coder(pending): new-file-from-RightRail create endpoint + modal

POST /api/sessions/:sessionId/pending/create queues a pending_changes create via queueCreate (WriteGuardError -> 422 with the guard message). RightRail gains a 'New file from pasted text' modal (path + content) wired through api.coder.createPendingFile; sessionId is threaded down from App.tsx. The staged change shows in the CoderPane DiffPanel for explicit apply.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/coder/src/routes/pending.ts

@@ -1,4 +1,5 @@
 import type { FastifyInstance } from 'fastify';
+import { z } from 'zod';
 import type { Sql } from '../db.js';
 import {
   listPending,
@@ -6,7 +7,14 @@ import {
   applyAll,
   rejectOne,
   rewindOne,
+  queueCreate,
 } from '../services/pending_changes.js';
+import { WriteGuardError } from '../services/write_guard.js';
+
+const CreateBody = z.object({
+  file_path: z.string().min(1),
+  content: z.string(),
+});
 
 /**
  * Resolve project root from a session's project path.
@@ -51,6 +59,49 @@ export function registerPendingRoutes(app: FastifyInstance, sql: Sql): void {
     },
   );
 
+  // POST /api/sessions/:sessionId/pending/create — queue a new-file create
+  // (manual create from the RightRail file browser; no inference involved).
+  // queueCreate runs resolveWritePath internally, so a path that escapes the
+  // project root or hits a secret file throws WriteGuardError → 422 with the
+  // guard message. Mirrors the { error } 404 shape used by the other routes
+  // and the 422 status used by apply/rewind on failure.
+  app.post<{ Params: { sessionId: string } }>(
+    '/api/sessions/:sessionId/pending/create',
+    async (req, reply) => {
+      const sessionId = req.params.sessionId;
+
+      const parsed = CreateBody.safeParse(req.body);
+      if (!parsed.success) {
+        reply.code(400);
+        return { error: 'invalid body', details: parsed.error.flatten() };
+      }
+
+      const projectRoot = await resolveProjectRoot(sql, sessionId);
+      if (!projectRoot) {
+        reply.code(404);
+        return { error: 'session or project not found' };
+      }
+
+      try {
+        const change = await queueCreate(
+          sql,
+          sessionId,
+          null,
+          parsed.data.file_path,
+          parsed.data.content,
+          projectRoot,
+        );
+        return change;
+      } catch (err) {
+        if (err instanceof WriteGuardError) {
+          reply.code(422);
+          return { error: err.message };
+        }
+        throw err;
+      }
+    },
+  );
+
   // POST /api/sessions/:sessionId/pending/apply — apply all pending changes
   app.post<{ Params: { sessionId: string } }>(
     '/api/sessions/:sessionId/pending/apply',