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[DNM] Only send the delta on the partial tool call #2105

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[DNM] Only send the delta on the partial tool call #2105

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19 changes: 16 additions & 3 deletions pkg/app/app.go
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
package app

import (
"cmp"
"context"
"encoding/base64"
"errors"
Expand Down Expand Up @@ -997,12 +998,24 @@ func (a *App) mergeEvents(events []tea.Msg) []tea.Msg {
result = append(result, merged)

case *runtime.PartialToolCallEvent:
// For PartialToolCallEvent, keep only the latest one per tool call ID
// Only merge consecutive events with the same ID
// For PartialToolCallEvent, merge consecutive events with the same tool call ID
// by concatenating argument deltas
latest := ev
for i+1 < len(events) {
if next, ok := events[i+1].(*runtime.PartialToolCallEvent); ok && next.ToolCall.ID == ev.ToolCall.ID {
latest = next
latest = &runtime.PartialToolCallEvent{
Type: ev.Type,
ToolCall: tools.ToolCall{
ID: ev.ToolCall.ID,
Type: ev.ToolCall.Type,
Function: tools.FunctionCall{
Name: cmp.Or(next.ToolCall.Function.Name, latest.ToolCall.Function.Name),
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@docker-agent docker-agent bot Mar 15, 2026

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🔴 HIGH: Function name lost during consecutive PartialToolCallEvent merges

The cmp.Or(next.ToolCall.Function.Name, latest.ToolCall.Function.Name) logic is incorrect for merging delta events.

The Problem:

  • The first event ev contains the full function name (accumulated from streaming.go)
  • Subsequent events next have empty names because they're just argument deltas
  • cmp.Or returns the first non-empty value, preferring next.ToolCall.Function.Name (empty) over latest.ToolCall.Function.Name
  • This causes the function name to be lost after the first merge iteration

The Fix:
Use ev.ToolCall.Function.Name (from the first event in the merge chain) instead:

Name: ev.ToolCall.Function.Name,

This preserves the name learned from the first event throughout all subsequent merges.

Arguments: latest.ToolCall.Function.Arguments + next.ToolCall.Function.Arguments,
},
},
ToolDefinition: next.ToolDefinition,
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@docker-agent docker-agent bot Mar 15, 2026

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🟡 MEDIUM: Inconsistent AgentContext and ToolDefinition sources in merged event

The merged event uses AgentContext from the first event but ToolDefinition from the last event, creating an inconsistency.

The Issue:

AgentContext:   ev.AgentContext,      // from first event
ToolDefinition: next.ToolDefinition,  // from last event

This means the timestamp/context metadata comes from when the tool call was initiated, but the tool definition comes from the last delta event. While tool definitions are unlikely to change mid-stream, this violates consistency and could cause subtle bugs if tool definitions are updated dynamically.

Recommendation:
For consistency, use the tool definition from the first event:

ToolDefinition: ev.ToolDefinition,

AgentContext: ev.AgentContext,
}
i++
} else {
break
Expand Down
15 changes: 13 additions & 2 deletions pkg/runtime/streaming.go
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Original file line number Diff line number Diff line change
Expand Up @@ -152,10 +152,21 @@ func (r *LocalRuntime) handleStream(ctx context.Context, stream chat.MessageStre
tc.Function.Arguments += delta.Function.Arguments
}

// Emit PartialToolCall once we have a name, and on subsequent argument deltas
// Emit PartialToolCall once we have a name, and on subsequent argument deltas.
// Only the current token (delta.Function.Arguments) is sent, not the
// full accumulated arguments, to avoid re-transmitting the entire
// payload on every token.
if tc.Function.Name != "" && (learningName || delta.Function.Arguments != "") {
if !emittedPartial[delta.ID] || delta.Function.Arguments != "" {
events <- PartialToolCall(*tc, toolDefMap[tc.Function.Name], a.Name())
partial := tools.ToolCall{
ID: tc.ID,
Type: tc.Type,
Function: tools.FunctionCall{
Name: tc.Function.Name,
Arguments: delta.Function.Arguments,
},
}
events <- PartialToolCall(partial, toolDefMap[tc.Function.Name], a.Name())
emittedPartial[delta.ID] = true
}
}
Expand Down
6 changes: 5 additions & 1 deletion pkg/tui/components/messages/messages.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1301,7 +1301,11 @@ func (m *model) AddOrUpdateToolCall(agentName string, toolCall tools.ToolCall, t
if msg.Type == types.MessageTypeToolCall && msg.ToolCall.ID == toolCall.ID {
msg.ToolStatus = status
if toolCall.Function.Arguments != "" {
msg.ToolCall.Function.Arguments = toolCall.Function.Arguments
if status == types.ToolStatusPending {
msg.ToolCall.Function.Arguments += toolCall.Function.Arguments
} else {
msg.ToolCall.Function.Arguments = toolCall.Function.Arguments
}
}
m.invalidateItem(i)
return nil
Expand Down
6 changes: 5 additions & 1 deletion pkg/tui/components/reasoningblock/reasoningblock.go
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Original file line number Diff line number Diff line change
Expand Up @@ -206,7 +206,11 @@ func (m *Model) UpdateToolCall(toolCallID string, status types.ToolStatus, args
}
entry.msg.ToolStatus = status
if args != "" {
entry.msg.ToolCall.Function.Arguments = args
if status == types.ToolStatusPending {
entry.msg.ToolCall.Function.Arguments += args
} else {
entry.msg.ToolCall.Function.Arguments = args
}
}
m.toolEntries[i] = entry
return
Expand Down
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