Preview a merge

Goal. Know what a merge will do before doing it. About a minute.

You need. A branch with changes on it.

Dry-run it

strata ./shop branch preview experiment default

source                    experiment
target                    default
strategy                  strict
branch_point              4
spaces_covered            default
capabilities_covered      kv json vector
capabilities_unsupported  vector_collection event graph_metadata graph_node graph_edge graph_ontology
conflicts                 -
derived_state
  CAPABILITY  DISPOSITION
  json        rebuild_required

Source first, then target. Nothing is written.

The two lines that matter

conflicts. A - means the merge will apply. Anything listed means it will be refused under the default strategy, and Resolve merge conflicts is the next page.

capabilities_unsupported. Read this one before you rely on a merge. Key-value, JSON and vector data move. Events and graph data do not. If your branch’s work was an event log or a graph, a clean preview does not mean your changes will arrive, it means there is nothing to carry.

That is not a bug you can work around with a flag; it is what merge covers today. Branches explains why.

The other fields

branch_point is the version the two branches diverged at.

derived_state lists work the merge implies rather than data it moves: rebuild_required for JSON means an index will be rebuilt on the target after the merge. It is not a warning.

What just happened

Nothing. preview runs the same comparison a merge does and reports the outcome without committing, so it is safe to run repeatedly and safe to run in CI as a gate.

Failure modes

invalid_argument.engine.branch_point. The two branches have no common ancestor, which means the branch came from branch create rather than branch fork. There is no recovery: redo the work on a forked branch.

Preview is clean and the merge still refuses. The target moved between the two calls. Preview describes the moment it ran.

Next

Merge changes.