Fold the decisions into the drawing-surface specification and stage the tickets

[QuentinRoy]

Question

Fold every settled decision into one specification for what bounds the drawing surfaces, and stage it as ready-for-agent tickets.

This is the map's destination. Nothing here is a decision; it is the write-up and the hand-off.

The specification covers:

• The sizing rule, its ink margins, and when it is re-evaluated.
• Which element is sized, and what that means for the wrapper Map: land the wedge-ring menu design and a configurable theming API #263 introduces.
• Containment: the mechanism, and whether it is part of the public interface.
• The coordinate seam, and which call sites change.
• All four surfaces, including the menu — even where the answer is "documentation, no code change".
• Migration: what breaks, the changesets, and the README contract. Coordinate with Update the README and write the upgrade note #246, which already owns the README.

Acceptance, required in the staged tickets rather than left to judgement: a case with a deliberately undersized parent that shows the drawing escaping, and a clipped counterpart proving containment still works. Nothing in the repo exercises either today. Note the existing snapshots that encode surface geometry (src/layout/__snapshots__/stroke.test.ts.snap) and the stubbed getBoundingClientRect in the renderer tests.

Then cut it into ready-for-agent tickets in the style of #244/#245/#246: scope and acceptance criteria settled, each one buildable without reopening a decision.