Four behaviour tests guarding the controller's contract with
the rest of the editor:
- openFlow seeds the graph + clears the dirty flag against
the freshly-captured baseline.
- graph edits re-emit YAML into the shared CodeController
so the text tab stays in lockstep.
- graph edits mark the buffer dirty against the baseline;
markSaved snaps it back to clean.
- selectStep is idempotent: re-selecting the same step
doesn't notify listeners (cheap rebuild guard for the
properties panel).
11/11 tests pass.
Signed-off-by: flemming-it <sf@flemming.it>
