Editor window: worktree support (chat.editorWindow.enableWorktree) - #348306

Stacked on #348304, #348298, #348294 and #348309. Review from the merges of those branches on. Merge order: #348304, #348298, #348294, #348309 (after #348292), then this PR.

It merges #348294 (375b387) because the feature moves the folder on its own: without #348294's folder location history, a listed or open chat of the primary folder would leave the sessions list (and its content be disposed) as the folder moves to a worktree.

Worktree support in an editor window with a single local folder, behind the experimental, experiment-controlled setting chat.editorWindow.enableWorktree (off by default). It works on every surface that shows chats: the Chat view, with or without its sessions list, and a host that replaces it once that host reports the chat it shows (IChatViewHostService.shownSession). It depends on no feature that registers such a host.

Changes

AgentHostWorktreeContribution (agentHostWorktree.contribution.ts, not in the Agents window), while the setting and AI features are on:

• Locations: registers AgentHostWorktreeLocationProvider, so the worktrees that local agent host sessions work in are locations of the folder, also for every picker that reads the folder's locations.
• A chat the user opens: the folder moves to where the chat works, the working directory of a local agent host session, and back to the folder's own location for a local chat. This supersedes any switch under way.
• Automatic follow: the shown session moves the folder on its own once its working directory is known, such as after its first request, and as it changes, such as to a worktree its agent created. Such a switch gives way to any other (ifIdle), and applies only while the user opened no chat since it started.
• Last chat per location: it remembers the last chat opened at each location, and opens it as the user moves the folder there themselves (not on its own moves).
• Terminals: terminals that started where the folder no longer is are marked.
• Turning off: as the setting or AI features are turned off, the folder returns from a worktree to its own location.
• Telemetry: editorWindow.worktreeFolderSwitch records how each switch ended. The setting's experimentTrigger is logged as a chat that the feature can follow (a local agent host session or a local chat) shows in a window whose folder can move, with the setting on or off. That moment precedes both the folder chip and any move of the folder.

The Chat view's folder chip (AgentHostWorktreeFolderChoices), for a new agent host session in a window with a single local folder:

• It offers New Worktree first, then the folder and the worktrees that sessions work in, in the shared Folder and Worktrees sections (groupFolderLocations from Workbench: worktree locations from agent host sessions, a shown-session seam and shared folder picker sections (infra, unused) #348304). Each section lists where the folder is now first, described as current.
• Picking the folder or a worktree makes it the session's working directory (IAgentHostNewSessionFolderService).
• New Worktree sets the session's isolation to worktree, and the chip's label shows it. It is offered only where the session's isolation allows a worktree.
• A multi-root window's chip is unchanged.
• The setting: chat.editorWindow.enableWorktree, boolean, default false, tags: ['experimental'], experiment: { mode: 'auto' }. It is an editor window UI setting, so it needs no runtime managed setting or policy.

Review fixes

• Any chat the user brings up, also one that moves nothing, and any move of the folder that is not the feature's own supersede every earlier switch.
• A worktree inside the folder follows; a folder inside the folder's own location that is no worktree works there.
• A restored chat's working directory, once the sessions list knows it, is not a change to follow.
• Disposing cancels and invalidates switches under way and clears its terminal marks.
• With the setting off, terminals are not marked; turning it off clears their marks.
• Each fix has a test that fails without it.
• Validation:
  • pnpm run typecheck-client: passed
  • pnpm run valid-layers-check: passed
  • oxlint: passed
  • ./scripts/test.sh --runGlob 'vs/workbench/contrib/chat/test/browser/agentSessions/agentHost/**/*.test.js': 78 passing
  • Together with the seam suites (chatViewHostService, chatViewPane, folderLocationSections): 61 passing in the targeted run

Review fixes, round 2

• A later open that moves nothing (a local chat at the folder, a chat where the folder is, a new chat) or disposing supersedes a move that the workspace is still making, by asking for where the folder is.
• A chat that works in a folder inside a worktree follows to that worktree, and stays where the folder is at it.
• The last chat of a location that the user moves the folder to opens as restored (IChatViewHostOpenOptions.restore), so it keeps the folder there.
• The last chat is remembered also where the folder already is, follows the session that a first request commits it to, and is forgotten once the sessions list no longer lists it. Moving to a location again refreshes its position among the most recent.
• The chat that a first request makes (shownSession reason commit) follows on its own (ifIdle), so a move that the user started still wins.
• The folder chip lists the worktree that the folder is at as Current, also one that no session lists any more.
• Worktrees are described by their branch, or the short commit of a detached HEAD, and are compared by their real paths (Workbench: worktree locations from agent host sessions, a shown-session seam and shared folder picker sections (infra, unused) #348304).

Decisions

• A session that a provider rebinds to another resource (ISessionReplacedEvent, from contrib/sessions, which contrib/chat may not import) is not carried over. Draft and untitled chats are never remembered, and the session that a first send commits is the one recorded: natively it is reported as commit, and an extension's commit fires onDidCommitSession, which rebinds the entry. A remembered chat that a provider rebinds later leaves the sessions list, so its entry is forgotten. Moving to that location then opens nothing, rather than a wrong chat.
• The folder's locations are the worktrees that non-archived local agent host sessions work in, not every worktree of the repository. This was a deliberate product decision for the shared provider.
• The earlier prototype's storage key for the last chat per location is not migrated. The feature is experimental, so it starts empty.
• Validation (round 2, macOS):
  • pnpm run build-fast --client-only, then ./scripts/test.sh --reporter dot --runGlob 'vs/workbench/contrib/chat/test/browser/agentSessions/agentHost/**/*.test.js': 85 passing
  • ./scripts/test.sh --reporter dot --run .../chatViewPane.test.ts --run .../chatViewHostService.test.ts --run .../folderLocationSections.test.ts: 47 passing
  • Red check against the sources before the fixes: 8 failing in agentHostWorktree.test.ts and agentHostWorktreeLocations.test.ts, and 1 failing in agentHostWorktreeFolderChoices.test.ts
  • pnpm run typecheck-client: passed; pnpm run valid-layers-check: passed; oxlint on the changed files: passed

Composers of the editor window (stacked on #348309)

AgentHostWorktreeComposerFolders (contrib/sessions/browser/agentsView/agentHostWorktreeComposerFolders.ts, loaded from workbench.common.main.ts):

• While the setting and AI features are on, it registers the folder options with IEditorWindowComposerFoldersService (Sessions: the chat part of editor windows, for any feature to enable #348309). It neither needs nor creates the chat part. The editor window's new-session composers then offer the window's folder, its own location and the worktrees that sessions work in: the chat part's composers, and the Chat view's once it registers its composer. They are presented as folder or worktree, with where the folder is now marked Current (IAllowedFolderPresentation from Sessions: group a composer's folders into Folder and Worktrees sections, with New Worktree first #348298).
• As the folder moves between its locations, composers still aimed at where it was follow it (IEditorWindowComposerFoldersService.retargetComposerFolders(to, from)).
• Every composer registered with that service follows: the chat part's (Sessions: the chat part of editor windows, for any feature to enable #348309) and the Chat view's (Chat view: list the sessions of the Agents window (chat.viewSessions.sessionsList.enabled) #348283, createChatViewComposerModel). Only idle composers still aimed at the folder their host chose follow; one aimed at a folder the user picked, or one that is sending, stays (ChatWindowComposerModel.retargetFolder). Test: a folder move retargets both registered composers through the real service, without a chat part (agentHostWorktreeComposerFolders.test.ts, 11 passing).

Review fixes, round 3

• The last chat of where the user moves the folder, when it is the chat shown already, is reported as restored without loading it again, so working-directory metadata that arrives later does not move the folder.
• The set of sessions known to be listed only keeps the remembered ones.
• (Workbench: worktree locations from agent host sessions, a shown-session seam and shared folder picker sections (infra, unused) #348304) A first send's session is reported as commit, both natively and through an extension's commit. Symbolic links of the repository's worktrees folder and of a worktree's .git file are followed.
• Validation (macOS, after pnpm run build-fast --client-only):
  • ./scripts/test.sh --reporter dot --runGlob 'vs/workbench/contrib/chat/test/browser/agentSessions/agentHost/**/*.test.js': 92 passing
  • --runGlob 'vs/workbench/contrib/sessions/test/browser/{agentsView,editorWindow,chatEditor}/**/*.test.js': 101 passing
  • --run chatViewPane, chatViewHostService, chatWidgetService, chatMoveActions and folderLocationSections: 82 passing
  • Red check against the previous sources: 4 failing in agentHostWorktree.test.ts and agentHostWorktreeComposerFolders.test.ts, and 3 failing in chatViewPane.test.ts and agentHostWorktreeLocations.test.ts (Workbench: worktree locations from agent host sessions, a shown-session seam and shared folder picker sections (infra, unused) #348304); all green after
  • pnpm run typecheck-client, pnpm run valid-layers-check, oxlint: passed

No Workspace and the two-line folder picker

• No Workspace in the Chat view's folder chip, while the Chat view's sessions list (chat.viewSessions.sessionsList.enabled) is on: IAgentHostNewSessionFolderService.isNoWorkspace/setNoWorkspace. Picking it is synchronous; the new session is created without a working directory, and it carries over a rebind of the provisional session. The chip shows the comment icon and "No Workspace", also for a restored session that has none (IAgentHostCustomizationService.isWorkspaceless).
• The old sessions list also lists workspaceless sessions for the window.
• The picker's layout matches the chat area's (Sessions: group a composer's folders into Folder and Worktrees sections, with New Worktree first #348298) and the Agents window's isolation picker: No Workspace, the folder (described as Current where the folder is) and New Worktree first, each with what it does on a detail line, then the worktrees under Worktrees. The two-line rows' CSS is scoped to this picker (agent-host-folder-picker-list in agentHostChatInputPicker.css), so no other action list changes.
• The chip always shows its icon and name, ellipsizes a long name (getMinimumWidth measures its fixed parts and up to 160px of the name), and stays visible but disabled in a started session.
• A <primary>.worktrees/<name> folder shows as a worktree only while it is pending, then as git proves it.
• Component fixtures: the folder service stubs gain isNoWorkspace, which fixed the Screenshots checks.

Up to date

• Merged Agent host sessions: keep sessions listed when switching a folder's location #348294 375b387 (36d7018, no conflicts). Its retention tests pass on this head: ./scripts/test.sh --reporter spec --run src/vs/workbench/contrib/chat/test/browser/agentSessions/agentHostChatContribution.test.ts --grep "keeps its sessions listed|keeps a session with multi-root": 2 passing ("switching the folder of a single-folder window to another location and back keeps its sessions listed", "a folder location switch keeps a session with multi-root metadata listed too, and Save Workspace As forgets the locations the folder had"). With the F4 suites plus agentHostChatContribution, editorCloudSandboxContribution, agentHostChatInputPicker and agentHostWorktree: 1617 passing; pnpm run typecheck-client: passed.

• Copilot code review: the worktree folder chip is offered only for local agent host chats (46793f6, red without it).

• Merged main 9bfb9e7 through Workbench: worktree locations from agent host sessions, a shown-session seam and shared folder picker sections (infra, unused) #348304's branch (b132856, merge-only, no conflicts).

• Validation on b132856 (macOS): pnpm run typecheck-client: passed; pnpm run build-fast --client-only, then ./scripts/test.sh --reporter dot with --run for agentHostWorktreeFolderChoices, agentHostFolderPickerActionItem, agentHostChatContribution, agentHostNewSessionFolderService, agentHostUntitledProvisionalSessionService, chatInputPart, agentHostWorktreeComposerFolders, agentHostWorktreeLocations, chatViewHostService, chatViewPane and folderLocationSections: 1360 passing.

How to test

agentHostWorktree.test.ts:

• following a chat the user opens, but not a restored one
• the automatic follow once the working directory is known and as it changes
• reopening the last chat on a user move
• the setting off (trigger only), turning it off at a worktree, and a folder that cannot move

agentHostWorktreeFolderChoices.test.ts: the order and the current folder, at a worktree and at the folder; No Workspace; New Worktree and back to a folder; and when the choices are active.

agentHostFolderPickerActionItem.test.ts (real DOM and CSS): the chip's label and minimum width in narrow and wide rows, No Workspace for a started or restored workspaceless session, and a two-line row with a description (the folder with Current) keeping its detail inside the row.

Validation (macOS):

• pnpm run typecheck-client: passed
• pnpm run valid-layers-check: passed
• oxlint on the changed files: passed
• ./scripts/test.sh --reporter dot --run .../agentHostWorktreeFolderChoices.test.ts --run .../agentHostWorktree.test.ts --run .../agentHostWorktreeLocations.test.ts --run .../chatViewHostService.test.ts --run .../folderLocationSections.test.ts: 16 passing (and 18 with workspaceFolderRepositories.test.ts before the chip commit)

Not run: the full unit suite, and a live Code OSS run.

Final sweep

• Final sweep: merged main 776b518, Sessions: group a composer's folders into Folder and Worktrees sections, with New Worktree first #348298 1cf86c1 and Agent host sessions: keep sessions listed when switching a folder's location #348294 cf34efb (9ab4ecf, clean). pnpm run typecheck-client: passed; ./scripts/test.sh --reporter dot --run <51 changed test files vs main>: 3449 passing, 4 pending.

Performance: the session layer's source

A trace of an editor window with worktree support on, while a large session ran, showed the renderer busy re-reading every session, chat and workspace of the editor window's session layer on each update of a busy session (its status, summary or git state), inside the provider's transaction.

• AgentHostWorktreeSessionLayerSource now reads every session again only as sessions are added or removed, as a provider invalidates what it lists, or as a provider replaces a session by a new object of it, such as a committed draft (reported as changed, under the same id).
• Each chat and session has a cached key of where it works, compared by strict string equality, so an update that moves nothing stops at that chat's key.
• Tests: 20 updates of a busy session that do not move it read no session again and read only that chat's workspace (before: 20 sweeps, 500 workspace reads); a replaced session is followed and the replaced object no longer notifies; archiving, unarchiving and adding or removing chats are followed.
• The counter test proves the work per update, not end-to-end CPU recovery: what remains per update is a few cheap change checks for the affected session and its chats, and the rebuild of the chat's workspace in the agent host sessions provider on main (baseAgentHostSessionsProvider.ts), which has no equality check (a follow-up for main).
• A session it does not read, such as one that getAllSessions does not list, still makes it read every session again each time it is reported as changed.
• Validation on 453649c and after: pnpm run typecheck-client: passed; ./scripts/test.sh --reporter dot --run src/vs/workbench/contrib/sessions/test/browser/agentsView/agentHostWorktreeComposerFolders.test.ts: 18 passing; F4's 51 changed test files: 3453 passing, 4 pending.