feat(skills): add provider skill management (#909)

* feat(skills): add provider skill management

Users need one settings surface to discover and install skills without manually navigating provider-specific directories.

Add provider-backed global skill installation for Claude, Codex, Gemini, and Cursor, while keeping OpenCode read-only because it reuses other providers' skill locations.

Add a responsive Skills settings tab with scoped discovery, search, refresh controls, markdown and folder uploads, upload feedback, and overflow-safe layouts.

Validate bundled skill files and paths before writing them, preserve scripts and assets, and cover provider discovery and installation behavior with tests.

* fix(skills): preserve uploaded skill folders

Folder drops discarded supporting scripts and assets.

Keep relative paths and upload every file from the selected skill folder.

Use the selected folder name for installation and cover it in provider tests.

* fix(skills): restrict standalone skill uploads

Only show Markdown files when selecting standalone skills.

Normalize browser file paths so SKILL.md is not mistaken for a folder named dot.

* fix(skills): validate installs before writing

Preserve bundled files and normalize fallback names across skill installation paths.

Validate complete batches before writing and reject existing targets to avoid partial installs.

Keep project metadata and make folder selection tolerant of casing and cancelled dialogs.

* fix(skills): overwrite existing installations

Replace an existing skill directory instead of rejecting a duplicate installation.

Remove stale supporting files so the installed directory exactly matches the new upload.

server/modules/providers/provider.routes.ts

@@ -12,6 +12,8 @@ import type {
   McpScope,
   McpTransport,
   ProviderChangeActiveModelInput,
+  ProviderSkillCreateFile,
+  ProviderSkillCreateInput,
   UpsertProviderMcpServerInput,
 } from '@/shared/types.js';
 import { AppError, asyncHandler, createApiSuccessResponse } from '@/shared/utils.js';
@@ -179,6 +181,104 @@ const parseMcpUpsertPayload = (payload: unknown): UpsertProviderMcpServerInput =
   };
 };
 
+const parseProviderSkillCreatePayload = (payload: unknown): ProviderSkillCreateInput => {
+  if (!payload || typeof payload !== 'object') {
+    throw new AppError('Request body must be an object.', {
+      code: 'INVALID_REQUEST_BODY',
+      statusCode: 400,
+    });
+  }
+
+  const body = payload as Record<string, unknown>;
+  const rawEntries = Array.isArray(body.entries)
+    ? body.entries
+    : typeof body.content === 'string'
+      ? [{
+          content: body.content,
+          directoryName: body.directoryName,
+          fileName: body.fileName,
+          files: body.files,
+        }]
+      : null;
+
+  if (!rawEntries || rawEntries.length === 0) {
+    throw new AppError('At least one skill entry is required.', {
+      code: 'PROVIDER_SKILLS_REQUIRED',
+      statusCode: 400,
+    });
+  }
+
+  const entries = rawEntries.map((entry, index) => {
+    if (!entry || typeof entry !== 'object') {
+      throw new AppError(`Skill entry ${index + 1} must be an object.`, {
+        code: 'INVALID_REQUEST_BODY',
+        statusCode: 400,
+      });
+    }
+
+    const record = entry as Record<string, unknown>;
+    const content = typeof record.content === 'string' ? record.content : '';
+    const directoryName = readOptionalQueryString(record.directoryName);
+    const fileName = readOptionalQueryString(record.fileName);
+    const rawFiles = record.files;
+
+    if (!content.trim()) {
+      throw new AppError(`Skill entry ${index + 1} must include markdown content.`, {
+        code: 'PROVIDER_SKILL_CONTENT_REQUIRED',
+        statusCode: 400,
+      });
+    }
+
+    if (rawFiles !== undefined && !Array.isArray(rawFiles)) {
+      throw new AppError(`Skill entry ${index + 1} files must be an array.`, {
+        code: 'INVALID_REQUEST_BODY',
+        statusCode: 400,
+      });
+    }
+
+    const files: ProviderSkillCreateFile[] | undefined = rawFiles?.map((file, fileIndex) => {
+      if (!file || typeof file !== 'object') {
+        throw new AppError(`Skill entry ${index + 1} file ${fileIndex + 1} must be an object.`, {
+          code: 'INVALID_REQUEST_BODY',
+          statusCode: 400,
+        });
+      }
+
+      const fileRecord = file as Record<string, unknown>;
+      const relativePath = readOptionalQueryString(fileRecord.relativePath);
+      const fileContent = typeof fileRecord.content === 'string' ? fileRecord.content : null;
+      const encoding = fileRecord.encoding === 'utf8' || fileRecord.encoding === 'base64'
+        ? fileRecord.encoding
+        : null;
+
+      if (!relativePath || fileContent === null || !encoding) {
+        throw new AppError(
+          `Skill entry ${index + 1} file ${fileIndex + 1} requires relativePath, content, and encoding.`,
+          {
+            code: 'INVALID_REQUEST_BODY',
+            statusCode: 400,
+          },
+        );
+      }
+
+      return {
+        relativePath,
+        content: fileContent,
+        encoding,
+      };
+    });
+
+    return {
+      content,
+      directoryName,
+      fileName,
+      files,
+    };
+  });
+
+  return { entries };
+};
+
 const parseProvider = (value: unknown): LLMProvider => {
   const normalized = normalizeProviderParam(value);
   if (
@@ -320,6 +420,16 @@ router.get(
   }),
 );
 
+router.post(
+  '/:provider/skills',
+  asyncHandler(async (req: Request, res: Response) => {
+    const provider = parseProvider(req.params.provider);
+    const input = parseProviderSkillCreatePayload(req.body);
+    const skills = await providerSkillsService.addProviderSkills(provider, input);
+    res.json(createApiSuccessResponse({ provider, skills }));
+  }),
+);
+
 // ----------------- MCP routes -----------------
 router.get(
   '/:provider/mcp/servers',