git-crypt blocks T3 Code worktree threads after unlocking the primary checkout

[bjesuiter]

A repository uses git-crypt. The main checkout has already been unlocked and works normally, but creating a T3 Code worktree thread fails with a generic GitVcsDriver.createWorktree: git worktree add failed message.

The underlying Git error is typically similar to:

git-crypt: Error: Unable to open key file - have you unlocked/initialized this repository yet?
fatal: example.secret: smudge filter git-crypt failed

Why can this happen after the primary checkout is unlocked, and how can linked worktrees be configured to check out encrypted files reliably?

[bjesuiter]

Unlocking the primary checkout is necessary but not sufficient.

A linked worktree has its own GIT_DIR under .git/worktrees/.... During git worktree add, Git runs the git-crypt smudge filter in that context. If the filter is configured as plain git-crypt smudge, git-crypt looks for the key in the linked-worktree metadata rather than the repository’s shared Git directory, and checkout fails before T3 Code can start the thread.

After unlocking the repository, run the following once from its primary checkout. It stores the commands in the clone-local Git configuration, so every linked worktree resolves the shared common directory:

git config --local filter.git-crypt.smudge \
  'GIT_DIR="$(git rev-parse --git-common-dir)" git-crypt smudge'
git config --local filter.git-crypt.clean \
  'GIT_DIR="$(git rev-parse --git-common-dir)" git-crypt clean'
git config --local filter.git-crypt.required true
git config --local diff.git-crypt.textconv \
  'GIT_DIR="$(git rev-parse --git-common-dir)" git-crypt diff'

Then retry the T3 Code worktree thread. To verify independently, create a disposable linked worktree with git worktree add --detach <temporary-path> HEAD and confirm that an encrypted file is checked out successfully.

This is a Git linked-worktree configuration issue rather than a T3 Code-specific encryption feature: T3 Code simply surfaces the failed git worktree add operation.