[zephyr45]

Purpose

Linked issue: close #4863

Replace the JSON Produce path's complete JsonNode tree with schema-compiled Jackson streaming converters. The new path preserves the existing coercion, strict parsing, projection, and rescue contracts while avoiding a global intermediate tree for ordinary values.

Brief change log

• Compile token converters for scalar, ROW, ARRAY, and MAP types and decode projected root fields in one streaming pass.
• Materialize only rescued values and container-to-string values, preserving raw numeric spelling for signed zero and extreme exponents.
• Preserve nested rescue overlays, valid siblings, parser advancement, strict UTF-8, duplicate detection, object-root/trailing-content checks, and resource limits.
• Reuse the tree conversion contract against the streaming converter and add regression coverage for numeric fidelity and array rescue positions.
• Add a JMH tree-versus-streaming benchmark for flat, nested, and rescue payloads.

Tests

• mvnw.cmd -pl fluss-kafka -Dtest=JsonKafkaFieldDecoderTest,JsonKafkaRescueTest,JsonToFlussComplexConvertersTest,JsonToFlussConvertersTest,JsonToFlussFlinkCompatibilityTest,JsonToFlussArrowTest -Dsurefire.failIfNoSpecifiedTests=false test — 172 tests passed.
• mvnw.cmd -o -B -pl fluss-kafka,fluss-jmh -DskipTests -Pjava8 clean test-compile — passed on JDK 8.
• Checkstyle, Spotless, and RAT passed for the affected build.
• A full fluss-kafka verify ran 413 tests: 386 passed and 27 cluster-backed tests errored during setup on Windows because the existing test harness constructs file://C:\... with a URI authority. There were no assertion failures.

JMH on JDK 17 (1 fork, 3 × 1 s warmup, 5 × 1 s measurement, GC profiler):

Shape	Tree ops/s	Streaming ops/s	Tree B/op	Streaming B/op
flat	1,170,344	1,567,340	4,112	3,256
nested	548,194	663,391	8,865	7,633
rescue	274,222	312,354	10,289	8,857

API and Format

No public API, Kafka protocol, or storage-format changes.

Documentation

No user-facing feature or configuration change.

• Generative AI tools used: Codex (GPT-6)