Request contract
GET /api/v1/portfolios/{portfolioId}/chart. Read portfolio chart points for visualization without reimplementing performance-window selection. Send the personal token in X-API-Key and keep it outside browser code and public logs.
Response and metering
Full format uses ISO timestamps and values; compact format can return timestamp-value tuples for charting clients. Successful metered responses publish X-Credit-Cost and X-Credits-Remaining so usage can be recorded without another request.
Production behavior
A compact response changes shape intentionally. Model the selected format explicitly instead of accepting an untyped array everywhere. Handle application/problem+json errors by stable code, preserve the correlation ID and never retry a mutation unless the workflow is idempotent.