`runtime.rs` had grown past the 500-line ceiling enforced by
`scripts/audit_source_lines.sh` once the grid-pref comment landed (522
lines). Peel the repaint/present pair — `paint_without_readback`,
`paint_without_readback_with_completion`, the private `paint_webview`,
and `paint_with_readback` — into a sibling `runtime_paint.rs`, exactly
the `paint.rs` boundary the embedding architecture doc prescribes.
`runtime_paint` is a child module of `runtime` (declared via `#[path]`,
mirroring `runtime_context`), so it keeps access to the private
`SoftwareServoHost` fields and the `webview()` / `wait_for_paint_completion`
/ `read_rendered_frame` helpers without widening any visibility. No
behaviour change: public API and call sites are identical.
runtime.rs 522 -> 469 lines. Build + clippy clean; full workspace test
suite green.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
ZacharyZhang-NY
