feat: LLM accuracy testing framework with 17-test catalog

Framework runs a category/subcategory test catalog against multiple
LLMs through an OpenAI-compatible endpoint. Deterministic evaluators
score each response. Reports render as table, markdown, or JSON.

internal/eval/extract_test.go

@@ -0,0 +1,51 @@
+package eval
+
+import "testing"
+
+func TestExtractCodeBlock(t *testing.T) {
+	tests := []struct {
+		name     string
+		response string
+		lang     string
+		want     string
+	}{
+		{
+			name:     "tagged block matches lang",
+			response: "Here:\n```go\nfunc F() {}\n```\nDone.",
+			lang:     "go",
+			want:     "func F() {}",
+		},
+		{
+			name:     "case insensitive lang tag",
+			response: "```GO\nfunc F() {}\n```",
+			lang:     "go",
+			want:     "func F() {}",
+		},
+		{
+			name:     "prefers matching lang over other tagged blocks",
+			response: "```json\n{\"x\":1}\n```\n```go\nfunc F() {}\n```",
+			lang:     "go",
+			want:     "func F() {}",
+		},
+		{
+			name:     "falls back to untagged block",
+			response: "```\nfunc F() {}\n```",
+			lang:     "go",
+			want:     "func F() {}",
+		},
+		{
+			name:     "no fences falls back to whole response",
+			response: "  func F() {}  ",
+			lang:     "go",
+			want:     "func F() {}",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := ExtractCodeBlock(tt.response, tt.lang)
+			if got != tt.want {
+				t.Errorf("ExtractCodeBlock(%q, %q) = %q, want %q", tt.response, tt.lang, got, tt.want)
+			}
+		})
+	}
+}