[LinuxDevil]

What changed

AppShell can now host a third grid column on the right: a docked panel that pushes the screen narrower (not an overlay), opens/closes, resizes from its left edge (360–640px, capped at 45vw), and remembers width + open state in localStorage. Below 860px the same content renders as a right-side sheet over a scrim. The panel's content is a prop; the Agent Author fills it in a later ticket.

• src/shell/dockState.ts (new): width constants/limits, dockMaxWidth, clampDockWidth, readDockWidth, readDockOpen on top of readStored/writeStored (forge.dock.width, forge.dock.open).
• src/shell/Dock.tsx (new): DockProvider / useDock (open + width state, lazy restore, re-clamp on viewport resize), Dock component (renders nothing while closed), useDockResize (pointer-capture drag, keyboard splitter), opener-focus capture/restore, sheet focus, Escape handling.
• src/shell/dock.css (new): third grid column rules, resize handle, sheet + scrim, reduced-motion handling.
• src/shell/AppShell.tsx: wraps the layout in DockProvider; ShellLayout sets data-dock/--dock-width and renders <Dock label="Agent Author"> when the dock prop is defined; opening the narrow nav drawer closes the dock (one drawer at a time). App.tsx does not pass dock, so nothing changes visually yet.

How tested

• npm test --workspace apps/agent-forge -- --run — 985 tests, 90 files, all green (incl. new dockState.test.ts 6 cases and Dock.test.tsx 8 cases)
• npm run typecheck --workspace apps/agent-forge + typecheck:server — clean; npm run test:server — 1121 tests green
• npm run lint --workspace apps/agent-forge — 0 errors (31 pre-existing warnings in server files, none in this diff)
• Root npx tsc --noEmit, npm run lint, npm run test:coverage (483 files green), npm run fallow (0 dead code, 0 above threshold), npm run docs:ratchet, npm run api:check, npm run docs:llms:check, npm run size-check — all clean

Acceptance criteria

• With dock undefined the shell renders exactly as before (2 columns, no data-dock) — covered by test + all existing AppShell tests stay green
• Open docked: grid has 3 columns, the screen narrows (push, not overlay), the dock card lines up with the floating screen card (8px gaps via --space-2 padding)
• Dragging the handle resizes between 360 and min(640, 45vw); release persists to forge.dock.width (live preview writes nothing mid-drag)
• Arrow keys resize by 16px; Home/End jump to the limits; the separator announces aria-valuenow / aria-valuemin / aria-valuemax
• Reload restores width and open state; broken storage falls back to closed / 490px without throwing
• ≤ 860px the content opens as a right sheet with a scrim; scrim click and Esc close it
• Reduced motion: no slide-in animation, no width transition (shell.css grid transition already gated; .dock-resize transition and sheet animation gated on prefers-reduced-motion)

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