feat: Plugin API Completeness — file mutations, prompt editor, and attachment APIs

- WorkspaceFiles: writeFile, deleteFile, moveFile with path safety
  - writeFile: text/binary, auto-create dirs, overwrite option
  - deleteFile: idempotent, uses lstat (removes symlinks not targets)
  - moveFile: unix mv semantics, overwrite defaults to false
  - All mutations auto-refreshFiles() in File Explorer
  - Symlink escape prevention via realpath(dirname) check

- PluginPromptEditor: insertText, getText, getSelection, onPaste, onKeyDown, focus
  - Uses CM6 EditorView.domEventHandlers() via Compartment (not raw DOM)
  - Handlers registered before mount are preserved and applied on mount
  - First-to-consume-wins ordering for multi-plugin scenarios
  - insertText replaces selection (not inserts after)

- PluginAttachments: insertFileReference, getAttachedFiles, removeFileReference
  - insertFileReference validates file exists before inserting @path
  - Does not auto-focus editor (unlike prompt.insertText)
  - @file regex requires file extension to avoid matching emails

- Server endpoints: PUT /file, DELETE /file, POST /file/move
  - All work for local and federated machines

- Tests: 31 unit tests, 9 integration tests, 5 client tests
- Docs: 3 new sections in plugins.md

src/server/workspaceExplorerRoutes.ts

@@ -1,12 +1,19 @@
 import type { FastifyInstance } from "fastify";
 import type { ProjectService } from "./projects/projectService.js";
 import type { WorkspaceService } from "./workspaces/workspaceService.js";
+import type { WriteWorkspaceFileOptions } from "../shared/apiTypes.js";
 import { resolveWorkspaceContext } from "./workspaces/workspaceContext.js";
 import { listWorkspaceTree } from "./workspaces/fileTreeService.js";
-import { readWorkspaceFile } from "./workspaces/fileContentService.js";
+import { deleteWorkspaceFile, moveWorkspaceFile, readWorkspaceFile, writeWorkspaceFile } from "./workspaces/fileContentService.js";
 import { readWorkspaceImagePreview } from "./workspaces/imagePreviewService.js";
 
 export function registerWorkspaceExplorerRoutes(app: FastifyInstance, projects: ProjectService, workspaces: WorkspaceService, prefix = "/api"): void {
+  // Register content type parsers for workspace file writes.
+  // Fastify's default parser only handles application/json.
+  // Guard against re-registration since this function may be called multiple times.
+  try { app.addContentTypeParser("text/plain", { parseAs: "string" }, (_req, body, done) => { done(null, Buffer.from(body)); }); } catch { /* already registered */ }
+  try { app.addContentTypeParser("application/octet-stream", { parseAs: "buffer" }, (_req, body, done) => { done(null, body); }); } catch { /* already registered */ }
+  try { app.addContentTypeParser(/^([a-z]+\/[a-z0-9.+-]+)$/, { parseAs: "buffer" }, (_req, body, done) => { done(null, body); }); } catch { /* already registered */ }
   app.get<{ Params: { projectId: string; workspaceId: string }; Querystring: { path?: string } }>(`${prefix}/projects/:projectId/workspaces/:workspaceId/tree`, async (request, reply) => {
     try {
       const context = await resolveWorkspaceContext(projects, workspaces, request.params.projectId, request.params.workspaceId);
@@ -25,6 +32,40 @@ export function registerWorkspaceExplorerRoutes(app: FastifyInstance, projects:
     }
   });
 
+  app.put<{ Params: { projectId: string; workspaceId: string }; Body: Buffer; Querystring: { path?: string; createDirs?: string; overwrite?: string } }>(`${prefix}/projects/:projectId/workspaces/:workspaceId/file`, async (request, reply) => {
+    try {
+      const context = await resolveWorkspaceContext(projects, workspaces, request.params.projectId, request.params.workspaceId);
+      const options: WriteWorkspaceFileOptions = {
+        createDirs: request.query.createDirs !== "false",
+        overwrite: request.query.overwrite !== "false",
+      };
+      return await writeWorkspaceFile(context.root, request.query.path, request.body, options);
+    } catch (error) {
+      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+    }
+  });
+
+  app.delete<{ Params: { projectId: string; workspaceId: string }; Querystring: { path?: string } }>(`${prefix}/projects/:projectId/workspaces/:workspaceId/file`, async (request, reply) => {
+    try {
+      const context = await resolveWorkspaceContext(projects, workspaces, request.params.projectId, request.params.workspaceId);
+      return await deleteWorkspaceFile(context.root, request.query.path);
+    } catch (error) {
+      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+    }
+  });
+
+  app.post<{ Params: { projectId: string; workspaceId: string }; Querystring: { fromPath?: string; toPath?: string; createDirs?: string; overwrite?: string } }>(`${prefix}/projects/:projectId/workspaces/:workspaceId/file/move`, async (request, reply) => {
+    try {
+      const context = await resolveWorkspaceContext(projects, workspaces, request.params.projectId, request.params.workspaceId);
+      return await moveWorkspaceFile(context.root, request.query.fromPath, request.query.toPath, {
+        createDirs: request.query.createDirs !== "false",
+        overwrite: request.query.overwrite === "true",
+      });
+    } catch (error) {
+      return reply.code(400).send({ error: error instanceof Error ? error.message : String(error) });
+    }
+  });
+
   app.get<{ Params: { projectId: string; workspaceId: string }; Querystring: { path?: string } }>(`${prefix}/projects/:projectId/workspaces/:workspaceId/file/preview`, async (request, reply) => {
     try {
       const context = await resolveWorkspaceContext(projects, workspaces, request.params.projectId, request.params.workspaceId);