diff --git a/src/index.ts b/src/index.ts
index d2ea568..f6de307 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,7 +1,7 @@
 import Database from "better-sqlite3";
 import { mkdirSync } from "node:fs";
-import { mkdir, readFile, stat, writeFile } from "node:fs/promises";
-import { dirname, join } from "node:path";
+import { appendFile, mkdir, readFile, stat, writeFile } from "node:fs/promises";
+import { dirname, join, resolve, sep } from "node:path";
 import { createId, nowIso, type ArtifactRecord, type LogChunk, type RuntimeEvent, type RuntimeRecord, type SessionRecord, type TaskRecord, type TaskStore } from "@agent-dispatch/core";
 
 export interface SqliteTaskStoreOptions {
@@ -75,9 +75,7 @@ export class SqliteTaskStore implements TaskStore {
 
   async appendLog(taskId: string, chunk: string): Promise<void> {
     await this.ensureReady();
-    const path = this.logPath(taskId);
-    const existing = await readFile(path, "utf8").catch(() => "");
-    await writeFile(path, `${existing}${chunk}`);
+    await appendFile(this.logPath(taskId), chunk);
   }
 
   async readLogs(taskId: string, cursor = 0, limit = 64_000): Promise<LogChunk> {
@@ -101,7 +99,7 @@ export class SqliteTaskStore implements TaskStore {
 
   async saveArtifactFile(taskId: string, name: string, bytes: Uint8Array, contentType = "application/octet-stream"): Promise<ArtifactRecord> {
     await this.ensureReady();
-    const uri = join(this.stateDir, "artifacts", taskId, name);
+    const uri = this.artifactPath(taskId, name);
     await mkdir(dirname(uri), { recursive: true });
     await writeFile(uri, bytes);
     const sizeBytes = (await stat(uri)).size;
@@ -110,6 +108,10 @@ export class SqliteTaskStore implements TaskStore {
     return artifact;
   }
 
+  close(): void {
+    this.db.close();
+  }
+
   private initialize(): void {
     this.db.exec("create table if not exists schema_migrations (id text primary key, applied_at text not null)");
     for (const migration of migrations) {
@@ -123,6 +125,15 @@ export class SqliteTaskStore implements TaskStore {
     }
   }
 
+  private artifactPath(taskId: string, name: string): string {
+    const root = resolve(this.stateDir, "artifacts", taskId);
+    const uri = resolve(root, name);
+    if (uri !== root && !uri.startsWith(`${root}${sep}`)) {
+      throw new Error("Artifact name must stay within the task artifact directory.");
+    }
+    return uri;
+  }
+
   private logPath(taskId: string): string {
     return join(this.stateDir, "logs", `${taskId}.log`);
   }
diff --git a/test/store.test.ts b/test/store.test.ts
index 1a33a30..dd2016e 100644
--- a/test/store.test.ts
+++ b/test/store.test.ts
@@ -1,4 +1,4 @@
-import { mkdtemp, rm } from "node:fs/promises";
+import { mkdtemp, readFile, rm, stat } from "node:fs/promises";
 import { join } from "node:path";
 import { tmpdir } from "node:os";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
@@ -14,6 +14,7 @@ beforeEach(async () => {
 });
 
 afterEach(async () => {
+  store.close();
   await rm(stateDir, { recursive: true, force: true });
 });
 
@@ -67,12 +68,35 @@ describe("SqliteTaskStore", () => {
     expect(second).toMatchObject({ data: "cde", nextCursor: 5 });
   });
 
+  it("appends log chunks without rewriting existing content", async () => {
+    await Promise.all(Array.from({ length: 25 }, (_, index) => store.appendLog("task_1", `${index}\n`)));
+    const logs = await store.readLogs("task_1", 0, 10_000);
+
+    for (let index = 0; index < 25; index += 1) {
+      expect(logs.data).toContain(`${index}\n`);
+    }
+  });
+
   it("persists artifact metadata and files", async () => {
     const artifact = await store.saveArtifactFile("task_1", "result.txt", Buffer.from("done"), "text/plain");
     const artifacts = await store.listArtifacts("task_1");
 
     expect(artifacts).toHaveLength(1);
     expect(artifacts[0]).toMatchObject({ id: artifact.id, kind: "file", contentType: "text/plain", sizeBytes: 4 });
+    await expect(readFile(artifact.uri, "utf8")).resolves.toBe("done");
+  });
+
+  it("rejects artifact paths outside the task artifact directory", async () => {
+    await expect(store.saveArtifactFile("task_1", "../escape.txt", Buffer.from("nope"))).rejects.toThrow("Artifact name");
+    await expect(store.saveArtifactFile("task_1", "/tmp/escape.txt", Buffer.from("nope"))).rejects.toThrow("Artifact name");
+    await expect(stat(join(stateDir, "artifacts", "escape.txt"))).rejects.toThrow();
+  });
+
+  it("closes the database connection explicitly", async () => {
+    store.close();
+    expect(() => store.appliedMigrations()).toThrow();
+    store = new SqliteTaskStore({ stateDir });
+    expect(store.appliedMigrations()).toEqual(["001_initial"]);
   });
 });