W1.4 — mcp_load tool, threshold gate, and Task.attachedMcpToolNames

[edelauna]

Context

This ticket wires the ToolRouter into actual API calls: the threshold gate at task start, the mcp_load escape hatch, and persistence of the attached set.

After this ticket, dynamic loading is functionally live (without the rolling window — that's W1.5).

Closes: RooCodeInc#11990 (strange context bloat — large tools arrays will be a frequent root cause once we look).

Developer Notes

• Add Task.attachedMcpToolNames: Set<string> (persisted with task state).
• build-tools.ts:
  • After ToolScopeFilter produces scopedTools, check scopedTools.length against mcp.dynamicLoad.threshold (default 50; replaces the old MAX_MCP_TOOLS_THRESHOLD = 60).
  • If under threshold: existing path.
  • If over: call ToolRouter.attachInitial(taskText, scopedTools, initialK). Initialize Task.attachedMcpToolNames. The API tools array is nativeTools + filter(scopedTools by attachedMcpToolNames) + mcp_load.
• New native tool mcp_load in src/core/prompts/tools/native-tools/mcp_load.ts:
  • Schema: { query: string }.
  • Handler at src/core/tools/mcpLoadTool.ts: calls ToolRouter.search(query, scopedTools, searchK), mutates Task.attachedMcpToolNames, returns the new tool names + 1-line descriptions.
  • Idempotent: re-attaching an already-attached tool returns the existing list with no churn.
• Remove the too_many_tools_warning from Task.ts:1957 — the new flow obsoletes it. (UI replacement comes in W2.1.)
• Settings: mcp.dynamicLoad.threshold (default 50), mcp.dynamicLoad.initialK (default 30), mcp.dynamicLoad.searchK (default 10). Register in the settings schema; surface in MCP settings UI.
• Files: src/core/task/Task.ts, src/core/task/build-tools.ts, src/core/prompts/tools/native-tools/mcp_load.ts, src/core/tools/mcpLoadTool.ts, packages/types/src/mcp.ts.
• Validation: integration test with 100 mock MCP tools — initial API call has 30 + native + mcp_load; model calling mcp_load("specific query") adds matching tools; subsequent API call includes them.