feat: implement instruction assembly and project instruction providers with tests

internal/ai/runtime/instruction/providers_test.go

@@ -0,0 +1,48 @@
+package instruction
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestProjectInstructionProviderResolveFromAgentsFile(t *testing.T) {
+	tmpDir := t.TempDir()
+	nestedDir := filepath.Join(tmpDir, "nested", "child")
+	if err := os.MkdirAll(nestedDir, 0o755); err != nil {
+		t.Fatalf("mkdir failed: %v", err)
+	}
+	content := "# AGENTS.md\n\nfrom temp file"
+	if err := os.WriteFile(filepath.Join(tmpDir, "AGENTS.md"), []byte(content), 0o644); err != nil {
+		t.Fatalf("write file failed: %v", err)
+	}
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("getwd failed: %v", err)
+	}
+	defer func() { _ = os.Chdir(wd) }()
+	if err := os.Chdir(nestedDir); err != nil {
+		t.Fatalf("chdir failed: %v", err)
+	}
+	got := NewProjectInstructionProvider().Resolve()
+	if !strings.Contains(got, "from temp file") {
+		t.Fatalf("expected provider to load AGENTS.md from file, got: %s", got)
+	}
+}
+
+func TestProjectInstructionProviderFallbacksToDefault(t *testing.T) {
+	tmpDir := t.TempDir()
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatalf("getwd failed: %v", err)
+	}
+	defer func() { _ = os.Chdir(wd) }()
+	if err := os.Chdir(tmpDir); err != nil {
+		t.Fatalf("chdir failed: %v", err)
+	}
+	got := NewProjectInstructionProvider().Resolve()
+	if !strings.Contains(got, "本文件定义本项目内 AI Agent 的强制开发规则") {
+		t.Fatalf("expected fallback project instruction, got: %s", got)
+	}
+}