Patching Workflows

Continuum.patched?/1 is for small, backward-compatible changes that should take effect for new executions without moving old in-flight runs onto a new branch mid-replay.

def run(input) do
  if Continuum.patched?(:add_fraud_check_v2) do
    activity FraudCheck.v2(input)
  else
    activity FraudCheck.v1(input)
  end
end

Inside a workflow, patched?/1 is journaled. The first live execution at that source location writes a patched event with value: true; later replays use the journaled value. Histories recorded before the patch line existed return false without consuming the next old event, so they stay on the old branch. The first decision for a patch name is also memoized per run: every use of the same name returns that decision, including calls in loops or at sites that cross from replayed history into the live tail.

Outside a workflow process, patched?/1 returns false.

When To Use It

Use patched?/1 when the old and new branches can both remain in the same workflow module until affected runs drain.

Prefer a new workflow version when the shape of the workflow state changes substantially, when you remove or reorder existing effects, or when you cannot keep both branches loaded.

Prefer a normal deploy with no patch marker only when there are no active runs that can replay through the edited code.

Operational Discipline

Patch markers are durable decisions. Once some runs have journaled true and older runs are still taking the false branch, removing either branch is a compatibility decision. Keep the marker and both branches until you know the old histories have completed or been cancelled.

Content-addressed workflow versioning protects runs from being dispatched into the wrong entrypoint, but it does not remove the need to keep code for old patch branches while old histories reference them.

Compatibility note

Older Continuum releases decided patches per call site. A run could therefore record a later true marker after first taking a pre-patch false branch. Those histories remain decodable, but after upgrading the first decision wins for every later use of the same patch name. Audit active histories for repeated patch names before deployment if code previously called one patch on both sides of a suspension point.

Telemetry

Continuum emits [:continuum, :patched, :hit] with the patch name and value.