Log selected model in Agent.Model() for alloy observability

pkg/agent/agent.go

@@ -131,11 +131,18 @@ func (a *Agent) HasSubAgents() bool {
 // If model override(s) are set, it returns one of the overrides (randomly for alloy).
 // Otherwise, it returns a random model from the available models.
 func (a *Agent) Model() provider.Provider {
+	var selected provider.Provider
+	var poolSize int
 	// Check for model override first (set via TUI model switching)
 	if overrides := a.modelOverrides.Load(); overrides != nil && len(*overrides) > 0 {
-		return (*overrides)[rand.Intn(len(*overrides))]
+		selected = (*overrides)[rand.Intn(len(*overrides))]
+		poolSize = len(*overrides)
+	} else {
+		selected = a.models[rand.Intn(len(a.models))]
+		poolSize = len(a.models)
 	}
-	return a.models[rand.Intn(len(a.models))]
+	slog.Info("Model selected", "agent", a.name, "model", selected.ID(), "pool_size", poolSize)
+	return selected
 }
 
 // SetModelOverride sets runtime model override(s) for this agent.

pkg/agent/agent_test.go

@@ -1,8 +1,10 @@
 package agent
 
 import (
+	"bytes"
 	"context"
 	"errors"
+	"log/slog"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -139,6 +141,42 @@ func TestModelOverride(t *testing.T) {
 	assert.Equal(t, "openai/gpt-4o", model.ID())
 }
 
+func TestModel_LogsSelection(t *testing.T) {
+	t.Parallel()
+
+	var buf bytes.Buffer
+	handler := slog.NewTextHandler(&buf, &slog.HandlerOptions{Level: slog.LevelInfo})
+	prev := slog.Default()
+	slog.SetDefault(slog.New(handler))
+	t.Cleanup(func() { slog.SetDefault(prev) })
+
+	model1 := &mockProvider{id: "anthropic/claude-sonnet-4-0"}
+	model2 := &mockProvider{id: "openai/gpt-4o"}
+
+	a := New("scanner", "test", WithModel(model1), WithModel(model2))
+
+	// Verify basic selection logging
+	selected := a.Model()
+	logOutput := buf.String()
+
+	assert.Contains(t, logOutput, "Model selected")
+	assert.Contains(t, logOutput, "agent=scanner")
+	assert.Contains(t, logOutput, selected.ID())
+	assert.Contains(t, logOutput, "pool_size=2")
+
+	// Verify override scenario logs correct pool_size
+	buf.Reset()
+	override := &mockProvider{id: "google/gemini-2.0-flash"}
+	a.SetModelOverride(override)
+
+	selected = a.Model()
+	logOutput = buf.String()
+
+	assert.Equal(t, "google/gemini-2.0-flash", selected.ID())
+	assert.Contains(t, logOutput, "google/gemini-2.0-flash")
+	assert.Contains(t, logOutput, "pool_size=1")
+}
+
 func TestModelOverride_ConcurrentAccess(t *testing.T) {
 	t.Parallel()