E14 · F11 · EN-021 — Shared test helpers, one path writer, one pass per corner

Pay the debt found by the audits of E01 (AUD-001 D1, D2; AUD-004 D3; CHK-002), without changing any behavior.

Acceptance criteria

• Given the playground tests, when they type, click or read the page, then they use one shared helper module, and seed their state through the page, not its attributes.
• Given the geometry tests, when they need a rectangle, an expected list of points or a signed area, then they use shared fixtures.
• Given the library, when a contour becomes path data, then one writer does it; SEPARATOR and CLOSE_PATH are declared once.
• Given a rounded contour, when it is computed, then each corner's triple and turning angle are computed once.

Tasks

One task = one commit, referenced as EN-021.Tn.

• T1 — Shared playground test helpers (2 h)
• T2 — Shared geometry fixtures (1 h)
• T3 — One path writer; one pass per corner (2 h)