TUI: main thread burns ~100% CPU continuously redrawing a spinner (~15fps writev to tty) with no active output

Environment

• opencode 1.18.18 (npm latest)
• Linux x86_64, run in a terminal (/dev/pts/*)

Observed (confirmed via strace + per-thread /proc sampling)

• The TUI main thread holds ~1 full core (~94-100%) even when the user is not interacting.
• strace shows the main thread repeatedly calling writev(1, ...) writing a ~106-byte spinner frame (~15 fps) to the tty, e.g. \x1b[?2026h\x1b[?25l\x1b[60;4H\x1b[38;2;42;67;101m ... \u2b1d\u2b1d\u2b1d ....
• In the same window there are no network / disk / log syscalls — the CPU time is spent between the writes.
• Behavior varies by process: in some instances the burn is entirely on the main thread (HeapHelper threads idle), in others HeapHelper threads also show elevated GC activity.

Why this looks like a bug

• Writing a 106-byte frame 15x/s should cost <1% CPU. The ~100% burn is in the rendering/layout work before each writev, and the spinner appears to keep animating even with no visible active turn, so the render loop never idles.

Not yet determined (needs a perf profile)

• Whether the spinner is "stuck" because a background task (e.g. title generation or a hung turn) never completes, vs. the render loop simply not being throttled. We did not capture a perf profile, so the exact hot function is unconfirmed. Filing this as a bug report rather than a definitive root cause.

Impact

• Each such session burns ~1 core and makes the terminal feel frozen/hung. We killed several opencode -c processes assuming a deadlock before tracing the actual CPU usage.

Notes

• app_toggle_animations keybind defaults to none, and there is no persistent config option to disable animations.
• npm latest is 1.18.18, so there is no newer version to try as a workaround.

Happy to provide full strace output or a perf profile if that helps narrow it down.