plan.md

Context

Read summary.md for all changes made so far. This plan covers the remaining flicker bug.

The Bug

When a remote workspace is added to the sidebar, the project group briefly flickers (appears as a separate group for 1-2 frames). This happens because:

Server-side set_snapshot in zed/crates/worktree/src/worktree.rs (~line 1205) unconditionally recomputes root_repo_common_dir from git_repositories:
```
new_snapshot.root_repo_common_dir = new_snapshot
    .local_repo_for_work_directory_path(RelPath::empty())
    .map(|repo| SanitizedPath::from_arc(repo.common_dir_abs_path.clone()));
```
During early scan passes, .git hasn't been discovered yet, so this overwrites the correct value (set by Worktree::local() during creation) with None.
The server sends an UpdateWorktree message with root_repo_common_dir = None.
The client's apply_remote_update in zed/crates/worktree/src/worktree.rs (~line 2437) currently has a partial fix that only updates when Some:
```
if let Some(dir) = update.root_repo_common_dir.map(...) {
    self.root_repo_common_dir = Some(dir);
}
```
This prevents the client from clearing it, but the real fix should be server-side.

What To Do

Step 1: Add flicker detection to the existing test

Extend test_clicking_closed_remote_thread_opens_remote_workspace in zed/crates/sidebar/src/sidebar_tests.rs to catch transient flicker. Use the observe_self pattern from test_clicking_worktree_thread_does_not_briefly_render_as_separate_project (line ~3326-3397), which installs an observer that fires on every notification and panics if more than one project header ever appears:

sidebar
    .update(cx, |_, cx| cx.observe_self(assert_sidebar_state))
    .detach();

Add this observer BEFORE the stale key injection / workspace addition steps. The callback should assert that there is never more than one project group header at any point during the test. This catches the case where an UpdateWorktree message with root_repo_common_dir = None temporarily creates a wrong project group key.

Since the full remote mock connection is hard to set up for a second connection, an alternative approach: simulate the UpdateWorktree message arriving with root_repo_common_dir = None by directly calling the worktree's update mechanism on the existing project. Or, test at a lower level by verifying that set_snapshot doesn't clear root_repo_common_dir.

Step 2: Fix the server-side root cause

In zed/crates/worktree/src/worktree.rs, find set_snapshot (~line 1200-1210). Change the root_repo_common_dir recomputation to not downgrade once set:

// Before (overwrites unconditionally):
new_snapshot.root_repo_common_dir = new_snapshot
    .local_repo_for_work_directory_path(RelPath::empty())
    .map(|repo| SanitizedPath::from_arc(repo.common_dir_abs_path.clone()));

// After (preserve existing value if scan hasn't discovered repo yet):
new_snapshot.root_repo_common_dir = new_snapshot
    .local_repo_for_work_directory_path(RelPath::empty())
    .map(|repo| SanitizedPath::from_arc(repo.common_dir_abs_path.clone()))
    .or(self.snapshot.root_repo_common_dir.clone());

This ensures the value discovered by Worktree::local() during creation is preserved until the scanner finds the repo and confirms/updates it.

Step 3: Verify the client-side guard is still useful

The apply_remote_update change (only update when Some) is a defense-in-depth measure. With the server fix, the server should never send None after having the correct value. But keeping the client guard is good practice. Verify the test passes with both fixes.

Step 4: Update `summary.md`

Add the flicker fix to the summary of changes.

Important Notes

Use sub-agents for research tasks to keep context manageable
The key test pattern is cx.observe_self(callback) which fires on every cx.notify() — this catches transient states that run_until_parked would miss
Read test_clicking_worktree_thread_does_not_briefly_render_as_separate_project (~line 3262-3397) for the full example of this testing pattern
After all changes, run cargo check on all affected packages and run the sidebar + agent_ui tests

Plan: Fix sidebar flicker when remote workspace is added