fix: drop trailing orphaned function responses

When the latest event is a function response whose IDs do not match any
function-call event in session history (stale client retry, reconnect,
session restart), drop only that trailing event and continue with the
remaining valid history instead of hard-failing content construction.

Fixes #760

Author: gustafvh

internal/llminternal/contents_processor.go

@@ -219,10 +219,10 @@ SearchLoop: // A label to allow breaking out of the nested loop
 	}
 
 	if functionCallEventIdx == -1 {
-		return nil, fmt.Errorf(
-			"no function call event found for function responses ids: %v",
-			responseIDs,
-		)
+		// Trailing function-response event has no matching call in history;
+		// treat as stale (e.g. retry/reconnect) and drop it instead of failing
+		// the whole turn. Earlier valid history is preserved.
+		return events[:len(events)-1], nil
 	}
 
 	// Collect all function response events *between* the call and the last response.

internal/llminternal/contents_processor_test.go

@@ -897,13 +897,26 @@ func TestContentsRequestProcessor_Rearrange(t *testing.T) {
 			},
 		},
 		{
-			name: "Error on function response without matching call",
+			name: "Orphaned function response without matching call is dropped",
 			events: []*session.Event{
 				{Author: "user", LLMResponse: model.LLMResponse{Content: &genai.Content{Role: "user", Parts: []*genai.Part{{Text: "Regular message"}}}}},
 				{Author: "user", LLMResponse: model.LLMResponse{Content: &genai.Content{Role: "user", Parts: []*genai.Part{{FunctionResponse: frOrphaned}}}}},
 			},
-			want:    nil,
-			wantErr: "no function call event found",
+			want: []*genai.Content{
+				genai.NewContentFromText("Regular message", "user"),
+			},
+		},
+		{
+			name: "Orphaned function response after text reply is dropped",
+			events: []*session.Event{
+				{Author: "user", LLMResponse: model.LLMResponse{Content: genai.NewContentFromText("Hello", "user")}},
+				{Author: agentName, LLMResponse: model.LLMResponse{Content: genai.NewContentFromText("Hi there", "model")}},
+				{Author: "user", LLMResponse: model.LLMResponse{Content: &genai.Content{Role: "user", Parts: []*genai.Part{{FunctionResponse: frOrphaned}}}}},
+			},
+			want: []*genai.Content{
+				genai.NewContentFromText("Hello", "user"),
+				genai.NewContentFromText("Hi there", "model"),
+			},
 		},
 	}