fix(web-shell): Preserve workspace navigation in standalone tasks

docs/design/web-shell/web-shell-new-task-workspace-scope.md

@@ -0,0 +1,88 @@
+# Web Shell New task workspace scope
+
+## Problem
+
+The sidebar's global **New task** action currently sends an unscoped creation
+intent. On daemons that support standalone sessions, that always starts a
+standalone draft even when trusted workspaces are available. Creating a task in
+a particular workspace is possible only from that workspace's row, which is
+easy to miss and makes the primary action inconsistent with the project-first
+sidebar.
+
+## Behavior
+
+The global action becomes a split button when more than one usable scope is
+available:
+
+- The main button starts a task in the current trusted workspace. If the
+  current context is standalone or has no trusted workspace, it falls back to
+  the trusted primary workspace.
+- The adjacent menu starts a task in any trusted, non-Live workspace.
+- **No workspace** is an explicit menu action only when the daemon advertises
+  standalone sessions.
+- Untrusted and Live workspaces are never creation targets.
+
+With only one usable scope, the control remains the existing single button.
+Locked-workspace embeds therefore continue to create only in their locked
+workspace, and older daemons without standalone support continue to create in
+the primary workspace. In the collapsed sidebar, the compact icon keeps the
+default one-click action; expanding the sidebar exposes the scope menu.
+
+The empty-state composer mirrors the same scope choice in its workspace menu.
+When standalone sessions are supported, **No workspace** appears alongside the
+trusted workspace choices even when only one workspace is registered. Choosing
+it switches the unsubmitted draft to standalone without creating a session;
+the first prompt performs the existing lazy standalone creation. The selector
+stays visible on that standalone draft so the user can see the active scope and
+switch back to a workspace before sending. Locked-workspace embeds and settled
+standalone sessions do not expose this retargeting control.
+
+Selecting a menu item starts the draft immediately. The menu does not introduce
+a second persistent workspace-selection state: `App` remains the authority for
+the effective session context, while the sidebar only forwards the selected
+cwd (or the existing unscoped value for standalone).
+
+## Failure and trust boundaries
+
+The existing new-session re-entry guard, busy state, error reporting, and
+catalog invalidation remain shared by the main button and every menu action.
+Workspace catalog refreshes stay cwd-qualified. The standalone action keeps
+passing no cwd, so it does not refresh the primary workspace catalog.
+
+## Workspace management from a standalone task
+
+Choosing **No workspace** keeps the conversation standalone, but it does not
+remove the daemon's workspace administration entry points:
+
+- **Plugins** remains visible when a trusted primary workspace exists. Opening
+  it manages that primary workspace and labels the target explicitly. It does
+  not change the current conversation context. Project skills can be managed,
+  but cannot be inserted directly into the standalone composer.
+- **Scheduled Tasks** remains visible and keeps its existing trusted-workspace
+  aggregation and workspace picker. Opening the page does not change the
+  current conversation context. Bound runs and history navigation carry the
+  task's explicit workspace back to the session loader. A legacy unbound task
+  fails closed outside its owning workspace instead of running in the
+  standalone conversation.
+
+Channels, Goals, Git, worktrees, workspace settings, and workspace-scoped slash
+commands remain unavailable without an active workspace conversation. Live
+contexts also keep all workspace-management entries hidden. If there is no
+trusted primary workspace, the standalone management entries stay hidden
+instead of silently targeting an untrusted workspace.
+
+## Verification
+
+- Component tests cover the trusted-current default, primary fallback,
+  explicit workspace and standalone menu actions, filtering, catalog refresh,
+  legacy capability behavior, locked-workspace behavior, and the composer's
+  **No workspace** scope.
+- Standalone Playwright coverage explicitly chooses **No workspace** from the
+  empty-state composer and checks the exact standalone route.
+- Workspace Playwright coverage clicks the main action and checks the exact
+  workspace cwd sent to session creation.
+- Manual cold-start verification switches among workspace and standalone
+  conversations and confirms the sidebar remains usable after each send.
+- Standalone navigation tests confirm Plugins and Scheduled Tasks stay visible,
+  display their workspace scope, preserve `context=standalone`, and issue no
+  session-creation request merely by opening a management page.