fix(cases): never delete another clone's files after a failed direct clone

A direct clone into an empty folder emptied the folder after any failure, which
deleted a concurrent attempt's finished clone when git had written nothing.
Clones into one folder are now mutually exclusive in-process, the cleanup is
skipped when git refused the folder, never ran, or the mount is unresponsive,
and a name linked while the clone ran is a 409 that keeps the folder.
Documents path for POST /api/cases/clone.

docs/api-reference.md

@@ -1315,6 +1315,8 @@ The target is judged before anything is written:
 
 Admin only in multi-user mode (`403`), like `POST /api/cases/link`: it writes outside the cases directory and into the shared, ownerless registry. If anything fails after the first write, what this call created is removed (the whole folder if it created it, otherwise only the scaffold inside the empty folder you picked) and the response is `500`.
 
+`POST /api/cases/clone` takes the same optional `path`, with `{ name, repository, ref?, shallow?, description?, path? }`. Without `path` the repository is cloned to `<cases dir>/<name>` as always. With `path` the repository is cloned **into that exact folder** (no `<name>` subfolder is added) and registered as a linked case, judged by the same rules as above: `400` for an invalid or blocked path (or a symlink or file at the target), `404` for a missing parent, `422` for an unreachable parent, and `409 ALREADY_EXISTS` for a folder that has files, a name already in use or a folder that is already a case. Admin only in multi-user mode (`403`). An existing empty folder is cloned into directly and is kept, emptied again, if the clone fails; a second clone into the same folder while one is running is refused with `409`. If the clone succeeds but the registry write fails (or the name was linked while git ran, which is `409`), the cloned folder is kept and the error names it: `500 OPERATION_FAILED`, then use Link Existing.
+
 ## Git status
 
 `GET /api/sessions/:id/git-status` is what the bottom-bar Git indicator and its panel read (Settings → Header & Panels → Bottom bar, per-device, default off). It reports what the session's workspace has not committed or pushed. **Read-only and offline:** it never fetches, pulls, commits or writes (it runs `git status` with `--no-optional-locks`, so it does not even refresh the index), which is why `behind` is as of the last `git fetch` (the panel's Fetch button is a separate route, below). The session is resolved like every session route (ownership via `findSessionOrFail`; another user's session is `404`). A repository whose root is, or is inside, a Docker case workspace is dropped (from the walk-up, the scan below a folder, and the diff route): a container can write there, and a repository's own clean filter or signature program would run on the host. When a branch's upstream does not exist on the remote (deleted and pruned, or never pushed, as after cloning an empty repository and committing), `upstreamGone` is `true` and the unpushed list falls back to commits on no remote-tracking ref at all.

docs/wiki/Core-Concepts.md

@@ -22,11 +22,11 @@ Codeman-side configuration:
 Three ways to get one, all under **New or link a case…** at the bottom of the case picker
 (the case dropdown in the bottom toolbar; on a phone, the case sheet's **Create New Case**):
 
-| How               | Result                                                                                                                                                                                                              |
-| ----------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| **Create New**    | A fresh `~/codeman-cases/<name>` with a scaffolded `CLAUDE.md`, or with **Create in a custom folder**, a new folder inside a parent you choose, scaffolded the same way and registered in place like a linked case. |
-| **Clone Repo**    | A repo cloned into `~/codeman-cases/<name>` (or straight into an empty folder you choose) and registered as a case. Private repos need this machine's own git credentials (see below).                              |
-| **Link Existing** | An existing folder anywhere on disk, registered in place. Nothing is copied or moved.                                                                                                                               |
+| How               | Result                                                                                                                                                                                                                |
+| ----------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| **Create New**    | A fresh `~/codeman-cases/<name>` with a scaffolded `CLAUDE.md`, or with **Create in a custom folder**, a new folder inside a parent you choose, scaffolded the same way and registered in place like a linked case.   |
+| **Clone Repo**    | A repo cloned into `~/codeman-cases/<name>` (or straight into a folder you choose, which must be empty or not exist yet) and registered as a case. Private repos need this machine's own git credentials (see below). |
+| **Link Existing** | An existing folder anywhere on disk, registered in place. Nothing is copied or moved.                                                                                                                                 |
 
 Linked cases keep living where they are. Deleting a case in Codeman removes the
 registration, and for a linked case that is all it removes.