Sidebar thread grouping — worktree path canonicalization

Problem

Threads in the sidebar are grouped by their folder_paths (a PathList stored in the thread metadata database). When a thread is created from a git worktree checkout (e.g. /Users/eric/repo/worktrees/zed/lasalle-lceljoj7/zed), its folder_paths records the worktree checkout path. Threads from different checkouts of the same repos (different branches) have different raw paths and don't group together.

What we've done

1. PathList equality fix (PR #52052 — open, awaiting review)

File: crates/util/src/path_list.rs

Manual PartialEq/Eq/Hash impls that only compare the sorted paths field, ignoring display order.

2. Canonical workspace grouping (this branch)

Replaced the old "absorption" model (worktree workspaces absorbed under main repo via index-based tracking) with canonical-key grouping: workspaces that share the same root repo paths are grouped under a single sidebar header.

Architecture

• build_worktree_root_mapping() — iterates ALL repos from all workspaces to build HashMap<PathBuf, Arc<Path>> mapping checkout paths → root repo paths. Uses all repos (not just root repos) for robustness when linked-worktree snapshots are temporarily incomplete.

• build_canonical_thread_index() — indexes all threads by their canonicalized folder_paths (checkout paths mapped to root repo paths).

• rebuild_contents() flow:

  1. Group workspaces by canonical key
  2. For each group: claim threads from canonical index, merge live info from all workspaces in the group, build thread entries with best-workspace selection (raw path match preferred)
  3. Historical groups: iterate unclaimed threads, group by raw folder_paths, create Closed project group sections

• Worktree chips — threads from single-root worktree checkouts that differ from the canonical key get a {worktree-name} chip via linked_worktree_short_name.

• Workspace::path_list() — moved from free function to method on Workspace.

• ProjectHeader.workspace is Option<Entity<Workspace>> to support closed historical group headers.

• find_current_workspace_for_path_list / find_open_workspace_for_path_list — canonicalize both sides before comparing.

• activate_archived_thread — when no matching workspace is found, saves metadata and sets focused_thread instead of opening a new workspace.

• prune_stale_worktree_workspaces — checks all_workspace_roots (from workspace.root_paths()) instead of git repo snapshots, so the check works even before git scan completes.

• thread_entry_from_metadata — extracted helper for building ThreadEntry.

• SidebarThreadMetadataStore::all_entries() — returns &[ThreadMetadata] for reference-based iteration.

Remaining issues (priority order)

1. save_thread overwrites folder_paths on every thread mutation

Severity: High — causes data loss

NativeAgent::save_thread() (in crates/agent/src/agent.rs) fires on every cx.observe of the thread entity. It always re-snapshots folder_paths from the session's project's visible_worktrees().abs_path(). When a thread is loaded in the wrong workspace (e.g. main repo instead of worktree checkout), viewing the thread overwrites its folder_paths with the wrong paths, permanently losing the worktree association.

Fix needed: Fix the loading side — when a thread is loaded (from sidebar click, session restore, or archive restore), route it to a workspace whose raw paths match its saved folder_paths. If no matching workspace exists, create one. This way save_thread naturally preserves the correct paths.

Affected code paths:

• Session restore: AgentPanel::load in crates/agent_ui/src/agent_panel.rs (~L907-920) — loads the last active thread into whichever workspace is being restored, regardless of the thread's work_dirs
• Sidebar click: confirm / render_thread → activate_thread → loads in the ThreadEntryWorkspace which may be the wrong workspace (fallback to first in group)
• Archive restore: activate_archived_thread — currently just saves metadata and focuses, but clicking the resulting entry still routes through open_workspace_and_activate_thread → find_existing_workspace

2. Click-to-open from Closed groups goes through find_existing_workspace

When a user clicks a thread under a Closed historical group header, open_workspace_and_activate_thread calls open_paths → find_existing_workspace, which routes to an existing workspace that contains the path instead of creating a new workspace tab.

Fix: Either pass open_new_workspace: Some(true) through the call chain, or use a direct workspace creation path that bypasses find_existing_workspace.

3. Best-workspace selection is O(group_size) per thread

group_workspaces.iter().find(|ws| ws.read(cx).path_list(cx) == row.folder_paths) scans all workspaces in the group for each thread. Should pre-build a HashMap<PathList, Entity<Workspace>> per group for O(1) lookup.

4. Label allocation in historical group sort

workspace_label_from_path_list allocates a SharedString on every comparison during the sort. Should cache labels before sorting.

5. Collapse state doesn't transfer between raw and canonical keys

If a user collapses a historical group (keyed by raw folder_paths), then opens that workspace (which uses the canonical key), the collapse state doesn't transfer. Minor UX issue.

6. Missing test coverage

• Clicking a thread in a historical (Closed) group
• The prune fix with all_workspace_roots vs snapshot-based check
• Multiple worktree checkouts grouped under one header (dedicated test)

7. Path set mutation (adding/removing folders)

When you add a folder to a project (e.g. adding ex to a zed workspace), existing threads saved with [zed] don't match the new [ex, zed] path list. Design decision still being discussed.

Key code locations

• Thread metadata storage: crates/agent_ui/src/thread_metadata_store.rs
  • SidebarThreadMetadataStore — in-memory cache + SQLite DB
  • threads_by_paths: HashMap<PathList, Vec<ThreadMetadata>>
• Sidebar rebuild: crates/sidebar/src/sidebar.rs
  • rebuild_contents() — canonical-key grouping + historical groups
  • build_worktree_root_mapping() — worktree→root path map
  • build_canonical_thread_index() — threads indexed by canonical path
  • canonicalize_path_list() — maps a PathList through the root mapping
  • thread_entry_from_metadata() — helper for building ThreadEntry
  • prune_stale_worktree_workspaces() — uses all_workspace_roots
• Thread saving: crates/agent/src/agent.rs
  • NativeAgent::save_thread() — snapshots folder_paths on every mutation
• Thread loading (session restore): crates/agent_ui/src/agent_panel.rs
  • AgentPanel::load (~L907-920) — deserializes last active thread
• Workspace opening: crates/workspace/src/workspace.rs
  • find_existing_workspace() — dedup/routing that swallows worktree checkouts
  • Workspace::new_local() — creates workspace, canonicalizes paths
  • Workspace::path_list() — returns PathList from visible worktrees
• Session restore: crates/workspace/src/workspace.rs
  • restore_multiworkspace() — restores workspace tabs from session DB
• PathList: crates/util/src/path_list.rs

Useful debugging queries

-- All distinct folder_paths in the sidebar metadata store
sqlite3 ~/Library/Application\ Support/Zed/db/0-{channel}/db.sqlite \
  "SELECT folder_paths, COUNT(*) FROM sidebar_threads GROUP BY folder_paths ORDER BY COUNT(*) DESC"

-- Find a specific thread
sqlite3 ~/Library/Application\ Support/Zed/db/0-{channel}/db.sqlite \
  "SELECT session_id, title, folder_paths FROM sidebar_threads WHERE title LIKE '%search term%'"

-- Check workspace session bindings
sqlite3 ~/Library/Application\ Support/Zed/db/0-{channel}/db.sqlite \
  "SELECT workspace_id, paths, session_id, window_id FROM workspaces WHERE paths LIKE '%search%' ORDER BY timestamp DESC"