Avoid updating pyproject.toml offsets on non-add edits (#7262)

## Summary

Closes #7259.

crates/uv/src/commands/project/add.rs

@@ -411,21 +411,20 @@ pub(crate) async fn add(
             }
         };
 
-        // Keep track of the exact location of the edit.
-        let index = edit.index();
-
         // If the edit was inserted before the end of the list, update the existing edits.
-        for edit in &mut edits {
-            if *edit.dependency_type == dependency_type {
-                match &mut edit.edit {
-                    ArrayEdit::Add(existing) => {
-                        if *existing >= index {
-                            *existing += 1;
+        if let ArrayEdit::Add(index) = &edit {
+            for edit in &mut edits {
+                if *edit.dependency_type == dependency_type {
+                    match &mut edit.edit {
+                        ArrayEdit::Add(existing) => {
+                            if *existing >= *index {
+                                *existing += 1;
+                            }
                         }
-                    }
-                    ArrayEdit::Update(existing) => {
-                        if *existing >= index {
-                            *existing += 1;
+                        ArrayEdit::Update(existing) => {
+                            if *existing >= *index {
+                                *existing += 1;
+                            }
                         }
                     }
                 }

crates/uv/tests/edit.rs

@@ -4539,3 +4539,53 @@ fn custom_dependencies() -> Result<()> {
     });
     Ok(())
 }
+
+/// Regression test for: <https://github.com/astral-sh/uv/issues/7259>
+#[test]
+fn update_offset() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = [
+            "iniconfig",
+        ]
+    "#})?;
+
+    uv_snapshot!(context.filters(), context.add().args(["typing-extensions", "iniconfig"]), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 3 packages in [TIME]
+    Prepared 2 packages in [TIME]
+    Installed 2 packages in [TIME]
+     + iniconfig==2.0.0
+     + typing-extensions==4.10.0
+    "###);
+
+    let pyproject_toml = fs_err::read_to_string(context.temp_dir.join("pyproject.toml"))?;
+
+    insta::with_settings!({
+        filters => context.filters(),
+    }, {
+        assert_snapshot!(
+            pyproject_toml, @r###"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = [
+            "iniconfig",
+            "typing-extensions>=4.10.0",
+        ]
+        "###
+        );
+    });
+    Ok(())
+}