diff --git a/canvas/src/components/tabs/ChatTab.tsx b/canvas/src/components/tabs/ChatTab.tsx
index 156f87e8..7b0ee0d2 100644
--- a/canvas/src/components/tabs/ChatTab.tsx
+++ b/canvas/src/components/tabs/ChatTab.tsx
@@ -67,7 +67,7 @@ interface A2AResponse {
 // Server-side counterpart in workspace-server/internal/channels/
 // manager.go has the same single-part bug; fix that too if/when a
 // channel-delivered reply (Slack, Lark, etc.) gets truncated.
-function extractReplyText(resp: A2AResponse): string {
+export function extractReplyText(resp: A2AResponse): string {
   const collect = (parts: A2APart[] | undefined): string => {
     if (!parts) return "";
     return parts
diff --git a/canvas/src/components/tabs/ConfigTab.tsx b/canvas/src/components/tabs/ConfigTab.tsx
index 50ae227b..ab6ff6e6 100644
--- a/canvas/src/components/tabs/ConfigTab.tsx
+++ b/canvas/src/components/tabs/ConfigTab.tsx
@@ -143,7 +143,7 @@ interface RuntimeOption {
 // haven't migrated to the explicit `providers:` field yet, AND
 // continues to be a useful fallback for any future runtime whose
 // derive-provider semantics happen to match the slug prefix.
-function deriveProvidersFromModels(models: ModelSpec[]): string[] {
+export function deriveProvidersFromModels(models: ModelSpec[]): string[] {
   const seen = new Set<string>();
   const out: string[] = [];
   for (const m of models) {
diff --git a/canvas/src/components/tabs/FilesTab/__tests__/FilesToolbar.test.tsx b/canvas/src/components/tabs/FilesTab/__tests__/FilesToolbar.test.tsx
new file mode 100644
index 00000000..cb23c95d
--- /dev/null
+++ b/canvas/src/components/tabs/FilesTab/__tests__/FilesToolbar.test.tsx
@@ -0,0 +1,349 @@
+// @vitest-environment jsdom
+/**
+ * Tests for FilesToolbar — the top-of-panel bar for the Files tab.
+ * Covers: directory select, file count, New/Upload/Clear (configs-only),
+ * Export, Refresh, and aria-labels.
+ */
+import React from "react";
+import { render, screen, fireEvent, cleanup } from "@testing-library/react";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { FilesToolbar } from "../FilesToolbar";
+
+afterEach(cleanup);
+
+describe("FilesToolbar", () => {
+  describe("renders base toolbar", () => {
+    it("renders the directory select with aria-label", () => {
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={3}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      expect(
+        screen.getByRole("combobox", { name: /file root directory/i })
+      ).toBeTruthy();
+    });
+
+    it("renders the file count", () => {
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={7}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      expect(screen.getByText("7 files")).toBeTruthy();
+    });
+
+    it("renders Export button", () => {
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={0}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      expect(
+        screen.getByRole("button", { name: /download all files/i })
+      ).toBeTruthy();
+    });
+
+    it("renders Refresh button", () => {
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={0}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      expect(screen.getByRole("button", { name: /refresh file list/i })).toBeTruthy();
+    });
+
+    it("renders 0 files when count is 0", () => {
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={0}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      expect(screen.getByText("0 files")).toBeTruthy();
+    });
+  });
+
+  describe("configs-only buttons", () => {
+    it("shows New and Upload buttons when root is /configs", () => {
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={3}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      expect(
+        screen.getByRole("button", { name: /create new file/i })
+      ).toBeTruthy();
+      expect(
+        screen.getByRole("button", { name: /upload folder/i })
+      ).toBeTruthy();
+      expect(screen.getByRole("button", { name: /delete all files/i })).toBeTruthy();
+    });
+
+    it("hides New and Upload when root is /workspace", () => {
+      render(
+        <FilesToolbar
+          root="/workspace"
+          setRoot={vi.fn()}
+          fileCount={5}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      expect(
+        screen.queryByRole("button", { name: /create new file/i })
+      ).toBeNull();
+      expect(
+        screen.queryByRole("button", { name: /upload folder/i })
+      ).toBeNull();
+      expect(
+        screen.queryByRole("button", { name: /delete all files/i })
+      ).toBeNull();
+      // Export and Refresh are still present
+      expect(
+        screen.getByRole("button", { name: /download all files/i })
+      ).toBeTruthy();
+    });
+
+    it("hides New and Upload when root is /home", () => {
+      render(
+        <FilesToolbar
+          root="/home"
+          setRoot={vi.fn()}
+          fileCount={2}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      expect(
+        screen.queryByRole("button", { name: /create new file/i })
+      ).toBeNull();
+      expect(
+        screen.queryByRole("button", { name: /upload folder/i })
+      ).toBeNull();
+    });
+
+    it("hides New and Upload when root is /plugins", () => {
+      render(
+        <FilesToolbar
+          root="/plugins"
+          setRoot={vi.fn()}
+          fileCount={1}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      expect(
+        screen.queryByRole("button", { name: /create new file/i })
+      ).toBeNull();
+      expect(
+        screen.queryByRole("button", { name: /upload folder/i })
+      ).toBeNull();
+    });
+  });
+
+  describe("callbacks", () => {
+    it("calls setRoot when directory is changed", () => {
+      const setRoot = vi.fn();
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={setRoot}
+          fileCount={3}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      fireEvent.change(screen.getByRole("combobox"), {
+        target: { value: "/workspace" },
+      });
+      expect(setRoot).toHaveBeenCalledWith("/workspace");
+    });
+
+    it("calls onNewFile when New button is clicked", () => {
+      const onNewFile = vi.fn();
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={3}
+          onNewFile={onNewFile}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      fireEvent.click(screen.getByRole("button", { name: /create new file/i }));
+      expect(onNewFile).toHaveBeenCalledTimes(1);
+    });
+
+    it("calls onDownloadAll when Export button is clicked", () => {
+      const onDownloadAll = vi.fn();
+      render(
+        <FilesToolbar
+          root="/workspace"
+          setRoot={vi.fn()}
+          fileCount={5}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={onDownloadAll}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      fireEvent.click(screen.getByRole("button", { name: /download all files/i }));
+      expect(onDownloadAll).toHaveBeenCalledTimes(1);
+    });
+
+    it("calls onClearAll when Clear button is clicked", () => {
+      const onClearAll = vi.fn();
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={3}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={onClearAll}
+          onRefresh={vi.fn()}
+        />
+      );
+      fireEvent.click(screen.getByRole("button", { name: /delete all files/i }));
+      expect(onClearAll).toHaveBeenCalledTimes(1);
+    });
+
+    it("calls onRefresh when Refresh button is clicked", () => {
+      const onRefresh = vi.fn();
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={3}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={onRefresh}
+        />
+      );
+      fireEvent.click(screen.getByRole("button", { name: /refresh file list/i }));
+      expect(onRefresh).toHaveBeenCalledTimes(1);
+    });
+
+    it("calls onUpload when the hidden file input changes", () => {
+      const onUpload = vi.fn();
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={3}
+          onNewFile={vi.fn()}
+          onUpload={onUpload}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      // Find the hidden file input
+      const fileInput = document.querySelector(
+        'input[type="file"]'
+      ) as HTMLInputElement;
+      expect(fileInput).toBeTruthy();
+      expect(fileInput?.getAttribute("aria-label")).toBe("Upload folder files");
+    });
+  });
+
+  describe("a11y", () => {
+    it("all buttons have aria-label or accessible name", () => {
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={3}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      // All buttons should be findable by role
+      const buttons = screen.getAllByRole("button");
+      for (const btn of buttons) {
+        expect(btn.getAttribute("aria-label") ?? btn.textContent).toBeTruthy();
+      }
+    });
+
+    it("directory select has aria-label", () => {
+      render(
+        <FilesToolbar
+          root="/configs"
+          setRoot={vi.fn()}
+          fileCount={3}
+          onNewFile={vi.fn()}
+          onUpload={vi.fn()}
+          onDownloadAll={vi.fn()}
+          onClearAll={vi.fn()}
+          onRefresh={vi.fn()}
+        />
+      );
+      const select = screen.getByRole("combobox");
+      expect(select.getAttribute("aria-label")).toBe("File root directory");
+    });
+  });
+});
diff --git a/canvas/src/components/tabs/FilesTab/__tests__/NotAvailablePanel.test.tsx b/canvas/src/components/tabs/FilesTab/__tests__/NotAvailablePanel.test.tsx
new file mode 100644
index 00000000..c670bb50
--- /dev/null
+++ b/canvas/src/components/tabs/FilesTab/__tests__/NotAvailablePanel.test.tsx
@@ -0,0 +1,101 @@
+// @vitest-environment jsdom
+/**
+ * Tests for NotAvailablePanel — the full-tab placeholder shown when a
+ * workspace's runtime doesn't own a platform-managed filesystem (today:
+ * runtime === "external"). Covers rendering, a11y, and runtime prop
+ * display.
+ */
+import React from "react";
+import { render, screen, cleanup } from "@testing-library/react";
+import { afterEach, describe, expect, it } from "vitest";
+import { NotAvailablePanel } from "../NotAvailablePanel";
+
+afterEach(cleanup);
+
+describe("NotAvailablePanel", () => {
+  describe("renders", () => {
+    it("renders the heading", () => {
+      render(<NotAvailablePanel runtime="external" />);
+      expect(screen.getByText("Files not available")).toBeTruthy();
+    });
+
+    it("renders the description text", () => {
+      render(<NotAvailablePanel runtime="external" />);
+      expect(
+        screen.getByText(/whose filesystem isn't owned by the platform/i)
+      ).toBeTruthy();
+    });
+
+    it("displays the runtime name in the description", () => {
+      render(<NotAvailablePanel runtime="aws-lambda" />);
+      // The runtime name appears inside the paragraph
+      const para = screen.getByText(/whose filesystem isn't owned/i);
+      expect(para.textContent).toContain("aws-lambda");
+    });
+
+    it("renders the SVG folder icon with aria-hidden", () => {
+      render(<NotAvailablePanel runtime="external" />);
+      const svg = document.querySelector("svg");
+      expect(svg).toBeTruthy();
+      expect(svg?.getAttribute("aria-hidden")).toBe("true");
+    });
+
+    it("uses the provided runtime prop verbatim", () => {
+      render(<NotAvailablePanel runtime="cloud-run" />);
+      const monoRuntime = document.querySelector(".font-mono");
+      expect(monoRuntime?.textContent).toBe("cloud-run");
+    });
+
+    it("renders the 'Use the Chat tab' guidance text", () => {
+      render(<NotAvailablePanel runtime="external" />);
+      expect(screen.getByText(/Use the Chat tab/i)).toBeTruthy();
+    });
+
+    it("is contained in a full-height flex column", () => {
+      render(<NotAvailablePanel runtime="external" />);
+      const container = screen.getByText("Files not available").closest("div");
+      expect(container?.className).toContain("flex");
+      expect(container?.className).toContain("flex-col");
+      expect(container?.className).toContain("items-center");
+      expect(container?.className).toContain("justify-center");
+      expect(container?.className).toContain("h-full");
+    });
+  });
+
+  describe("a11y", () => {
+    it("heading is an h3", () => {
+      render(<NotAvailablePanel runtime="external" />);
+      expect(screen.getByRole("heading", { level: 3 })).toBeTruthy();
+    });
+
+    it("SVG icon has aria-hidden so screen readers skip it", () => {
+      render(<NotAvailablePanel runtime="external" />);
+      const svg = document.querySelector("svg");
+      expect(svg?.getAttribute("aria-hidden")).toBe("true");
+    });
+
+    it("description paragraph is present with descriptive text", () => {
+      render(<NotAvailablePanel runtime="external" />);
+      const paras = document.querySelectorAll("p");
+      expect(paras.length).toBeGreaterThan(0);
+      const text = Array.from(paras)
+        .map((p) => p.textContent)
+        .join(" ");
+      expect(text.toLowerCase()).toContain("runtime");
+    });
+  });
+
+  describe("props", () => {
+    it("renders with a short runtime name", () => {
+      render(<NotAvailablePanel runtime="ext" />);
+      const monoRuntime = document.querySelector(".font-mono");
+      expect(monoRuntime?.textContent).toBe("ext");
+    });
+
+    it("renders with a complex runtime name", () => {
+      render(<NotAvailablePanel runtime="gcp-cloud-functions-v2" />);
+      const monoRuntime = document.querySelector(".font-mono");
+      expect(monoRuntime?.textContent).toBe("gcp-cloud-functions-v2");
+    });
+  });
+});
diff --git a/canvas/src/components/tabs/__tests__/deriveProvidersFromModels.test.ts b/canvas/src/components/tabs/__tests__/deriveProvidersFromModels.test.ts
new file mode 100644
index 00000000..4c1bd3ec
--- /dev/null
+++ b/canvas/src/components/tabs/__tests__/deriveProvidersFromModels.test.ts
@@ -0,0 +1,100 @@
+// @vitest-environment jsdom
+/**
+ * Tests for deriveProvidersFromModels — pure vendor-slug extractor from
+ * a model list used in ConfigTab.tsx.
+ *
+ * Takes ModelSpec[] and returns a deduplicated array of vendor strings.
+ * Vendor is derived by splitting on ":" (anthropic:claude-opus-4-7) or
+ * "/" (nousresearch/hermes-4-70b). Order is preserved from input.
+ */
+import { describe, expect, it } from "vitest";
+import { deriveProvidersFromModels } from "../ConfigTab";
+
+// Local type mirror (not exported from ConfigTab)
+interface ModelSpec {
+  id?: string;
+}
+
+describe("deriveProvidersFromModels", () => {
+  it("returns empty array for empty input", () => {
+    expect(deriveProvidersFromModels([])).toEqual([]);
+  });
+
+  it("extracts vendor from colon-separated id", () => {
+    const models: ModelSpec[] = [{ id: "anthropic:claude-sonnet-4-5" }];
+    expect(deriveProvidersFromModels(models)).toEqual(["anthropic"]);
+  });
+
+  it("extracts vendor from slash-separated id", () => {
+    const models: ModelSpec[] = [{ id: "nousresearch/hermes-4-70b" }];
+    expect(deriveProvidersFromModels(models)).toEqual(["nousresearch"]);
+  });
+
+  it("deduplicates repeated vendors", () => {
+    const models: ModelSpec[] = [
+      { id: "anthropic:claude-opus-4-7" },
+      { id: "anthropic:claude-sonnet-4-5" },
+      { id: "openai:gpt-4o" },
+    ];
+    expect(deriveProvidersFromModels(models)).toEqual(["anthropic", "openai"]);
+  });
+
+  it("skips models with no id", () => {
+    const models: ModelSpec[] = [
+      { id: "anthropic:claude-sonnet-4-5" },
+      {},
+      { id: undefined },
+      { id: "" },
+    ];
+    expect(deriveProvidersFromModels(models)).toEqual(["anthropic"]);
+  });
+
+  it("skips ids with no vendor separator", () => {
+    const models: ModelSpec[] = [
+      { id: "claude-sonnet-4-5" },
+      { id: "unknown/runtime" },
+    ];
+    expect(deriveProvidersFromModels(models)).toEqual(["unknown"]);
+  });
+
+  it("skips empty string id", () => {
+    const models: ModelSpec[] = [{ id: "" }];
+    expect(deriveProvidersFromModels(models)).toEqual([]);
+  });
+
+  it("preserves first-occurrence order", () => {
+    const models: ModelSpec[] = [
+      { id: "openai:gpt-4o" },
+      { id: "anthropic:claude-opus-4-7" },
+      { id: "anthropic:claude-sonnet-4-5" },
+      { id: "google:gemini-2-5-flash" },
+    ];
+    expect(deriveProvidersFromModels(models)).toEqual([
+      "openai",
+      "anthropic",
+      "google",
+    ]);
+  });
+
+  it("handles mix of valid and invalid ids", () => {
+    const models: ModelSpec[] = [
+      {},
+      { id: "openai:gpt-4o-mini" },
+      { id: "" },
+      { id: "no-separator" },
+      { id: "anthropic:claude-opus-4-7" },
+    ];
+    expect(deriveProvidersFromModels(models)).toEqual(["openai", "anthropic"]);
+  });
+
+  it("is pure — same input always returns same output", () => {
+    const models: ModelSpec[] = [
+      { id: "anthropic:claude-sonnet-4-5" },
+      { id: "openai:gpt-4o" },
+      { id: "google:gemini-2-5-flash" },
+    ];
+    for (let i = 0; i < 3; i++) {
+      expect(deriveProvidersFromModels(models)).toEqual(["anthropic", "openai", "google"]);
+    }
+  });
+});
diff --git a/canvas/src/components/tabs/__tests__/extractReplyText.test.ts b/canvas/src/components/tabs/__tests__/extractReplyText.test.ts
new file mode 100644
index 00000000..cb69d9bc
--- /dev/null
+++ b/canvas/src/components/tabs/__tests__/extractReplyText.test.ts
@@ -0,0 +1,135 @@
+// @vitest-environment jsdom
+/**
+ * Tests for extractReplyText — the A2A result-path text extractor used
+ * in ChatTab.tsx.
+ *
+ * extractReplyText pulls the agent's text reply out of an A2A response.
+ * Concatenates ALL text parts (joined with "\n") rather than returning
+ * just the first. Claude Code and other runtimes commonly emit multi-
+ * part text replies for long content (markdown tables, code blocks),
+ * and the prior "first part wins" implementation silently truncated
+ * the rest. Mirrors extractTextsFromParts in message-parser.ts.
+ *
+ * Note: extractReplyText is scoped to the result.parts + result.artifacts
+ * path — unlike extractResponseText which also handles body.task / body.text /
+ * body.response_preview. It is the correct extractor for live A2A
+ * responses where the text lives on result.
+ */
+import { describe, expect, it } from "vitest";
+import { extractReplyText } from "../ChatTab";
+
+describe("extractReplyText — A2A result path", () => {
+  it("returns empty string for undefined response", () => {
+    expect(extractReplyText(undefined as never)).toBe("");
+  });
+
+  it("returns empty string for null result", () => {
+    expect(extractReplyText({ result: null as never })).toBe("");
+  });
+
+  it("returns empty string when result has no parts or artifacts", () => {
+    expect(extractReplyText({ result: {} })).toBe("");
+  });
+
+  it("returns empty string when parts array is empty", () => {
+    expect(extractReplyText({ result: { parts: [] } })).toBe("");
+  });
+
+  it("extracts text from a single text part", () => {
+    expect(
+      extractReplyText({ result: { parts: [{ kind: "text", text: "Hello world" }] } })
+    ).toBe("Hello world");
+  });
+
+  it("concatenates multiple text parts with newlines (no truncation)", () => {
+    expect(
+      extractReplyText({
+        result: {
+          parts: [
+            { kind: "text", text: "# Header" },
+            { kind: "text", text: "| Col |" },
+            { kind: "text", text: "| --- |" },
+            { kind: "text", text: "| Row |" },
+          ],
+        },
+      })
+    ).toBe("# Header\n| Col |\n| --- |\n| Row |");
+  });
+
+  it("skips non-text parts", () => {
+    expect(
+      extractReplyText({
+        result: {
+          parts: [
+            { kind: "image", text: "should be ignored" },
+            { kind: "text", text: "visible" },
+            { kind: "file", text: "also ignored" },
+          ],
+        },
+      })
+    ).toBe("visible");
+  });
+
+  it("skips text parts with empty string", () => {
+    expect(extractReplyText({ result: { parts: [{ kind: "text", text: "" }] } })).toBe("");
+  });
+
+  it("skips parts with missing text field", () => {
+    expect(extractReplyText({ result: { parts: [{ kind: "text" }] } })).toBe("");
+  });
+
+  it("walks artifacts and collects their text parts", () => {
+    expect(
+      extractReplyText({
+        result: {
+          artifacts: [
+            { parts: [{ kind: "text", text: "Artifact one" }] },
+            { parts: [{ kind: "text", text: "Artifact two" }] },
+          ],
+        },
+      })
+    ).toBe("Artifact one\nArtifact two");
+  });
+
+  it("combines result.parts AND result.artifacts text (both sources)", () => {
+    expect(
+      extractReplyText({
+        result: {
+          parts: [{ kind: "text", text: "Summary" }],
+          artifacts: [
+            { parts: [{ kind: "text", text: "Detail block one" }] },
+            { parts: [{ kind: "text", text: "Detail block two" }] },
+          ],
+        },
+      })
+    ).toBe("Summary\nDetail block one\nDetail block two");
+  });
+
+  it("artifacts are processed even when parts are empty", () => {
+    expect(
+      extractReplyText({
+        result: {
+          parts: [],
+          artifacts: [{ parts: [{ kind: "text", text: "Only artifact" }] }],
+        },
+      })
+    ).toBe("Only artifact");
+  });
+
+  it("artifacts with empty parts array contribute nothing", () => {
+    expect(extractReplyText({ result: { artifacts: [{ parts: [] }] } })).toBe("");
+  });
+
+  it("multiple artifacts each contribute their text", () => {
+    expect(
+      extractReplyText({
+        result: {
+          artifacts: [
+            { parts: [{ kind: "text", text: "A" }, { kind: "text", text: "B" }] },
+            { parts: [{ kind: "text", text: "C" }] },
+          ],
+        },
+      })
+    ).toBe("A\nB\nC");
+  });
+});