[FEATURE] Subagent inherited context

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Subagents can't utilize session context, meaning the main agent has to pass the context explicitly, losing fidelity, filling the context window, and wasting tokens.

Proposed Solution

Add a parameter to the subagent invocation (including the generic Task) that causes it to inherit/fork the context.

Alternative Solutions

• Perform task in main agent, then rewind: no model autonomy, no concurrency, no subagent completion message
• Fork manually: similar to above + cumbersome
• Fork context via command (#14661): less general and natural

Priority

Medium - Would be very helpful

Feature Category

API and model interactions

Use Case Example

Most subagent use-cases would benefit, enabling more frequent delegation even as the context window grows, without wasting context:

• Explore again mid session as new information becomes available
• Perform web research on an issue
• Test a new feature using a browser integration
• Write tests

Some new use cases may emerge:

• git commiting frequently throughout the session
• branching off to turn a new insight into a skill asynchronously / writing to a memory system
• frequently checking for relevant skills/memories as new user prompts or environment interactions come in

Additional Context

_No response_