Subtle pulse animation on sidebar tabs when their session is emitting output

[AThraen]

Generated from a competitor-analysis pass (TerminalConductor, May 2026).

Summary

When a session is actively emitting PTY output, the sidebar entry's accent stripe softly pulses, giving a visual cue that the session is "doing something" — distinct from the alert/waiting badges, which only fire on detected prompts.

Motivation

Today the only signal that a background session is active is the alert badge (AlertDetector fires on detected prompts). Long-running output — a test run, a build, a streaming agent reply — gives no visual signal until it finishes. A pulse fills that gap without competing with the alert badge.

Proposed behaviour

Trigger

• TerminalBridge.RawOutputReceived already fires on every PTY chunk.
• Per-session, accumulate bytes emitted in a rolling 500ms window. If > ~32 bytes/500ms (tunable), the session is "emitting".
• Stop emitting state when no output for >500ms.

Animation

• Target: the existing 4px accent stripe on the sidebar entry.
• A Storyboard animates Opacity 0.55 → 1.0 → 0.55 over ~1.0s, looping while emitting.
• Begin() on first transition to emitting; Stop() on transition to idle.
• Hard-skip for the active session — we can see its output ourselves; pulsing its own sidebar entry is visual noise.

Settings

• Add AppSettings.ShowActivityPulse (default true).
• Pulses also disabled while a session has NeedsAttention == true — alert badge wins, no need for both.

Out of scope

• Pulse on the terminal pane itself (sidebar only to start).
• Pulse intensity based on output volume (binary on/off is plenty).
• Differentiating agent-emitting from shell-emitting.

Inspiration

TerminalConductor's "Activity pulses" — subtle tab animation while a session emits output. See https://terminalconductor.com/.