Enforce one Space per Git repository with worktree adoption

[alexandreroman]

Implement the core grouping logic for Git worktrees: a folder that is a linked worktree of a repository already open as a Space is now adopted into that Space as a linked workspace, and opening a repository whose worktrees are already open as Spaces reunifies them into a single Space.

Summary

This change enforces the invariant that Casper maintains one Space per Git repository, identified by the repository's common .git directory (shared by all working trees). The implementation handles three scenarios:

1. Worktree adoption: When adding a folder that is a linked worktree of an already-open repository, it joins that repository's Space as a linked workspace instead of becoming a separate Space.
2. Reunification: When opening a repository whose worktrees are already open as Spaces, those worktree Spaces are folded into the new repository Space, with their workspaces moving whole (same ids, ports, layouts, live terminals).
3. Deduplication: A folder already tracked (as a Space or workspace) is selected instead of added twice.

Key changes

• Repository identity: Extended Repository to expose commonDirPath (the shared .git directory) and isLinkedWorktree flag via libgit2. Updated WorkspaceFactory.GitInfo to carry these fields for routing decisions.

• Worktree adoption: AppModel.addSpace now detects when a folder is a linked worktree of an open repository and calls adoptWorktree to add it as a linked workspace instead of creating a new Space. The adopted workspace is named after its branch, inherits the primary workspace's branch as its base, and runs no setup hook (the worktree already exists).

• Reunification: When opening a repository, addSpace identifies any Spaces rooted at that repository's worktrees via worktreeSpaces and folds them into the new Space via reunify. Absorbed workspaces move whole; an ex-primary becomes a linked workspace named after its branch, and workspaces with no recorded base branch inherit the primary's branch as their base (those with a recorded base keep it).

• Deduplication: trackedWorkspaceID checks both Space roots and workspace worktree paths (canonicalized to handle symlink variations) and selects the workspace instead of adding a duplicate.

• Worktree removal: WorktreeManager.registeredName resolves a worktree's admin entry by path, so removing an adopted worktree (which may carry a name other than its branch) finds the correct entry to prune.

Implementation details

• Paths are canonicalized (symlinks resolved) for comparison across different spellings of the same folder.
• The main working tree of a repository takes precedence when both it and a worktree are open as Spaces (the main tree is where worktree operations run).
• Reunification happens in a single write, so absorbed workspaces never momentarily disappear from the model.
• Absorbed workspaces that cannot be moved (e.g., a second workspace on the absorbing Space's own working tree) are torn down: their ports released, surface views discarded, and transient state pruned.
• Tests cover adoption, reunification, deduplication, and edge cases (unopened repositories, different sessions, Casper-created worktrees dropped and re-added).

https://claude.ai/code/session_01K9NWyCjBz5QJd37EP1n2YJ