Projection and Replay Semantics

This document freezes how the reference projector turns the append-only log into queryable state.

Projection Tables

The reference projector maintains:

• dg_cg_nodes
• dg_cg_edges
• dg_trace_summary
• dg_policy_eval_index
• dg_precedent_index
• dg_projection_meta

Projection Cursor

The cursor is stored in dg_projection_meta.last_processed_log_seq for the context_graph projection name.

Frozen behavior:

• cursor starts at 0
• cursor advances only after a projected event succeeds
• rollback restores the previous cursor
• projection-backed queries reject reads when cursor is behind the store’s last_log_seq

Replay Order

• replay happens in global log_seq order
• per-trace monotonic trace_seq is revalidated during replay
• payload hash is revalidated during replay
• replay failure rolls back the active transaction or batch

Rebuild Semantics

rebuild() clears all projection tables and resets:

• graph nodes
• graph edges
• precedent index
• policy evaluation index
• trace summary
• projection cursor

It does not mutate the event log.

Event-Specific Projection Effects

• TraceStarted: seeds dg_trace_summary and trace graph nodes
• PolicyEvaluated: appends a dg_policy_eval_index row
• TraceFinished: updates dg_trace_summary.outcome, finished_at, last_log_seq, and rebuilds dg_precedent_index for the finished trace

Precedent Index Build Rule

When a trace finishes, the projector scans that trace’s events in trace_seq order and materializes precedent rows from:

• each PolicyEvaluated
• each ExceptionRequested

The index row carries the trace’s primary entity information from TraceStarted when available.

Graph-Specific Notes

• graph nodes and edges are stored with deterministic IDs
• placeholder nodes are created for externally referenced nodes, such as cited trace IDs
• TraceFinished itself does not add graph nodes or edges

Batching

Batch projection is semantically equivalent to single-event projection:

• order remains log_seq ascending
• rollback restores pre-batch cursor and trace tracker state
• batch size affects transaction boundaries, not output semantics