conn: Fix incremental update with ambiguous section refs

stack-info: PR: #344, branch: artempyanykh/stack/4

Marksman/Syms.fs

@@ -175,7 +175,7 @@ module ScopeSlug =
         | Def.LinkDef _ -> None
         | Def.Doc -> Some(ofDocId docId)
         | Def.Header(1, id) -> Some(ScopeSlug(Slug.ofString id))
-        | Def.Header _ -> None
+        | Def.Header _ -> Some(ofDocId docId)
 
     let ofScopedDef (scope: Scope, def: Def) =
         match Scope.asDoc scope with

Tests/ConnTest.fs

@@ -191,6 +191,23 @@ module ConnGraphTests =
         let connDiff = Conn.difference fromScratch incr
         checkInlineSnapshot id [ connDiff.CompactFormat() ] [ "" ]
 
+    [<Fact>]
+    let addTitle_CrossSection () =
+        let d1 =
+            FakeDoc.Mk(path = "d1.md", contentLines = [| "# D1"; "[[d2#sub]]" |])
+
+        let d2 = FakeDoc.Mk(path = "d2.md", contentLines = [| "# D2"; "## Sub" |])
+
+        let d1Upd =
+            FakeDoc.Mk(path = "d1.md", contentLines = [| "# D2"; "[[d2#sub]]" |])
+
+        let incr = mkFolder [ d1; d2 ] |> Folder.withDoc d1Upd |> Folder.conn
+
+        let fromScratch = mkFolder [ d1Upd; d2 ] |> Folder.conn
+
+        let connDiff = Conn.difference fromScratch incr
+        checkInlineSnapshot id [ connDiff.CompactFormat() ] [ "" ]
+
     [<Fact>]
     let fixRef () =
         let d1 =