@@ -1012,9 +1012,15 @@
     color: var(--text_default_tertiary);
   }
   /* "This row is pinned", drawn by the row itself rather than by the button that
-   * toggles it. Pinned rows sort to the top, which is a statement about order
-   * and not about the row: it stops being true the moment a fresher session
-   * arrives, and it was never visible while reading the list.
+   * toggles it, because sort position is not a claim about the row: it stops
+   * being true the moment a fresher session arrives, and it was never visible
+   * while reading the list.
+   *
+   * Narrower than it looks: that ordering lives only in the project view's
+   * `sortWebuiProjectSessionIds`. The running, unread and favourites views sort
+   * by activity alone, so inside those a pin buys the mark and nothing else --
+   * which is the point of drawing it, and the reason nothing here depends on
+   * the sort.
    *
    * Tertiary grey, inherited from the meta block, on purpose. The two colours
    * already in this cluster each carry a meaning that is not "the user chose
 
@@ -72,7 +72,7 @@ describe("selectWebuiRailViewTabs", () => {
   });
 
   it("counts zero rather than going negative or blank when nothing is running", () => {
-    const idle = selectWebuiRailViewTabs(SESSIONS, {});
+    const idle = selectWebuiRailViewTabs(SESSIONS, {}, {});
     expect(idle.find((entry) => entry.view === "running")?.count).toBe(0);
     expect(idle.find((entry) => entry.view === "unread")?.count).toBe(0);
   });
@@ -152,7 +152,7 @@ describe("filterWebuiRailViewSessions", () => {
       mvs_gone: { lastActivityAt: 9_999, unread: 7, busy: { turnId: "t9", busyReason: "turn" } },
     };
     expect(selectWebuiRailViewTabs(SESSIONS, stale, {}).find((e) => e.view === "running")?.count).toBe(2);
-    expect(selectWebuiRailViewTabs(SESSIONS, stale).find((e) => e.view === "unread")?.count).toBe(1);
+    expect(selectWebuiRailViewTabs(SESSIONS, stale, {}).find((e) => e.view === "unread")?.count).toBe(1);
     expect(ids(filterWebuiRailViewSessions(SESSIONS, stale, "running", {}))).toEqual([
       "mvs_c",
       "mvs_a",
@@ -295,7 +295,7 @@ describe("the rail view tabs", () => {
     // sessions; there are just none of the kind this tab collects, and the
     // reader needs to know which kind they emptied.
     const labels = new Map(
-      selectWebuiRailViewTabs(SESSIONS, BUSY).map((entry) => [entry.view, entry.emptyLabel]),
+      selectWebuiRailViewTabs(SESSIONS, BUSY, {}).map((entry) => [entry.view, entry.emptyLabel]),
     );
     expect(labels.get("running")).toBe("没有运行中的会话");
     expect(labels.get("unread")).toBe("没有未读会话");
@@ -308,7 +308,7 @@ describe("the rail view tabs", () => {
   it("keeps no English in a Chinese rail", () => {
     // The rail is Chinese throughout. An untranslated string here is how
     // "Waiting messages" and "No sessions yet" got shipped in the first place.
-    for (const entry of selectWebuiRailViewTabs(SESSIONS, BUSY)) {
+    for (const entry of selectWebuiRailViewTabs(SESSIONS, BUSY, {})) {
       expect(entry.label, entry.view).not.toMatch(/[A-Za-z]{2,}/u);
       expect(entry.emptyLabel, entry.view).not.toMatch(/[A-Za-z]{2,}/u);
     }
 
@@ -10,6 +10,7 @@ import {
 } from "../../src/client/rail-buckets.js";
 import { WebuiIconSessionStar } from "../../src/client/icons.js";
 import { WebuiProjectList } from "../../src/client/components/SessionRail.js";
+import type { WebuiSessionActivityMap } from "../../src/client/session-activity.js";
 import type { WebuiClientProject, WebuiClientSession } from "../../src/client/contracts.js";
 
 /**
@@ -51,7 +52,12 @@ const SESSIONS: readonly WebuiClientSession[] = [
   session("mvs_e", 5),
 ];
 
-const ACTIVITY = {
+// Annotated, not inferred. Without it `busyReason: "turn"` widens to `string`
+// and stops being assignable to `WebuiSessionActiveTurn["busyReason"]`, which
+// is a union -- and nothing in this repo's tsc programs compiles test files, so
+// the thirteen call sites below would hand a wrongly typed map to the filter
+// and the suite would stay green on a fixture the product could never produce.
+const ACTIVITY: WebuiSessionActivityMap = {
   mvs_a: { lastActivityAt: 5_000, busy: { turnId: "t1", busyReason: "turn" } },
   mvs_b: { lastActivityAt: 9_000, unread: 3 },
   mvs_c: { lastActivityAt: 7_000 },
 
@@ -357,6 +357,21 @@ test("a starred child row shows its mark once the parent is expanded", async ({
   await expect(starMark(page, "C")).toBeVisible();
   // The parent's own state is untouched by the child's.
   await expect(starMark(page, "A")).toHaveCount(0);
+
+  // ⚠️ Read this before adding star to a child row's context menu.
+  //
+  // `filterWebuiRailViewSessions` filters `page.sessions`, and a child is not
+  // in `page.sessions` -- it only ever appears in the tree. So the moment
+  // `openSessionMenu`'s `isChild` branch grows a star item, a starred child
+  // becomes unreachable in TWO ways at once: it still cannot be starred (no
+  // menu item today), and if it were, it would carry a mark, sit in localStorage
+  // and still never appear in 收藏 or count toward its badge.
+  //
+  // The fixture is already staged for exactly that: C is deliberately outside
+  // `sessions`, so the test above can star it and the count test can prove the
+  // badge reads 0. Whoever wires child starring has to decide whether the
+  // favourites view also walks the tree, and that decision belongs with the
+  // feature, not with this spec.
 });
 
 test("the context menu offers unstar on a starred row", async ({ page }) => {