Module render_certificate 

Production render certificates (bd-6b9nr): explicit, named skip decisions for the diff stage — never opaque heuristics.

The runtime’s TerminalWriter builds a RenderCertificateInputs from facts it can prove locally each frame and asks evaluate_render_certificate for a decision. The certificate maps to a DiffSkipHint consumed by BufferDiff::compute_certified_into:

• FullRequired — no previous frame, viewport change, or a due full-redraw probe: a full-fidelity pass is mandatory;
• SkipAll — zero dirty rows: the frame provably introduces no cell changes relative to the tracked baseline, so the diff scan is skipped entirely;
• NarrowToDirty — the diff scan is narrowed to exactly the dirty rows (soundness inherited from the buffer’s dirty-tracking invariant: dirty rows ⊇ changed rows, which in turn requires that the buffer’s dirty state was cleared while its content was identical to the diff’s old baseline — see BufferDiff::compute_dirty’s precondition; the production writer guarantees this by diffing consecutive frames of one buffer lineage).

The decision tree is deliberately conservative and fail-open: any condition that cannot be proven falls back to FullRequired. Every certificate names its causes so evidence logs explain why work was skipped or performed (the mirror of this model used by the offline gauntlet lives in ftui-harness::render_certificate; this module is the production-side evaluator, kept in ftui-render because the harness is downstream of the runtime).

Structs

RenderCertificate

An explicit, explainable skip decision for one frame.

RenderCertificateInputs

Facts the writer can prove about the frame before diffing.

Enums

RenderCertificateLevel

The certified level of work elimination.

Functions

evaluate_render_certificate

Evaluate the conservative production decision tree.