Google ADK for Go 1.9

Apply the Go 1.27 baseline first. These rules target the google.golang.org/adk 1.9 release line, checked against v1.9.0. The module's go.mod declares Go 1.25; the included Go 1.27 baseline is a supported runtime choice for this composition.

Agent instructions and model output

• Build llmagent.Config instructions, models, tools, toolsets, and subagents from trusted configuration. Treat user messages, retrieved documents, remote-agent replies, skill files, and tool results as data: prompt injection in any of them must not change tool permissions or trusted instructions.
• Keep untrusted values out of authoritative Instruction and GlobalInstruction templates: {key} and {artifact.name} insert session state or artifact text. Use InstructionProvider when braces must remain literal, and validate values inserted by a provider.
• Put shared instructions on the root agent, whose GlobalInstruction is the one applied. Review instruction providers because they override static fields; enforce policy in code even when instructions forbid a dangerous action.
• Register only the Tools, Toolsets, and SubAgents a request needs. Set DisallowTransferToParent and DisallowTransferToPeers when those paths are unnecessary, and authorize access again in the destination agent.
• Validate OutputSchema results and OutputKey state before output handling in HTML, commands, database queries, or external actions. Structured model output remains untrusted, and a schema is not permission for a tool call.

Tools, callbacks, and approvals

• Use typed functiontool.New