High-frequency terminal title updates cause sidebar CPU thrash; no user-configurable coalescing window

[arzafran]

Tracking upstream cmux manaflow-ai#6599 — applicable to our fork but needs a product/scope decision.

Assessment: The 33ms coalescer (TabManager.swift:852) is already in place and mitigates the worst case, but $title is not in the debounced sidebarObservationPublisher (Workspace.swift:6649-6675) — it fires via the immediate publisher on every flush. A user-facing config knob (e.g. terminal.titleUpdates.coalescing.milliseconds) does not exist. Whether the current 33ms is sufficient for all workloads (shell prompts with clock, tmux status bar) needs a product call before adding config surface.

Upstream: manaflow-ai#6599

[arzafran]

Decision: Defer — subsumed by #20. The 33ms coalescer stays; no new user-facing config knob. The real fix is routing $title off the immediate publisher, handled by the #20 generation-counter split. Closing in favor of #20.

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