feat(api): inject folder manifest into task brief agent

Add _fetch_project_manifest helper that calls read_project_folder_manifest
via execute_on_client. Wire it into run_task_brief_research_stream (new
optional project_id param) so the <linked_folder> block is prepended to the
system prompt when the task belongs to a linked project. Also bind
FOLDER_TOOLS into the task-brief tool palette so the agent can read folder
files. device_ws extracts project_id / projectId from the task_brief_request
frame and forwards it.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/core/deep_agent.py

@@ -95,6 +95,21 @@ def format_folder_manifest(manifest: dict | None) -> str:
     return header + body + "</linked_folder>"
 
 
+async def _fetch_project_manifest(project_id: str) -> dict | None:
+    """Fetch manifest from Electron via execute_on_client. Returns None if unlinked or error."""
+    from app.core.ws_context import execute_on_client
+    try:
+        result = await execute_on_client(
+            action="read_project_folder_manifest",
+            data={"projectId": project_id},
+        )
+        if not result or not result.get("folderPath"):
+            return None
+        return result
+    except Exception:
+        return None
+
+
 def _datetime_context_injection(context: dict[str, Any]) -> str:
     """Build a comprehensive DATE CONTEXT block with pre-computed ms-epoch boundaries for common ranges."""
     fp = context.get("format_prefs")
@@ -1456,6 +1471,7 @@ async def run_task_brief_research_stream(
     user_id: str,
     task_id: str,
     context: dict[str, Any],
+    project_id: str | None = None,
 ) -> AsyncGenerator[tuple[str, Any], None]:
     """Stage-1 executive assistant: deep research for one task.
 
@@ -1463,8 +1479,10 @@ async def run_task_brief_research_stream(
     The final concatenated text may contain a ``<canvas kind="...">...</canvas>`` block
     which the WS handler strips and emits as a ``canvas_draft`` mutation.
     """
+    from app.agents.folder_agent import FOLDER_TOOLS
+
     prepared_context = await _prepare_context(f"task:{task_id}", context)
-    tools = _brief_research_tools(user_id, _trace_id_from_context(prepared_context))
+    tools = [*_brief_research_tools(user_id, _trace_id_from_context(prepared_context)), *FOLDER_TOOLS]
 
     # Inject task_id so the agent knows what to look up first.
     research_message = (
@@ -1481,6 +1499,12 @@ async def run_task_brief_research_stream(
         prepared_context,
     )
 
+    manifest_block = ""
+    if project_id:
+        manifest = await _fetch_project_manifest(project_id)
+        manifest_block = format_folder_manifest(manifest)
+    system_prompt = system_prompt + ("\n\n" + manifest_block if manifest_block else "")
+
     async for event in _run_single_agent_stream(
         user_id=user_id,
         system_prompt=system_prompt,