diff --git a/fixtures/ads-account.json b/fixtures/ads-account.json
new file mode 100644
index 0000000..3e46352
--- /dev/null
+++ b/fixtures/ads-account.json
@@ -0,0 +1,37 @@
+{
+  "accounts": [
+    {
+      "accountId": "demo-account",
+      "baseDays": 7,
+      "campaigns": [
+        {
+          "campaignId": "cmp-scale",
+          "name": "Scale Winners",
+          "spend": 4200,
+          "impressions": 140000,
+          "clicks": 3500,
+          "conversions": 210,
+          "revenue": 12600
+        },
+        {
+          "campaignId": "cmp-low-ctr",
+          "name": "Creative Fatigue",
+          "spend": 2800,
+          "impressions": 160000,
+          "clicks": 1600,
+          "conversions": 35,
+          "revenue": 4200
+        },
+        {
+          "campaignId": "cmp-high-cpa",
+          "name": "Broad Prospecting",
+          "spend": 3000,
+          "impressions": 100000,
+          "clicks": 3000,
+          "conversions": 50,
+          "revenue": 5000
+        }
+      ]
+    }
+  ]
+}
diff --git a/packages/harness/src/errors/harness-error.ts b/packages/harness/src/errors/harness-error.ts
new file mode 100644
index 0000000..0c438f9
--- /dev/null
+++ b/packages/harness/src/errors/harness-error.ts
@@ -0,0 +1,10 @@
+export class HarnessError extends Error {
+  public constructor(
+    public readonly code: string,
+    message: string,
+    public readonly details: Record<string, unknown> = {},
+  ) {
+    super(message);
+    this.name = "HarnessError";
+  }
+}
diff --git a/packages/harness/src/index.ts b/packages/harness/src/index.ts
index 93bfccf..0723f64 100644
--- a/packages/harness/src/index.ts
+++ b/packages/harness/src/index.ts
@@ -1,2 +1,7 @@
 export * from "./events/event-store.js";
 export * from "./events/in-memory-event-store.js";
+export * from "./errors/harness-error.js";
+export * from "./tools/mock-ads-metrics.js";
+export * from "./tools/save-report-draft.js";
+export * from "./tools/tool-policy.js";
+export * from "./workspace/safe-workspace.js";
diff --git a/packages/harness/src/tools/mock-ads-metrics.ts b/packages/harness/src/tools/mock-ads-metrics.ts
new file mode 100644
index 0000000..eb2583a
--- /dev/null
+++ b/packages/harness/src/tools/mock-ads-metrics.ts
@@ -0,0 +1,142 @@
+import { readFile } from "node:fs/promises";
+import { defineTool } from "@earendil-works/pi-coding-agent";
+import { type Static, Type } from "typebox";
+import { Check } from "typebox/value";
+import { HarnessError } from "../errors/harness-error.js";
+
+export const mockAdsMetricsInputSchema = Type.Object({
+  accountId: Type.String({ minLength: 1, maxLength: 100 }),
+  days: Type.Integer({ minimum: 1, maximum: 30 }),
+}, { additionalProperties: false });
+
+const campaignSchema = Type.Object({
+  campaignId: Type.String(),
+  name: Type.String(),
+  spend: Type.Number({ minimum: 0 }),
+  impressions: Type.Integer({ minimum: 0 }),
+  clicks: Type.Integer({ minimum: 0 }),
+  conversions: Type.Integer({ minimum: 0 }),
+  revenue: Type.Number({ minimum: 0 }),
+}, { additionalProperties: false });
+
+const fixtureSchema = Type.Object({
+  accounts: Type.Array(Type.Object({
+    accountId: Type.String(),
+    baseDays: Type.Integer({ minimum: 1 }),
+    campaigns: Type.Array(campaignSchema),
+  }, { additionalProperties: false })),
+}, { additionalProperties: false });
+
+export type MockAdsMetricsInput = Static<typeof mockAdsMetricsInputSchema>;
+type CampaignFixture = Static<typeof campaignSchema>;
+
+export type CampaignMetrics = CampaignFixture & {
+  ctr: number;
+  cpa: number;
+  roas: number;
+};
+
+export type AdsMetrics = {
+  accountId: string;
+  days: number;
+  spend: number;
+  impressions: number;
+  clicks: number;
+  ctr: number;
+  conversions: number;
+  cpa: number;
+  revenue: number;
+  roas: number;
+  campaigns: CampaignMetrics[];
+};
+
+export async function executeMockAdsMetrics(
+  fixturePath: string,
+  input: MockAdsMetricsInput,
+): Promise<AdsMetrics> {
+  if (!Check(mockAdsMetricsInputSchema, input)) {
+    throw new HarnessError("INVALID_TOOL_ARGUMENTS", "Invalid mock_ads_metrics arguments");
+  }
+
+  const parsed: unknown = JSON.parse(await readFile(fixturePath, "utf8"));
+  if (!Check(fixtureSchema, parsed)) {
+    throw new HarnessError("INVALID_ADS_FIXTURE", "Ads fixture has an invalid structure");
+  }
+  const fixture = parsed;
+  const account = fixture.accounts.find((candidate) => candidate.accountId === input.accountId);
+  if (account === undefined) {
+    throw new HarnessError("ADS_ACCOUNT_NOT_FOUND", "Mock advertising account not found", {
+      accountId: input.accountId,
+    });
+  }
+
+  const scale = input.days / account.baseDays;
+  const campaigns = account.campaigns.map((campaign) => scaleCampaign(campaign, scale));
+  const spend = sum(campaigns, "spend");
+  const impressions = sum(campaigns, "impressions");
+  const clicks = sum(campaigns, "clicks");
+  const conversions = sum(campaigns, "conversions");
+  const revenue = sum(campaigns, "revenue");
+
+  return {
+    accountId: input.accountId,
+    days: input.days,
+    spend: round2(spend),
+    impressions: Math.round(impressions),
+    clicks: Math.round(clicks),
+    ctr: ratio(clicks * 100, impressions),
+    conversions: Math.round(conversions),
+    cpa: ratio(spend, conversions),
+    revenue: round2(revenue),
+    roas: ratio(revenue, spend),
+    campaigns,
+  };
+}
+
+export function createMockAdsMetricsTool(fixturePath: string) {
+  return defineTool({
+    name: "mock_ads_metrics",
+    label: "Mock Ads Metrics",
+    description: "Read deterministic training metrics for a mock advertising account. This does not access a real ad platform.",
+    promptSnippet: "Read mock advertising account metrics",
+    parameters: mockAdsMetricsInputSchema,
+    async execute(_toolCallId, params) {
+      const details = await executeMockAdsMetrics(fixturePath, params);
+      return {
+        content: [{ type: "text", text: JSON.stringify(details) }],
+        details,
+      };
+    },
+  });
+}
+
+function scaleCampaign(campaign: CampaignFixture, scale: number): CampaignMetrics {
+  const spend = round2(campaign.spend * scale);
+  const impressions = Math.round(campaign.impressions * scale);
+  const clicks = Math.round(campaign.clicks * scale);
+  const conversions = Math.round(campaign.conversions * scale);
+  const revenue = round2(campaign.revenue * scale);
+  return {
+    ...campaign,
+    spend,
+    impressions,
+    clicks,
+    conversions,
+    revenue,
+    ctr: ratio(clicks * 100, impressions),
+    cpa: ratio(spend, conversions),
+    roas: ratio(revenue, spend),
+  };
+}
+
+function sum(items: CampaignMetrics[], key: "spend" | "impressions" | "clicks" | "conversions" | "revenue"): number {
+  return items.reduce((total, item) => total + item[key], 0);
+}
+
+function ratio(numerator: number, denominator: number): number {
+  return denominator === 0 ? 0 : round2(numerator / denominator);
+}
+
+function round2(value: number): number {
+  return Math.round((value + Number.EPSILON) * 100) / 100;
+}
diff --git a/packages/harness/src/tools/save-report-draft.ts b/packages/harness/src/tools/save-report-draft.ts
new file mode 100644
index 0000000..d5dff3c
--- /dev/null
+++ b/packages/harness/src/tools/save-report-draft.ts
@@ -0,0 +1,26 @@
+import { defineTool } from "@earendil-works/pi-coding-agent";
+import { Type } from "typebox";
+import type { SafeWorkspace } from "../workspace/safe-workspace.js";
+
+export const saveReportDraftInputSchema = Type.Object({
+  title: Type.Optional(Type.String({ minLength: 1, maxLength: 200 })),
+  body: Type.String({ minLength: 1, maxLength: 200_000 }),
+}, { additionalProperties: false });
+
+export function createSaveReportDraftTool(workspace: SafeWorkspace) {
+  return defineTool({
+    name: "save_report_draft",
+    label: "Save Report Draft",
+    description: "Save a report draft to the fixed report.md file in the current training Session. Requires approval.",
+    promptSnippet: "Save a report draft after analysis",
+    parameters: saveReportDraftInputSchema,
+    executionMode: "sequential",
+    async execute(_toolCallId, params) {
+      const details = await workspace.writeReportDraft(params);
+      return {
+        content: [{ type: "text", text: `Saved report draft to ${details.relativePath}` }],
+        details,
+      };
+    },
+  });
+}
diff --git a/packages/harness/src/tools/tool-policy.ts b/packages/harness/src/tools/tool-policy.ts
new file mode 100644
index 0000000..093acb8
--- /dev/null
+++ b/packages/harness/src/tools/tool-policy.ts
@@ -0,0 +1,9 @@
+export type ToolPolicyDecision = "allow" | "ask" | "deny";
+
+const allowedTools = new Set(["read", "grep", "find", "ls", "mock_ads_metrics"]);
+
+export function decideToolPolicy(toolName: string): ToolPolicyDecision {
+  if (allowedTools.has(toolName)) return "allow";
+  if (toolName === "save_report_draft") return "ask";
+  return "deny";
+}
diff --git a/packages/harness/src/workspace/safe-workspace.ts b/packages/harness/src/workspace/safe-workspace.ts
new file mode 100644
index 0000000..fb0b246
--- /dev/null
+++ b/packages/harness/src/workspace/safe-workspace.ts
@@ -0,0 +1,142 @@
+import { randomUUID } from "node:crypto";
+import { lstat, open, realpath, rename, rm } from "node:fs/promises";
+import { isAbsolute, join, parse, relative, resolve, sep } from "node:path";
+import { HarnessError } from "../errors/harness-error.js";
+
+const protectedSegments = new Set([
+  ".env",
+  ".git",
+  ".ssh",
+  "id_rsa",
+  "id_ed25519",
+]);
+
+export type ReportDraftInput = {
+  title?: string;
+  body: string;
+};
+
+export class SafeWorkspace {
+  private constructor(public readonly root: string) {}
+
+  public static async create(root: string): Promise<SafeWorkspace> {
+    const canonicalRoot = await realpath(resolve(root));
+    if (canonicalRoot === parse(canonicalRoot).root) {
+      throw new HarnessError("UNSAFE_WORKSPACE_ROOT", "Filesystem root cannot be used as a workspace");
+    }
+    const metadata = await lstat(canonicalRoot);
+    if (!metadata.isDirectory() || metadata.isSymbolicLink()) {
+      throw new HarnessError("UNSAFE_WORKSPACE_ROOT", "Workspace root must be a regular directory");
+    }
+    return new SafeWorkspace(canonicalRoot);
+  }
+
+  public async resolveReadable(inputPath: string): Promise<string> {
+    const candidate = isAbsolute(inputPath) ? resolve(inputPath) : resolve(this.root, inputPath);
+    this.#assertContained(candidate);
+    this.#assertUnprotected(candidate);
+    await this.#assertNoSymlinkSegments(candidate);
+    const canonical = await realpath(candidate);
+    this.#assertContained(canonical);
+    const metadata = await lstat(canonical);
+    if (!metadata.isFile()) {
+      throw new HarnessError("NOT_A_REGULAR_FILE", "Only regular files may be read");
+    }
+    return canonical;
+  }
+
+  public async writeReportDraft(input: ReportDraftInput): Promise<{ relativePath: "report.md"; byteSize: number }> {
+    if (input.body.trim().length === 0) {
+      throw new HarnessError("REPORT_BODY_REQUIRED", "Report body cannot be empty");
+    }
+
+    const target = join(this.root, "report.md");
+    const temporary = join(this.root, `.report-${randomUUID()}.tmp`);
+    this.#assertContained(target);
+    await this.#assertNoSymlinkSegments(this.root);
+
+    const title = input.title?.trim();
+    const content = title === undefined || title.length === 0
+      ? `${input.body.trim()}\n`
+      : `# ${title}\n\n${input.body.trim()}\n`;
+    const bytes = Buffer.from(content, "utf8");
+    let handle: Awaited<ReturnType<typeof open>> | undefined;
+
+    try {
+      handle = await open(temporary, "wx", 0o600);
+      await handle.writeFile(bytes);
+      await handle.sync();
+      await handle.close();
+      handle = undefined;
+
+      try {
+        const existing = await lstat(target);
+        if (existing.isSymbolicLink()) {
+          throw new HarnessError("SYMLINK_NOT_ALLOWED", "Report target cannot be a symbolic link");
+        }
+      } catch (error) {
+        if (error instanceof HarnessError) throw error;
+        if (!isMissingFileError(error)) throw error;
+      }
+
+      await rename(temporary, target);
+      return { relativePath: "report.md", byteSize: bytes.byteLength };
+    } finally {
+      await handle?.close().catch(() => undefined);
+      await rm(temporary, { force: true }).catch(() => undefined);
+    }
+  }
+
+  public async remove(): Promise<void> {
+    const metadata = await lstat(this.root).catch((error: unknown) => {
+      if (isMissingFileError(error)) return undefined;
+      throw error;
+    });
+    if (metadata === undefined) return;
+    if (!metadata.isDirectory() || metadata.isSymbolicLink()) {
+      throw new HarnessError("UNSAFE_WORKSPACE_ROOT", "Refusing to remove a non-directory workspace root");
+    }
+    await rm(this.root, { recursive: true, force: false });
+  }
+
+  #assertContained(candidate: string): void {
+    const pathFromRoot = relative(this.root, candidate);
+    if (pathFromRoot === "") return;
+    if (pathFromRoot === ".." || pathFromRoot.startsWith(`..${sep}`) || isAbsolute(pathFromRoot)) {
+      throw new HarnessError("PATH_OUTSIDE_WORKSPACE", "Path is outside the Session workspace");
+    }
+  }
+
+  #assertUnprotected(candidate: string): void {
+    const pathFromRoot = relative(this.root, candidate);
+    const segments = pathFromRoot.split(sep);
+    if (segments.some((segment) => protectedSegments.has(segment.toLowerCase()))) {
+      throw new HarnessError("PROTECTED_PATH", "Protected paths cannot be accessed");
+    }
+  }
+
+  async #assertNoSymlinkSegments(candidate: string): Promise<void> {
+    this.#assertContained(candidate);
+    const pathFromRoot = relative(this.root, candidate);
+    if (pathFromRoot === "") {
+      const rootMetadata = await lstat(this.root);
+      if (rootMetadata.isSymbolicLink()) {
+        throw new HarnessError("SYMLINK_NOT_ALLOWED", "Symbolic links are not allowed");
+      }
+      return;
+    }
+
+    let current = this.root;
+    for (const segment of pathFromRoot.split(sep)) {
+      current = join(current, segment);
+      const metadata = await lstat(current);
+      if (metadata.isSymbolicLink()) {
+        throw new HarnessError("SYMLINK_NOT_ALLOWED", "Symbolic links are not allowed");
+      }
+    }
+  }
+}
+
+function isMissingFileError(error: unknown): boolean {
+  return error instanceof Error && "code" in error && error.code === "ENOENT";
+}
diff --git a/packages/harness/tests/safe-workspace.test.ts b/packages/harness/tests/safe-workspace.test.ts
new file mode 100644
index 0000000..0a423ee
--- /dev/null
+++ b/packages/harness/tests/safe-workspace.test.ts
@@ -0,0 +1,61 @@
+import { mkdtemp, mkdir, readFile, realpath, rm, symlink, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import * as harness from "../src/index.js";
+
+type Workspace = {
+  resolveReadable(path: string): Promise<string>;
+  writeReportDraft(input: { title?: string; body: string }): Promise<{ relativePath: "report.md"; byteSize: number }>;
+  remove(): Promise<void>;
+};
+
+type WorkspaceConstructor = {
+  create(root: string): Promise<Workspace>;
+};
+
+let root = "";
+let outside = "";
+let workspace: Workspace;
+
+beforeEach(async () => {
+  root = await mkdtemp(join(tmpdir(), "agent-studio-workspace-"));
+  outside = await mkdtemp(join(tmpdir(), "agent-studio-outside-"));
+  await writeFile(join(root, "inside.txt"), "inside", "utf8");
+  await writeFile(join(outside, "secret.txt"), "secret", "utf8");
+  const Constructor = Reflect.get(harness, "SafeWorkspace") as WorkspaceConstructor | undefined;
+  expect(Constructor, "SafeWorkspace must be exported").toBeDefined();
+  workspace = await Constructor!.create(root);
+});
+
+afterEach(async () => {
+  await rm(root, { recursive: true, force: true });
+  await rm(outside, { recursive: true, force: true });
+});
+
+describe("SafeWorkspace", () => {
+  it("resolves an existing regular file inside the Session root", async () => {
+    await expect(workspace.resolveReadable("inside.txt")).resolves.toBe(await realpath(join(root, "inside.txt")));
+  });
+
+  it.each(["../outside/secret.txt", "/tmp/outside.txt"])("rejects path escape %s", async (path) => {
+    await expect(workspace.resolveReadable(path)).rejects.toMatchObject({ code: "PATH_OUTSIDE_WORKSPACE" });
+  });
+
+  it("rejects symlinks before following them", async () => {
+    await symlink(outside, join(root, "link"));
+    await expect(workspace.resolveReadable("link/secret.txt")).rejects.toMatchObject({ code: "SYMLINK_NOT_ALLOWED" });
+  });
+
+  it("rejects protected path segments", async () => {
+    await mkdir(join(root, ".git"));
+    await writeFile(join(root, ".git", "config"), "credential", "utf8");
+    await expect(workspace.resolveReadable(".git/config")).rejects.toMatchObject({ code: "PROTECTED_PATH" });
+  });
+
+  it("writes only the fixed report.md path", async () => {
+    const result = await workspace.writeReportDraft({ title: "广告账户报告", body: "账户总结" });
+    expect(result.relativePath).toBe("report.md");
+    await expect(readFile(join(root, "report.md"), "utf8")).resolves.toBe("# 广告账户报告\n\n账户总结\n");
+  });
+});
diff --git a/packages/harness/tests/tools.test.ts b/packages/harness/tests/tools.test.ts
new file mode 100644
index 0000000..9f558a4
--- /dev/null
+++ b/packages/harness/tests/tools.test.ts
@@ -0,0 +1,55 @@
+import { resolve } from "node:path";
+import { Check } from "typebox/value";
+import { describe, expect, it } from "vitest";
+import {
+  decideToolPolicy,
+  executeMockAdsMetrics,
+  mockAdsMetricsInputSchema,
+} from "../src/index.js";
+
+const fixturePath = resolve(import.meta.dirname, "../../../fixtures/ads-account.json");
+
+describe("mock_ads_metrics", () => {
+  it("uses an integer 1-30 day TypeBox schema", () => {
+    expect(Check(mockAdsMetricsInputSchema, { accountId: "demo-account", days: 7 })).toBe(true);
+    expect(Check(mockAdsMetricsInputSchema, { accountId: "demo-account", days: 0 })).toBe(false);
+    expect(Check(mockAdsMetricsInputSchema, { accountId: "demo-account", days: 7.5 })).toBe(false);
+    expect(Check(mockAdsMetricsInputSchema, { accountId: "demo-account", days: 31 })).toBe(false);
+  });
+
+  it("returns hand-checked zero-safe metrics and campaign details", async () => {
+    const result = await executeMockAdsMetrics(fixturePath, { accountId: "demo-account", days: 7 });
+    expect(result).toMatchObject({
+      spend: 10000,
+      impressions: 400000,
+      clicks: 8100,
+      ctr: 2.03,
+      conversions: 295,
+      cpa: 33.9,
+      revenue: 21800,
+      roas: 2.18,
+      days: 7,
+    });
+    expect(result.campaigns).toContainEqual(expect.objectContaining({
+      campaignId: "cmp-low-ctr",
+      ctr: 1,
+      cpa: 80,
+    }));
+  });
+
+  it("rejects unknown accounts with a stable error code", async () => {
+    await expect(executeMockAdsMetrics(fixturePath, { accountId: "missing", days: 7 }))
+      .rejects.toMatchObject({ code: "ADS_ACCOUNT_NOT_FOUND" });
+  });
+});
+
+describe("tool policy", () => {
+  it("allows only the explicit safe set, asks for report save, and denies unknown tools", () => {
+    expect(["read", "grep", "find", "ls", "mock_ads_metrics"].map(decideToolPolicy)).toEqual([
+      "allow", "allow", "allow", "allow", "allow",
+    ]);
+    expect(decideToolPolicy("save_report_draft")).toBe("ask");
+    expect(decideToolPolicy("bash")).toBe("deny");
+    expect(decideToolPolicy("unknown_tool")).toBe("deny");
+  });
+});