Two paths in `WebSurfaceStore::tick` were downgrading a perfectly good
Ready frame back to Failed / Loading on every transient hiccup:
- `WebSurfaceRuntimeFrame::Failed` overwrote the surface state
unconditionally. Combined with the 125 Hz tick (which submits a Poll
for every visible tab and any transient ensure / poll error becomes
a Failed response), even one parse glitch wiped the rendered page.
- The `initial_display_gate_message` and `should_hold_initial_frame`
checks for incoming Ready frames hardcoded `has_previous_frame =
false`, so a stray empty paint pass after the page had already
rendered would knock the surface back to Loading or Failed.
Detect whether the surface already has a `Ready(_)` state and:
- ignore Failed responses (logging through `tracing` for diagnostics)
while a real frame is on screen;
- pass that "had ready" signal into the gate / hold checks so they only
apply to the very first paint, not later refreshes.
The page now stays put even when Servo emits a momentary error; only
the first-paint failure path can mark the surface Failed.
ZacharyZhang-NY
80cff6dad3