feat: a bare URL opens on FiDi, not on 1,551 km of tan

One California is the product; the first frame is still the coarsest
pose the pack owns, because createScene opens on chapters[0] and the
state tour starts there. Capture and ?city=california keep that.
A visitor typing tera.lumbridgecorp.com gets openingChapter fidi —
a city they can read — without reordering the pack.

src/engine/scene.ts

@@ -459,6 +459,18 @@ export interface SceneOptions {
    * `stage.setScene(handle.stageScene)` that presents it.
    */
   present?: boolean;
+  /**
+   * Which chapter the camera opens on. Defaults to `chapters[0]`.
+   *
+   * The pack's chapter list is a numbered tour and a capture contract — index
+   * 0 is the state's whole-board pose, and twenty-nine shot-list guards aim at
+   * buttons by that order. The *visitor* landing is a different question: a
+   * bare tera.lumbridgecorp.com should open on a city you can read, not on
+   * 1,551 km of tan. Passing `fidi` here does that without reordering the pack.
+   * Unknown ids throw rather than silently falling back, so a renamed chapter
+   * cannot photograph the state under a caption about downtown.
+   */
+  openingChapter?: string;
 }
 
 export interface SceneHandle {
@@ -1419,8 +1431,14 @@ export async function createScene(
   const chapterById = Object.fromEntries(city.chapters.map((c) => [c.id, c]));
   const first = city.chapters[0];
   if (!first) throw new Error(`City "${city.id}" declares no chapters`);
+  if (options.openingChapter !== undefined && chapterById[options.openingChapter] === undefined) {
+    throw new Error(
+      `openingChapter "${options.openingChapter}" is not a chapter of city "${city.id}"`,
+    );
+  }
+  const landing = chapterById[options.openingChapter ?? first.id] ?? first;
 
-  let currentChapter = first.id;
+  let currentChapter = landing.id;
   const chapterListeners: ((id: string) => void)[] = [];
   const controlModeListeners: ((mode: CityControlMode) => void)[] = [];
 
@@ -1518,10 +1536,10 @@ export async function createScene(
    * Two rules govern everything below and both were learned from a picture.
    *
    * **The board settles exactly where the pack said it would.** `openingPose`
-   * is `chapterPose(first)` unchanged, so the resting frame is the one the pack
-   * authored, chapter 01 keeps meaning what it says, and a capture of this
-   * board is the same capture it was before an arrival existed. The wow is the
-   * *approach*; nothing about the destination is second-guessed here.
+   * is `chapterPose(landing)` — `chapters[0]` unless the caller named a
+   * chapter, so a capture that does not pass `openingChapter` is the same
+   * capture it was, and a bare URL that does can land on a city without
+   * reordering the pack. The wow is the *approach*.
    *
    * **Under `prefers-reduced-motion` there is no move at all.** Not a shorter
    * one — none: the camera is placed on the resting pose and that is the whole
@@ -1529,7 +1547,7 @@ export async function createScene(
    * capture harness honest, because a screenshot of a board mid-flight is a
    * screenshot of a different board every time you take it.
    */
-  const openingPose = chapterPose(first);
+  const openingPose = chapterPose(landing);
 
   /**
    * The opening move, or `null` when there is not one running.

src/main.ts

@@ -339,9 +339,10 @@ const CITIES: { id: string; label: string; city: City }[] = ONE_CALIFORNIA
 /*
  * With one board there is nothing to choose: the argument above is entirely
  * about which of three products a bare URL lands on, and `?one=1` is the answer
- * that there are not three. The landing *pose* is a separate question and still
- * belongs to the chapter list — `california-overview` frames the state, and the
- * metro rungs restored in `cities/unify.ts` are how you get down from it.
+ * that there are not three. The landing *pose* is a separate question: the
+ * pack still opens its chapter list on `california-overview` so capture and
+ * `?city=california` frame the state, and a bare URL passes `openingChapter:
+ * "fidi"` so a visitor's first frame is a city they can read.
  */
 const DEFAULT_CITY_ID = ONE_CALIFORNIA ? "california" : "sf";
 
@@ -1916,6 +1917,9 @@ async function buildBoard(
   const drawsMigration = carriesSky && access.feeds?.birds === true;
   const handle = await createScene(stage, {
     city: entry.city,
+    // Bare URL on one California: land in the city, not on 1,551 km of state.
+    // `?city=california` (and every capture shot) still opens on chapters[0].
+    ...(ONE_CALIFORNIA && CITY_PARAM === null ? { openingChapter: "fidi" } : {}),
     // The page's one rig, shared with the office. Handed in rather than built
     // per board; see the note where it is constructed.
     environment,

src/test/integration/sceneWiring.test.ts

@@ -601,6 +601,17 @@ test("the water reflects rather than absorbing, now that there is a sky to refle
 
 const MAIN = readFileSync(path.join(ROOT, "src/main.ts"), "utf8");
 
+test("a bare URL on one California opens on FiDi, not on the whole state", () => {
+  assert.ok(
+    MAIN.includes('openingChapter: "fidi"'),
+    "the visitor landing lost its city; they will see 1,551 km of tan",
+  );
+  assert.ok(
+    MAIN.includes("CITY_PARAM === null"),
+    "the fidi opening must not apply to ?city=california — that is the capture harness",
+  );
+});
+
 test("main.ts makes exactly one call into the chrome, and writes no visibility itself", () => {
   const applies = [...MAIN.matchAll(/chrome\?\.apply\(chromeState\(/g)].length;
   assert.equal(

src/test/unify.test.ts

@@ -165,6 +165,7 @@ describe("one California's chapters", () => {
     // Nothing merged twice, which a naive concat of two packs sharing an id
     // would do without failing anything else.
     assert.equal(new Set(ids).size, ids.length);
+    assert.ok(ids.includes("fidi"), "the visitor landing names a chapter the merge dropped");
   });
 
   it("restates each merged rung in this board's units, keeping its true metres", () => {