Sidebar: visual divider between pinned and unpinned threads

[jvitormelo]

Problem

Pinned threads sit at the top of the sidebar, but nothing marks where they end. The only cue is the small pin icon, which is easy to miss when scanning, so it's hard to tell at a glance where the pinned block stops and the regular threads begin.

My use case: I keep my recurring automations (threads bound to schedule_task) pinned, because that's the only stable place for them today. The pinned block is effectively my "automations" area, and without a visual boundary it blends into the threads I'm actively working in.

Proposal

Render a thin divider after the last pinned thread.

Mockup (the first three threads are pinned):

A nice extra, not required: let the pinned block collapse, the way Working / Snoozed / Settled can.

Smallest useful scope

Just the divider. No new setting needed, unless the maintainers prefer it opt-in.

Related

• [Feature]: A persistent thread per automation, kept out of the active sidebar #18039 describes the underlying need much better (a dedicated, collapsed "Automations" section for threads bound to scheduled tasks). If that lands, this divider matters less for my case, but it's still a cheap readability win for pinned threads in general.
• Theme role for pinned sidebar threads (`sidebarRowPinned`) #14453 proposes a theme color role for pinned rows; a divider is a complementary, theme-independent cue.

[juliomuhlbauer]

Related: #22958 proposes making Pinned a collapsible section (expanded by default, with a count and activity dot when collapsed), plus a separate collapsible "Saved" section for long-lived reference threads. A collapsible header would also give the visible boundary this discussion asks for.