ADR 0007 — Latent-Branch Conditional Lowering

Conditionals compile to condition anchors with latent branch fragments; Pulse materializes only the selected branch.

On this page
  1. Status
  2. Context
  3. Decision
  4. Alternatives considered
  5. Consequences
  6. Positive
  7. Negative
  8. Obligations
  9. Related

ADR 0007 — Latent-Branch Conditional Lowering

Status

Accepted — the conditional lowering model is now the documented execution semantics for built-in workflow conditionals.

Context

Conditionals exposed a real semantic gap in the workflow stack. If a conditional were lowered as plain DAG fan-out, both branches would become runnable under ordinary readiness rules. If it were hidden in stage-local imperative code, the workflow artifact would stop telling the truth about future obligations.

The missing piece was not a new runtime mutation mechanism. The runtime already had rewrite and materialization machinery. What was missing was a truthful representation of latent alternatives at the workflow boundary.

Decision

Compile conditionals as condition anchors with latent branch fragments.

  • the compiled artifact carries a real condition node plus the branch alternatives attached to it
  • at runtime, evaluating the condition selects one branch
  • Pulse materializes only the selected branch into the materialized graph
  • the condition anchor remains available for lineage and provenance

This makes branch selection a first-class lowering concept rather than plain graph fan-out or hidden imperative logic.

Alternatives considered

  • Lower conditionals as ordinary fan-out — rejected because both branches would appear runnable under current graph readiness semantics.
  • Hide branch choice inside stage-local imperative code — rejected because it destroys the honesty of the compiled artifact and weakens operator explanation.
  • Treat every conditional as an open-ended rewrite authored at runtime — rejected because built-in conditionals are structured semantic alternatives, not arbitrary planner invention.

Consequences

Positive

  • The compiled artifact can represent what obligations may arise without materializing all of them.
  • Pulse reuses existing rewrite and materialization machinery instead of gaining a special conditional executor path.
  • Provenance and lineage remain attached to the condition anchor rather than disappearing into branch-local code.

Negative

  • The workflow layer must now model latent possibilities, not just already-materialized topology.
  • Conditional semantics are more explicit and therefore more demanding to document.

Obligations

  • Keep conditional branch selection expressed at the workflow or circuit boundary, not as product-only convention.
  • Preserve the distinction between the compiled artifact and the materialized graph in docs and operator tooling.
  • Revisit this ADR only if the retained-anchor model is intentionally replaced by a different provenance law.