feat: turn session recording into a plugin (B13)

src/backend/plugins/ctx.ts

@@ -250,6 +250,20 @@ export function createPluginContext(
     { action: "kv_list" },
   );
 
+  const filesDataDir = guarded(
+    manifest,
+    "files:own",
+    async () => {
+      const fs = await import("node:fs/promises");
+      const path = await import("node:path");
+      const base = process.env.DATA_DIR ?? "./db/data";
+      const dir = path.join(base, "plugins", pluginId);
+      await fs.mkdir(dir, { recursive: true });
+      return dir;
+    },
+    { action: "files_data_dir" },
+  );
+
   const dbDefine = guarded(
     manifest,
     "db:own",
@@ -422,6 +436,10 @@ export function createPluginContext(
       list: () => kvList(),
     },
 
+    files: {
+      dataDir: () => filesDataDir(),
+    },
+
     registry: {
       provide: (key, value) => {
         registry.provide(key, value);

src/backend/plugins/events.ts

@@ -47,6 +47,13 @@ export const TOPICS = {
    * the row is not gone, only unrecoverable, and should go with it.
    */
   userDataWiped: "user.data_wiped",
+  /**
+   * A user account was deleted. For a plugin whose rows should outlive the
+   * account (evidence, audit trail) rather than cascade with a refUser()
+   * column: it keeps a plain userId column and anonymizes its own rows here,
+   * the way core's own session recordings did before this event existed.
+   */
+  userDeleted: "user.deleted",
 } as const;
 
 export type EventListener = (payload: unknown) => void;