Fix guided generation: include <|endoftext|> as stop token

swift/Sources/CoreAILanguageModels/Bundle/LanguageConfig.swift

@@ -126,7 +126,7 @@ public struct LanguageConfig: Codable, Sendable, Equatable {
         // 3. Check added_tokens_decoder for turn-ending special tokens
         //    (e.g. Gemma's <end_of_turn> ID 106, Qwen's <|im_end|>)
         //    Only include tokens whose content matches known turn-ending patterns.
-        let turnEndPatterns = ["end_of_turn", "im_end", "eot_id"]
+        let turnEndPatterns = ["end_of_turn", "im_end", "eot_id", "endoftext"]
         if let addedTokens = json["added_tokens_decoder"] as? [String: Any] {
             for (idString, value) in addedTokens {
                 guard let dict = value as? [String: Any],

swift/Sources/CoreAILanguageModels/DecodingStrategies/ConstrainedDecodingStrategy.swift

@@ -324,17 +324,18 @@ extension ConstrainedDecodingStrategy.ConstrainedDecodedSequence {
                 generatedTokens.append(bestToken)
                 tokenStep += 1
 
+                if terminatedAfterAccept {
+                    finished = true
+                    return nil
+                }
+
                 let delta = ConstrainedDecodingStrategy.computeTextDelta(
                     generatedTokens: generatedTokens,
                     previousDecodedText: &previousDecodedText,
                     tokenizer: tokenizer,
                     tokenStep: tokenStep
                 )
 
-                if terminatedAfterAccept {
-                    finished = true
-                }
-
                 return GenerationResult(text: delta, tokenId: bestToken, rawLogits: logits)
             }