tui: selecting the current directory in the picker creates a worktree and switches session instead of no-op

Summary

While working in an existing repository in the TUI, a directory-selection dialog
appeared. The user selected the same directory the session was already running in.
Selecting the current directory should be a no-op, but instead OpenCode created a git
worktree of the repo under ~/.local/share/opencode/worktree/<repo-hash>/new and
switched the active session's working directory to it mid-session. The user never
requested a workspace or worktree.

Environment

• opencode version: v0.0.0-beta-17793
• OS: Windows_NT 10.0.22631 (win32 x64) — Windows 11 23H2
• Terminal: TERM=xterm-256color, COLORTERM=truecolor
• Shell: cmd.exe (ComSpec)
• Install/channel: beta
• Active plugins: @plannotator/opencode@latest, micode, superpowers (git),
  local plugins herdr-agent-state.js, planning-canvas.js; no project-local config

Reproduction

1. Launch opencode2 in an existing git repo (master branch) on Windows.

2. Work in a session normally — no workspace requested or created by the user.

3. A directory-selection dialog appears; select the directory the session is
   already in (the repo root).

4. Session emits "working directory has been changed" notices; the execution
   context moves from the repo to ~/.local/share/opencode/worktree/d89da5/new.

5. git worktree list in the repo shows a new worktree in detached HEAD:

   C:/Users/<user>/source/repos/ca-fl-system                  b9d75e7 [master]
   C:/Users/<user>/.local/share/opencode/worktree/d89da5/new  205246f (detached HEAD)
   

Expected Behavior

Selecting the directory the session is already in should be a no-op: no worktree
creation, no session directory switch. More generally, no worktree should be created
and no execution-context switch should happen unless the user explicitly creates or
opens a different workspace.

Actual Behavior

Re-selecting the current directory was treated as a change: a worktree was created
(detached HEAD at the repo's current commit) and the running session's working
directory was switched to it mid-session. Uncommitted changes in the original working
copy are invisible from the new context, which silently changes what the agent sees
and edits — misleading for both user and model.

Additional Context

• The generated workspace name was new, suggesting an auto-created default rather
  than anything user-initiated.
• Frequency: single occurrence so far.
• Workaround: keep working from the original repo directory; clean up with
  git worktree remove ~/.local/share/opencode/worktree/d89da5/new && git worktree prune.
• Possibly related: #20262 (workspace-bound sessions still execute at repo root),
  #28581 (resume uses launch directory instead of stored session directory),
  #31593 (workspace redirects to main repository path).