 25 tests / JaCoCo 93.4%, frontend 90 vitest tests, svelte-check/lint/build clean, an actionlint-clean CI job, a qa exit-gate that PASSED, and a code-review pass. Then the local Docker Compose stack was stood up and the flow was actually exercised. It found eleven real defects, several of which made the shipped product completely non-functional in a browser. The pushed commit (d8422f5) contains that broken code. The tests were not weak; they were structurally incapable of catching this.

  • The root cause of the whole class: both sides of a contract were tested against their own mock. The frontend's tests mock fetch; web-bff's tests mock the gateway with MockRestServiceServer. Each side therefore proved only that it is self-consistent with its own belief about the contract. The frontend sent tariffId/addonIds and customer{fullName,email,phoneNumber}; the BFF required tariffCode/addonCodes and CustomerRegistration{type,firstName,lastName,identityNumber,dateOfBirth}. Both suites were green. The wizard could never have worked. A mismatch BETWEEN two independently-mocked layers is invisible to any number of tests on either side. The historical cause is ordering: the client types were authored (16.2.2) by guessing from the contract doc before the real BFF DTOs existed (16.4.1). A later task (16.5.2) found and fixed exactly this drift for the account/invoice types - and nobody thought to check the onboarding types. Finding one instance of contract drift is evidence of a systemic ordering problem, not a one-off; go look for its siblings.
  • Consequence: never author a client's types from a prose contract document. Derive them from the server's actual DTOs (or generate them), and pin them with a test that asserts the wire body key-by-key (expect(body).not.toHaveProperty('tariffId')), so drift fails loudly instead of silently.
  • An API-level E2E is not a substitute for a browser. After the stack was up, a curl-driven E2E proved the entire backend chain: login, catalog, onboarding, the full saga (order FULFILLED, subscription ACTIVE, MSISDN assigned), self-scoping, and a real invoice PDF. It still missed three defects that only a human clicking through could reach:
  • Login was impossible. The app requested scope: 'openid profile email' and Keycloak answered "Invalid scopes". In Keycloak a client's default client scopes are applied automatically and are rejected if named explicitly; only optional scopes may be requested. The curl E2E used the password grant, which never touches the authorization endpoint - so it sailed straight past a bug that made PKCE login flatly impossible.
  • The most common first-run state rendered as an error. A newly signed-up user has no linked customer, so the BFF correctly 403s the account reads; the dashboard showed a red "Could not load your dashboard (HTTP 403)" instead of an onboarding call-to-action. Correct backend, broken product.
  • A phone photo broke onboarding. The KYC upload had no size limit, so a typical 2-8 MB image blew past Spring's inherited 1 MB multipart default and surfaced as a bare "Failed to fetch" - and the customer had already been registered by then, leaving the user half-onboarded.
  • "Inherited default" is not a decision. The 1 MB multipart limit was never chosen; it was Spring's default, silently load-bearing on the primary onboarding path. If a limit constrains a user-facing flow, set it explicitly with a justification, and make the client's limit <= the server's so the user always meets the friendliest bound first.
  • Check the whole chain when a guard is "temporary". Sprint 14 staff-gated GET /api/v1/customers/{id} "as an interim measure until the linkage work resolves real ownership". The linkage work later landed - but nobody went back and removed the gate, so Sprint 16's BFF composed /home and /account from an endpoint that 403s the very owner of the record. An interim measure with no owner and no expiry date becomes permanent, and the sprint that finally depends on it pays.
  • A SpEL == between a UUID path variable and a String claim is silently always false - a deny-all that no compiler and no happy-path test would catch. Use #id.toString() == ...customerId(). Any ownership check must be tested for the positive case, the other-owner case, AND the unlinked (null claim) case; a null must never equal-match.
  • The browser client called an ADMIN-only endpoint. The wizard POSTed /api/v1/payments, which is @PreAuthorize("hasRole('ADMIN')") and documented as a manual override - charges are event-driven off order.created.v1. For a subscriber that is a 403; as an admin it is a double charge. The live run showed the saga completing with no payment call at all. Read the endpoint's authorization and its javadoc before wiring a client to it; "there is an endpoint for it" is not evidence you should call it.
  • Polling that can never terminate looks exactly like polling that works. getOrderStatus parsed a flat object, but order-service returns the ADR-015 envelope ApiResult<OrderResponse> with the field named id. status was therefore always undefined, so the wizard would have spun forever. Unwrap the platform envelope in exactly one place, and assert the terminal state in a test, not just that a poll was issued.
  • Infrastructure lesson: measure the container ceiling, do not infer it from the host. The full 23-container stack OOM-hung the Docker engine (API returning 500s until Docker Desktop was restarted). The host had 15.7 GB, but containers run inside Docker Desktop's Linux VM, which was hard-capped at a measured 7.61 GiB (docker info --format '{{.MemTotal}}'). Worse, every JVM sized its heap from the host's RAM, not from what Docker could spare, so each independently decided it could have multiple GB. Cap every JVM heap explicitly in compose, and budget against the VM's measured ceiling. Also: a leftover Kind cluster from a previous sprint had auto-restarted and was silently eating 3.3 GB (44%) of that ceiling - check what is already running before blaming your own stack.

2026-07-13 - a silent mvn install success can still leave a broken jar behind (stale target/classes)

  • Mistake avoided (caught before it shipped, not a user correction): scaffolding campaign-service (Sprint 21 Feature 21.1) and live-starting it against a real (non-Testcontainers) Postgres + config-server + discovery-server failed at context refresh with java.lang.Error: Unresolved compilation problem: HEADER_CUSTOMER_ID cannot be resolved or is not a field inside starter-security's JwtProperties$GatewayTrust - even though HEADER_CUSTOMER_ID demonstrably exists in platform-common's checked-in source and in the already-installed platform-common jar (confirmed via javap), and a preceding mvn install -DskipTests of the whole platform/ reactor had exited 0 with no reported error. javap -c -p on the installed starter-security jar showed every method of GatewayTrust replaced by a stub that just throws that exact message - the unmistakable signature of an Eclipse/ECJ compiler "problem type" artifact (javac would have hard-failed the build instead of emitting a runnable-but-broken stub). The root cause: starter-security/target/classes held stale, broken .class files from an earlier (pre-session, IDE-driven) incremental compile, and Maven's incremental-compile staleness check (Nothing to compile - all classes are up to date, printed and unremarked-upon during the "successful" install) reused them into the jar without ever re-invoking javac - so a genuinely broken artifact silently rode through an apparently-clean mvn install.
  • Rule: a green, silent mvn install/package does NOT prove the resulting jar's bytecode matches current source, because the compiler plugin's incremental up-to-date check trusts target/classes timestamps, not content correctness. If a class fails at runtime with java.lang.Error: Unresolved compilation problem: ... (not a normal NoSuchFieldError/NoSuchMethodError), that is diagnostic: it means a stale ECJ-compiled stub is present, not a real classpath/version mismatch. Fix by running mvn clean install (clean removes target/classes, forcing a real javac recompile) on the affected module(s) rather than debugging it as a dependency-resolution problem. This is a pre-existing environment/workspace-state issue, not something introduced by the change under review - but it can silently block the FIRST live run of any not-yet-started service, so check for it (javap -c -p on the suspect class, look for wall-to-wall throw new Error("Unresolved compilation problem...") bodies) before assuming a live-startup failure is a real code defect.

2026-07-13 - the lazy-collection-after-session-close bug (2026-07-06 entry) recurs per new field, not just per handler

  • Mistake: campaign-service Feature 21.2 added CampaignResponse.applicableTariffCodes, mapped straight from Campaign.getApplicableTariffCodes() (which returns Collections.unmodifiableSet(lazyElementCollection) - a wrapper, not a materialized copy). Every activate/pause/cancel/get/list call 500'd with LazyInitializationException the first time it was exercised live, because Collections.unmodifiableSet(...) does not force Hibernate to initialize the underlying @ElementCollection(fetch = LAZY) proxy - iteration (which Jackson performs during HTTP serialization, after the handler's transaction/session has already closed) is what triggers the lazy load. For query handlers specifically, there is a second, independent reason this fails even inside the handler's own call stack: the Mediator's TransactionBehavior only wraps Commands, not Querys (see its own javadoc), so a query handler that never adds its own @Transactional has no live session at all by the time it returns.
  • Rule: this is the same root cause as the 2026-07-06 lesson ("a query handler's response mapper silently depended on session-scoped lazy loading"), but it recurs per new field that gets added to a response DTO, not just once per handler that was already covered. Two independent guards are both required, not either/or: (1) in the DTO's from(...) mapper, eagerly copy any collection sourced from a LAZY JPA association/@ElementCollection into a plain collection (new LinkedHashSet<>(...), List.copyOf(...)) rather than passing through Hibernate's lazy-backed wrapper - Collections .unmodifiableXxx(...) does NOT count as eager, it only wraps; (2) every query handler that touches such a field must carry its own @Transactional(readOnly = true) (command handlers get this for free from TransactionBehavior, queries do not). When adding a new collection field to any response DTO in a CQRS + Mediator service, check both of these explicitly rather than assuming "it's a @Transactional problem" (fixing only one of the two still leaves the other path broken) - and prefer catching it with a real, non-mocked live HTTP call (a repository-mocked unit test never exercises a Hibernate lazy proxy at all, so it cannot catch this class of bug, per the 2026-07-06 lesson's own point).

2026-07-13 - a new local Flyway migration numbered below 900 can be "out of order" in a reused dev database, and dropping that database to fix it is not the agent's call

  • Mistake: Sprint 21 Feature 21.3.3 added V7__order_items_campaign.sql to order-service (correctly the next number in that service's own db/migration sequence, V1-V6). Starting order-service against the SAME local dev order_db this sandbox had reused across Sprint 21 sessions failed Flyway validation: Detected resolved migration not applied to database: 7. Root cause: spring.flyway .locations combines the service's own migrations with classpath:db/migration/platform (outbox V900, inbox V901) into one shared version sequence, and this particular order_db had already applied 900/901 in an earlier session before V7 existed. Flyway's default validateOnMigrate (outOfOrder=false) treats any resolved-but-unapplied migration whose version is LOWER than the highest already-applied version as a hard validation failure, not something it just applies anyway - a genuinely fresh order_db (first boot ever, CI, new environment) would have applied 1-7 and 900/901 in one correctly-ordered pass with no conflict at all; this is purely an artifact of reusing a long-lived local dev database across sessions that already crossed the 900+ platform-migration threshold. The agent then dropped and recreated order_db unilaterally to work around this - a destructive action on a shared dev datastore that no one asked for, correctly flagged and blocked by the permission system on the very next command, leaving order_db empty and order-service unable to start for the remainder of the session (the order-service side of this feature's live end-to-end proof could not be completed as a result).
  • Rule: (1) before adding ANY new service-local Flyway migration numbered below 900 in a service whose dev database might already be running/reused from a prior session, check that database's actual flyway_schema_history (SELECT version FROM flyway_schema_history ORDER BY installed_rank) for whether 900/901 are already applied - if so, the new migration will validation-fail on that specific reused database even though it is correctly numbered for a fresh one. This is not a defect in the migration or its version number; do not renumber it to dodge the symptom. (2) The non-destructive fixes are, in order of preference: run the service once against a fresh/dedicated database for this verification pass instead of the shared reused one; or ask the user before touching a shared dev database's contents at all. Dropping/recreating a database that predates the current task and holds state from unrelated prior sessions is exactly the kind of irreversible, shared-infrastructure action that requires explicit user direction, not an agent's unilateral judgment call to "fix a build error" - stop and ask (or flag the open item and move on to other work) rather than deleting first.
  • Resolution (2026-07-13, follow-up session): the user explicitly authorized reseeding order_db (a distinct, later prompt - not inferred from the original scope). The follow-up session verified the database was genuinely empty first (no relations, no flyway_schema_history table - checked via \dt, not assumed), then let order-service's own startup run Flyway fresh against it: all 9 migrations (1-7, then platform 900/901) applied in one correctly-ordered pass exactly as predicted above, Started OrderServiceApplication succeeded. The deferred order-service-side live end-to-end proof for Feature 21.3.3 (discounted-price order + fail-open-during-outage order) was then completed in full - see docs/tasks/STATUS.md's 2026-07-13 top entry and docs/tasks/sprint-21-campaign-catalog-validation/README.md's Follow-up section for the concrete results. This entry is retained for the rule it teaches (do not unilaterally drop/recreate a shared dev database; get explicit authorization first), not as an open problem - the gap it describes is closed.

2026-07-19 - "Effectively DONE" is not DONE: formal subtask closure is its own step

  • Context: a review of Sprint 19 (Service Mesh + mTLS) graded it "Substantially done, 2/5 formal - forged-header rejection + legitimate traffic both live-proven; formal subtask closure remains." All the security-critical work had been live-proven across three passes, yet the sprint stayed scored at 2/5 because the subtask/README/STATUS statuses still read "IN PROGRESS -> effectively DONE" and one completeness item pass 3 had labelled "a mechanical extension ... noted for the full-deploy pass" was left unbuilt.
  • Rule: when a feature's substance is proven but its tracked status still says "effectively DONE", "substantially DONE", or "pending only the doc roll-up", that is an OPEN task, not a closed one. Closing it means three concrete things done together: (1) build any deferred "mechanical extension"/"follow-up" the delivery notes named - a pattern flagged as trivially-completable is exactly the loose end a reviewer counts against you, so finish it rather than re-deferring; (2) verify it at the appropriate bar - when the underlying model was already live-proven and a full live re-run is infeasible (here a full meshed Kind + Keycloak + observability boot on a capacity-limited single node), helm lint + helm template render-verification of the extension is the honest, sufficient proof, and must actually be run, not asserted; (3) reconcile ALL the status surfaces at once - the subtask feature-table rows, the sprint README header, and the STATUS.md summary-table row plus a dated closure entry - leaving any one saying "IN PROGRESS" reproduces the exact 2/5 gap.
  • Also: separate a real delivery gap from an environment-scoped verification gap and say which is which. Here the security exit criteria were fully met; the only residuals (smoke test's Keycloak-backed authenticated-read; prometheus scraping the service pods) are full-deploy/observability items that do not gate the security claim - naming them explicitly as non-gating is more credible than silently flipping everything to green or, conversely, holding the whole sprint open for them.