diff --git a/internal/queue/queue.go b/internal/queue/queue.go
index 4c87a87c..6de48bf5 100644
--- a/internal/queue/queue.go
+++ b/internal/queue/queue.go
@@ -84,7 +84,9 @@ func NewTaskQueue(legacyWorkers int, processor JobProcessor, jobRepo repository.
 
 	// Calculate optimal worker counts, fallback to legacy parameter
 	min, max := getOptimalWorkerCount()
-	if legacyWorkers > 0 {
+	// Only use legacy parameter as fallback when QUEUE_WORKERS env var is not set
+	// TODO: Deprecate `legacyWorkers` and rely on `getOptimalWorkerCount` instead.
+	if os.Getenv("QUEUE_WORKERS") == "" && legacyWorkers > 0 {
 		min = legacyWorkers
 		max = legacyWorkers
 	}
diff --git a/internal/queue/queue_test.go b/internal/queue/queue_test.go
new file mode 100644
index 00000000..d8f0719f
--- /dev/null
+++ b/internal/queue/queue_test.go
@@ -0,0 +1,119 @@
+package queue
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// TestGetOptimalWorkerCount_DefaultBehavior verifies that without QUEUE_WORKERS,
+// the function returns positive CPU-based defaults with min <= max.
+func TestGetOptimalWorkerCount_DefaultBehavior(t *testing.T) {
+	t.Setenv("QUEUE_WORKERS", "")
+
+	min, max := getOptimalWorkerCount()
+
+	assert.Positive(t, min, "min workers should be positive")
+	assert.Positive(t, max, "max workers should be positive")
+	assert.LessOrEqual(t, min, max, "min should be <= max")
+}
+
+// TestGetOptimalWorkerCount_RespectsEnvVar verifies that QUEUE_WORKERS env var
+// pins both min and max to the exact value specified.
+func TestGetOptimalWorkerCount_RespectsEnvVar(t *testing.T) {
+	tests := []struct {
+		name     string
+		envValue string
+		want     int
+	}{
+		{"single worker", "1", 1},
+		{"four workers", "4", 4},
+		{"ten workers", "10", 10},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Setenv("QUEUE_WORKERS", tt.envValue)
+
+			min, max := getOptimalWorkerCount()
+
+			assert.Equal(t, tt.want, min, "min workers")
+			assert.Equal(t, tt.want, max, "max workers")
+		})
+	}
+}
+
+// TestGetOptimalWorkerCount_IgnoresInvalidEnvVar verifies that non-numeric,
+// zero, and negative QUEUE_WORKERS values are ignored, falling back to
+// CPU-based defaults rather than crashing or using bad values.
+func TestGetOptimalWorkerCount_IgnoresInvalidEnvVar(t *testing.T) {
+	tests := []struct {
+		name     string
+		envValue string
+	}{
+		{"non-numeric", "abc"},
+		{"zero", "0"},
+		{"negative", "-1"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Setenv("QUEUE_WORKERS", tt.envValue)
+
+			min, max := getOptimalWorkerCount()
+
+			assert.Positive(t, min, "should fall back to positive CPU-based default")
+			assert.Positive(t, max, "should fall back to positive CPU-based default")
+		})
+	}
+}
+
+// TestNewTaskQueue_DefaultWorkerCount verifies that without QUEUE_WORKERS,
+// the legacy parameter (2) is used as default, preserving existing behavior.
+func TestNewTaskQueue_DefaultWorkerCount(t *testing.T) {
+	t.Setenv("QUEUE_WORKERS", "")
+
+	tq := NewTaskQueue(2, nil, nil)
+	defer tq.cancel()
+
+	assert.Equal(t, 2, tq.minWorkers, "default minWorkers should match legacy parameter")
+	assert.Equal(t, 2, tq.maxWorkers, "default maxWorkers should match legacy parameter")
+}
+
+// TestNewTaskQueue_EnvOverridesLegacy verifies that QUEUE_WORKERS takes
+// precedence over the hardcoded legacy parameter.
+func TestNewTaskQueue_EnvOverridesLegacy(t *testing.T) {
+	tests := []struct {
+		name          string
+		envValue      string
+		legacyWorkers int
+		want          int
+	}{
+		{"env=1 overrides legacy=2", "1", 2, 1},
+		{"env=4 overrides legacy=2", "4", 2, 4},
+		{"env=3 overrides legacy=2", "3", 2, 3},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Setenv("QUEUE_WORKERS", tt.envValue)
+
+			tq := NewTaskQueue(tt.legacyWorkers, nil, nil)
+			defer tq.cancel()
+
+			assert.Equal(t, tt.want, tq.minWorkers, "QUEUE_WORKERS should override legacy minWorkers")
+			assert.Equal(t, tt.want, tq.maxWorkers, "QUEUE_WORKERS should override legacy maxWorkers")
+		})
+	}
+}
+
+// TestNewTaskQueue_AutoScaleDisabledWithFixedWorkers verifies that
+// auto-scaling is disabled when QUEUE_WORKERS sets a fixed count.
+func TestNewTaskQueue_AutoScaleDisabledWithFixedWorkers(t *testing.T) {
+	t.Setenv("QUEUE_WORKERS", "3")
+
+	tq := NewTaskQueue(2, nil, nil)
+	defer tq.cancel()
+
+	assert.False(t, tq.autoScale, "auto-scaling should be disabled when QUEUE_WORKERS sets fixed count")
+}