Variant 1 — Fixed icon rail + right panel with header close Simplest fix
Keep the current layout, just fix the affordances.
What changes: The left nav becomes a permanent icon rail — no toggle, no collapse, it's always 64px. The right panel close button moves into the panel header. A toolbar button in the main header reopens the panel. All scrollbar/toggle conflicts disappear because there are no edge toggles anywhere.
When to use: If people genuinely work with Activity open alongside the timesheet. This is the smallest change from your current design.
Variant 2 — Activity as a bottom drawer
Reclaim the horizontal space. Activity lives below the timesheet.
What changes: No right panel at all. Activity becomes a collapsible bottom drawer with a horizontal card layout. Clicking the drawer header toggles it. The timesheet gets the full width, which matters on narrower screens.
When to use: If Activity is a quick-reference feed — something you glance at but don't scroll through. Horizontal cards let you scan times at a glance. This pattern is common for console/terminal panels in dev tools.
Tradeoff: Loses vertical space instead of horizontal. Doesn't scale if Activity items are long or numerous.
Variant 3 — Activity as a slide-over overlay Recommended
The panel appears on demand over the content, not beside it.
What changes: Activity is not a persistent panel — it's a slide-over sheet triggered by a toolbar button. It overlays the main content with a subtle scrim. Clicking outside or the × closes it. The main layout is always just: icon rail + full-width timesheet.
When to use: If Activity is something you check occasionally rather than monitor continuously. This is the pattern Google uses for side panels in Gmail/Calendar, and Apple uses in many macOS apps.
Why I'd recommend this: It eliminates every edge/scroll/toggle issue. The main content always has full width. The panel only exists when you want it. And it works identically on every screen size.
Variant 4 — Activity as a tab alongside the timesheet
No panels at all. Activity is a peer view within the main content area.
What changes: The main area has tabs: "Timesheet" and "Activity." You switch between them. There's no secondary panel, no collapse button, no competing scrollbars. The layout is just: icon rail + one content area.
When to use: If Activity and the timesheet are never needed side-by-side. This is the most radical simplification but also the cleanest. It's essentially the mobile pattern applied to desktop.
Tradeoff: You lose the ability to see Activity while editing the timesheet. If that's important, this won't work. But if Activity is mostly reviewed separately, this removes all complexity.