feat(web-shell): add contextual task panels

docs/design/web-shell-context-panels.md

@@ -0,0 +1,108 @@
+# Web Shell context panels
+
+## Goal
+
+Add a persistent header to active chat sessions and move supported workspace
+and background-task context into a fixed-width environment panel. Keep the
+existing artifact panel as an independent right-side surface.
+
+## Header
+
+The active chat header is opt-in so existing integrations without header props
+keep their previous layout. Passing `header` enables the default header, whose
+content is the current session title. `header.items` controls the title,
+environment action, and artifact-panel action independently; an empty items
+array hides the complete header. Passing `renderChatHeader` also enables the
+header and replaces it completely; the renderer receives the session metadata,
+enabled items, controlled panel state, and panel open-change callbacks. The
+compact sidebar toggle remains owned by `sidebar` and renders outside the
+custom header. While the artifact panel is closed, its toggle is in the chat
+header. While it is open, that same toggle moves to the right edge of the
+artifact-panel header, leaving the environment action at the right edge of the
+chat header adjacent to the panel.
+
+The artifact-panel action remains available when no tab exists. Opening an
+The empty panel shows Review and, when session-source metadata is supported,
+side-task history plus New side task. Once a tab is open, the panel header add
+menu contains Review and New side task without repeating the side-task history.
+Review opens the most recent transcript turn containing reviewable file
+changes, is disabled when no such turn exists, and is hidden from the add menu
+while a review tab is already open. Closing a populated artifact panel keeps
+its tabs so the header action can reopen the existing content.
+
+`rightPanel.items` independently controls whether Review and Side task appear
+on the empty panel page. Both items are enabled by default.
+
+## Side tasks
+
+A side task is a distinct daemon thread session in the same workspace as its
+parent. It renders the existing interactive chat pane, including the transcript,
+composer, approval-mode selector, model selector, streaming state, and
+permission handling. Creation uses the dedicated side-task endpoint to snapshot
+the main session's complete model context at that moment, then continues
+independently. Inherited records are not replayed in the side-task transcript;
+only messages created inside the side task are shown.
+
+Side-task sessions record `sourceType: side_task` and the parent session id as
+`sourceId`. The Web Shell session catalog filters this source type, so side
+tasks do not appear as top-level sessions. With saved side tasks, hovering Side
+task on the empty right-panel page opens a menu of those sessions and a New
+action. With no saved task, clicking the row creates one directly. Selecting a
+saved task restores it as a tab. Closing a tab only detaches its client; the
+daemon transcript remains available for later conversation.
+
+`/fork sider` opens a new side-task draft directly. Hosts can trigger the same
+action through `shellRef.current.createSideTask()`.
+
+## Environment panel
+
+The environment panel uses only existing Web Shell capabilities:
+
+- workspace path;
+- Git branch and working-tree summary;
+- working-tree diff and commit history entry points;
+- configured agents entry point;
+- background agent, shell, and monitor task summaries.
+
+The environment action and environment section remain available throughout an
+active chat session. A clean working tree is shown explicitly; agent and
+background-task sections appear only when they have content.
+
+`environmentPanel.items` independently controls the environment, subagent, and
+background-task sections. All three sections are enabled by default.
+
+The local `/fork` command refreshes the session task snapshot as soon as its
+background agent launches. Fork agents have no parent transcript tool call, so
+their right-panel detail resolves the virtual subagent session by agent task ID
+instead of `toolUseId`.
+
+The local `/tasks` command opens the environment panel and refreshes its task
+snapshot instead of opening the legacy task dialog.
+
+Side-task, subagent, and fork transcripts expose their own file changes and
+artifacts through the main right panel. Their source session scopes tab
+identities and workspace actions, so opening a nested output creates a separate
+tab without replacing the main session's review or artifact tabs.
+
+It is a fixed-width, non-resizable layout column styled as a floating card with
+a border and shadow. At narrower message widths it opens as a dismissible
+floating popover instead of consuming chat width.
+
+The environment panel and artifact panel are independent. At desktop widths the
+two may be visible together. When the viewport cannot fit both, the artifact
+panel normally takes priority and the environment panel is hidden without
+losing its open state. Opening a subagent or background task from the
+environment panel keeps that panel visible beside the resulting detail. A
+floating environment panel is positioned within the remaining message area and
+never overlaps the artifact panel.
+
+## Responsive behavior
+
+The environment panel is hidden for split/full-page views. When the message
+area cannot keep at least 800 pixels after docking the panel, the panel closes
+and can be reopened as a floating popover. An open artifact panel takes
+priority when both panels cannot fit, but the environment action remains
+available for explicitly reopening the popover. The existing artifact drawer
+behavior on narrow screens is unchanged. On desktop, the artifact panel is a
+top-level layout column beside the chat shell, so it starts at the top of the
+page and the chat header ends at the panel boundary.

packages/acp-bridge/src/bridge.test.ts

@@ -61,6 +61,7 @@ import { TurnBoundaryCompactionEngine } from './compactionEngine.js';
 import {
   CHANNEL_STARTUP_PROFILE_META_KEY,
   CHANNEL_STARTUP_PROFILE_VERSION,
+  LOAD_REPLAY_HIDE_INHERITED_META_KEY,
 } from './bridgeTypes.js';
 import {
   ApprovalMode,
@@ -10820,6 +10821,57 @@ describe('createAcpSessionBridge', () => {
       await bridge.shutdown();
     });
 
+    it('creates a side task with hidden inherited replay', async () => {
+      const handle = makeChannel({
+        extMethodImpl: async (method) => {
+          if (method === SERVE_CONTROL_EXT_METHODS.sessionSideTask) {
+            return { newSessionId: 'side-1', title: 'Side task' };
+          }
+          if (method === SERVE_CONTROL_EXT_METHODS.sessionSource) {
+            return { persisted: true };
+          }
+          return {};
+        },
+        resumeSessionImpl: () => ({}),
+      });
+      const bridge = makeBridge({
+        channelFactory: async () => handle.channel,
+      });
+      const parent = await bridge.spawnOrAttach({
+        workspaceCwd: WS_A,
+        sessionScope: 'thread',
+      });
+
+      const sideTask = await bridge.createSideTaskSession(parent.sessionId, {
+        name: 'Side task',
+      });
+
+      expect(sideTask).toMatchObject({
+        sessionId: 'side-1',
+        sourceType: 'side_task',
+        sourceId: parent.sessionId,
+        sourcePersisted: true,
+        parentSessionId: parent.sessionId,
+      });
+      expect(bridge.getSessionSummary(sideTask.sessionId)).toMatchObject({
+        sourceType: 'side_task',
+        sourceId: parent.sessionId,
+      });
+      expect(handle.agent.extMethodCalls).toContainEqual({
+        method: SERVE_CONTROL_EXT_METHODS.sessionSource,
+        params: {
+          sessionId: sideTask.sessionId,
+          sourceType: 'side_task',
+          sourceId: parent.sessionId,
+        },
+      });
+      expect(handle.agent.loadSessionCalls[0]?._meta).toMatchObject({
+        [LOAD_REPLAY_HIDE_INHERITED_META_KEY]: true,
+      });
+
+      await bridge.shutdown();
+    });
+
     it('does not replace the source when single scope attaches', async () => {
       const bridge = makeBridge({
         channelFactory: async () => makeChannel().channel,