v0.9.0 - reject non-fast-forward pushes

[0.9.0] - 2026-09-04

In plain terms: Until now, when you pushed your saved work to a shared
repository, the server did not check whether anyone else had pushed newer
work in the meantime. That meant a push based on older data could quietly
overwrite or orphan someone else's newer commits, with no warning at all —
exactly the kind of silent data loss git protects you from. From now on, the
server behaves like git: if the remote "main" branch has advanced beyond the
version your push was based on, it refuses the push and tells you to pull
first. deltix push then shows a clear message instead of silently moving
ahead.

New

• Reject non-fast-forward pushes (mirrors git's default refusal). The
  push-commits endpoint now accepts an optional from — the remote head the
  client last pulled from. Before importing any commit, the server compares
  from against the current head of its main branch; if they don't match
  (because another dev pushed in the meantime), it responds 409 with a
  non-fast-forward code instead of importing the commits. This prevents a
  stale-base push from overwriting or orphaning a newer commit on the remote
  branch.
• Backwards-compatible protocol. A client that does not send from
  (older versions) is treated as before — the server skips the check, so
  existing clients and the push path keep working unchanged.

Fixed

• (None — this is a new safety guard, not a bug fix.)

Tests

• Unit suite: 92 passing tests in the versioning context, including new
  cases that a matching from is accepted, a mismatched from is rejected
  with NonFastForwardError (and no commits are imported), and an absent
  from is accepted for backwards compatibility.