0004: The seal is rendered in memory

Status: accepted, implemented. The plan marked this "to be confirmed during implementation, the imaging bridge may impose restrictions"; it was confirmed.

Context

v1 generated the visual seal as a file, then read it back to stamp it into the document. That is an intermediate file, on a path that already had a cleanup problem (0003), for data that never needed to leave the process.

Decision

The SealRenderer contract returns bytes. Seal\InterventionSealRenderer implements it on Intervention Image v3, and Signing\Incremental\SealAppearance stamps the widget from those bytes.

Consequences

• No intermediate file between generating the seal and stamping it.
• Everything v1 hard-coded (driver, font path, size, colour, background, placement) comes from configuration, with SealPlacement carrying position and page.
• Omitting seal() produces an invisible signature, which is still a valid one: the seal is an appearance, not part of the cryptography.
• sealFrom($path) skips the renderer for callers who already have an image.