Node state-transition model#263
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Adds docs/node-state-model.md, a design proposal consolidating the node-status work for issues #240 (skipped downstream nodes) and #171 (race-loser nodes left running/pending). Defines instance and node lifecycle states, legal transitions, a coarse status set plus nullable status_reason, loop iteration-scoping/reset semantics, and prior-art alignment with Airflow/Temporal/BPMN/Step Functions. The #240 skipped-node work shipped earlier in PR #249; this PR (#263) defines the consolidated model and will add the remaining implementation (cancelled, status_reason, race-loser reconciliation, loop reset) after review. Design only; implementation to follow on this PR.
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Summary
Introduces a formal node & instance state-transition model for
pg_durable, then implements it. This consolidates two related node-status gaps:running/pendingafter aRACEresolves; they should reach a terminal state.skipped(initialskippedsupport landed in WIP: start issue #240 implementation for skipped downstream node status #249; this PR formalizes the model and itsstatus_reason).What's here now
The first commit adds the design proposal: docs/node-state-model.md. It defines:
pending,running,completed,failed,skipped,cancelled) plus a nullablestatus_reason(upstream_failed,branch_not_taken,race_lost,scope_cancelled) — avoiding an ever-growing enum under the strict schema-upgrade contract.THEN/IF/LOOP/JOIN/RACE/BREAK).df.nodesrow behaves acrosscontinue_as_new, and the body-subgraph reset that prevents stale terminal marks leaking between iterations.ContinueAsNew), BPMN 2.0 (withdrawn), and AWS Step Functions.pending → skippedterminal sweep) and df.instance_nodes leaves race-loser nodes running or pending after race completion #171 (running → cancelledsubtree reconciliation at race resolution).Plan
This PR starts as a design proposal for review. After incorporating colleague feedback, the implementation (status set additions,
status_reasoncolumn, race-loser reconciliation, and loop-reset) will land on this same PR.Upgrade & migration
The model is explicit about backward compatibility: new status/
status_reasonrequire install + upgrade DDL, and every reconciliation activity must no-op gracefully against schemas that predate the relevant column/status (the schema-probe pattern already used forskipped).