feat: validate skills installation

Author: KartikJha

internal/ai/skills/validate.go

@@ -0,0 +1,82 @@
+package skills
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+// SkillInstallStatus reports the installation state of one (agent, skill) pair.
+type SkillInstallStatus struct {
+	SkillName string
+	AgentID   string
+	LinkPath  string
+	Status    string // "ok" | "missing" | "broken_symlink" | "invalid_skill" | "copy" | "unknown"
+	Error     string
+}
+
+// ValidateInstall checks each skill in skills for the given agent.
+// sourcePluginDir is the directory containing skill subdirectories (pluginDir/skills/).
+func ValidateInstall(agentID, agentSkillsDir, sourcePluginDir string, skills []string) []SkillInstallStatus {
+	out := make([]SkillInstallStatus, 0, len(skills))
+	for _, skillName := range skills {
+		expectedSource := filepath.Join(sourcePluginDir, skillName)
+		linkPath := filepath.Join(agentSkillsDir, skillName)
+
+		s := SkillInstallStatus{
+			SkillName: skillName,
+			AgentID:   agentID,
+			LinkPath:  linkPath,
+		}
+
+		switch CheckSkillLink(agentSkillsDir, skillName, expectedSource) {
+		case "missing":
+			s.Status = "missing"
+		case "broken":
+			s.Status = "broken_symlink"
+			s.Error = "symlink target does not exist or is inaccessible"
+		case "wrong_target":
+			s.Status = "broken_symlink"
+			s.Error = "symlink points to wrong target"
+		case "ok":
+			if err := checkSkillMeta(expectedSource, skillName); err != nil {
+				s.Status = "invalid_skill"
+				s.Error = err.Error()
+			} else {
+				s.Status = "ok"
+			}
+		case "copy":
+			fi, statErr := os.Stat(linkPath)
+			if statErr != nil || !fi.IsDir() {
+				s.Status = "invalid_skill"
+				s.Error = fmt.Sprintf("%s is a regular file, not a skill directory", linkPath)
+			} else if err := checkSkillMeta(linkPath, skillName); err != nil {
+				s.Status = "invalid_skill"
+				s.Error = err.Error()
+			} else {
+				s.Status = "copy"
+			}
+		default:
+			s.Status = "unknown"
+			s.Error = "unexpected link state"
+		}
+
+		out = append(out, s)
+	}
+	return out
+}
+
+// checkSkillMeta verifies that skillDir contains a readable SKILL.md whose name field matches skillName.
+func checkSkillMeta(skillDir, skillName string) error {
+	meta, err := ParseSkillMeta(skillDir)
+	if err != nil {
+		return fmt.Errorf("read SKILL.md: %w", err)
+	}
+	if meta.Name == "" {
+		return fmt.Errorf("SKILL.md has no frontmatter or empty name field")
+	}
+	if meta.Name != skillName {
+		return fmt.Errorf("SKILL.md name %q does not match directory name %q", meta.Name, skillName)
+	}
+	return nil
+}