Preserve empty Go slices and maps in JSON

[qmuntal]

Summary

Use Go's json:",omitzero" tag for optional generated slices/maps, and for hand-authored public fields where an empty-but-present value has distinct wire semantics.

This preserves the difference between:

nil        // omitted from JSON; use runtime/default/absent behavior
[]T{}      // emitted as []; explicit empty list
map[...]{} // emitted as {}; explicit empty object

Why

omitempty collapses nil and empty slices/maps into the same JSON shape by omitting both. That loses information for APIs where "not provided" and "provided but empty" mean different things. omitzero keeps nil as absent while allowing callers to intentionally send empty arrays/objects.

Concrete examples:

• CustomAgentConfig.Tools
  • omitted: inherit/default tool behavior
  • []: explicitly expose no tools
• Tool.Parameters
  • omitted: no parameter schema supplied
  • {}: an explicit JSON Schema object that accepts any parameters
• CanvasDeclaration.InputSchema
  • omitted: no canvas input schema declared
  • {}: explicit schema accepting any canvas input
• ElicitationResult.Content
  • omitted: no form values, e.g. cancel/decline paths
  • {}: accepted form with no fields/values

The generated Go code now applies this consistently to optional slices/maps, while scalar/pointer optionals continue to use omitempty.

Testing

• cd scripts/codegen && npm run generate:go
• cd go && go test
• cd nodejs && npm test -- session-event-codegen.test.ts
• Focused Go serialization tests for nil vs empty CustomAgentConfig, Tool, CanvasDeclaration, and ElicitationResult values

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates Go JSON serialization semantics to distinguish between nil and empty values for slice/map fields by emitting omitzero tags (and generating them via codegen), with tests validating the behavior.

Changes:

• Add Go codegen helpers to generate json tags using omitzero for optional slice/map fields.
• Update Go struct tags for slice/map fields to use ,omitzero (omit only when nil/zero).
• Add Go tests covering nil vs empty serialization for affected fields.

Show a summary per file

File	Description
scripts/codegen/go.ts	Centralizes JSON tag generation and switches optional slice/map fields to omitzero semantics.
go/types.go	Updates struct tags (and comments) to preserve empty slice/map values while omitting nils.
go/canvas.go	Updates InputSchema tag to ,omitzero for nil vs empty behavior.
go/types_test.go	Adds tests asserting nil fields are omitted while empty slice/map fields are included.

Copilot's findings

Files not reviewed (4)

• go/rpc/zrpc.go: Language not supported
• go/rpc/zrpc_encoding.go: Language not supported
• go/rpc/zsession_encoding.go: Language not supported
• go/rpc/zsession_events.go: Language not supported

• Files reviewed: 4/8 changed files
• Comments generated: 5