feat(delegate): MCP workspace guard for subagents#3632
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Prevents subagents from corrupting shared codebase-index state via: - Thread-local guard flag (_tl.subagent_guard) - Blocked tools: set_project_root, switch_project, reindex - Activated in delegate_tool before child.run_conversation() - Auto-disabled in finally block (thread-isolated) Read-only MCP tools remain available.
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Safety fix: prevents subagents from corrupting shared codebase-index state.
The Problem
Subagents run in separate threads but share the parent's MCP codebase-index session. If a subagent calls
set_project_root,switch_project, orreindex, it corrupts the index for the parent and all sibling subagents mid-execution.The Solution
Thread-local guard blocks workspace-mutating MCP tools inside subagent threads:
_tl.subagent_guardflag (thread-local, default False)set_project_root,switch_project,reindexchild.run_conversation(), disabled in finally blockget_functions,search_codebase, etc.) remain availableImplementation
mcp_tool.py:
_tlthread-local storage_SUBAGENT_BLOCKED_TOOL_NAMESfrozensetset_subagent_mcp_guard(active)public API_make_tool_handlerchecks guard before dispatchdelegate_tool.py:
set_subagent_mcp_guardtests/tools/test_mcp_subagent_guard.py:
10 tests covering block behavior, thread isolation, read-only pass-through
Part 2/3 of #3387 review response: