fix: file upload UI issues in Swagger documentation

core/src/main/java/com/opencontext/controller/DocsSourceController.java

@@ -46,9 +46,12 @@ public interface DocsSourceController {
             **Authentication Required:** X-API-KEY header must be provided.
 
             **Supported File Types:**
-            - PDF documents (application/pdf)
-            - Markdown files (text/markdown)
-            - Plain text files (text/plain)
+            - PDF documents (application/pdf, .pdf files)
+            - Markdown files (text/markdown, .md or .markdown files)
+            - Plain text files (text/plain, .txt files)
+
+            **Note:** The system automatically detects file types based on both the Content-Type header 
+            and file extension. the system will properly recognize Markdown files regardless of how the browser sends the Content-Type.
 
             **File Size Limit:** 100MB
 
@@ -60,9 +63,9 @@ public interface DocsSourceController {
             required = true,
             content = @Content(
                 mediaType = MediaType.MULTIPART_FORM_DATA_VALUE,
-                examples = @ExampleObject(
-                    name = "Upload a Markdown file",
-                    value = "(Use the file picker UI to attach a .md file)"
+                encoding = @io.swagger.v3.oas.annotations.media.Encoding(
+                    name = "file",
+                    contentType = "application/octet-stream"
                 )
             )
         )
@@ -151,8 +154,11 @@ public interface DocsSourceController {
         @ApiResponse(responseCode = "415", description = "Unsupported Media Type - invalid file format")
     })
     ResponseEntity<CommonResponse<SourceUploadResponse>> uploadFile(
-            @Parameter(description = "File to upload (PDF, Markdown, or plain text)", required = true)
-            @RequestParam("file") @NotNull MultipartFile file
+            @Parameter(
+                description = "File to upload (PDF, Markdown, or plain text)", 
+                required = true
+            )
+            @RequestParam("file") MultipartFile file
     );
 
     /**

core/src/main/java/com/opencontext/service/FileStorageService.java

@@ -53,8 +53,8 @@ public class FileStorageService {
     @Value("${app.elasticsearch.index:document-chunks}")
     private String indexName;
 
-    // Supported file types for document processing
-    private static final List<String> SUPPORTED_CONTENT_TYPES = List.of(
+    // Supported file types for document processing (canonical)
+    private static final List<String> ALLOWED_CANONICAL_CONTENT_TYPES = List.of(
             "application/pdf",
             "text/markdown",
             "text/plain"
@@ -69,7 +69,7 @@ public class FileStorageService {
     public SourceDocument uploadFileWithMetadata(MultipartFile file) {
         String filename = file.getOriginalFilename();
         long fileSize = file.getSize();
-        String contentType = file.getContentType();
+        String contentType = resolveContentType(file);
 
         log.info("📤 [UPLOAD] Starting file upload with metadata: filename={}, size={} bytes, contentType={}", 
                 filename, fileSize, contentType);
@@ -98,15 +98,15 @@ public SourceDocument uploadFileWithMetadata(MultipartFile file) {
         try {
             // Upload file to MinIO
             log.debug("☁️ [UPLOAD] Step 4/5: Uploading file to MinIO: {}", filename);
-            String objectKey = uploadFile(file);
+            String objectKey = uploadFile(file, contentType);
             log.info("✅ [UPLOAD] File uploaded to MinIO successfully: {} -> {}", filename, objectKey);
 
             // Create SourceDocument entity
             log.debug("💾 [UPLOAD] Step 5/5: Creating database record: {}", filename);
             SourceDocument sourceDocument = SourceDocument.builder()
                     .originalFilename(file.getOriginalFilename())
                     .fileStoragePath(objectKey)
-                    .fileType(determineFileType(file.getContentType()))
+                    .fileType(determineFileType(contentType))
                     .fileSize(file.getSize())
                     .fileChecksum(fileChecksum)
                     .ingestionStatus(IngestionStatus.PENDING)
@@ -139,7 +139,7 @@ public SourceDocument uploadFileWithMetadata(MultipartFile file) {
      * @param file the multipart file to upload
      * @return the object key where the file was stored
      */
-    public String uploadFile(MultipartFile file) {
+    public String uploadFile(MultipartFile file, String resolvedContentType) {
         try {
             // Ensure bucket exists
             ensureBucketExists();
@@ -152,7 +152,7 @@ public String uploadFile(MultipartFile file) {
                     .bucket(minioConfig.getBucketName())
                     .object(objectKey)
                     .stream(file.getInputStream(), file.getSize(), -1)
-                    .contentType(file.getContentType())
+                    .contentType(resolvedContentType)
                     .build();
 
             minioClient.putObject(putObjectArgs);
@@ -562,18 +562,23 @@ private void validateFile(MultipartFile file) {
                     "File size exceeds maximum limit of 100MB");
         }
 
-        String contentType = file.getContentType();
-        if (contentType == null || !SUPPORTED_CONTENT_TYPES.contains(contentType)) {
-            throw new BusinessException(ErrorCode.UNSUPPORTED_MEDIA_TYPE, 
-                    "Unsupported file type. Supported types: PDF, Markdown, and plain text files.");
-        }
-
         String filename = file.getOriginalFilename();
         if (filename == null || filename.trim().isEmpty()) {
             throw new BusinessException(ErrorCode.INVALID_REQUEST, "Filename cannot be empty");
         }
 
-        log.debug("✅ [UPLOAD] File validation passed: filename={}", filename);
+        // Resolve canonical content type from both content-type header and filename extension
+        String resolvedContentType = resolveContentType(file);
+
+        // Check if the resolved content type is supported
+        if (!ALLOWED_CANONICAL_CONTENT_TYPES.contains(resolvedContentType)) {
+            log.debug("❌ [UPLOAD] Unsupported content type: filename={}, original={}, resolved={}", 
+                    filename, file.getContentType(), resolvedContentType);
+            throw new BusinessException(ErrorCode.UNSUPPORTED_MEDIA_TYPE,
+                    "Unsupported file type. Supported types: PDF, Markdown, and plain text files.");
+        }
+
+        log.debug("✅ [UPLOAD] File validation passed: filename={}, resolved_type={}", filename, resolvedContentType);
     }
 
     /**
@@ -612,6 +617,46 @@ private String determineFileType(String contentType) {
         };
     }
 
+    /**
+     * Resolves the effective content type for the uploaded file.
+     * If the inbound content type is null or generic (e.g., application/octet-stream),
+     * infer from the filename extension and normalize to a canonical, allowed type.
+     */
+    private String resolveContentType(MultipartFile file) {
+        String inbound = file.getContentType();
+        // If clearly an allowed canonical type, return as-is
+        if (ALLOWED_CANONICAL_CONTENT_TYPES.contains(inbound)) {
+            return inbound;
+        }
+
+        // Try to infer from file extension for generic or alternate types
+        String filename = file.getOriginalFilename();
+        String ext = (filename == null) ? null : getFileExtension(filename).toLowerCase();
+
+        if (ext != null) {
+            return switch (ext) {
+                case "pdf" -> "application/pdf";
+                case "md", "markdown" -> "text/markdown";
+                case "txt" -> "text/plain";
+                default -> (inbound != null ? inbound : "application/octet-stream");
+            };
+        }
+
+        // Fallback to inbound or generic
+        return inbound != null ? inbound : "application/octet-stream";
+    }
+
+    /**
+     * Returns the extension without the leading dot. Example: "README.md" -> "md".
+     */
+    private String getFileExtension(String filename) {
+        int lastDot = filename.lastIndexOf('.');
+        if (lastDot == -1 || lastDot == filename.length() - 1) {
+            return "";
+        }
+        return filename.substring(lastDot + 1);
+    }
+
     /**
      * Converts SourceDocument entity to DTO.
      */

core/src/main/java/com/opencontext/service/SearchService.java

@@ -63,7 +63,7 @@ public List<SearchResultItem> search(String query, int topK) {
             Map<String, Object> searchResponse = executeElasticsearchQuery(query, queryEmbedding, topK);
 
             // 3단계: 검색 결과를 DTO로 변환
-            List<SearchResultItem> results = parseSearchResults(searchResponse);
+            List<SearchResultItem> results = parseSearchResults(searchResponse); 
 
             long duration = System.currentTimeMillis() - startTime;
             log.info("하이브리드 검색 완료: query='{}', 결과수={}, 소요시간={}ms",