Go: Phase 4 — Tools

[juliomenendez]

Summary

• FunctionTool type with NewTool(fn) — auto-generates JSON Schema from input struct via reflection
• internal/jsonschema package for struct-to-JSON-Schema (supports string, int, float, bool, slice, nested struct, pointer/optional)
• Tool invocation loop in BaseAgent.runCore() — detects function calls, invokes tools through function middleware, sends results back to LLM
• OpenAI client maps tools to/from OpenAI format (tool definitions, tool call responses, tool result messages)
• WithTools, WithMaxToolRounds, WithToolDefs options
• ToSnakeCase for function name derivation

Test plan

• go test ./... -count=1 — all tests pass across 4 packages
• go vet ./... — no issues
• go mod tidy — module is clean
• Schema generation tests (7 subtests: types, tags, pointers, slices)
• NewTool tests (6 subtests: schema, invoke, options, signature validation)
• Tool name derivation tests (5 cases)
• OpenAI tool mapping test (request tools + response tool calls)
• Tool loop tests (happy path, max rounds, error forwarding)

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