fix(tui): cap session tab pulse frame rate - #39681

What

Cap animated session tabs at one shared 60 Hz clock instead of marking every TabPulseRenderable as OpenTUI live.

The visual animation is unchanged, but a busy tab no longer drives the renderer thousands of times per second.

Before / After

Before: the first busy tab set live: true. Although OpenCode creates one global renderer with targetFps: 60 and OpenTUI reports maxFps: 60, a pulse-only benchmark measured 1,000–3,500 renderer-reported FPS (typically 1,600–1,900). The request stayed busy for 20 seconds without emitting text or tool deltas, so this isolates the animation loop from session traffic.

After: active pulses join one module-global 60 Hz clock. The clock advances every active pulse, requests rendering through the existing global renderer, and stops when the last pulse finishes. The same benchmark measures 51–55 frames/sec with OpenTUI reporting a stable 55–56 FPS.

How

packages/tui/src/component/tab-pulse.tsx:

• Keep TabPulseRenderable.live disabled, avoiding the uncapped OpenTUI live loop.
• Maintain one Set of active pulse renderables and one 60 Hz timer for the process.
• Advance all active envelopes from the same measured delta.
• Remove stopped/destroyed pulses and clear the timer when none remain.

sequenceDiagram
    participant S as Session status
    participant P as Active pulses
    participant C as Shared 60 Hz clock
    participant R as Global renderer

    S->>P: tab becomes busy
    P->>C: join clock
    loop while any pulse is active
        C->>P: advance(delta)
        P->>R: requestRender()
    end
    S->>P: pulse/fade completes
    P->>C: leave clock

Scope

• This is a localized workaround for the OpenTUI live scheduling path. It does not change the global renderer configuration.
• No animation timing, easing, color, glow, or completion behavior changes.
• CPU improves only modestly because the excess frames were cheap: pulse-only steady-state samples moved from roughly 20–32% to 18–22%. The important invariant is that renderer work is now bounded.

Testing

• bun typecheck in packages/tui
• bun run test in packages/tui: 566 pass, 5 skip, 0 fail
• bun run test test/component/tab-pulse.test.ts: 5 pass, 0 fail
• Repo-pinned Prettier and oxlint clean on the changed file
• Isolated opencode-drive pulse benchmark, 160×45 viewport, busy background session with zero streamed deltas:
  • before: typically 1,600–1,900 FPS, renderer-reported peaks above 3,000
  • after: 51–55 measured FPS, renderer-reported 55–56 FPS