W1.5 — Rolling-search window across first N turns (union-only growth)

[edelauna]

Context

A single ranking at task start can miss tools the conversation drifts toward in the first few turns. The rolling window re-runs ranking for the first N turns (default 7) and unions the result into attachedMcpToolNames — so tools are only ever appended, never removed. After turn N, the set is frozen and only mcp_load can grow it.

The union-only rule preserves prompt caching: the API tools array prefix stays stable, so the cached prefix grows but never breaks.

Developer Notes

• Setting: mcp.dynamicLoad.searchTurns (default 7). 0 disables dynamic loading entirely; 1 is sticky-from-start (no rolling).
• Hardcoded constant MAX_ATTACHED_DURING_ROLLING = 60 (export from packages/types/src/mcp.ts). If |attachedMcpToolNames| ≥ this after a proposed append, stop appending in that turn and log a warning.
• In build-tools.ts, before each API call within the first N turns:
  • Compute taskText = last user message (or last 2 messages, whichever is shorter).
  • Call ToolRouter.search(taskText, scopedTools, initialK).
  • attachedMcpToolNames ← attachedMcpToolNames ∪ result.
• Tool array is built deterministically (sorted by attach order, then by tool name) so cached prefix is stable.
• Files: src/core/task/build-tools.ts, packages/types/src/mcp.ts (constants + setting).
• Validation: unit test simulates 10 turns with diverging topics — attachedMcpToolNames grows during turns 1-7, stays constant during turns 8-10. Cache stability test asserts the API tools array order across turns.