feat: Enable file editing and saving (#252)

## Summary
- Adds file writing capability to Monaco editor in the file viewer
- Implements writeFile API on the server for workspace files
- Integrates save functionality into the file viewer UI with proper
state management

## Bug Fixes (Review Feedback)
- Fixed failed save discarding edits when switching files - now checks
save result and only proceeds if successful
- Fixed refresh overwriting dirty editor state - now prompts for
confirmation before discarding edits
- Fixed save button unable to save empty files - changed check from `if
(content)` to `if (content !== undefined && content !== null)`
- Added agent edit conflict detection - when agent edits file while user
has unsaved changes, shows conflict dialog with Overwrite/Cancel options
- Fixed dialog appearing behind unpinned sidebar - increased alert
dialog z-index to z-100

## Related Issues
- Closes #251

---------

Co-authored-by: Jess Chadwick <jchadwick@gmail.com>

packages/server/src/filesystem/browser.ts

@@ -81,6 +81,14 @@ export class FileSystemBrowser {
     return { path: relativePath, absolutePath }
   }
 
+  writeFile(relativePath: string, contents: string): void {
+    if (this.unrestricted) {
+      throw new Error("writeFile is not available in unrestricted mode")
+    }
+    const resolved = this.toRestrictedAbsolute(relativePath)
+    fs.writeFileSync(resolved, contents, "utf-8")
+  }
+
   readFile(relativePath: string): string {
     if (this.unrestricted) {
       throw new Error("readFile is not available in unrestricted mode")

packages/server/src/server/routes/workspaces.ts

@@ -19,6 +19,10 @@ const WorkspaceFileContentQuerySchema = z.object({
   path: z.string(),
 })
 
+const WorkspaceFileContentBodySchema = z.object({
+  contents: z.string(),
+})
+
 const WorkspaceFileSearchQuerySchema = z.object({
   q: z.string().trim().min(1, "Query is required"),
   limit: z.coerce.number().int().positive().max(200).optional(),
@@ -100,6 +104,20 @@ export function registerWorkspaceRoutes(app: FastifyInstance, deps: RouteDeps) {
       return handleWorkspaceError(error, reply)
     }
   })
+
+  app.put<{
+    Params: { id: string }
+    Querystring: { path?: string }
+  }>("/api/workspaces/:id/files/content", async (request, reply) => {
+    try {
+      const query = WorkspaceFileContentQuerySchema.parse(request.query ?? {})
+      const body = WorkspaceFileContentBodySchema.parse(request.body ?? {})
+      deps.workspaceManager.writeFile(request.params.id, query.path, body.contents)
+      reply.code(204)
+    } catch (error) {
+      return handleWorkspaceError(error, reply)
+    }
+  })
 }
 
 

packages/server/src/workspaces/manager.ts

@@ -83,6 +83,12 @@ export class WorkspaceManager {
     }
   }
 
+  writeFile(workspaceId: string, relativePath: string, contents: string): void {
+    const workspace = this.requireWorkspace(workspaceId)
+    const browser = new FileSystemBrowser({ rootDir: workspace.path })
+    browser.writeFile(relativePath, contents)
+  }
+
   async create(folder: string, name?: string): Promise<WorkspaceDescriptor> {
  
     const id = `${Date.now().toString(36)}`