builds failing to initialize cause incremental building to be lost

[ArsenArsen]

a build that failed to fetch bootstrap-managarm lead to the subsequent builds having no repos to increment off of.

coordinator log:

[xbbs @ 2025-11-18 20:36:54+0000  INFO] Start delay of 600.0 seconds present.  Waiting...
[xbbs @ 2025-11-18 20:46:54+0000  INFO] Starting build...
[xbbs @ 2025-11-18 20:46:54+0000  INFO] Fetching https://github.com/managarm/bootstrap-managarm.git
[xbbs @ 2025-11-18 20:46:54+0000  INFO] Running command git clone https://github.com/managarm/bootstrap-managarm.git . (env=None, cwd='/var/lib/xbbs/projects/managarm/2025-11-18T20:36:54/src')
Cloning into '.'...
remote: Internal Server Error
fatal: unable to access 'https://github.com/managarm/bootstrap-managarm.git/': The requested URL returned error: 500
[xbbs @ 2025-11-18 20:48:54+0000  INFO] Exit code: 128
[xbbs @ 2025-11-18 20:48:55+0000 ERROR] Coordinator failed
Traceback (most recent call last):
  File "/var/lib/xbbs/xbbs_virtualenv/lib/python3.11/site-packages/xbbs/coordinator/build_run.py", line 290, in run
    build_result = await _run(
                   ^^^^^^^^^^^
  File "/var/lib/xbbs/xbbs_virtualenv/lib/python3.11/site-packages/xbbs/coordinator/build_run.py", line 240, in _run
    await _cmd(src_dir, "git", "clone", self.project_config.git, ".")
  File "/var/lib/xbbs/xbbs_virtualenv/lib/python3.11/site-packages/xbbs/coordinator/build_run.py", line 217, in _cmd
    await xbu_proc.do_command(self.log_io, *args, cwd=cwd)
  File "/var/lib/xbbs/xbbs_virtualenv/lib/python3.11/site-packages/xbbs/utils/proc.py", line 63, in do_command
    raise CalledProcessError(rc, args)
subprocess.CalledProcessError: Command '('git', 'clone', 'https://github.com/managarm/bootstrap-managarm.git', '.')' returned non-zero exit status 128.

repos:

arsen@hades:~$ tree /var/lib/xbbs/projects/managarm/2025-11-18T20\:36\:54/repo/
/var/lib/xbbs/projects/managarm/2025-11-18T20:36:54/repo/

0 directories, 0 files
arsen@hades:~$ 

these were, in fact, started as incremental builds:

[18/Nov/2025:20:36:54 +0000] "GET /projects/managarm/start?delay=600&increment=1 HTTP/1.1" 200 194 "-" "python-requests/2.32.5"
[18/Nov/2025:20:36:54 +0000] "GET /projects/managarm_aarch64/start?delay=600&increment=1 HTTP/1.1" 200 194 "-" "python-requests/2.32.5"
[18/Nov/2025:20:36:54 +0000] "GET /projects/managarm_riscv64/start?delay=600&increment=1 HTTP/1.1" 200 194 "-" "python-requests/2.32.5"

we should probably reflink the old packages eagerly