fix(merge): preserve state when source table versions lag target

crates/omnigraph-gqt/cases/merge_adopt_equal_source_version_collides.gqt

@@ -0,0 +1,74 @@
+# issue: none
+# red_on: 2026-09-07, main @ 5f94a741: `branch merge main into feature` failed with `storage: Concurrent modification: table version 4 already exists for identity … (edge:Knows) with different state`
+# notes: sibling of merge_adopt_lower_source_version_keeps_edges: two edge writes
+# notes: on `feature` instead of three make the two edge tables reach the same
+# notes: version number on different native branches. Adopting `main` into
+# notes: `feature` must fast-forward and show all four edges.
+
+--- schema
+node Person {
+    name: String @key
+}
+
+edge Knows: Person -> Person
+
+--- seed
+{"type":"Person","data":{"name":"a"}}
+{"type":"Person","data":{"name":"b"}}
+{"type":"Person","data":{"name":"c"}}
+{"edge":"Knows","from":"a","to":"b"}
+
+--- mutate
+branch create feature
+
+--- expect ok
+
+--- mutate branch: feature
+query add_b_c() {
+    insert Knows { from: "b", to: "c" }
+}
+
+--- expect affected: nodes=0 edges=1
+
+--- mutate branch: feature
+query add_c_a() {
+    insert Knows { from: "c", to: "a" }
+}
+
+--- expect affected: nodes=0 edges=1
+
+--- mutate
+branch merge feature
+
+--- expect outcome: fast_forward
+
+--- mutate
+query add_a_c_on_main() {
+    insert Knows { from: "a", to: "c" }
+}
+
+--- expect affected: nodes=0 edges=1
+
+--- mutate
+branch merge main into feature
+
+--- expect outcome: fast_forward
+
+--- query branch: feature
+query edges_on_feature() {
+    match {
+        $x: Person
+        $x knows $y
+    }
+    return { $x.name, $y.name }
+}
+
+--- expect unordered
+{"x.name": "a", "y.name": "b"}
+{"x.name": "b", "y.name": "c"}
+{"x.name": "c", "y.name": "a"}
+{"x.name": "a", "y.name": "c"}
+
+--- expect shape
+x.name: String
+y.name: String

crates/omnigraph-gqt/cases/merge_adopt_lazy_target_below_inherited_version.gqt

@@ -0,0 +1,92 @@
+# issue: none
+# notes: from PR 630, the lazy-target arm. `main` writes its node table four
+# notes: times; `feature` writes once, takes `main` by a three-way merge, then
+# notes: sets a's age; `child` forks from `main` and never writes, so its node
+# notes: table is `main`'s at a version above `feature`'s. Merging `feature`
+# notes: into `child` must show feature's value on child.
+
+--- schema
+node Person {
+    name: String @key
+    age: I32
+}
+
+--- seed
+{"type":"Person","data":{"name":"a","age":1}}
+{"type":"Person","data":{"name":"b","age":1}}
+
+--- mutate
+branch create feature
+
+--- expect ok
+
+--- mutate
+query a_2_on_main() {
+    update Person set { age: 2 } where name = "a"
+}
+
+--- expect affected: nodes=1 edges=0
+
+--- mutate
+query a_3_on_main() {
+    update Person set { age: 3 } where name = "a"
+}
+
+--- expect affected: nodes=1 edges=0
+
+--- mutate
+query a_4_on_main() {
+    update Person set { age: 4 } where name = "a"
+}
+
+--- expect affected: nodes=1 edges=0
+
+--- mutate
+query a_5_on_main() {
+    update Person set { age: 5 } where name = "a"
+}
+
+--- expect affected: nodes=1 edges=0
+
+--- mutate branch: feature
+query b_9_on_feature() {
+    update Person set { age: 9 } where name = "b"
+}
+
+--- expect affected: nodes=1 edges=0
+
+--- mutate
+branch merge main into feature
+
+--- expect outcome: merged
+
+--- mutate branch: feature
+query a_50_on_feature() {
+    update Person set { age: 50 } where name = "a"
+}
+
+--- expect affected: nodes=1 edges=0
+
+--- mutate
+branch create child
+
+--- expect ok
+
+--- mutate
+branch merge feature into child
+
+--- expect outcome: fast_forward
+
+--- query branch: child
+query ages_on_child() {
+    match { $p: Person }
+    return { $p.name, $p.age }
+}
+
+--- expect unordered
+{"p.name": "a", "p.age": 50}
+{"p.name": "b", "p.age": 9}
+
+--- expect shape
+p.name: String
+p.age: I32

crates/omnigraph-gqt/cases/merge_adopt_lower_source_version_keeps_edges.gqt

@@ -0,0 +1,113 @@
+# issue: none
+# red_on: 2026-09-07, main @ 5f94a741: after `branch merge main into feature` reported fast_forward, feature's edges lacked a->c; merging feature back then dropped a->c from main
+# notes: from PR 630. `feature` writes its edge table three times, so its table
+# notes: version passes `main`'s. Merge `feature` into `main`, add an edge on
+# notes: `main`, merge `main` into `feature`: the adopted edge must be visible
+# notes: on `feature`. Then edit only a node on `feature` and merge back: `main`
+# notes: must keep the edge.
+
+--- schema
+node Person {
+    name: String @key
+}
+
+edge Knows: Person -> Person
+
+--- seed
+{"type":"Person","data":{"name":"a"}}
+{"type":"Person","data":{"name":"b"}}
+{"type":"Person","data":{"name":"c"}}
+{"edge":"Knows","from":"a","to":"b"}
+
+--- mutate
+branch create feature
+
+--- expect ok
+
+--- mutate branch: feature
+query add_b_c() {
+    insert Knows { from: "b", to: "c" }
+}
+
+--- expect affected: nodes=0 edges=1
+
+--- mutate branch: feature
+query add_c_a() {
+    insert Knows { from: "c", to: "a" }
+}
+
+--- expect affected: nodes=0 edges=1
+
+--- mutate branch: feature
+query drop_b_c() {
+    delete Knows where from = "b"
+}
+
+--- expect affected: nodes=0 edges=1
+
+--- mutate
+branch merge feature
+
+--- expect outcome: fast_forward
+
+--- mutate
+query add_a_c_on_main() {
+    insert Knows { from: "a", to: "c" }
+}
+
+--- expect affected: nodes=0 edges=1
+
+--- mutate
+branch merge main into feature
+
+--- expect outcome: fast_forward
+
+--- query branch: feature
+query edges_on_feature() {
+    match {
+        $x: Person
+        $x knows $y
+    }
+    return { $x.name, $y.name }
+}
+
+--- expect unordered
+{"x.name": "a", "y.name": "b"}
+{"x.name": "a", "y.name": "c"}
+{"x.name": "c", "y.name": "a"}
+
+--- expect shape
+x.name: String
+y.name: String
+
+--- mutate branch: feature
+query add_d_on_feature() {
+    insert Person { name: "d" }
+}
+
+--- expect affected: nodes=1 edges=0
+
+--- mutate
+branch merge feature
+
+--- expect outcome: fast_forward
+
+--- restart
+
+--- query
+query edges_on_main() {
+    match {
+        $x: Person
+        $x knows $y
+    }
+    return { $x.name, $y.name }
+}
+
+--- expect unordered
+{"x.name": "a", "y.name": "b"}
+{"x.name": "a", "y.name": "c"}
+{"x.name": "c", "y.name": "a"}
+
+--- expect shape
+x.name: String
+y.name: String

crates/omnigraph/src/db/manifest/state.rs

@@ -26,6 +26,19 @@ pub struct DatasetEntry {
     pub(crate) version_metadata: TableVersionMetadata,
 }
 
+impl DatasetEntry {
+    /// Field-for-field equal registration, the Lance manifest metadata included.
+    pub fn same_registration(&self, other: &DatasetEntry) -> bool {
+        self.identity == other.identity
+            && self.type_key == other.type_key
+            && self.dataset_path == other.dataset_path
+            && self.published_dataset_version == other.published_dataset_version
+            && self.native_dataset_branch == other.native_dataset_branch
+            && self.entity_count == other.entity_count
+            && self.version_metadata == other.version_metadata
+    }
+}
+
 #[derive(Debug, Clone)]
 pub(super) struct ManifestState {
     pub(super) version: u64,