Answer the review: send the worker one request at a time, keep only the latest, and never wait for a dead one

The adversarial review confirmed three defects in this PR, all reproduced in
the browser.

1. Superseded graphs queued up in front of routes. The worker answers
   messages one at a time and cannot drop one it has started. With the
   jump-link layer on, every pause on the range slider posted a full graph
   build, seconds of work at 6-8 pc. Answers no longer wanted were thrown
   away only once built. A route asked for afterwards waited behind every
   one of them: a one-jump route took 44 s.

   RoutingClient now holds requests and sends them one at a time. While one
   is out, only the latest of each kind waits: a newer graph replaces an
   older one before it is ever built, and the older promise is rejected with
   SupersededRequest. Routes go ahead of graphs. The same question asked
   again while outstanding shares the answer rather than being worked twice,
   as when the layer is turned off and on during a build.

   The same scenario in the browser (layer on, range stepped 5 -> 8 pc with
   400 ms pauses, then Sol to Proxima): the route came back in 110 ms. The
   worker was sent "links 3, links 5, route, links 8"; 6 and 7 were never
   built.

2. A worker that failed left the panel stuck. With no error handling, a
   worker that failed to load (a 404 on its chunk after a redeploy) or
   threw left "Plotting…" and a disabled button for good, and a graph at a
   range could not be asked for again.

   The worker now answers an exception with a 'failed' message, which
   rejects that request. A worker that fails to load or dies is abandoned,
   and what it left outstanding, and everything asked afterwards, is
   answered in place. The scene releases the panel when a route fails, and
   forgets a graph range that was never drawn so it can be asked for again.

3. Nothing type-checked the worker. The application builder never reads
   webWorkerTsConfig, and bundles the worker with esbuild, which strips
   types without checking them. tsconfig.app.json leaves the file out. A
   type error in the worker shipped.

   `npm run worker:typecheck` (tsc -p tsconfig.worker.json) now runs in CI
   beside the other project checks. webWorkerTsConfig is removed from
   angular.json, since it only suggested that something checked the worker.

Tests with a fake worker cover one request at a time, a waiting graph
replaced and a route sent ahead of it, a question shared, a failure rejected
and the next request sent, and a failed worker's requests answered in place.
A scene test covers the panel released after a failed route. Negative
controls, each caught: several requests sent at once, a waiting graph kept,
graphs ahead of routes, a question asked twice, a failure answered as a
success, a failed worker waited on, the panel left pending, and a type error
in the worker (caught by worker:typecheck).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jxMkwA2rbicdGxHosecYi

src/app/features/galaxy-system/galaxy-system-scene.component.spec.ts

@@ -294,6 +294,23 @@ describe('GalaxySystemSceneComponent camera-flight transitions', () => {
     expect(component.routePending()).toBe(false);
   });
 
+  it('releases the routes panel when a route cannot be worked out, so it can be tried again', async () => {
+    const component = fixture.componentInstance as unknown as {
+      routing: { route(): Promise<never>; links(): Promise<Float32Array>; dispose(): void };
+      routePending(): boolean;
+      onRouteRequested(request: { fromId: number; toId: number; rangePc: number }): void;
+    };
+    const logged = vi.spyOn(console, 'error').mockImplementation(() => undefined);
+    component.routing = { route: () => Promise.reject(new Error('worker gone')), links: () => Promise.resolve(new Float32Array(0)), dispose: () => undefined };
+
+    component.onRouteRequested({ fromId: SUN.id, toId: PROXIMA.id, rangePc: 2 });
+    await flushAsync();
+
+    expect(component.routePending()).toBe(false);
+    expect(logged).toHaveBeenCalled();
+    logged.mockRestore();
+  });
+
   it('asks for no more label candidates once the last label it will show is placed', () => {
     // Near the Sun a label candidate past the fifteenth can sit at the far end of the catalogue's
     // brightness order, so asking for one more than is used can cost a walk of the whole order.

src/app/features/galaxy-system/galaxy-system-scene.component.ts

@@ -1424,18 +1424,29 @@ export class GalaxySystemSceneComponent implements AfterViewInit, OnDestroy {
     }
     const request = ++this.routeRequest;
     this.routePending.set(true);
-    void this.routing.route(fromId, toId, rangePc, ROUTE_RANGE_CEILING_PC).then(({ route, neededRangePc }) => {
-      if (request !== this.routeRequest) {
-        return;
+    void this.routing.route(fromId, toId, rangePc, ROUTE_RANGE_CEILING_PC).then(
+      ({ route, neededRangePc }) => {
+        if (request !== this.routeRequest) {
+          return;
+        }
+        this.routePending.set(false);
+        this.routeResult.set({
+          stars: route ? route.stars.map((id) => ({ id, name: this.starsById.get(id)?.name ?? `Star ${id}` })) : [],
+          totalPc: route?.totalPc ?? 0,
+          neededRangePc
+        });
+        this.jumpLinks?.setRoute(route?.stars ?? [], (id) => this.starsById.get(id));
+      },
+      (error: unknown) => {
+        // A request replaced by a newer one is settled this way too; only the latest matters.
+        if (request !== this.routeRequest) {
+          return;
+        }
+        // Released rather than left saying "Plotting…" with the button held, so it can be tried again.
+        this.routePending.set(false);
+        console.error('Route could not be plotted.', error);
       }
-      this.routePending.set(false);
-      this.routeResult.set({
-        stars: route ? route.stars.map((id) => ({ id, name: this.starsById.get(id)?.name ?? `Star ${id}` })) : [],
-        totalPc: route?.totalPc ?? 0,
-        neededRangePc
-      });
-      this.jumpLinks?.setRoute(route?.stars ?? [], (id) => this.starsById.get(id));
-    });
+    );
   }
 
   /**
@@ -1460,11 +1471,20 @@ export class GalaxySystemSceneComponent implements AfterViewInit, OnDestroy {
       return;
     }
     this.drawnJumpRangePc = rangePc;
-    void this.routing.links(rangePc).then((segments) => {
-      if (this.drawnJumpRangePc === rangePc) {
-        this.jumpLinks?.setSegments(segments);
+    void this.routing.links(rangePc).then(
+      (segments) => {
+        if (this.drawnJumpRangePc === rangePc) {
+          this.jumpLinks?.setSegments(segments);
+        }
+      },
+      () => {
+        // Replaced by a newer range, or failed. Either way this range is not drawn, and must not be
+        // remembered as if it were, or asking for it again would be skipped.
+        if (this.drawnJumpRangePc === rangePc) {
+          this.drawnJumpRangePc = null;
+        }
       }
-    });
+    );
   }
 
   /** A pinned body wins over a hovered one, so the card does not change under the pointer. */

src/app/features/galaxy-system/routing-client.spec.ts

@@ -1,9 +1,10 @@
 import { describe, expect, it } from 'vitest';
 
 import { jumpLinkSegments, routeBetween } from '../../shared/astro/jump-links';
+import { RoutingRequest, RoutingResponse } from '../../shared/astro/routing';
 import { StarNeighbourhood } from '../../shared/astro/star-neighbourhood';
 import { StarRecord } from '../../shared/models/star.model';
-import { RoutingClient } from './routing-client';
+import { RoutingClient, SupersededRequest } from './routing-client';
 
 const STARS: StarRecord[] = Array.from({ length: 6 }, (_, i) => ({
   id: 100 + i,
@@ -16,11 +17,51 @@ const STARS: StarRecord[] = Array.from({ length: 6 }, (_, i) => ({
   colorIndex: 0.6
 }));
 const POSITIONS = Float32Array.from(STARS.flatMap((star) => [star.x, star.y, star.z]));
+const index = new StarNeighbourhood(STARS);
+
+/** Flushes settled promises and their handlers. */
+const flush = () => new Promise((resolve) => setTimeout(resolve, 0));
+
+/** A worker that records what it is sent and answers only when told to. */
+class FakeWorker {
+  readonly sent: Array<RoutingRequest | { kind: 'catalogue' }> = [];
+  private readonly listeners: Record<string, Array<(event: { data?: unknown }) => void>> = {};
+  terminated = false;
+
+  postMessage(message: RoutingRequest | { kind: 'catalogue' }): void {
+    this.sent.push(message);
+  }
+
+  addEventListener(type: string, listener: (event: { data?: unknown }) => void): void {
+    (this.listeners[type] ??= []).push(listener);
+  }
+
+  terminate(): void {
+    this.terminated = true;
+  }
+
+  /** The requests sent so far, catalogue aside. */
+  get requests(): RoutingRequest[] {
+    return this.sent.filter((message): message is RoutingRequest => message.kind !== 'catalogue');
+  }
+
+  answer(response: RoutingResponse): void {
+    for (const listener of this.listeners['message'] ?? []) listener({ data: response });
+  }
+
+  fail(): void {
+    for (const listener of this.listeners['error'] ?? []) listener({});
+  }
+}
+
+function clientWithFake(): { client: RoutingClient; worker: FakeWorker } {
+  const worker = new FakeWorker();
+  const client = new RoutingClient(STARS, POSITIONS, index, () => worker as unknown as Worker);
+  return { client, worker };
+}
 
 // The unit tests' DOM has no Worker, which is exactly the case the client answers in place.
 describe('RoutingClient without a worker', () => {
-  const index = new StarNeighbourhood(STARS);
-
   it('has no Worker to use here, so the in-place answers are what is being tested', () => {
     expect(typeof Worker).toBe('undefined');
   });
@@ -49,3 +90,87 @@ describe('RoutingClient without a worker', () => {
     client.dispose();
   });
 });
+
+describe('RoutingClient with a worker', () => {
+  it('sends the catalogue first, then one request at a time', () => {
+    const { client, worker } = clientWithFake();
+
+    void client.links(8);
+    void client.links(3);
+
+    expect(worker.sent[0].kind).toBe('catalogue');
+    expect(worker.requests).toHaveLength(1);
+    client.dispose();
+  });
+
+  // A graph at 8 pc is seconds of work the worker cannot drop once started. Every pause on the
+  // range slider used to queue another, and a route asked for after them waited behind them all.
+  it('replaces a waiting graph with the newer one before it is ever built, and sends a route ahead of it', async () => {
+    const { client, worker } = clientWithFake();
+    const first = client.links(5);
+    const superseded = client.links(6).catch((error: unknown) => error);
+    const latest = client.links(8);
+    const route = client.route(100, 104, 1.5, 8);
+
+    const building = worker.requests[0];
+    worker.answer({ kind: 'links', requestId: building.requestId, segments: new Float32Array(6) });
+    await flush();
+
+    expect(await superseded).toBeInstanceOf(SupersededRequest);
+    expect(worker.requests.map((request) => request.kind)).toEqual(['links', 'route']);
+    await expect(first).resolves.toHaveLength(6);
+
+    const routeRequest = worker.requests[1];
+    worker.answer({ kind: 'route', requestId: routeRequest.requestId, route: null, neededRangePc: 4 });
+    await expect(route).resolves.toEqual({ route: null, neededRangePc: 4 });
+    await flush();
+
+    expect(worker.requests.map((request) => (request.kind === 'links' ? request.rangePc : request.kind))).toEqual([5, 'route', 8]);
+    const lastGraph = worker.requests[2];
+    worker.answer({ kind: 'links', requestId: lastGraph.requestId, segments: new Float32Array(12) });
+    await expect(latest).resolves.toHaveLength(12);
+    client.dispose();
+  });
+
+  it('shares the answer to a question already on its way rather than asking it twice', async () => {
+    const { client, worker } = clientWithFake();
+    const once = client.links(7.5);
+    const again = client.links(7.5);
+
+    expect(worker.requests).toHaveLength(1);
+    worker.answer({ kind: 'links', requestId: worker.requests[0].requestId, segments: new Float32Array(6) });
+
+    expect(await again).toBe(await once);
+    expect(worker.requests).toHaveLength(1);
+    client.dispose();
+  });
+
+  it('rejects a request the worker failed on, and goes on to the next', async () => {
+    const { client, worker } = clientWithFake();
+    const failing = client.route(100, 104, 1.5, 8).catch((error: unknown) => error);
+    const next = client.links(3);
+
+    worker.answer({ kind: 'failed', requestId: worker.requests[0].requestId, message: 'out of memory' });
+
+    expect(((await failing) as Error).message).toBe('out of memory');
+    await flush();
+    expect(worker.requests.map((request) => request.kind)).toEqual(['route', 'links']);
+    worker.answer({ kind: 'links', requestId: worker.requests[1].requestId, segments: new Float32Array(0) });
+    await expect(next).resolves.toHaveLength(0);
+    client.dispose();
+  });
+
+  it('answers in place what a worker that failed to load left outstanding, and everything after', async () => {
+    const { client, worker } = clientWithFake();
+    const route = client.route(100, 104, 1.5, 8);
+    const graph = client.links(1.5);
+
+    worker.fail();
+
+    await expect(route).resolves.toEqual({ route: routeBetween(index, 100, 104, 1.5), neededRangePc: null });
+    expect(Array.from(await graph)).toEqual(Array.from(jumpLinkSegments(index, 1.5)));
+    await expect(client.route(100, 105, 1.5, 8)).resolves.toMatchObject({ route: null });
+    expect(worker.terminated).toBe(true);
+    client.dispose();
+  });
+});

src/app/features/galaxy-system/routing-client.ts

@@ -8,27 +8,75 @@ export interface RouteAnswer {
   readonly neededRangePc: number | null;
 }
 
-type Pending = (response: RoutingResponse) => void;
+/** A request dropped before it was sent, because a newer one of the same kind replaced it. */
+export class SupersededRequest extends Error {
+  constructor() {
+    super('Superseded by a newer request');
+  }
+}
+
+/** A request made and not yet answered: what was asked, and the promise whoever asked is holding. */
+interface Outstanding {
+  readonly request: RoutingRequest;
+  /** The question without its id, so the same question asked twice can be recognised. */
+  readonly question: string;
+  readonly promise: Promise<RoutingResponse>;
+  readonly resolve: (response: RoutingResponse) => void;
+  readonly reject: (error: Error) => void;
+}
+
+function outstanding(request: RoutingRequest): Outstanding {
+  let resolve!: (response: RoutingResponse) => void;
+  let reject!: (error: Error) => void;
+  const promise = new Promise<RoutingResponse>((onResolve, onReject) => {
+    resolve = onResolve;
+    reject = onReject;
+  });
+  // eslint-disable-next-line @typescript-eslint/no-unused-vars
+  const { requestId, ...question } = request;
+  return { request, question: JSON.stringify(question), promise, resolve, reject };
+}
+
+/** The routing worker, where this environment has one. */
+function startRoutingWorker(): Worker | undefined {
+  return typeof Worker === 'undefined' ? undefined : new Worker(new URL('../../shared/astro/routing.worker', import.meta.url), { type: 'module' });
+}
 
 /**
  * Asks the route questions of a worker holding its own copy of the catalogue, and hands back
- * promises. Where there is no `Worker` — the unit tests' DOM has none — the same answers are
- * worked out in place, from the index the scene already holds.
+ * promises.
+ *
+ * The worker answers one request at a time and cannot drop one it has started: a jump-link graph
+ * at 8 pc is seconds of work. So requests are held here and sent one by one, and while one is out,
+ * only the latest of each kind waits behind it — a newer graph replaces an older one before it is
+ * ever built, and the older promise is rejected with {@link SupersededRequest}. Routes go ahead of
+ * graphs, being quick and asked for by a click. The same question asked again while it is still
+ * outstanding shares the answer rather than being worked out twice.
+ *
+ * Where there is no worker — the unit tests' DOM has none, and a worker can fail to load or crash —
+ * the same answers are worked out in place, from the index the scene already holds.
  */
 export class RoutingClient {
-  private readonly worker?: Worker;
-  private readonly pending = new Map<number, Pending>();
+  private worker?: Worker;
+  private inFlight?: Outstanding;
+  private readonly waiting: Partial<Record<RoutingRequest['kind'], Outstanding>> = {};
   private nextRequestId = 0;
 
-  constructor(stars: readonly StarRecord[], positions: Float32Array, private readonly localIndex: StarNeighbourhood) {
-    if (typeof Worker === 'undefined') {
+  constructor(
+    stars: readonly StarRecord[],
+    positions: Float32Array,
+    private readonly localIndex: StarNeighbourhood,
+    startWorker: () => Worker | undefined = startRoutingWorker
+  ) {
+    this.worker = startWorker();
+    if (!this.worker) {
       return;
     }
-    this.worker = new Worker(new URL('../../shared/astro/routing.worker', import.meta.url), { type: 'module' });
-    this.worker.addEventListener('message', ({ data }: MessageEvent<RoutingResponse>) => {
-      this.pending.get(data.requestId)?.(data);
-      this.pending.delete(data.requestId);
-    });
+    this.worker.addEventListener('message', ({ data }: MessageEvent<RoutingResponse>) => this.settle(data));
+    // A worker that fails to load, or dies, answers nothing further: everything outstanding, and
+    // everything asked from here on, is worked out in place instead of waiting for good.
+    this.worker.addEventListener('error', () => this.abandonWorker());
+    this.worker.addEventListener('messageerror', () => this.abandonWorker());
     // Copies, since the scene goes on using its own; transferred, so the copy is sent and not cloned again.
     const ids = Int32Array.from(stars, (star) => star.id);
     const copy = positions.slice();
@@ -50,16 +98,70 @@ export class RoutingClient {
 
   dispose(): void {
     this.worker?.terminate();
-    this.pending.clear();
+    this.worker = undefined;
+    this.inFlight = undefined;
+    delete this.waiting.route;
+    delete this.waiting.links;
   }
 
   private ask(request: RoutingRequest): Promise<RoutingResponse> {
     if (!this.worker) {
-      return Promise.resolve(answerRouting(this.localIndex, request));
+      return new Promise((resolve) => resolve(answerRouting(this.localIndex, request)));
+    }
+    const asked = outstanding(request);
+    const same = [this.inFlight, this.waiting[request.kind]].find((other) => other?.question === asked.question);
+    if (same) {
+      return same.promise;
+    }
+    this.waiting[request.kind]?.reject(new SupersededRequest());
+    this.waiting[request.kind] = asked;
+    this.sendNext();
+    return asked.promise;
+  }
+
+  private sendNext(): void {
+    if (this.inFlight || !this.worker) {
+      return;
+    }
+    const next = this.waiting.route ?? this.waiting.links;
+    if (!next) {
+      return;
+    }
+    delete this.waiting[next.request.kind];
+    this.inFlight = next;
+    this.worker.postMessage(next.request);
+  }
+
+  private settle(response: RoutingResponse): void {
+    const answered = this.inFlight;
+    if (!answered || answered.request.requestId !== response.requestId) {
+      return;
+    }
+    this.inFlight = undefined;
+    if (response.kind === 'failed') {
+      answered.reject(new Error(response.message));
+    } else {
+      answered.resolve(response);
+    }
+    this.sendNext();
+  }
+
+  private abandonWorker(): void {
+    this.worker?.terminate();
+    this.worker = undefined;
+    const stranded = [this.inFlight, this.waiting.route, this.waiting.links];
+    this.inFlight = undefined;
+    delete this.waiting.route;
+    delete this.waiting.links;
+    for (const request of stranded) {
+      if (!request) {
+        continue;
+      }
+      try {
+        request.resolve(answerRouting(this.localIndex, request.request));
+      } catch (error) {
+        request.reject(error instanceof Error ? error : new Error(String(error)));
+      }
     }
-    return new Promise((resolve) => {
-      this.pending.set(request.requestId, resolve);
-      this.worker!.postMessage(request);
-    });
   }
 }

src/app/shared/astro/routing.ts

@@ -23,7 +23,9 @@ export type RoutingRequest =
 
 export type RoutingResponse =
   | { readonly kind: 'route'; readonly requestId: number; readonly route: Route | null; readonly neededRangePc: number | null }
-  | { readonly kind: 'links'; readonly requestId: number; readonly segments: Float32Array };
+  | { readonly kind: 'links'; readonly requestId: number; readonly segments: Float32Array }
+  /** The question threw in the worker. Sent back so the request settles instead of waiting for good. */
+  | { readonly kind: 'failed'; readonly requestId: number; readonly message: string };
 
 /** A spatial index over a catalogue sent as a {@link RoutingCatalogue}. */
 export function indexCatalogue({ ids, positions }: RoutingCatalogue): StarNeighbourhood {

src/app/shared/astro/routing.worker.ts

@@ -16,6 +16,10 @@ addEventListener('message', ({ data }: MessageEvent<RoutingCatalogue | RoutingRe
     return;
   }
   // The catalogue is always the first message, and a worker's messages arrive in order.
-  const response = answerRouting(index!, data);
-  postMessage(response, response.kind === 'links' ? [response.segments.buffer] : []);
+  try {
+    const response = answerRouting(index!, data);
+    postMessage(response, response.kind === 'links' ? [response.segments.buffer] : []);
+  } catch (error) {
+    postMessage({ kind: 'failed', requestId: data.requestId, message: error instanceof Error ? error.message : String(error) });
+  }
 });