fix(tools): defensively recover concatenated streamed tool arguments

parse_defensive_test.go

@@ -0,0 +1,34 @@
+package cogito
+
+import "testing"
+
+func TestParseStreamedToolArgs_Defensive(t *testing.T) {
+	cases := []struct {
+		name, raw, key string
+		val            any
+		wantErr        bool
+	}{
+		{"plain valid", `{"query":"x"}`, "query", "x", false},
+		{"concatenated duplicate", `{"query":"x"}{"query":"x"}`, "query", "x", false},
+		{"concatenated different -> first", `{"city":"NYC"}{"city":"LA"}`, "city", "NYC", false},
+		{"malformed", `{"query":`, "", nil, true},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			out := make(map[string]any)
+			err := parseStreamedToolArgs(c.raw, &out)
+			if c.wantErr {
+				if err == nil {
+					t.Fatalf("want err")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("err: %v", err)
+			}
+			if out[c.key] != c.val {
+				t.Fatalf("got %v want %v", out[c.key], c.val)
+			}
+		})
+	}
+}

tools.go

@@ -16,6 +16,25 @@ import (
 	"github.com/sashabaranov/go-openai/jsonschema"
 )
 
+// parseStreamedToolArgs unmarshals streamed tool-call arguments into out, tolerant of a known
+// defect where the full arguments object is concatenated more than once ("{...}{...}") — e.g.
+// some providers behind a proxy that maps Anthropic/Gemini tool-call streaming into OpenAI
+// deltas re-emit the complete object. A plain json.Unmarshal then fails with
+// "invalid character '{' after top-level value". On that failure we recover the FIRST complete
+// top-level JSON object via json.Decoder; correct incremental-delta streams take the fast path.
+func parseStreamedToolArgs(raw string, out *map[string]any) error {
+	if err := json.Unmarshal([]byte(raw), out); err == nil {
+		return nil
+	}
+	dec := json.NewDecoder(strings.NewReader(raw))
+	recovered := make(map[string]any)
+	if err := dec.Decode(&recovered); err != nil {
+		return err
+	}
+	*out = recovered
+	return nil
+}
+
 var (
 	ErrNoToolSelected              error = errors.New("no tool selected by the LLM")
 	ErrLoopDetected                error = errors.New("loop detected: same tool called repeatedly with same parameters")
@@ -402,7 +421,7 @@ func decisionWithStreaming(ctx context.Context, llm LLM, conversation []openai.C
 		allParsed := true
 		for _, toolCall := range toolCalls {
 			arguments := make(map[string]any)
-			if err := json.Unmarshal([]byte(toolCall.Function.Arguments), &arguments); err != nil {
+			if err := parseStreamedToolArgs(toolCall.Function.Arguments, &arguments); err != nil {
 				lastErr = err
 				xlog.Warn("Attempt to parse streamed tool arguments failed", "attempt", attempts+1, "error", err)
 				allParsed = false
@@ -505,7 +524,7 @@ func decision(ctx context.Context, llm LLM, conversation []openai.ChatCompletion
 		for _, toolCall := range msg.ToolCalls {
 			arguments := make(map[string]any)
 
-			if err := json.Unmarshal([]byte(toolCall.Function.Arguments), &arguments); err != nil {
+			if err := parseStreamedToolArgs(toolCall.Function.Arguments, &arguments); err != nil {
 				lastErr = err
 				xlog.Warn("Attempt to parse tool arguments failed", "attempt", attempts+1, "error", err)
 				if werr := backoffOrCancel(ctx, attempts); werr != nil {