feat(plugin): surface agent and parentAgent in plugin hook input

[ArmirKS]

Issue for this PR

Fixes #15403

Type of change

• New feature

What does this PR do?

This adds parentAgent to the plugin hook inputs that need subagent context.
The main fix here is making sure that value actually survives the full prompt flow, so it reaches tool.execute.before, tool.execute.after, shell.env, chat.params, and chat.headers consistently.
Everything is additive, so existing plugins keep working.

How did you verify your code works?

• added coverage for the new prompt/message shapes
• ran bun test test/plugin/parent-agent.test.ts
• ran bun typecheck in packages/plugin
• ran bun typecheck in packages/opencode

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[bbo76]

any news for this ?

[bnema]

This is great, one gap though: chat.headers and chat.params in llm.ts don't get parentAgent. The PR adds it to tool.execute.* and shell.env, but the LLM hook inputs still only have agent (the name string).

Adding it would be a small change in llm.ts. parentAgent just needs to flow from StreamInput into the Plugin.trigger("chat.headers", ...) and Plugin.trigger("chat.params", ...) calls. That would let plugins adjust headers or model params based on whether the request comes from a subagent.

[tassiocaique]

any new for this?

[ArmirKS]

Thanks @bnema I fixed the llm.ts gap you called out. parentAgent now reaches both chat.params and chat.headers and is carried through subagent flows consistently