Spec 011 — Every panel closeable

Graph, Agent, Terminal, Links, Git, History, Search, Explorer and Settings are closable: false today (PanelContribution.closable in each extension), so their tabs have no ×. Wanted: an × on all of them — closing a panel just removes it from its tile; nothing is lost because none of them holds unsaved state (the terminal asks first if a process is running).

Behaviour: every panel is closeable; reopening is via the activity bar / View → Show ▸ / the palette (view.panel.<id>) — 009. When a tile becomes empty it collapses (the side bar folds, the bottom panel hides) and the neighbouring split takes the space; Reset Layout restores the defaults. The last main-tile panel closing leaves the empty “open something” tile as now. The phone shell keeps its bottom bar regardless.

Change: closable: true in all contributions (the on_panel_closed hook already exists in the shell), the empty-tile collapse in shell.rs, and view.panel.* commands for every panel (not just five). E2E: close Graph, reopen from the View menu; close Terminal with a running process → prompt.

Done 2026-09-20. Every panel is closeable (closable: true in all contributions). A closed static panel (Graph, Agent, Terminal, Explorer, Search, Links, Git, History, Settings, Typst preview) goes into Workspace::closed_panels and contributes nothing until brought back; documents still close through their extension. Bringing one back: the palette’s View: Show — now generated for every static panel, not just five — the phone bar, the Explorer rail button, Ctrl+Shift+F / agent focus, or any Command::ShowPanel. When the last panel of a tile is closed the workbench prunes the tile, so the side bar / bottom panel collapse and the neighbours take the space; on reopening, the panel docks back at its edge (home_zone: side → left, bottom → bottom, right → right) and the new split gets the default proportion (22 % / 72 % / 70 %) instead of 50 %. The terminal’s sessions live in the extension, so closing the Terminal panel hides it and reopening shows the same sessions — no prompt needed. Reset Layout still restores the defaults. Suite panels.mjs (close Graph → back via palette; close all side panels → main widens by >100 px; Show Explorer → left, 22 %; Terminal close/show).