ProjectGroup Refactor — Implementation Handoff

Goal

Introduce ProjectGroup as an explicit entity that owns both its workspaces and its threads. Replace the current system where:

• Project groups are identified by ProjectGroupKey (derived from filesystem paths — structural identity)
• Thread-to-group association is derived at runtime via path matching across two HashMap indices
• Three parallel collections on MultiWorkspace are joined on every read

With a system where:

• Each ProjectGroup has a stable ProjectGroupId (UUID)
• ProjectGroup directly contains its Vec<Entity<Workspace>>
• Threads store a project_group_id: Option<ProjectGroupId> for direct ownership
• MultiWorkspace.active_workspace is an independent Entity<Workspace> field (not an enum with index)

What already exists

ProjectGroupId has already been added to zed/crates/project/src/project.rs (around L6120):

#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, serde::Serialize, serde::Deserialize)]
pub struct ProjectGroupId(uuid::Uuid);

impl ProjectGroupId {
    pub fn new() -> Self {
        Self(uuid::Uuid::new_v4())
    }
}

The uuid dependency has been added to project/Cargo.toml.

File-by-file changes (in dependency order)

1. crates/project/src/project.rs

Already done: ProjectGroupId type exists.

No further changes needed to this file. ProjectGroupKey stays as-is with path-based Eq/Hash — it's still useful as a computed descriptor for matching.

2. crates/workspace/src/persistence/model.rs

Current state (lines 65–110):

#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct SerializedProjectGroupKey {
    pub path_list: SerializedPathList,
    pub(crate) location: SerializedWorkspaceLocation,
}
// From impls for ProjectGroupKey <-> SerializedProjectGroupKey
pub struct MultiWorkspaceState {
    pub active_workspace_id: Option<WorkspaceId>,
    pub sidebar_open: bool,
    pub project_group_keys: Vec<SerializedProjectGroupKey>,
    pub sidebar_state: Option<String>,
}

Changes:

1. Rename SerializedProjectGroupKey → SerializedProjectGroup and add an id field:

#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
pub struct SerializedProjectGroup {
    #[serde(default)] // absent in old blobs → None
    pub id: Option<ProjectGroupId>,
    pub path_list: SerializedPathList,
    pub(crate) location: SerializedWorkspaceLocation,
}

1. Update the From impls. The From<ProjectGroupKey> impl no longer makes sense because we need an ID. Instead, create a method or From<(&ProjectGroupId, &ProjectGroupKey)>:

impl SerializedProjectGroup {
    pub fn from_group(id: ProjectGroupId, key: &ProjectGroupKey) -> Self {
        Self {
            id: Some(id),
            path_list: key.path_list().serialize(),
            location: match key.host() {
                Some(host) => SerializedWorkspaceLocation::Remote(host),
                None => SerializedWorkspaceLocation::Local,
            },
        }
    }

    pub fn to_key_and_id(self) -> (ProjectGroupId, ProjectGroupKey) {
        let id = self.id.unwrap_or_else(ProjectGroupId::new);
        let path_list = PathList::deserialize(&self.path_list);
        let host = match self.location {
            SerializedWorkspaceLocation::Local => None,
            SerializedWorkspaceLocation::Remote(opts) => Some(opts),
        };
        (id, ProjectGroupKey::new(host, path_list))
    }
}

1. Update MultiWorkspaceState:

pub struct MultiWorkspaceState {
    pub active_workspace_id: Option<WorkspaceId>,
    pub sidebar_open: bool,
    pub project_group_keys: Vec<SerializedProjectGroup>, // renamed type
    pub sidebar_state: Option<String>,
}

1. Add use project::ProjectGroupId; to imports.

2. The old From<SerializedProjectGroupKey> for ProjectGroupKey impl should be removed since callers now use to_key_and_id().