Add Jackson 3 migration plan: remove Confluent dependencies, retain Everit, migrate Spring Boot to Jackson 3

[Copilot]

Confluent's kafka-json-schema-serializer and related libraries are pinned to Jackson 2, blocking migration to Jackson 3. This PR adds a detailed migration plan to remove all io.confluent dependencies, in-source the small API surface actually used, and migrate Spring Boot classes to Jackson 3.

Analysis

Audited the full codebase — 23 files import from io.confluent, 3 from org.everit. The actual API surface used is narrow:

• JsonSchema: validate(JsonNode), rawSchema(), toJsonNode(), deepEquals(), version(), toString()
• SchemaDiff: compare(Schema, Schema), COMPATIBLE_CHANGES_STRICT (56 types, extracted from bytecode)
• Difference.Type: 114 enum values, only 2 directly referenced (PROPERTY_REMOVED_FROM_CLOSED_CONTENT_MODEL, REQUIRED_PROPERTY_ADDED_TO_UNOPEN_CONTENT_MODEL)
• Everit JSON Schema (com.github.erosb:everit-json-schema): Depends on org.json:json, not on Jackson — safe to retain as explicit dependency after Confluent removal
• Spring Boot Jackson 2: 3 POMs use spring-boot-jackson2, 4 auto-config classes use Jackson2ObjectMapperBuilderCustomizer, 10+ test files use Jackson2ObjectMapperBuilder

Plan (plans/jackson3-migration.md)

• Phase 0 — Pre-verify jackson-dataformat-protobuf Jackson 3 availability, kafka-protobuf-serializer runtime usage, and Everit as explicit dependency
• Phase 1 — In-source JsonSchema (wrapping Everit internally), SchemaDiff (operating on Everit Schema objects), and Difference in org.elasticsoftware.akces.schemas
• Phases 2–6 — Update shared/runtime/client/query-support/eventcatalog/test-apps modules (import swaps, type simplification); retain org.everit.json.schema.ValidationException as-is
• Phase 7 — Remove Confluent deps, repository, and properties from parent POM; add everit-json-schema as explicit dependency
• Phase 8 — Full Jackson 2→3 migration including Spring Boot 4 / Spring Framework 7:
  • 8.1: Core Jackson migration (com.fasterxml.jackson → tools.jackson across 64 files)
  • 8.2: Spring Boot Jackson 3 integration — replace spring-boot-jackson2 → spring-boot-jackson, Jackson2ObjectMapperBuilderCustomizer → JsonMapperBuilderCustomizer in 4 auto-config classes and 10+ test files
  • 8.3: Remove all Jackson 2 dependencies

Includes COMPATIBLE_CHANGES_STRICT reference extracted from Confluent bytecode, file-by-file change matrix, Spring Boot Jackson 2→3 class mapping table, and risk mitigations.

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[jwijgerd]

@copilot looks good so far, can you also specifically mention to update all Spring (Boot) classes to use Jackson 3 (which is the default option now for Spring Boot 4 and Spring Framework 7). Also it should be find to keep using the Everit JSON Schema library since it doesn't depend on Jackson at all

[Copilot]

@copilot looks good so far, can you also specifically mention to update all Spring (Boot) classes to use Jackson 3 (which is the default option now for Spring Boot 4 and Spring Framewo...

Updated in 365a3dd:

1. Everit retained — confirmed everit-json-schema depends on org.json:json, not Jackson. Plan now keeps it as-is and adds it as explicit dependency after Confluent removal. Removed the JsonSchemaValidationException replacement class. JsonSchema wrapper and SchemaDiff now operate on Everit's schema objects internally.

2. Spring Boot Jackson 3 migration added to Phase 8 with full detail:

   • Replace spring-boot-jackson2 → spring-boot-jackson in 3 module POMs
   • Replace Jackson2ObjectMapperBuilderCustomizer → JsonMapperBuilderCustomizer in 4 auto-config classes (AggregateServiceApplication, AkcesClientAutoConfiguration, AkcesQueryModelAutoConfiguration, AkcesDatabaseModelAutoConfiguration)
   • Replace Jackson2ObjectMapperBuilder in 10+ test files
   • Added mapping table for Jackson 2 → 3 Spring Boot class equivalents