fix(app): show New workspace action on non-git sidebar projects (#1857)

* fix(app): show New workspace action on non-git sidebar projects

The per-project "New workspace" affordance in the sidebar (the project-
header + button and the empty-project ghost row) was gated on
host.canCreateWorktree, i.e. projectKind === "git". Non-git projects
(non_git / directory) therefore showed no way to add a workspace, even
though a host with the workspaceMultiplicity capability can create
additional local workspaces for them.

Thread the per-host workspaceMultiplicity flag into the sidebar project
row model and show the affordance when canCreateWorktree ||
supportsWorkspaceMultiplicity, matching the gate already used by the
global "New workspace" button and the Cmd+N handler. Rename the internal
trailing-action kind new_worktree -> new_workspace (a client-only UI
model, not a wire type) to reflect that it now also covers non-git
workspaces.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* test(app): expect the per-row New workspace icon on non-git projects

The sidebar "+" now shows for non-git projects on a multiplicity-capable
host, so the Model B sidebar spec no longer asserts the non-git project
has zero new-worktree icons — it now expects the icon, like git projects.
Also refresh the now-stale "no new-worktree icon" comments in the
entry-points spec (the picker is still one valid entry point).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

packages/app/src/utils/sidebar-project-row-model.ts

@@ -6,7 +6,7 @@ export interface SidebarProjectHostTarget {
 }
 
 export type SidebarProjectTrailingAction =
-  | { kind: "new_worktree"; target: SidebarProjectHostTarget }
+  | { kind: "new_workspace"; target: SidebarProjectHostTarget }
   | { kind: "none" };
 
 export interface SidebarProjectSectionRowModel {
@@ -17,6 +17,8 @@ export interface SidebarProjectSectionRowModel {
 
 export type SidebarProjectRowModel = SidebarProjectSectionRowModel;
 
+const EMPTY_MULTIPLICITY_MAP: ReadonlyMap<string, boolean> = new Map();
+
 function hostTarget(input: {
   serverId: string;
   iconWorkingDir: string;
@@ -40,9 +42,18 @@ export function resolveSidebarProjectIconTarget(
   return null;
 }
 
-function resolveNewWorktreeTarget(project: SidebarProjectEntry): SidebarProjectHostTarget | null {
+// A project can host a brand-new workspace on a host when that host can create a
+// git worktree (git projects) OR the host supports running multiple independent
+// workspaces per directory (`workspaceMultiplicity`), which is what lets non-git
+// directories add a second workspace. Mirrors the gate used by the global "New
+// workspace" affordances (use-global-new-workspace-action.ts and left-sidebar's
+// SidebarNewWorkspaceHeaderRow): `canCreateWorktree || supportsMultiplicity`.
+function resolveNewWorkspaceTarget(
+  project: SidebarProjectEntry,
+  supportsMultiplicityByServerId: ReadonlyMap<string, boolean>,
+): SidebarProjectHostTarget | null {
   for (const host of project.hosts) {
-    if (!host.canCreateWorktree) {
+    if (!host.canCreateWorktree && !supportsMultiplicityByServerId.get(host.serverId)) {
       continue;
     }
     const target = hostTarget(host);
@@ -53,18 +64,25 @@ function resolveNewWorktreeTarget(project: SidebarProjectEntry): SidebarProjectH
   return null;
 }
 
-function projectTrailingAction(project: SidebarProjectEntry): SidebarProjectTrailingAction {
-  const target = resolveNewWorktreeTarget(project);
-  return target ? { kind: "new_worktree", target } : { kind: "none" };
+function projectTrailingAction(
+  project: SidebarProjectEntry,
+  supportsMultiplicityByServerId: ReadonlyMap<string, boolean>,
+): SidebarProjectTrailingAction {
+  const target = resolveNewWorkspaceTarget(project, supportsMultiplicityByServerId);
+  return target ? { kind: "new_workspace", target } : { kind: "none" };
 }
 
 export function buildSidebarProjectRowModel(input: {
   project: SidebarProjectEntry;
   collapsed: boolean;
+  supportsMultiplicityByServerId?: ReadonlyMap<string, boolean>;
 }): SidebarProjectRowModel {
   return {
     kind: "project_section",
     chevron: input.collapsed ? "expand" : "collapse",
-    trailingAction: projectTrailingAction(input.project),
+    trailingAction: projectTrailingAction(
+      input.project,
+      input.supportsMultiplicityByServerId ?? EMPTY_MULTIPLICITY_MAP,
+    ),
   };
 }