fix: MCP file ops use the connected OperationContext engine, not the global DB singleton (#3869)

Wave-assembled from PR #3869 by @dpaluy.

Co-Authored-By: David Paluy <dpaluy@users.noreply.github.com>

src/core/operations.ts

@@ -3246,8 +3246,9 @@ const file_list: Operation = {
   },
   scope: 'admin',
   localOnly: true,
-  handler: async (_ctx, p) => {
-    const sql = db.getConnection();
+  handler: async (ctx, p) => {
+    const { sqlQueryForEngine } = await import('./sql-query.ts');
+    const sql = sqlQueryForEngine(ctx.engine);
     const slug = p.slug as string | undefined;
     const rows = slug
       ? await sql`SELECT id, page_slug, filename, storage_path, mime_type, size_bytes, content_hash, created_at FROM files WHERE page_slug = ${slug} ORDER BY filename LIMIT ${FILE_LIST_LIMIT}`
@@ -3304,7 +3305,8 @@ const file_upload: Operation = {
     };
     const mimeType = MIME_TYPES[extname(filePath).toLowerCase()] || null;
 
-    const sql = db.getConnection();
+    const { sqlQueryForEngine } = await import('./sql-query.ts');
+    const sql = sqlQueryForEngine(ctx.engine);
     const existing = await sql`SELECT id FROM files WHERE content_hash = ${hash} AND storage_path = ${storagePath}`;
     if (existing.length > 0) {
       return { status: 'already_exists', storage_path: storagePath };
@@ -3354,8 +3356,9 @@ const file_url: Operation = {
   },
   scope: 'admin',
   localOnly: true,
-  handler: async (_ctx, p) => {
-    const sql = db.getConnection();
+  handler: async (ctx, p) => {
+    const { sqlQueryForEngine } = await import('./sql-query.ts');
+    const sql = sqlQueryForEngine(ctx.engine);
     const rows = await sql`SELECT storage_path, mime_type, size_bytes FROM files WHERE storage_path = ${p.storage_path as string}`;
     if (rows.length === 0) {
       throw new OperationError('storage_error', `File not found: ${p.storage_path}`);

test/file-upload-engine-context.test.ts

@@ -0,0 +1,69 @@
+/**
+ * Regression: MCP file_upload must use the connected OperationContext engine.
+ *
+ * A long-running `gbrain serve` owns the PGLite connection. The handler must not
+ * reach for the module-global db singleton, which is intentionally uninitialized
+ * in the MCP dispatch path and throws "connect() has not been called".
+ */
+
+import { afterAll, beforeAll, describe, expect, test } from 'bun:test';
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { PGLiteEngine } from '../src/core/pglite-engine.ts';
+import { dispatchToolCall } from '../src/mcp/dispatch.ts';
+
+let engine: PGLiteEngine;
+let fixtureDir: string;
+
+beforeAll(async () => {
+  engine = new PGLiteEngine();
+  await engine.connect({ engine: 'pglite' } as never);
+  await engine.initSchema();
+
+  // Remote MCP uploads are intentionally confined to the server working tree.
+  fixtureDir = mkdtempSync(join(process.cwd(), '.file-upload-engine-context-'));
+});
+
+afterAll(async () => {
+  if (engine) await engine.disconnect();
+  if (fixtureDir) rmSync(fixtureDir, { recursive: true, force: true });
+});
+
+describe('file_upload engine ownership', () => {
+  test('uses the MCP context engine instead of the module-global DB singleton', async () => {
+    const fixture = join(fixtureDir, 'capture.json');
+    writeFileSync(fixture, '{"source":"camofox"}\n');
+
+    const result = await dispatchToolCall(engine, 'file_upload', {
+      path: fixture,
+      page_slug: 'concepts/hermes-kanban',
+    }, { remote: true, sourceId: 'default' });
+
+    expect(result.isError).toBeFalsy();
+    expect(JSON.parse(result.content[0].text)).toEqual({
+      status: 'uploaded',
+      storage_path: 'concepts/hermes-kanban/capture.json',
+      size_bytes: 21,
+    });
+
+    const listed = await dispatchToolCall(engine, 'file_list', {
+      slug: 'concepts/hermes-kanban',
+    }, { remote: true, sourceId: 'default' });
+    expect(listed.isError).toBeFalsy();
+    expect(JSON.parse(listed.content[0].text)).toEqual([
+      expect.objectContaining({
+        page_slug: 'concepts/hermes-kanban',
+        storage_path: 'concepts/hermes-kanban/capture.json',
+      }),
+    ]);
+
+    const url = await dispatchToolCall(engine, 'file_url', {
+      storage_path: 'concepts/hermes-kanban/capture.json',
+    }, { remote: true, sourceId: 'default' });
+    expect(url.isError).toBeFalsy();
+    expect(JSON.parse(url.content[0].text)).toEqual({
+      storage_path: 'concepts/hermes-kanban/capture.json',
+      url: 'gbrain:files/concepts/hermes-kanban/capture.json',
+    });
+  });
+});