Conflicts were the two mesh/shader implementations meeting: kept the
remote's newer complete version (typed shader uniforms, shader color
uniform binding, mesh vertex editing defaults, status-bar shell stroke
handling); deduped two identically-replayed RenderBackend methods.
finish_if_epoch previously routed the empty-queue case through
drain_finished_run, which set the process-global needs_final_frame flag
even though a run that never queued a reveal never put a cursor on
screen. That stray flag made next_reveal_deadline_ms return a redraw
deadline out of an idle registry, and — because the registry is shared
across the whole test binary — perturbed an unrelated exact
animation-deadline assertion whenever a design-session test dropped an
empty session in parallel.
Clear an empty finish inline without arming the flag; the paint-path
drain still arms it after real reveals prune, where a cursor genuinely
was on screen. Adds a regression test.
Verification note: the op-editor-core suite could not be run for this
commit because the shared workspace is transiently non-compiling under a
concurrent mesh-gradient/SkSL-shader jian bump (new PenFill variants not
yet handled in fills.rs — unrelated files). Change is trace-verified and
touches only agent_indicators; re-run pending the tree compiling again.
