Root router: "When in doubt, invoke the skill" routes to skills the user has disabled #3018

The root SKILL.md (checked on 1.91.13, lines 225-235) lists about 40 routes by skill name, then says:

When in doubt, invoke the skill. A false positive ... is cheaper than a false negative ...

Two effects on current Claude models (Opus 5.5, Sonnet 5.5), which follow routing text literally:

1. Claude Code's skillOverrides lets users turn skills off ("benchmark": "off", "learn": "off", ...). The router still names them, so the model tries to invoke skills that are not loaded, and every disabled entry is a dangling reference.
2. "When in doubt, invoke" tips borderline requests into a full workflow. On these models that over-triggers more than it used to.

Possible fix: describe the routing by intent and let each skill's own description do the matching (the harness already lists only the enabled skills), and drop the "when in doubt" line or replace it with when not to invoke.

Setup: gstack 1.84.1 locally, the lines checked unchanged on main (1.91.13); Claude Code with about 50 gstack skills set to "off".