From bbf53dca72d1ea29bc6769bc968cfadbaaa5cb6a Mon Sep 17 00:00:00 2001
From: Christian Rocha <christian@rocha.is>
Date: Mon, 13 Apr 2026 11:53:22 -0400
Subject: [PATCH] fix(agent): buffer tool calls

Wait until streaming has finished before dispatching tool calls to avoid
getting tool results without a matching call: essentially orphans.
---
 agent.go                              | 12 ++++++++++--
 providers/anthropic/anthropic_test.go |  3 ++-
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/agent.go b/agent.go
index 34d4f8a1fb6efa1c6d0028bba905b1d52896ed1e..f0b981be6c57d6d3308dafc9e73541e6b4017471 100644
--- a/agent.go
+++ b/agent.go
@@ -1248,6 +1248,7 @@ func (a *agent) processStepStream(ctx context.Context, stream StreamResponse, op
 		parallel bool
 	}
 	toolChan := make(chan toolExecutionRequest, 10)
+	var pendingDispatches []toolExecutionRequest
 	var toolExecutionWg sync.WaitGroup
 	var toolStateMu sync.Mutex
 	toolResults := make([]ToolResultContent, 0)
@@ -1475,8 +1476,9 @@ func (a *agent) processStepStream(ctx context.Context, stream StreamResponse, op
 					isParallel = tool.Info().Parallel
 				}
 
-				// Send tool call to execution channel
-				toolChan <- toolExecutionRequest{toolCall: validatedToolCall, parallel: isParallel}
+				// Buffer dispatch until stream is fully consumed so that all
+				// OnToolCall callbacks complete before any tool result is written.
+				pendingDispatches = append(pendingDispatches, toolExecutionRequest{toolCall: validatedToolCall, parallel: isParallel})
 
 				// Clean up active tool call
 				delete(activeToolCalls, part.ID)
@@ -1534,6 +1536,12 @@ func (a *agent) processStepStream(ctx context.Context, stream StreamResponse, op
 		}
 	}
 
+	// Dispatch all buffered tool calls now that the complete set is known and
+	// every OnToolCall callback has been called.
+	for _, req := range pendingDispatches {
+		toolChan <- req
+	}
+
 	// Close the tool execution channel and wait for all executions to complete
 	close(toolChan)
 	toolExecutionWg.Wait()
diff --git a/providers/anthropic/anthropic_test.go b/providers/anthropic/anthropic_test.go
index 4387a34faf7fe8900383e26859de13d306505664..d447954cbf1d78819e6091aedfa3da6af8b742fc 100644
--- a/providers/anthropic/anthropic_test.go
+++ b/providers/anthropic/anthropic_test.go
@@ -1574,7 +1574,8 @@ func TestComputerUseToolJSON(t *testing.T) {
 		}
 		_, err := computerUseToolJSON(pdt)
 		require.Error(t, err)
-			require.Contains(t, err.Error(), "tool_version arg is missing")	})
+		require.Contains(t, err.Error(), "tool_version arg is missing")
+	})
 
 	t.Run("returns error for unsupported version", func(t *testing.T) {
 		t.Parallel()