fix(opencode): carry parent agent through prompt execution

Ensures parentAgent is persisted on user messages, included in
Tool.Context during tool resolution, and passed through the main
loop's resolveTools call.

Author: ArmirKS

packages/opencode/src/session/prompt.ts

@@ -359,6 +359,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
           callID: options.toolCallId,
           extra: { model: input.model, bypassAgentCheck: input.bypassAgentCheck },
           agent: input.agent.name,
+          parentAgent: input.parentAgent,
           messages: input.messages,
           metadata: (val) =>
             Effect.runPromise(
@@ -992,6 +993,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
           time: { created: Date.now() },
           tools: input.tools,
           agent: ag.name,
+          parentAgent: input.parentAgent,
           model: {
             providerID: model.providerID,
             modelID: model.modelID,
@@ -1486,6 +1488,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
                 tools: lastUser.tools,
                 processor: handle,
                 bypassAgentCheck,
+                parentAgent: lastUser.parentAgent,
                 messages: msgs,
               })