Environment

• Upgrade path: OneDev 14.1.9 → 16.9.5 (Docker image 1dev/server:16.9.5, single server, embedded HSQLDB, data volume mounted at /opt/onedev). Also reproduced with 1dev/server:16.8.8.
• Enterprise subscription active on the 14.1.9 server.

Symptom After the upgrade the server starts and the UI/API work, but no branch's .onedev-buildspec.yml can be parsed, so pushes trigger no builds and scheduled jobs don't run. On startup every branch logs:

WARN  i.o.server.job.DefaultJobService - Error caching branch schedules (project: <project>, branch: <branch>)
...
Caused by: org.yaml.snakeyaml.error.YAMLException: Invalid tag: !DefaultInterpreter

Our build spec declares version: 46 (written by 14.1.x) and its command steps use interpreter: !DefaultInterpreter, which the 16.0 incompatibility notes say is migrated automatically.

Root cause (as far as we can see) Calling io.onedev.server.buildspec.BuildSpec.parse(byte[]) on the same file inside the 16.9.5 image (classpath /app/boot + /app/lib) throws during migration:

java.lang.NoSuchMethodError: 'void org.yaml.snakeyaml.nodes.ScalarNode.<init>(org.yaml.snakeyaml.nodes.Tag, java.lang.String)'
  at io.onedev.server.buildspec.BuildSpec.migrate53(BuildSpec.java:2814)
  at io.onedev.server.data.migration.MigrationHelper.migrate(MigrationHelper.java:149)
  at io.onedev.server.data.migration.VersionedYamlDoc.toBean(VersionedYamlDoc.java:63)
  at io.onedev.server.buildspec.BuildSpec$1.load(BuildSpec.java:80)
  at io.onedev.server.buildspec.BuildSpec$1.load(BuildSpec.java:72)
  at io.onedev.server.buildspec.BuildSpec.parse(BuildSpec.java:573)

The image ships org.yaml.snakeyaml-2.7.jar (14.1.9 shipped 2.2). migrate53 uses the ScalarNode(Tag, String) constructor, which isn't present in snakeyaml 2.7, so migration from any build spec at version ≤ 52 aborts, and the un-migrated YAML (still containing !DefaultInterpreter) is then constructed and rejected.

Workarounds we tried:

• Replacing !DefaultInterpreter with !PosixInterpreter while keeping version: 46 → the same Invalid tag: !DefaultInterpreter (migration still aborts in migrate53).
• Declaring version: 56 to skip migration → fails on fields that later migrations would have changed (e.g. Unable to find property 'maxRetries' on class: io.onedev.server.buildspec.job.Job).

Questions

1. Is this a known issue, and is there a fixed version (or a planned patch release)?
2. Until then, what's the supported way to upgrade a 14.1.x install whose build specs are at version 46 — e.g. an intermediate version to upgrade through first that migrates and re-saves build specs, or a way to export a migrated build spec from a working version?
3. Is there a safe way to get the migrated (version 56) YAML for our existing spec, so we can commit it before upgrading?

We've rolled back to 14.1.9 for now and have a separate test instance on 16.9.5 that reproduces the problem, and we're happy to run any diagnostic you need there.