The identity writer appends as 06 promised — clearing is the one sanctioned edit

Claude-Session: https://claude.ai/code/session_014PtZdPwqZuqEDLc6wZMtEy

KanbanTests/BranchSwitchTests.swift

@@ -983,8 +983,8 @@ struct GitIdentityWriteTests {
         #expect(read.email == "[email protected]")
     }
 
-    @Test("An existing value is replaced in place and everything else survives verbatim")
-    func replacesInPlace() {
+    @Test("A new value appends a fresh section that wins on read — existing lines survive verbatim")
+    func appendsAndWins() {
         let original = """
             [core]
             \trepositoryformatversion = 0
@@ -1001,11 +1001,15 @@ struct GitIdentityWriteTests {
 
         #expect(written.contains("\tname = New Name"))
         #expect(written.contains("\temail = [email protected]"))
-        #expect(!written.contains("Old Name"))
+        #expect(written.contains("\tname = Old Name"), "sets never edit existing sections — 06's append-only rule")
         #expect(written.contains("\tsigningkey = ABC123"), "a key this app has no opinion about survives")
         #expect(written.contains("[remote \"origin\"]"))
         #expect(written.contains("\turl = [email protected]:board.git"))
         #expect(written.contains("\tbare = false"))
+
+        let read = GitConfigFile.identity(inConfigText: written)
+        #expect(read.name == "New Name", "the appended section is last, and reads take the last")
+        #expect(read.email == "[email protected]")
     }
 
     @Test("An empty field clears its key, and clearing both removes the section entirely")