fix(canvas/chat): IME-safe Enter + markdown link target/scheme handling

Two production-reported regressions in the same chat surface, fixed
in one focused PR.

Issue 1 — IME composition + Enter sends half-typed message
----------------------------------------------------------

ChatTab's textarea onKeyDown was:

  if (e.key === "Enter" && !e.shiftKey) {
    e.preventDefault();
    sendMessage();
  }

For agents typing CJK / Japanese / Korean via the system IME, Enter
commits the candidate selection — not a newline, not a send. With
the old check, every IME-commit Enter accidentally sent the
half-typed message ("你好" + half-typed-pinyin + Enter to commit
the next candidate → message goes out before the user finishes).

Fix: guard on `event.nativeEvent.isComposing` AND `e.keyCode !== 229`.
The latter covers older Safari / WebKit-based mobile browsers that
delay setting isComposing on the composition-end Enter.

Issue 2 — markdown links land at about:blank
---------------------------------------------

ReactMarkdown's default `<a>` rendering passes the agent-supplied
href directly to the DOM with no target / scheme handling:

  - http(s) → navigates the canvas tab away (canvas state lost)
  - workspace://path / file:///workspace/... / /workspace/... →
    browser hits unhandled-protocol click → about:blank, no
    download (the reported bug)

Fix: ReactMarkdown `components.a` override:

  - In-container paths (workspace:, file:///{workspace,configs,home,
    plugins}, bare /{workspace,configs,...}) → preventDefault, route
    through downloadChatFile (same auth path the AttachmentChip
    uses). Filename is derived from the path's last segment.
  - External (http/https/mailto/unknown scheme) → target="_blank"
    rel="noopener noreferrer" so canvas state survives.

Tests
-----

ChatTab.imeAndLinks.test.tsx (4 tests):
  - Enter with isComposing=true → does NOT send, input preserved
  - Enter with keyCode=229 (older-Safari IME) → does NOT send
  - Enter with no IME signal → DOES send (happy path intact)
  - Shift+Enter → does NOT send (newline path intact)

The link-component override is exercised through the full ChatTab
render — the IME tests are jsdom-only and don't load chat history
with markdown messages, so the link test would need a more elaborate
fixture. Manual verification on staging post-deploy is the practical
gate; if the link test grows critical the AttachmentViews-style chip
test can extend.

Verified:
- tsc --noEmit clean
- 4/4 IME tests pass

Reported on production 2026-05-05.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

canvas/src/components/tabs/ChatTab.tsx

@@ -1061,7 +1061,80 @@ function MyChatPanel({ workspaceId, data }: Props) {
                       : "dark:prose-invert dark:[--tw-prose-invert-body:theme(colors.zinc.100)] dark:[--tw-prose-invert-headings:theme(colors.white)] dark:[--tw-prose-invert-bold:theme(colors.white)] dark:[--tw-prose-invert-code:theme(colors.zinc.100)]"
                   }`}
                 >
-                  <ReactMarkdown remarkPlugins={[remarkGfm]}>{msg.content}</ReactMarkdown>
+                  <ReactMarkdown
+                    remarkPlugins={[remarkGfm]}
+                    components={{
+                      // Default ReactMarkdown renders `<a href="...">`
+                      // with no target and no scheme handling, so:
+                      //
+                      //   1. http/https links navigate the canvas tab
+                      //      itself away — user loses canvas state.
+                      //   2. workspace://, file://, and bare /workspace/
+                      //      paths from agent-authored markdown produce
+                      //      an unhandled-protocol click → browser ends
+                      //      up at about:blank with no download (the
+                      //      reported bug from 2026-05-05).
+                      //
+                      // Override: external URLs open in a new tab with
+                      // rel="noopener noreferrer"; in-container paths
+                      // route through downloadChatFile so the browser
+                      // gets a real Blob with proper auth headers.
+                      a: ({ href, children, ...rest }) => {
+                        const url = String(href ?? "");
+                        const containerPath = url.startsWith("workspace:") ||
+                          url.startsWith("file:///workspace") ||
+                          url.startsWith("file:///configs") ||
+                          url.startsWith("file:///home") ||
+                          url.startsWith("file:///plugins") ||
+                          url.startsWith("/workspace") ||
+                          url.startsWith("/configs") ||
+                          url.startsWith("/home") ||
+                          url.startsWith("/plugins");
+                        if (containerPath) {
+                          return (
+                            <a
+                              href={url}
+                              {...rest}
+                              onClick={(e) => {
+                                e.preventDefault();
+                                // Construct a synthetic ChatAttachment
+                                // and route through the same
+                                // authenticated download path the
+                                // download chips use. Filename is the
+                                // last path segment so Save-As prefills
+                                // sensibly.
+                                const name = url.split(/[\\/]/).pop() || "download";
+                                downloadChatFile(workspaceId, {
+                                  uri: url,
+                                  name,
+                                }).catch((err) => {
+                                  setError(
+                                    err instanceof Error
+                                      ? `Download failed: ${err.message}`
+                                      : "Download failed",
+                                  );
+                                });
+                              }}
+                            >
+                              {children}
+                            </a>
+                          );
+                        }
+                        // External (http(s) / mailto / unknown scheme):
+                        // open in new tab so canvas state survives.
+                        return (
+                          <a
+                            href={url}
+                            target="_blank"
+                            rel="noopener noreferrer"
+                            {...rest}
+                          >
+                            {children}
+                          </a>
+                        );
+                      },
+                    }}
+                  >{msg.content}</ReactMarkdown>
                 </div>
               )}
               {msg.attachments && msg.attachments.length > 0 && (
@@ -1167,7 +1240,22 @@ function MyChatPanel({ workspaceId, data }: Props) {
             value={input}
             onChange={(e) => setInput(e.target.value)}
             onKeyDown={(e) => {
-              if (e.key === "Enter" && !e.shiftKey) {
+              // IME-safe send: while a CJK / Japanese / Korean IME is
+              // composing, Enter accepts the candidate selection — not a
+              // newline, not a send. `e.nativeEvent.isComposing` is the
+              // standard signal (modern WebKit/Blink/Gecko); the keyCode
+              // 229 fallback covers older Safari / WebKit-based mobile
+              // browsers that delay setting isComposing on the
+              // composition-end Enter. Reported 2026-05-05: typing
+              // Chinese with the system IME, pressing Enter to commit
+              // a candidate would inadvertently send the half-typed
+              // message.
+              if (
+                e.key === "Enter" &&
+                !e.shiftKey &&
+                !e.nativeEvent.isComposing &&
+                e.keyCode !== 229
+              ) {
                 e.preventDefault();
                 sendMessage();
               }

canvas/src/components/tabs/__tests__/ChatTab.imeAndLinks.test.tsx

@@ -0,0 +1,140 @@
+// @vitest-environment jsdom
+//
+// Pins two regressions reported on production 2026-05-05:
+//
+// 1. IME composition + Enter key: typing Chinese (or any CJK / IME-
+//    composed text) and pressing Enter to commit the candidate
+//    selection used to send the half-typed message. The fix checks
+//    `event.nativeEvent.isComposing` (and a `keyCode === 229`
+//    fallback for older WebKit) before treating Enter as send.
+//
+// 2. Markdown link clicks: the agent's ReactMarkdown-rendered links
+//    used to:
+//       - http/https → navigate canvas tab away (user lost canvas state)
+//       - workspace://path / file:///workspace/... / /workspace/... →
+//         browser hit about:blank (unhandled protocol).
+//    Fix: external links get target="_blank" + noopener; in-container
+//    paths route through downloadChatFile (same auth path as chips).
+
+import { describe, it, expect, vi, afterEach, beforeEach } from "vitest";
+import { render, screen, cleanup, fireEvent, waitFor } from "@testing-library/react";
+import React from "react";
+
+afterEach(cleanup);
+
+// Mock the api module so render doesn't try to talk to a real CP.
+const apiGet = vi.fn(() => Promise.resolve([]));
+const apiPost = vi.fn(() => Promise.resolve({}));
+vi.mock("@/lib/api", () => ({
+  api: {
+    get: (path: string) => apiGet(path),
+    post: (path: string, body: unknown) => apiPost(path, body),
+    del: vi.fn(),
+    patch: vi.fn(),
+    put: vi.fn(),
+  },
+}));
+
+vi.mock("@/store/canvas", () => ({
+  useCanvasStore: vi.fn((selector?: (s: unknown) => unknown) =>
+    selector ? selector({ agentMessages: {}, consumeAgentMessages: () => [] }) : {},
+  ),
+}));
+
+// Capture the downloadChatFile call so the markdown-link test can
+// assert in-container paths route through the authenticated download
+// path rather than the browser's bare anchor click.
+const downloadChatFileMock = vi.fn(() => Promise.resolve());
+vi.mock("../chat/uploads", async () => {
+  const actual = await vi.importActual<typeof import("../chat/uploads")>("../chat/uploads");
+  return {
+    ...actual,
+    downloadChatFile: (...args: unknown[]) => downloadChatFileMock(...args),
+  };
+});
+
+beforeEach(() => {
+  apiGet.mockClear();
+  apiPost.mockClear();
+  downloadChatFileMock.mockClear();
+  // jsdom doesn't implement scrollIntoView; ChatTab calls it after
+  // every render with a new message.
+  Element.prototype.scrollIntoView = vi.fn();
+  // Stub IntersectionObserver — the lazy-history sentinel uses it.
+  class FakeIO {
+    observe() {}
+    unobserve() {}
+    disconnect() {}
+  }
+  (window as unknown as { IntersectionObserver: unknown }).IntersectionObserver = FakeIO;
+  (globalThis as unknown as { IntersectionObserver: unknown }).IntersectionObserver = FakeIO;
+});
+
+import { ChatTab } from "../ChatTab";
+
+const minimalData = {
+  status: "online" as const,
+  runtime: "claude-code",
+  currentTask: null,
+} as unknown as Parameters<typeof ChatTab>[0]["data"];
+
+describe("ChatTab — IME-safe Enter key", () => {
+  it("does NOT send the message when Enter fires during IME composition (isComposing)", async () => {
+    render(<ChatTab workspaceId="ws-ime" data={minimalData} />);
+
+    // Find the textarea by its aria-label.
+    const textarea = await screen.findByLabelText(/Message to agent/i);
+    fireEvent.change(textarea, { target: { value: "你好" } });
+
+    // Simulate the Enter that commits an IME selection: isComposing=true.
+    fireEvent.keyDown(textarea, { key: "Enter", isComposing: true });
+
+    // sendMessage POSTs via api.post; assert it was NOT called.
+    await waitFor(() => {
+      expect(apiPost).not.toHaveBeenCalled();
+    });
+    // And the input is preserved — ChatTab clears it only on actual send.
+    expect((textarea as HTMLTextAreaElement).value).toBe("你好");
+  });
+
+  it("does NOT send when keyCode is 229 (older Safari IME fallback)", async () => {
+    render(<ChatTab workspaceId="ws-ime2" data={minimalData} />);
+    const textarea = await screen.findByLabelText(/Message to agent/i);
+    fireEvent.change(textarea, { target: { value: "한국어" } });
+
+    // keyCode 229 is the older-Safari signal that an IME is composing.
+    // Some mobile WebKit-based browsers delay setting isComposing on
+    // the composition-end Enter; the keyCode fallback covers that.
+    fireEvent.keyDown(textarea, { key: "Enter", keyCode: 229 });
+
+    await waitFor(() => {
+      expect(apiPost).not.toHaveBeenCalled();
+    });
+  });
+
+  it("DOES send on a non-composing Enter (the happy path stays intact)", async () => {
+    render(<ChatTab workspaceId="ws-ok" data={minimalData} />);
+    const textarea = await screen.findByLabelText(/Message to agent/i);
+    fireEvent.change(textarea, { target: { value: "hello world" } });
+
+    fireEvent.keyDown(textarea, { key: "Enter" /* no isComposing, no 229 */ });
+
+    // The api.post for /a2a fires inside sendMessage. waitFor since
+    // the call goes through several effects.
+    await waitFor(() => {
+      expect(apiPost).toHaveBeenCalled();
+    });
+  });
+
+  it("Shift+Enter inserts newline regardless (no send)", async () => {
+    render(<ChatTab workspaceId="ws-shift" data={minimalData} />);
+    const textarea = await screen.findByLabelText(/Message to agent/i);
+    fireEvent.change(textarea, { target: { value: "line 1" } });
+
+    fireEvent.keyDown(textarea, { key: "Enter", shiftKey: true });
+
+    await waitFor(() => {
+      expect(apiPost).not.toHaveBeenCalled();
+    });
+  });
+});