[tconley1428]

Java generation handles native Nexus declarations and protobuf transfer types, enabling workflow-side signal-with-start in the Java SDK. It emits models, builders, operations, resources, variants, generics, outbound interceptor hooks, serialization-context factories, and an operation-root manifest for SDK payload visitor generation. An inheritable operations class exposes generated APIs without handwritten facade methods. Java formatting landed separately in #246.

Operation parameters contain only function references/names and their inputs. All other fields, including required fields, belong to a mandatory generated options object. Typed overloads support primary callable arities zero through six and other callable arities zero or one, preserving argument and result types for value-returning and void methods. Name-based calls accept an Object[] after each callable name. Shared private invocation/request helpers avoid duplicating validation, extraction, and merging across overloads.

Java-only @nexus.merge-from-function function="workflow" java="..." annotations select helpers that merge callable metadata with explicit options. Existing parser/model mappings retain the helper reference and metadata type without a new compiler pass. Required fields with merge hooks may be omitted from Java options and are validated after resolution at invocation; wire-model requiredness is unchanged. Other languages ignore these Java hooks.

The shared workflow-service WIT uses these hooks for workflow ID and retry/cron annotations. Typed calls derive ID from the workflow reference, reject conflicting explicit IDs and run-pinned references, and ignore the signal reference's execution identity. Untyped calls require an explicit ID. Task queue remains required. Helpers own these policies; generation has no workflow/start/signal-specific branches or synthesized WorkflowOptions.

Protobuf conversion uses the existing descriptor index and SDK-owned converter scope for embedded user values. Required payload fields serialize null values; optional null fields remain absent. Conversion helpers reuse SDK utilities where available. The sample support helper contains its own implementation, matching the package-private SDK helper rather than delegating to it. Runtime helpers are emitted Rust strings. JSON Schema orchestration remains in its Java submodule. Shared WIT and temporary SDK copies are byte-identical.

Signal-with-start serializes its request and receives a payload-free response. Future payload responses need generic models and concrete result types. The known packing-codec limitation in request-model deserialization remains outside this call path.

Validation for the latest changes: nine generator tests, Java samples including 51 compiler cases, 18 focused companion SDK tests, and two real-server signing-codec/replay tests passed. Compiler cases cover arity/type/result errors, nested generics, void methods, mandatory options, and untyped fallback. Full cross-language validation passed on earlier revisions; it was not rerun for these latest changes, per the requested iteration scope.

Companion SDK draft: temporalio/sdk-java#3154. Java samples use TEMPORAL_JAVA_SDK_DIR for unreleased SDK integration.