fix(studio): review round 2 - a conversion that fails after its commit recovers without a restart

- The convert job reloads the course on success and on failure, so learners
  get the intact import (rolled back) or the published studio course, never a
  course whose folder moved away.
- POST /convert on a course with an incomplete conversion (.converting-<id>,
  staging or retired folders) queues a job that recovers and finishes it
  instead of answering 409; the studio page shows "Conversion incomplete" with
  Retry for the owner.
- The 409 for pending import jobs names their kinds and ids; the dead withLock
  in git.ts is gone; the dot-folder discovery rule is documented in
  docs/operations.md and spec section 5.
- Route tests (SQLite and Postgres) inject a failed cross-filesystem copy, a
  checksum mismatch and a pre-commit failure.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/feature-studio/src/server/git.ts

@@ -55,15 +55,3 @@ export async function gitOk(cwd: string, args: string[], who?: Identity): Promis
 export function splitZ(out: string): string[] {
   return out.split("\0").filter(Boolean);
 }
-
-const locks = new Map<string, Promise<unknown>>();
-
-/** Serialises git work per key (the course's bare repo path) across every store instance in the process. */
-export function withLock<T>(key: string, fn: () => Promise<T>): Promise<T> {
-  const prev = locks.get(key) ?? Promise.resolve();
-  const next = prev.then(fn, fn);
-  const tail = next.catch(() => {});
-  locks.set(key, tail);
-  tail.then(() => { if (locks.get(key) === tail) locks.delete(key); });
-  return next;
-}