fix(security): improve JSON output safety and path traversal protection

- [x] Replace unsafe JSON string formatting with proper json.Marshal in export handler
- [x] Remove escapeJSONString helper function in favor of standard JSON marshaling
- [x] Add safeResolvePath function to validate paths and prevent directory traversal
- [x] Apply path traversal validation in captureFileMtimes operations
- [x] Cap result slice capacity in getRecentSearchQueries to prevent DoS via excessive allocation

internal/mcp/server.go

@@ -2620,8 +2620,21 @@ func (s *Server) handleExportObservations(ctx context.Context, args json.RawMess
 			}
 			lines = append(lines, string(line))
 		}
-		output = fmt.Sprintf(`{"format":"jsonl","count":%d,"data":"%s"}`,
-			len(observations), escapeJSONString(strings.Join(lines, "\n")))
+		// Use proper JSON marshaling to avoid injection issues
+		jsonlOutput := struct {
+			Format string `json:"format"`
+			Data   string `json:"data"`
+			Count  int    `json:"count"`
+		}{
+			Format: "jsonl",
+			Count:  len(observations),
+			Data:   strings.Join(lines, "\n"),
+		}
+		outputBytes, err := json.Marshal(jsonlOutput)
+		if err != nil {
+			return "", fmt.Errorf("marshal jsonl output: %w", err)
+		}
+		output = string(outputBytes)
 
 	case "markdown":
 		// Markdown format for human reading
@@ -2685,16 +2698,6 @@ func (s *Server) handleExportObservations(ctx context.Context, args json.RawMess
 	return output, nil
 }
 
-// escapeJSONString escapes a string for use in JSON.
-func escapeJSONString(s string) string {
-	b, _ := json.Marshal(s)
-	// Remove surrounding quotes
-	if len(b) >= 2 {
-		return string(b[1 : len(b)-1])
-	}
-	return s
-}
-
 // handleCheckSystemHealth performs comprehensive system health checks.
 func (s *Server) handleCheckSystemHealth(ctx context.Context) (string, error) {
 	type SubsystemHealth struct {

internal/worker/sdk/processor.go

@@ -782,6 +782,32 @@ func toJSONString(v any) string {
 	return string(b)
 }
 
+// safeResolvePath resolves a path relative to cwd and validates it doesn't escape the cwd directory.
+// Returns the resolved absolute path and true if valid, or empty string and false if path traversal detected.
+func safeResolvePath(path, cwd string) (string, bool) {
+	if filepath.IsAbs(path) {
+		// Absolute paths are allowed as-is
+		return filepath.Clean(path), true
+	}
+	if cwd == "" {
+		return filepath.Clean(path), true
+	}
+
+	// Clean the cwd first
+	cleanCwd := filepath.Clean(cwd)
+
+	// Join and clean the path
+	absPath := filepath.Clean(filepath.Join(cleanCwd, path))
+
+	// Verify the resolved path is still within cwd (prevents path traversal via ..)
+	// Use HasPrefix on cleaned paths to detect escapes
+	if !strings.HasPrefix(absPath, cleanCwd+string(filepath.Separator)) && absPath != cleanCwd {
+		return "", false
+	}
+
+	return absPath, true
+}
+
 // captureFileMtimes captures current modification times for tracked files.
 // Returns a map of absolute file paths to their mtime in epoch milliseconds.
 // For large file lists (>10 files), uses parallel stat calls for better performance.
@@ -809,9 +835,10 @@ func captureFileMtimesSequential(paths map[string]struct{}, cwd string) map[stri
 	mtimes := make(map[string]int64, len(paths))
 
 	for path := range paths {
-		absPath := path
-		if !filepath.IsAbs(path) && cwd != "" {
-			absPath = filepath.Join(cwd, path)
+		absPath, ok := safeResolvePath(path, cwd)
+		if !ok {
+			// Skip paths that attempt directory traversal
+			continue
 		}
 
 		info, err := os.Stat(absPath)
@@ -841,9 +868,10 @@ func captureFileMtimesParallel(paths map[string]struct{}, cwd string) map[string
 			sem <- struct{}{}        // Acquire
 			defer func() { <-sem }() // Release
 
-			absPath := p
-			if !filepath.IsAbs(p) && cwd != "" {
-				absPath = filepath.Join(cwd, p)
+			absPath, ok := safeResolvePath(p, cwd)
+			if !ok {
+				// Skip paths that attempt directory traversal
+				return
 			}
 
 			info, err := os.Stat(absPath)

internal/worker/service.go

@@ -1443,7 +1443,12 @@ func (s *Service) getRecentSearchQueries(project string, limit int) []RecentSear
 	}
 
 	// Filter by project (iterate from newest to oldest)
-	result := make([]RecentSearchQuery, 0, limit)
+	// Cap capacity to maxRecentQueries to prevent excessive allocation from user input
+	capacity := limit
+	if capacity > maxRecentQueries {
+		capacity = maxRecentQueries
+	}
+	result := make([]RecentSearchQuery, 0, capacity)
 	for i := 0; i < s.recentQueriesLen; i++ {
 		idx := (s.recentQueriesHead + i) % maxRecentQueries
 		q := s.recentQueriesBuf[idx]