feat(workspace): a session in its own worktree, Claude's way

Desktop-parity phase 6, following Claude Desktop:
- the workspace home's Worktree checkbox starts the pane with
  `claude --worktree=<name>`, so Claude Code makes, populates
  (.worktreeinclude, WorktreeCreate hook) and cleans up
  <repo>/.claude/worktrees/<name>; AgentHub only excludes
  /.claude/worktrees/ at the repo root (Claude does not)
- server/lib/session-worktree.js resolves a session's worktree from the
  session row only (owned by the workspace, registered by git worktree
  list); every lane git route takes ?session= and answers ENOWORKTREE
  instead of falling back to the main folder
- the session view's Changes panel works in the opened run's worktree
  (dashboard_runs.worktree, GitTarget in the client api)
- Resume/Fork start in the session's worktree; a gone one is ENOWORKTREE
- Archive of a worktree session removes the worktree after asking:
  git worktree remove without --force, git branch -d (unmerged work keeps
  its branch), a lock held by a live pid refused, a stale one cleared
- listWorktrees reads `locked <reason>` locks
- tests scrub GIT_* env so the pre-commit suite cannot act on this repo

client/src/components/lanes/WorkspaceSessionList.tsx

@@ -16,12 +16,13 @@
  */
 
 import { useEffect, useState, type ReactNode } from "react";
-import { Archive } from "lucide-react";
+import { Archive, GitBranch } from "lucide-react";
 import { useTranslation } from "react-i18next";
 import { Link, useNavigate } from "react-router-dom";
 import { api, type RunHandle } from "../../lib/api";
 import { isSessionAwaitingInput, type Lane, type Session } from "../../lib/types";
 import { timeAgo } from "../../lib/format";
+import { ConfirmModal } from "../ConfirmModal";
 
 export const SESSION_LIMIT = 20;
 
@@ -38,6 +39,14 @@ export function liveRunFor(lane: Lane, runs: RunHandle[], sessionId: string): Ru
   );
 }
 
+/** The name of the git worktree a session ran in (`claude --worktree` puts it
+ *  at `<repo>/.claude/worktrees/<name>`), or null for one in the folder. */
+export function sessionWorktreeName(lane: Lane, s: Session): string | null {
+  const strip = (p: string) => p.replace(/\/+$/, "");
+  if (!s.cwd || strip(s.cwd) === strip(lane.cwd)) return null;
+  return /\/\.claude\/worktrees\/([^/]+)\/?$/.exec(s.cwd)?.[1] ?? null;
+}
+
 /** A session row's dot: waiting for the user, failed, held by a live pane, or
  *  at rest. */
 export function sessionDot(session: Session, live: boolean): string {
@@ -178,6 +187,10 @@ export function WorkspaceSessionList({
   const [renaming, setRenaming] = useState<string | null>(null);
   const [draft, setDraft] = useState("");
   const [error, setError] = useState<string | null>(null);
+  // A worktree session asked to be archived: Claude Desktop removes its
+  // worktree too, so that is confirmed first.
+  const [archiving, setArchiving] = useState<Session | null>(null);
+  const [busy, setBusy] = useState(false);
 
   // The lane's own session/status/needs-you move on every hook, which is when
   // a session can appear or change state — re-read then, not on a timer.
@@ -205,6 +218,44 @@ export function WorkspaceSessionList({
     }
   };
 
+  // Archive: a worktree session with no live pane loses its worktree first
+  // (never forced — git refuses unsaved work, which then stops the archive);
+  // one Claude already cleaned up is just archived.
+  const archive = (s: Session) =>
+    sessionWorktreeName(lane, s) && !runFor(s)
+      ? setArchiving(s)
+      : void patch(s, { archived: true });
+  const archiveWithWorktree = async (s: Session) => {
+    setBusy(true);
+    setError(null);
+    try {
+      await api.lanes.removeSessionWorktree(lane.id, s.id).catch((err: unknown) => {
+        if ((err as { code?: string }).code !== "ENOWORKTREE") throw err;
+      });
+      await patch(s, { archived: true });
+    } catch (err) {
+      setError(err instanceof Error ? err.message : String(err));
+    } finally {
+      setBusy(false);
+      setArchiving(null);
+    }
+  };
+  const confirmArchive = (
+    <ConfirmModal
+      open={archiving !== null}
+      title={t("tree.archiveWorktreeTitle")}
+      message={t("tree.archiveWorktreeBody", {
+        name: archiving ? sessionWorktreeName(lane, archiving) : "",
+      })}
+      confirmLabel={t("tree.archiveWorktreeConfirm")}
+      cancelLabel={t("home.cancel")}
+      destructive
+      busy={busy}
+      onConfirm={() => archiving && void archiveWithWorktree(archiving)}
+      onCancel={() => setArchiving(null)}
+    />
+  );
+
   if (hidden) return null;
   const failure = error && (
     <p role="alert" className="pl-7 text-[11px] text-status-danger">
@@ -216,6 +267,7 @@ export function WorkspaceSessionList({
       <>
         <p className="py-1 pl-8 text-[11px] text-fg-muted">{t("tree.noSessions")}</p>
         {failure}
+        {confirmArchive}
       </>
     );
   }
@@ -269,9 +321,11 @@ export function WorkspaceSessionList({
                   setDraft(s.name || "");
                   setRenaming(s.id);
                 }}
-                title={`${s.name || s.id}\n${timeAgo(s.last_activity ?? s.started_at)}\n${
-                  run ? t("tree.splitHint") : t("tree.transcriptHint")
-                }`}
+                title={`${s.name || s.id}\n${timeAgo(s.last_activity ?? s.started_at)}${
+                  sessionWorktreeName(lane, s)
+                    ? `\n${t("tree.worktreeSession", { name: sessionWorktreeName(lane, s) })}`
+                    : ""
+                }\n${run ? t("tree.splitHint") : t("tree.transcriptHint")}`}
                 className={`flex w-full items-center gap-2 rounded-md py-1 pl-7 pr-7 text-left text-[12px] ${
                   selected
                     ? "bg-accent/10 text-fg-primary"
@@ -283,11 +337,18 @@ export function WorkspaceSessionList({
                   className={`h-1.5 w-1.5 shrink-0 rounded-full ${sessionDot(s, !!run)}`}
                 />
                 <span className="truncate">{s.name || s.id.slice(0, 8)}</span>
+                {sessionWorktreeName(lane, s) && (
+                  <GitBranch
+                    data-testid={`workspace-session-worktree-${s.id}`}
+                    aria-label={t("tree.worktreeSession", { name: sessionWorktreeName(lane, s) })}
+                    className="h-3 w-3 shrink-0 text-fg-muted"
+                  />
+                )}
               </button>
               <button
                 type="button"
                 data-testid={`workspace-session-archive-${s.id}`}
-                onClick={() => void patch(s, { archived: true })}
+                onClick={() => archive(s)}
                 title={t("tree.archiveSession")}
                 aria-label={t("tree.archiveSession")}
                 className="absolute right-1 top-1/2 hidden -translate-y-1/2 rounded p-0.5 text-fg-muted hover:bg-surface-4 hover:text-fg-primary focus:block group-hover:block"
@@ -299,6 +360,7 @@ export function WorkspaceSessionList({
         })}
       </ul>
       {failure}
+      {confirmArchive}
     </>
   );
 }