perf(desktop): kill sidebar + overlay render churn from hot store subscriptions

[OutThisLife]

Summary

Overlays and workspace pages showed heavy render churn while a session streamed. The measured cause splits into three independent mechanisms, not one:

1. Sidebar bleed (dominant, cross-cutting). The sidebar stays mounted in the shell beneath/beside every overlay and page. It subscribes to hot stores that republish on every streaming delta, and its rows were unmemoized — so one token re-rendered the whole session list, and the global render counter attributes that churn to whatever surface is open at the time. This is why Cron, Profiles, Agents, Starmap, Webhooks all showed the same Codicon/SidebarRowLabel/SessionStatusDot churn despite sharing no page code.
2. Per-surface hot-store subscriptions. Command Center, Skills, and Settings each subscribed to a hot store ($sessions, $gateway) unconditionally, re-rendering the overlay itself on every tick even when the subscribed data wasn't on screen.
3. Per-surface local loops. Artifacts has a self-sustaining tooltip/link-title cycle that churns at idle with nothing streaming — unrelated to the stores above.

Each is addressed (or scoped out) separately below.

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Hot stores involved and what ticks them

store	republishes on	consumers hit
$sessions	every session title update / new session / stream-driven mutation (gateway-event.ts writes on title deltas)	sidebar list, Command Center
$workingSessionIds	a session starting/finishing a turn	sidebar rows, every SessionStatusDot
$attentionSessionIds, $stalledSessionIds, $unreadFinishedSessionIds, $backgroundRunningSessionIds	per-session status transitions during streaming	every SessionStatusDot
$gateway	connect / disconnect / reconnect	Skills view (only needed by MCP tab)

Each is a plain nanostore that publishes a new array/object reference per write, so useStore(store) re-renders every consumer on every write regardless of whether the slice they read changed.

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Per-surface breakdown (measured, 2s window, CDP render counter)

Origin column: sidebar = churn from the shell's session list captured by the global counter while this surface is open; own = components rendered by this surface itself.

surface	dominant churning components	origin	before (wasted)	after
Cron	Codicon 218, SidebarRowLabel 90, DisclosureCaret 9	100% sidebar	407	~30 (idle-own: 0)
Starmap	Codicon 78, SidebarRowLabel 30	100% sidebar	188	56 (idle-own: 0)
Profiles	Codicon 370, SidebarRowLabel 150 (sidebar) + TooltipContent 7 (own)	~95% sidebar	732	~80
Agents	Codicon 73, SidebarRowLabel 30	100% sidebar	132	9
Webhooks	Codicon 76, SidebarRowLabel 30	100% sidebar	154	22
Command Center › System	Codicon 169, SidebarRowLabel 60, Kbd 28, GitBranch 18	sidebar + own $sessions sub	425	0–10
Messaging	Codicon 80, PlatformAvatar 65, StatusDot 64, PlatformRow 31	sidebar + own platform rows	312	~170 (own residual ~17)
Skills (Skills tab)	Kbd 12, Codicon 11, GitBranch 9, KbdCombo 5	own $gateway sub (keybind bar)	88	8
Settings › Model	SelectItem 123, Primitive.span 408, SelectItemProvider 123	own model-<Select> re-rendering under parent churn	1,477*	0
Settings (Appearance/Notifications/Providers/Keybinds/API Keys/Plugins/Archived/About)	—	—	0	0
Artifacts	TooltipContent/Presence/Tooltip/Popper (mount cascade)	own (mount)	5,528 (mount) → 12 settled	12
CmdK root (typing "setting")	Block 833, Ct 833, inlineCode 807 (transcript behind modal) + PaletteRow/CommandItem 51 (own)	own + transcript	5,519	3,201
CmdK theme / color-mode submenus	PaletteRow/CommandItem 51	own	209	≈neutral

* Settings › Model's 1,477 was captured during an active stream tick landing while the model <Select> was mounted; at idle it is 0. It re-rendered because its parent (SettingsView) re-rendered — fixed indirectly by memoizing navGroups so the overlay stops rebuilding, plus the sidebar no longer forcing shell-wide work. Not a targeted <Select> change.

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Fixes (mechanism per file)

chat/sidebar/session-row.tsx — the cross-cutting fix.
SidebarSessionRow is now memo() with a custom comparator. The row's callback props (onArchive, onResume, onPin, …) are fresh closures every render by design — they close over the row's session id — so a default memo never bails. They are pure id-forwarders (identical behavior for a given row), so the comparator ignores them and compares only paint-affecting data: session, isPinned, isSelected, isWorking, branchStem, reorderable, dragging, showProfile, dragHandleProps, className, style. A row whose data is unchanged now bails while a sibling session streams. Verified: after clicking through 6 sessions, SidebarSessionRow no longer appears in the render report at all.

chat/session-status-dot.tsx — per-session selector.
The five $…SessionIds arrays were read as useStore(array).includes(id) — re-rendering every dot on every array tick. Now each reads via useStoreSelector(array, ids => ids.includes(storedSessionId)), which returns a boolean and bails on Object.is, so a dot repaints only when its own membership flips. This is what stops the SessionStatusDot and downstream Codicon churn that dominated every overlay's numbers.

command-center/index.tsx — gate + memo.
$sessions/$pinnedSessionIds are read through useStoreSelector returning a stable empty array when section !== 'sessions', so the System/Usage/Maintenance tabs never re-render from session churn. navGroups moved into useMemo.

skills/index.tsx — gate.
$gateway (needed only by the MCP tab) read through useStoreSelector returning null unless mode === 'mcp', so the Skills/Toolsets/Hub tabs stop re-rendering on connect/disconnect. Dropped the now-unused HermesGateway import.

settings/index.tsx — memo + stable callbacks.
navGroups (previously rebuilt inline with fresh onSelect closures for every nav item on every render) moved into useMemo; openSubView/openProviderView/openKeysView wrapped in useCallback so the memo deps are honest and stable.

overlays/overlay-split-layout.tsx — leaf memo.
OverlayNavItem wrapped in memo() so a nav rail item doesn't re-render when a sibling's active state flips.

command-palette/index.tsx — leaf memo.
Extracted PaletteRow as a memo() component so palette items don't re-render on unrelated parent state (open/close, theme). Cut CmdK-root wasted renders 5,519 → 3,201 (42%).

artifacts/index.tsx — stable ctx + cell memo.
cellCtx moved into useMemo with a useCallback'd onOpenChat (was a fresh object + closure every render, re-rendering every cell). PrimaryCell/LocationCell/SessionCell wrapped in memo() so one row's async link-title fetch doesn't re-render the whole table during the mount cascade. Correction to an earlier draft of this description: the ~5,500 Artifacts number was the one-time mount/load cascade (fetching artifacts, resolving link titles, mounting per-row tooltips), NOT a steady-state loop — measured settled (4s after mount) Artifacts is 12 wasted renders / 3s. The cell memo lowers the mount-cascade cost; there is no idle loop to fix.

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What is NOT fixed (scoped to follow-up PRs)

• Messaging platform-section churn (settled). PlatformAvatar/StatusDot re-render ~32×/3s (prop-driven, state:0) from the sidebar messaging section on stream ticks — a real steady-state loop, separate follow-up PR.
• Artifacts mount cascade. Not an idle loop (settled = 12 wasted/3s); the mount cost is inherent to loading + link-title resolution + tooltip mount. Cell memo already trims it. No further action needed.

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Metrics methodology

Measured on a live desktop instance via the in-app CDP render counter (__RENDER_COUNTS__), medians over 3 runs where noted. Sidebar-bleed numbers were captured with a session actively streaming (the only condition under which those stores tick); at idle both before and after read ~0 for those surfaces, because the churn is stream-driven — which is exactly when the app felt laggy. Artifacts was initially reported as an idle loop; on re-measurement it is a one-time mount cascade (settled = 12 wasted/3s), corrected above.

Pattern

Same invariant as #72504: hot-path state must reach leaves through stable identities. A parent subscribing to a store that ticks, then rendering a .map() of children, converts one store tick into N subtree renders. The fix is useStoreSelector (subscribe to a scalar, bail on Object.is) + memo on the leaf — with a comparator that ignores callbacks whose behavior is stable even when their identity is not.

Verification

• apps/desktop typecheck: clean
• apps/desktop lint: 0 errors
• apps/desktop tests: 104 passed

[github-actions]

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_{ran on 50d0de0}

all good!