fix(api): allow setting default project when none is currently set

The v2 set_default_project_by_id handler fetched the current default
solely to echo it as old_project in the response, and raised 404
"No default project is currently set" when none existed. That guard
(marked # pragma: no cover, never tested) made the bootstrap/recovery
case impossible: with no default row in the DB, `bm project default
<name>` always failed -- yet that is exactly the command you reach for
when no default is set.

ProjectStatusResponse.old_project is already Optional, so the guard
served no schema requirement. Remove it and build old_project only
when a previous default exists, else pass None.

Add a regression test that clears is_default, sets a default via the
endpoint, and asserts 200, old_project is None, the new project is
default, and a follow-up read-back returns it.

Closes #975

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Drew Cain <groksrc@gmail.com>

src/basic_memory/api/v2/routers/project_router.py

@@ -559,12 +559,10 @@ async def set_default_project_by_id(
     logger.info(f"API v2 request: set_default_project_by_id for project_id={project_id}")
 
     try:
-        # Get the old default project from database
+        # Get the old default project from database. It may be absent during
+        # bootstrap/recovery (no default row yet); that is a valid state, not an
+        # error, so we only echo it back when one exists.
         default_project = await project_repository.get_default_project()
-        if not default_project:
-            raise HTTPException(  # pragma: no cover
-                status_code=404, detail="No default project is currently set"
-            )
 
         # Get the new default project by external_id
         new_default_project = await project_repository.get_by_external_id(project_id)
@@ -576,17 +574,27 @@ async def set_default_project_by_id(
         # Set as default using project name (service layer still uses names internally)
         await project_service.set_default_project(new_default_project.name)
 
-        return ProjectStatusResponse(
-            message=f"Project '{new_default_project.name}' set as default successfully",
-            status="success",
-            default=True,
-            old_project=ProjectItem(
+        # Trigger: a previous default existed
+        # Why: ProjectStatusResponse.old_project is Optional; the no-default
+        #   bootstrap case must succeed with old_project=None
+        # Outcome: response echoes the prior default only when there was one
+        old_project = (
+            ProjectItem(
                 id=default_project.id,
                 external_id=default_project.external_id,
                 name=default_project.name,
                 path=default_project.path,
                 is_default=False,
-            ),
+            )
+            if default_project
+            else None
+        )
+
+        return ProjectStatusResponse(
+            message=f"Project '{new_default_project.name}' set as default successfully",
+            status="success",
+            default=True,
+            old_project=old_project,
             new_project=ProjectItem(
                 id=new_default_project.id,
                 external_id=new_default_project.external_id,