# Explorer sidebar and side pane

The Explorer sidebar and the side pane share panel implementations, but they have different shell
contracts.

| Surface          | Purpose                      | Lifecycle                                  |
| ---------------- | ---------------------------- | ------------------------------------------ |
| Explorer sidebar | Files and Changes navigation | Cmd+E shows or hides the dedicated dock    |
| Side pane        | Ordinary workspace content   | Created and closed like any workspace pane |
| Workspace sheet  | Compact look-ups             | Holds one tab; closes or becomes a tab     |

## Panel host contract

Every desktop panel registers its supported `PaneHost` values and presentation. Launchers derive
fixed-target labels and icons from that registration, filter by host, and never substitute one
panel type for another. Tab moves reject unsupported destinations, and placement resolves only to
a compatible pane.

Files and Changes are the Explorer defaults. Their panel manifests mark them as singletons,
so a pane’s + menu omits each while that pane already contains it. Closing one makes its menu
item available again. Other compatible tabs, including agents, terminals, files, and diffs,
can move between Explorer and main panes.
Keep panel implementations independent of either shell. `WorkspacePanelHost` owns mounting and
retention, while each shell owns its tabs, focus, dragging, resizing, and shortcuts.

## Workspace sheet

On compact layouts, files and subagents open in a closable sheet over the workspace, so the tab
switcher keeps only agents and terminals. A panel kind opts in with `compactSheet` in its manifest
(`packages/app/src/panels/panel-manifest.ts`), and the layout store's `openTab` decides between
sheet and tab, so callers open targets the same way on every layout. The sheet holds one ordinary
`WorkspaceTab`, which is not persisted.

The sheet is modal and covers the whole compact column, header included. It renders in the
workspace tree rather than through `IsolatedBottomSheetModal`: its panel needs the navigator and
every workspace provider an ordinary pane has, and a portal drops them
([floating-panels.md Gotcha 7](floating-panels.md#gotcha-7--a-sheet-cannot-read-context-from-its-call-site)).

A sheet holding unsaved work is never implicitly displaced; only its guarded close removes it.
Moving its tab to another host remounts the panel, and the file editor keeps unsaved text in the
mounted view, so the move would drop it. Widening the layout is the known exception: it still moves
the sheet's tab into a pane, and edits the autosave has not started writing are lost.

## Explorer sidebar

`packages/app/src/workspace-tabs/explorer-sidebar.ts` owns show, hide, toggle, and view selection.
On desktop, the shell is rendered outside the workspace split canvas so it divides the full
workspace, including the header. It has its own persisted width and resize handle. Main-pane splits
never read or modify that width.

`packages/app/src/workspace-tabs/open-supporting-view.ts` owns semantic Changes and pull-request
opens. Compact and wide native layouts select the matching Explorer tab. Desktop Changes opens
follow the shared diff preference. Desktop pull requests use their Main panel, On the side, or
Explorer sidebar setting. Automatic PR discovery follows that preference once per workspace without
interrupting the user's work. Closing the tab opts that workspace out of future automatic opens,
even for a different PR; moving or reordering it remains the user's choice.
Callers request the content and never choose the shell.
The composer Changes pill is a two-stage desktop action: it first reveals Explorer on Changes, then
routes later presses to the working diff through the shared diff preference.

The persisted layout still contains the Explorer pane so tabs survive reloads. The renderer removes
that pane from the workspace split tree and docks it separately. Persisted identifiers retain the
literal `"explorer"` pane id and `explorerPaneIdByWorkspace` key for compatibility.

Explorer uses the shared workspace tab row and ordinary tab context menus. Files and Changes
hide their close buttons through the panel manifest; close them from the tab context menu.
Other tabs reveal the close control on hover. The + menu opens compatible panels in the dock and
omits Agent and terminal profiles. Agents and terminals can still be dragged into Explorer.
Bulk-close actions apply only to the dock's tabs. Explorer tabs can be reordered and dragged
between compatible panes, but the dock cannot be split or maximized. Selecting an Explorer tab
does not change workspace focus.

Cmd+E shows or hides Explorer without changing its selected view. Compact layouts use the combined
full-screen Explorer overlay for Changes, Files, and pull requests, and close it after a file opens. Compact Changes has no tree rail; its overview is the Jump to file action (`packages/app/src/git/jump-to-file/`), a sheet over the same changed-files tree the desktop rail renders.
Wide native layouts without pane splits use the same combined content in a resizable inline dock;
opening a file leaves that dock visible. Both presentations keep their selection in the panel store
and reuse the layout store's per-workspace Explorer width. They do not create a second Explorer
lifecycle.

## Side pane

`packages/app/src/workspace-tabs/open-beside.ts` owns content opened beside the user's work. The
layout store remembers one ordinary pane per workspace. The first side open creates a full-height
right split around the workspace root; later side opens reuse it. Only the `split-panes` layout
mode opens beside. Compact and single-pane layouts (touch tablets) open the same target in the main
pane, so callers never check whether splits render.

Removing a pane clears its remembered id; a later side open creates a new pane. The last visible
ordinary pane stays when its final tab closes and shows the New launcher. An empty workspace does
not automatically create an agent draft tab; choosing Agent opens one. Explorer cannot replace the
workspace canvas, even when visible. Restoring a saved layout enforces the same rule while preserving Explorer and saved
tab content. There is no hidden side-pane lifecycle.

Placement intent still controls existing tabs:

| Mode      | New target                  | Existing target                   |
| --------- | --------------------------- | --------------------------------- |
| `pane`    | opens in the requested pane | moves to the requested pane       |
| `prefer`  | opens in the requested pane | stays where the user placed it    |
| `focused` | opens in the focused pane   | focuses it where it already lives |
| `ambient` | opens in a compatible pane  | focuses it where it already lives |

Explicit **Open to Side** uses `pane`. Implicit opens use `prefer`, so a preference affects only a
new target and never yanks an existing tab out of a user-selected pane.

## Routing preferences

Desktop **Settings → Layout → Open location** has independent Main panel or On the side choices for
Explorer Files, diffs, chat files, files opened from diffs, and subagents. They default to Main
panel. Mobile ignores them.

Pull requests have a three-way open location: Main panel, On the side, or Explorer sidebar. Explorer
sidebar is the default. Compact layouts always open pull requests in Explorer regardless of this
desktop preference.

Panels request an implicit open through the narrow `openPreferredTarget(target, source)` pane
contract. Entry points outside panels use `openPreferredWorkspaceTarget`. Do not branch on a
specific shell inside a panel.