E14 · F11 — A code base ready for curves

Benefit hypothesis: the debt E01 left — repeated test helpers, two path writers, a folder of 50 model files, functions without a property test — is paid before curves add a second kind of point, so that E14 builds on one structure instead of two.

Written at RET-001 (2026-10-13), at the Product Owner's request: plan the clean-up and the folder structure before the next epic. Its stories are drafts; the Product Owner sets them ready.

Acceptance criteria

1. The test helpers repeated across files (typing in a field, reading a text, mounting the playground, building a rectangle, the shoelace area) live once, in shared test modules.
2. The library has one writer of path data; contourToPathData and its separators are gone or are the writer's oracle only, declared once.
3. A rounded contour computes each corner's triple and turning angle once.
4. The folders of src/ and playground/ follow the layout chosen by SP-010, written in docs/conventions/files.md; no folder holds more than the limit it sets.
5. Every function of src/math/ and src/geometry/ has a property test: the list of tests/fitness.test.ts is empty.
6. Behavior is unchanged: every existing test passes, with the same values.

Stories

In delivery order.

ID	Type	Title	Status
SP-010	Spike	Research for F11: folder layouts and test placement	draft
EN-020	Enabler	Property tests for the nine functions without one	draft
EN-021	Enabler	Shared test helpers, one path writer, one pass per corner	draft
CHK-010	Checkpoint	Checkpoint in the middle of F11	draft
EN-022	Enabler	Folders of the library and the playground	draft
AUD-010	Audit	Audit F11	draft
VAL-010	Validation	Validate F11	draft

Feature plan

Acceptance criterion	Realized by	Verified by
F11.AC1	EN-021	AUD-010
F11.AC2	EN-021	AUD-010
F11.AC3	EN-021	AUD-010
F11.AC4	SP-010, EN-022	AUD-010
F11.AC5	EN-020	tests/fitness.test.ts
F11.AC6	every story	npm run check:all