feat(documents): open the doc-scoped Coach in the side drawer, not a full page

"Ask the Coach" on a document used to navigate to /coach?doc=<id> — a full-page
jump away from the vault. It now opens the real, doc-scoped conversation in the
shared side drawer, and the drawer's maximize control expands it to the full
/coach page while preserving scope.

- Thread an optional documentId through the launch context: askCoach gains a
  fourth argument, the provider tracks it alongside prefill/scope and clears it
  on close, and LayoutCoachMount forwards it to the drawer as initialDocumentId.
  The open-state precedence moves into a pure resolveLaunchState helper.
- The vault detail sheet closes itself and calls askCoach(..., doc.id) instead
  of routing away, so the drawer owns the surface.
- Maximize preserves continuity: the drawer reads the live conversation id via
  a new imperative getter out of the conversation surface (parallel to the
  reset registration) and hands off to /coach?c=<id> once a thread exists,
  falling back to /coach?doc=<id> for a chat maximized before its first turn.

The send path is untouched: every document turn still routes through the
hardened fenced endpoint keyed on documentId — only where the conversation
renders (drawer vs page) changed. The documents-chat e2e now asserts the
drawer opens in place, doc-scoped, rather than a URL change.

src/components/documents/__tests__/document-coach-launch-wiring.test.ts

@@ -0,0 +1,66 @@
+import { describe, expect, it } from "vitest";
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+/**
+ * v1.28.52 (Documents R3) — "Ask the Coach" opens the REAL fenced coach
+ * conversation in the shared SIDE DRAWER, scoped to the document, instead of a
+ * full-page nav to `/coach?doc=<id>` (the v1.28.51 behaviour Marc corrected).
+ *
+ * The wiring is source-structural (the send-path fence itself is covered by the
+ * coach-send-target unit tests — untouched here). These guards pin:
+ *   1. the detail sheet drives the drawer via `askCoach(..., doc.id)`, closing
+ *      the sheet first, and no longer navigates to `/coach?doc=`;
+ *   2. the launch context → mount → drawer → conversation `documentId` thread
+ *      stays connected end-to-end.
+ */
+const ROOT = join(__dirname, "../../../..");
+const DETAIL_SHEET = join(
+  ROOT,
+  "src/components/documents/document-detail-sheet.tsx",
+);
+const MOUNT = join(ROOT, "src/components/insights/layout-coach-mount.tsx");
+const DRAWER = join(
+  ROOT,
+  "src/components/insights/coach-panel/coach-drawer.tsx",
+);
+
+function load(path: string): string {
+  return readFileSync(path, "utf8");
+}
+
+describe("document detail sheet — Ask the Coach opens the drawer", () => {
+  const src = load(DETAIL_SHEET);
+
+  it("launches the doc-scoped coach drawer via askCoach(..., doc.id)", () => {
+    expect(src).toContain("useCoachLaunch");
+    expect(src).toMatch(/askCoach\(null,\s*undefined,\s*false,\s*doc\.id\)/);
+  });
+
+  it("closes the detail sheet when handing off to the drawer", () => {
+    // The Ask-the-Coach onClick closes the sheet before opening the drawer so
+    // the drawer owns the surface (no stacked dialogs).
+    expect(src).toMatch(
+      /onClick=\{\(\)\s*=>\s*\{[\s\S]*?onOpenChange\(false\);[\s\S]*?askCoach\(null,\s*undefined,\s*false,\s*doc\.id\)/,
+    );
+  });
+
+  it("no longer navigates to the full-page /coach?doc= route", () => {
+    expect(src).not.toContain("/coach?doc=");
+    expect(src).not.toContain('from "next/navigation"');
+  });
+});
+
+describe("documentId threads launch context → mount → drawer", () => {
+  it("the mount forwards launch.documentId to the drawer", () => {
+    expect(load(MOUNT)).toContain("documentId={launch.documentId}");
+  });
+
+  it("the drawer seeds CoachConversation with initialDocumentId + a conversation-id getter", () => {
+    const src = load(DRAWER);
+    expect(src).toContain("initialDocumentId={documentId}");
+    expect(src).toContain(
+      "registerConversationIdGetter={registerConversationIdGetter}",
+    );
+  });
+});