The CLI status bar tracked /background agent tasks (▶ N) but not shell
processes spawned via terminal(background=true). Both kinds of work can
run concurrently and a user has no in-bar signal for shell processes.
Add an independent indicator (⚙ N) sourced from
tools.process_registry.process_registry._running. The two indicators
render side-by-side when both are active (▶ 1 │ ⚙ 2), hidden when their
count is zero. Renders at all four status-bar tiers (text fallback +
prompt_toolkit fragments, narrow + wide widths). The narrow <52 tier
still drops both for space — unchanged.
New ProcessRegistry.count_running() returns len(_running) without
acquiring _lock; CPython dict len is atomic and we're polling on every
status-bar tick, so lock-free is the right tradeoff.
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