feat: add AI agent skills inventory scanning support

SCAN_COVERAGE.md

@@ -88,6 +88,14 @@ On Windows, `~` refers to the user's home directory (`%USERPROFILE%`). Claude De
 | Open Interpreter | `~/.config/open-interpreter/config.yaml`                         | _(same)_                                       | OpenSource|
 | Codex            | `~/.codex/config.toml`                                           | _(same)_                                       | OpenAI    |
 
+## AI Agent Skills
+
+Dev Machine Guard inventories every installed **agent skill** — a directory containing a `SKILL.md` manifest — across Claude Code, Codex, OpenCode, Cursor, the cross-agent `~/.agents` convention, and skills installed via [skills.sh](https://skills.sh). It probes each agent's global, system, project, and plugin skill directories; skills.sh lock files add upstream provenance (joined by symlink-resolved path). Detection is pure filesystem reads (no subprocesses), bounded by a 60-second budget and per-root caps.
+
+**Privacy: only metadata and a single SHA-256 hash of each `SKILL.md` are collected — no other file is ever read, and file contents are never transmitted.** The file census (counts, sizes, timestamps) comes entirely from directory listings and `stat`. For skills installed from a local path, the on-disk source path is never serialized — only the skill's alias.
+
+Per skill, the scan records identity and frontmatter (name, description, version, license, allowed tools), capability flags (load-time shell execution, hooks, plugin manifest, subagent context), a stat-only file census, the `SKILL.md` hash, and — when lock-managed — upstream provenance.
+
 ## IDE Extensions & Plugins
 
 ### VS Code-Family Extensions

internal/detector/claudeprojects.go

@@ -0,0 +1,42 @@
+package detector
+
+import (
+	"encoding/json"
+
+	"github.com/step-security/dev-machine-guard/internal/executor"
+)
+
+// discoverClaudeProjects reads the "projects" map from ~/.claude.json and
+// returns its keys — the absolute root paths of every project the user has
+// opened in Claude Code. This is Claude Code's own project registry and the
+// highest-signal source of project roots for per-project scanning (MCP configs,
+// agent skills, …).
+//
+// It never fails a scan: any read error, parse error, or empty/missing map
+// yields a nil slice. Paths are returned verbatim and unsorted — callers that
+// need determinism must sort/dedupe (both the MCP and skills detectors do).
+//
+// homeDir is resolved via getHomeDir(exec) internally so callers need not thread
+// it through; the result is identical to expanding "~/.claude.json" against the
+// scanning user's home.
+func discoverClaudeProjects(exec executor.Executor) []string {
+	claudeJSONPath := expandTilde("~/.claude.json", getHomeDir(exec))
+
+	content, err := exec.ReadFile(claudeJSONPath)
+	if err != nil || len(content) == 0 {
+		return nil
+	}
+
+	var parsed struct {
+		Projects map[string]json.RawMessage `json:"projects"`
+	}
+	if err := json.Unmarshal(content, &parsed); err != nil || len(parsed.Projects) == 0 {
+		return nil
+	}
+
+	paths := make([]string, 0, len(parsed.Projects))
+	for projectPath := range parsed.Projects {
+		paths = append(paths, projectPath)
+	}
+	return paths
+}

internal/detector/mcp.go

@@ -61,7 +61,7 @@ func (d *MCPDetector) Detect(_ context.Context, userIdentity string, enterprise
 	}
 
 	// Discover project-level .mcp.json files from known project paths
-	for _, projectMCP := range d.discoverProjectMCPConfigs(homeDir) {
+	for _, projectMCP := range d.discoverProjectMCPConfigs() {
 		results = append(results, model.MCPConfig{
 			ConfigSource: projectMCP.SourceName,
 			ConfigPath:   projectMCP.ConfigPath,
@@ -106,7 +106,7 @@ func (d *MCPDetector) DetectEnterprise(_ context.Context) []model.MCPConfigEnter
 	}
 
 	// Discover project-level .mcp.json files from known project paths
-	for _, projectMCP := range d.discoverProjectMCPConfigs(homeDir) {
+	for _, projectMCP := range d.discoverProjectMCPConfigs() {
 		content, err := d.exec.ReadFile(projectMCP.ConfigPath)
 		if err != nil || len(content) == 0 {
 			continue
@@ -128,27 +128,14 @@ func (d *MCPDetector) DetectEnterprise(_ context.Context) []model.MCPConfigEnter
 	return results
 }
 
-// discoverProjectMCPConfigs finds project-level .mcp.json files by reading project paths
-// from ~/.claude.json's "projects" section.
-func (d *MCPDetector) discoverProjectMCPConfigs(homeDir string) []mcpConfigSpec {
-	claudeJSONPath := expandTilde("~/.claude.json", homeDir)
-
-	content, err := d.exec.ReadFile(claudeJSONPath)
-	if err != nil || len(content) == 0 {
-		return nil
-	}
-
-	var parsed struct {
-		Projects map[string]json.RawMessage `json:"projects"`
-	}
-	if err := json.Unmarshal(content, &parsed); err != nil || len(parsed.Projects) == 0 {
-		return nil
-	}
-
+// discoverProjectMCPConfigs finds project-level .mcp.json files in the roots
+// from Claude Code's project registry (~/.claude.json). Project-root discovery
+// is shared with the skills detector via discoverClaudeProjects.
+func (d *MCPDetector) discoverProjectMCPConfigs() []mcpConfigSpec {
 	var specs []mcpConfigSpec
 	seen := make(map[string]bool)
 
-	for projectPath := range parsed.Projects {
+	for _, projectPath := range discoverClaudeProjects(d.exec) {
 		mcpPath := filepath.Join(projectPath, ".mcp.json")
 		if seen[mcpPath] {
 			continue