feat: authorship + change annotations in the built-in Markdown preview (D3/D21, PUC-3); cowriting.annotations toggle

Task 7 of the native-surfaces migration plan. Pure previewAnnotations.ts
(annotateSource + cowritingMarkdownItPlugin) reuses trackChangesModel.ts's
sentinel discipline (#33/#47), generalized to a 3-way ins-claude/ins-human/del
tag (exported injectSentinels/sentinelsToSpans, colorByAuthor unaffected,
84/84 existing tests pass unmodified). Host hook in extension.ts wires
registry/diffView/attribution/proposals/config into the plugin, exposed via
CowritingApi.extendMarkdownIt + a previewAnnotationHost test seam.
cowriting.annotations setting + toggleAnnotations command/menu. Q4 mermaid
(previewScripts + options.highlight fence override) implemented per the
proven bierner.markdown-mermaid pattern; intra-diagram diff augmentation
scoped out (unverifiable via the structural E2E harness) — see
task-7-report.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/e2e/suite/previewAnnotations.test.ts

@@ -0,0 +1,79 @@
+import * as assert from "node:assert";
+import MarkdownIt from "markdown-it";
+import * as vscode from "vscode";
+import { cowritingMarkdownItPlugin } from "../../../src/previewAnnotations";
+import { activateApi, settle } from "./helpers";
+
+// Task 7 (D3/D21, PUC-3): the built-in preview's DOM isn't queryable from a
+// host E2E test (§6.8), so this asserts the pure transform's INPUTS/OUTPUTS
+// through the real `CowritingApi` seams instead — the production
+// `previewAnnotationHost.inputsFor` (not a hand-rolled reimplementation) fed
+// through the real `cowritingMarkdownItPlugin` + a fresh markdown-it instance
+// (mirroring the unit suite's own `render()` helper), so this exercises the
+// ACTUAL registry/diffView/attribution/proposals/config wiring end to end.
+suite("PUC-3 annotate-toggle (built-in Markdown preview annotations)", () => {
+  test("a machine-attributed change renders cw-ins-claude; disabling the setting passes the source through unchanged", async () => {
+    const api = await activateApi();
+    const doc = await vscode.workspace.openTextDocument({
+      language: "markdown",
+      content: "hello world\n",
+    });
+    await vscode.window.showTextDocument(doc);
+    await vscode.commands.executeCommand("cowriting.coeditDocument");
+    await settle();
+
+    const start = doc.getText().indexOf("world");
+    const ok = await vscode.commands.executeCommand<boolean>("cowriting.applyAgentEdit", {
+      uri: doc.uri.toString(),
+      start,
+      end: start + "world".length,
+      newText: "brave new world",
+      model: "sonnet",
+      sessionId: "e2e-preview-annotations",
+      turnId: "turn-e2e-preview-annotations",
+    });
+    assert.strictEqual(ok, true, "seam edit applies");
+    await settle();
+
+    // Annotations ON (default): render the CURRENT buffer through the real
+    // markdown-it plugin + the production host — proves the full pipeline
+    // (core-rule swap → full-render sentinel walk) reaches a live doc.
+    const md = new MarkdownIt();
+    cowritingMarkdownItPlugin(md, api.previewAnnotationHost);
+    const html = md.render(doc.getText());
+    assert.ok(html.includes("cw-ins-claude"), `expected cw-ins-claude in:\n${html}`);
+
+    // Toggle OFF: the config-gated `enabled` flag reaches `annotateSource` and
+    // the transform becomes the identity (no core-rule swap, no marks).
+    const config = vscode.workspace.getConfiguration("cowriting");
+    await config.update("annotations", false, vscode.ConfigurationTarget.Global);
+    try {
+      const inputs = api.previewAnnotationHost.inputsFor(undefined);
+      assert.ok(inputs, "inputsFor still resolves a coedited doc while disabled");
+      assert.strictEqual(inputs!.enabled, false);
+      const md2 = new MarkdownIt();
+      cowritingMarkdownItPlugin(md2, api.previewAnnotationHost);
+      const plainMd = new MarkdownIt();
+      assert.strictEqual(md2.render(doc.getText()), plainMd.render(doc.getText()));
+    } finally {
+      await config.update("annotations", true, vscode.ConfigurationTarget.Global);
+    }
+  });
+
+  test("cowriting.toggleAnnotations flips the setting", async () => {
+    const api = await activateApi();
+    const doc = await vscode.workspace.openTextDocument({ language: "markdown", content: "toggle me\n" });
+    await vscode.window.showTextDocument(doc);
+    await vscode.commands.executeCommand("cowriting.coeditDocument");
+    await settle();
+
+    const config = () => vscode.workspace.getConfiguration("cowriting");
+    const before = config().get<boolean>("annotations", true);
+    await vscode.commands.executeCommand("cowriting.toggleAnnotations");
+    assert.strictEqual(config().get<boolean>("annotations", true), !before);
+    // restore
+    await vscode.commands.executeCommand("cowriting.toggleAnnotations");
+    assert.strictEqual(config().get<boolean>("annotations", true), before);
+    void api; // keep the activated extension alive for the duration of the test
+  });
+});

test/previewAnnotations.test.ts

@@ -0,0 +1,46 @@
+import MarkdownIt from "markdown-it";
+import { describe, expect, it } from "vitest";
+import { cowritingMarkdownItPlugin } from "../src/previewAnnotations";
+
+function render(src: string, inputs: any): string {
+  const md = new MarkdownIt();
+  cowritingMarkdownItPlugin(md, { inputsFor: () => inputs });
+  return md.render(src);
+}
+
+const base = { baselineReason: "entered", proposals: [], enabled: true };
+
+describe("preview annotations (PUC-3/D21)", () => {
+  it("renders clean when disabled", () => {
+    const html = render("hello brave world\n", { ...base, enabled: false, baselineText: "hello world\n", spans: [] });
+    expect(html).not.toContain("cw-");
+  });
+  it("colors machine spans blue and human insertions green vs baseline", () => {
+    const html = render("hello brave new world\n", {
+      ...base,
+      baselineText: "hello world\n",
+      spans: [{ start: 6, end: 12, author: "claude" }, { start: 12, end: 16, author: "human" }],
+    });
+    expect(html).toContain('class="cw-ins-claude"');
+    expect(html).toContain('class="cw-ins-human"');
+  });
+  it("strikes deletions vs baseline", () => {
+    const html = render("hello world\n", { ...base, baselineText: "hello cruel world\n", spans: [] });
+    expect(html).toContain("cw-del");
+    expect(html).toContain("cruel");
+  });
+  it("pinned baseline renders clean even with spans (pin→clean, INV-33/#48)", () => {
+    const html = render("hello brave world\n", {
+      ...base, baselineReason: "pinned", baselineText: "hello brave world\n",
+      spans: [{ start: 6, end: 12, author: "claude" }],
+    });
+    expect(html).not.toContain("cw-ins");
+  });
+  it("survives intra-emphasis boundaries (#33 discipline)", () => {
+    const html = render("a *bold claim* here\n", {
+      ...base, baselineText: "a here\n", spans: [{ start: 2, end: 14, author: "claude" }],
+    });
+    expect(html).toContain("cw-ins-claude");
+    expect(html).not.toMatch(/[-]/); // no PUA sentinel leaks
+  });
+});