fix: history load notifies and never overwrites unreadable file; dictionary keeps ids across external edits, undo safety

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Sources/SstData/DictionaryFile.swift

@@ -70,6 +70,21 @@ public struct DictionaryFile: Equatable, Sendable {
         return .entry(DictionaryEntry(kind: .term(trimmed)))
     }
 
+    /// Reuses the ids of `old` for entries with equal content (first unused match, in order), so ids survive a reload.
+    public func preservingIDs(from old: DictionaryFile) -> DictionaryFile {
+        var available = old.entries
+        var result = self
+        result.lines = lines.map { line in
+            guard case .entry(let entry) = line else { return line }
+            if let index = available.firstIndex(where: { $0.kind == entry.kind }) {
+                let reused = available.remove(at: index)
+                return .entry(DictionaryEntry(id: reused.id, kind: entry.kind))
+            }
+            return line
+        }
+        return result
+    }
+
     public func serialized() -> String {
         let out = lines.map { line -> String in
             switch line {