D342 - A grammar shape is disabled with a reason

Status: decided Date: 2026-08-27

PatternSpec::disabled is an Option<String>; its presence disables the shape and its text states the cost and what would bring the shape back. A disabled shape is validated before it is filtered out. The two shapes that repeat learned are disabled, and the names only they spell are on the ceiling list with that reason.

Why: a shape using learned twice makes a round quadratic in that list and caps the vocabulary far below what the unsplittable names need, while spelling only a few names. The shape is early rather than wrong, so it stays in the file. A bare flag grows into a file of unexplained exceptions. Validating first stops a stale part name surfacing only on re-enable.

Rejected:

• Deleting the shape: loses a shape that returns when the vocabulary grows.
• A boolean flag: no record of why.