feat: add plugin worker protocol, bootstrap and plugin_storage table

Worker-side ctx proxy plus the message envelope it talks over, and the
per-plugin key/value table behind ctx.storage with migrations for all
three dialects. Rows cascade with the plugin so uninstalling leaves
nothing behind.

src/backend/tests/database/repositories/plugin-storage-repository.test.ts

@@ -0,0 +1,96 @@
+import { afterEach, describe, expect, it } from "vitest";
+import { TestSqliteDatabase } from "./test-support.js";
+import { PluginStorageRepository } from "../../../database/repositories/plugin-storage-repository.js";
+
+describe("PluginStorageRepository", () => {
+  let adapter: TestSqliteDatabase | null = null;
+
+  afterEach(async () => {
+    if (adapter) {
+      await adapter.close();
+      adapter = null;
+    }
+  });
+
+  async function createRepository(
+    onWrite?: () => void | Promise<void>,
+  ): Promise<PluginStorageRepository> {
+    adapter = new TestSqliteDatabase();
+    const context = await adapter.connect();
+    await adapter.exec(`
+      INSERT INTO plugins (id, name, version, manifest_json)
+      VALUES ('plugin-a', 'Plugin A', '1.0.0', '{}');
+      INSERT INTO plugins (id, name, version, manifest_json)
+      VALUES ('plugin-b', 'Plugin B', '1.0.0', '{}');
+    `);
+
+    return new PluginStorageRepository(context, onWrite);
+  }
+
+  it("round-trips a value", async () => {
+    const repo = await createRepository();
+
+    expect(await repo.get("plugin-a", "missing")).toBeNull();
+
+    await repo.set("plugin-a", "token", '{"v":1}');
+    expect(await repo.get("plugin-a", "token")).toBe('{"v":1}');
+  });
+
+  it("overwrites rather than duplicating an existing key", async () => {
+    const repo = await createRepository();
+
+    await repo.set("plugin-a", "counter", "1");
+    await repo.set("plugin-a", "counter", "2");
+
+    expect(await repo.get("plugin-a", "counter")).toBe("2");
+    expect(await repo.listKeys("plugin-a")).toEqual(["counter"]);
+  });
+
+  it("keeps each plugin's keys separate", async () => {
+    const repo = await createRepository();
+
+    await repo.set("plugin-a", "shared-key", "from-a");
+    await repo.set("plugin-b", "shared-key", "from-b");
+
+    expect(await repo.get("plugin-a", "shared-key")).toBe("from-a");
+    expect(await repo.get("plugin-b", "shared-key")).toBe("from-b");
+  });
+
+  it("deletes a key and reports whether a row changed", async () => {
+    let writes = 0;
+    const repo = await createRepository(() => {
+      writes += 1;
+    });
+
+    await repo.set("plugin-a", "k", "v");
+    expect(writes).toBe(1);
+
+    expect(await repo.delete("plugin-a", "nope")).toBe(false);
+    expect(writes).toBe(1);
+
+    expect(await repo.delete("plugin-a", "k")).toBe(true);
+    expect(writes).toBe(2);
+    expect(await repo.get("plugin-a", "k")).toBeNull();
+  });
+
+  it("deletes everything belonging to one plugin", async () => {
+    const repo = await createRepository();
+
+    await repo.set("plugin-a", "one", "1");
+    await repo.set("plugin-a", "two", "2");
+    await repo.set("plugin-b", "keep", "3");
+
+    expect(await repo.deleteByPlugin("plugin-a")).toBe(2);
+    expect(await repo.listKeys("plugin-a")).toEqual([]);
+    expect(await repo.listKeys("plugin-b")).toEqual(["keep"]);
+  });
+
+  it("drops rows when the owning plugin is removed", async () => {
+    const repo = await createRepository();
+    await repo.set("plugin-a", "k", "v");
+
+    await adapter!.exec(`DELETE FROM plugins WHERE id = 'plugin-a';`);
+
+    expect(await repo.listKeys("plugin-a")).toEqual([]);
+  });
+});