omnigraph/docs/dev/merge.md

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# Merging (three-way) and Conflicts
`exec/merge.rs`.
## Strategy
Ordered, row-by-row cursor merge:
- `OrderedTableCursor` scans each table sorted by `id` and supports peek/pop matching.
- `StagedTableWriter` buffers `MERGE_STAGE_BATCH_ROWS = 8192` rows into a temp Lance dataset (`OMNIGRAPH_MERGE_STAGING_DIR`).
- The merge runs per sub-table; results are published as one atomic manifest update.
## Outcome enum
`MergeOutcome { AlreadyUpToDate | FastForward | Merged }`
## Conflict types (`error.rs`)
```
MergeConflictKind:
DivergentInsert // same id inserted on both branches
DivergentUpdate // updated differently on both branches
DeleteVsUpdate // one side deletes, other updates
OrphanEdge // edge references a node deleted by the other side
UniqueViolation
CardinalityViolation
ValueConstraintViolation
```
Returned as `OmniError::MergeConflicts(Vec<MergeConflict { table_key, row_id?, kind, message }>)`. The HTTP server surfaces this as a 409 with structured `merge_conflicts[]` (top 3 + "+N more").