SurrealDB: `RELATE` overwrites existing edge records without `UPDATE` permission

Summary

`RELATE` creates an edge record between two existing records, and SurrealDB enforces the `CREATE` permission on the edge table for this operation. When the statement included a `SET id = edge:existing` clause, however, the new edge's id ended up pointing at an record that was already in storage. Rather than failing because the target already existed — which is what a create operation should do — the storage layer silently overwrote the existing edge. A caller with `CREATE` permission could therefore replace any existing edge on the table, even without `UPDATE` permission for that record. ### Impact An authenticated user with `CREATE` permission on an edge table could overwrite any existing record on that table — including edges they had no `UPDATE` permission for — by issuing a `RELATE` whose `SET id = …` resolved to the target record's id. The attack is integrity-only. ### Patches A patch has been introduced that adds an explicit `Statement::Relate` arm using `put_record` instead of `set_record` when the create path is selected. Conflicting writes now return a `RecordExists` error. - Versions 3.1.0 and later are not affected by this issue. This is a behaviour change for applications that relied on RELATE … SET id = … to silently replace existing edges; after the patch those calls return RecordExists instead. Applications that need "create or replace" semantics should use UPSERT (which is correctly permission-gated for the update half). ### Workarounds The defect only fires when the `RELATE` statement includes a `SET id = …` clause that resolves to an existing edge id. Applications that let SurrealDB auto-generate the edge id (the default — `RELATE a:1 -> edge -> b:1 SET <data>` with no `id` override) are not affected, because auto-generated ids do not collide with existing records. Where applications must use `SET id = …` (for example, to produce deterministic edge ids for idempotency), they should first verify that no record with the target id exists before issuing the statement, or restrict `CREATE` permission on the edge table to principals trusted with `UPDATE` on the same table.