fix: keep page errors local and preserve Workspace error details

tools/web-ux/browser-tests/ticket_shell_test.ts

@@ -72,6 +72,49 @@ async function queryRequests(base: string) {
   return requests.filter((row: { path: string }) => row.path === "/tickets/query");
 }
 
+Deno.test("Ticket parser failures stay local, retain Workspace navigation, and recover on retry", async () => {
+  await withFixture(async (browser, base) => {
+    const page = await browser.newPage();
+    const wire = await detail(base, "T-1");
+    delete wire.initial_post;
+    let invalid = true;
+    await page.route("**/api/w/tickets/tickets/T-1", async (route) => {
+      if (invalid) await route.fulfill({ status: 200, json: wire });
+      else await route.continue();
+    });
+    await page.goto(`${base}/w/tickets/tickets/T-1`);
+    await page.getByRole("alert").filter({ hasText: "Ticket detail.initial_post must be an object" }).waitFor();
+    assertEquals(await page.getByText("The selected Workspace cannot be opened", { exact: true }).count(), 0);
+    assertEquals(await page.getByText("Workspace unavailable", { exact: true }).count(), 0);
+    assert(await page.getByRole("navigation", { name: "Current workspace location" }).isVisible());
+    invalid = false;
+    await page.getByRole("button", { name: "Retry", exact: true }).click();
+    await page.locator(".ticket-detail-header").waitFor();
+    assertEquals(await page.getByRole("alert").filter({ hasText: "initial_post must be an object" }).count(), 0);
+    await page.close();
+  });
+});
+
+Deno.test("Workspace HTTP failure retains its real status and recovers without recreating the Workspace", async () => {
+  await withFixture(async (browser, base) => {
+    const page = await browser.newPage();
+    let unavailable = true;
+    await page.route("**/api/w/tickets/workspace", async (route) => {
+      if (unavailable) await route.fulfill({ status: 503, body: "private server failure" });
+      else await route.continue();
+    });
+    await page.goto(`${base}/w/tickets/tickets/T-1`);
+    await page.getByRole("heading", { name: "Workspace details could not be loaded" }).waitFor();
+    assert(await page.locator(".workspace-page [role=alert]").filter({ hasText: "HTTP 503" }).isVisible());
+    assertEquals(await page.getByText("The selected Workspace cannot be opened", { exact: true }).count(), 0);
+    assertEquals(await page.getByText("private server failure", { exact: true }).count(), 0);
+    unavailable = false;
+    await page.getByRole("button", { name: "Retry", exact: true }).click();
+    await page.locator(".ticket-detail-header").waitFor();
+    await page.close();
+  });
+});
+
 Deno.test("single Ticket query searches beyond loaded rows and preserves qualifiers on pagination", async () => {
   await withFixture(async (browser, base) => {
     const page = await browser.newPage();

web/workspace/src/lib/workspace/api/http.ts

@@ -12,6 +12,8 @@ import {
 export type ApiResult<T> = {
   data: T | null;
   error: string | null;
+  /** HTTP failure status, when a response was received; absent for local/transport failures. */
+  status?: number;
 };
 
 export type { SkillCatalogResponse, SkillDetailResponse };
@@ -19,6 +21,8 @@ export type { SkillCatalogResponse, SkillDetailResponse };
 export type JsonLoadPolicy = {
   diagnosticLabel: string;
   maxResponseBytes: number;
+  /** Only explicitly trusted validator errors may expose bounded field diagnostics. */
+  describeValidationError?: (error: unknown) => string | undefined;
 };
 
 const SKILL_API_LOAD_POLICY: JsonLoadPolicy = {
@@ -96,6 +100,7 @@ export async function loadJson<T>(
   parse: (value: unknown) => T = (value) => value as T,
   policy?: JsonLoadPolicy,
 ): Promise<ApiResult<T>> {
+  let stage: "request" | "decode" | "validate" = "request";
   try {
     const response = await fetchFn(path, init);
     if (!response.ok) {
@@ -103,6 +108,7 @@ export async function loadJson<T>(
         await response.body?.cancel();
         return {
           data: null,
+          status: response.status,
           error:
             `${policy.diagnosticLabel} request failed with HTTP ${response.status}`,
         };
@@ -110,19 +116,31 @@ export async function loadJson<T>(
       const text = await response.text();
       return {
         data: null,
+        status: response.status,
         error: text || `${path} request failed (${response.status})`,
       };
     }
+    stage = "decode";
     const payload: unknown = policy
       ? await readBoundedJson(response, policy.maxResponseBytes)
       : await response.json();
+    stage = "validate";
     return { data: parse(payload), error: null };
   } catch (error) {
     if (policy) {
+      const validationDiagnostic = stage === "validate"
+        ? policy.describeValidationError?.(error)
+        : undefined;
       const diagnostic = error instanceof SkillApiContractError
         ? error.message
+        : validationDiagnostic !== undefined
+        ? `${policy.diagnosticLabel}: ${validationDiagnostic}`
         : error instanceof ResponseByteLimitError
         ? `${policy.diagnosticLabel} response exceeds its byte limit`
+        : stage === "request"
+        ? `${policy.diagnosticLabel} request could not be completed`
+        : stage === "decode"
+        ? `${policy.diagnosticLabel} response could not be decoded as JSON`
         : `${policy.diagnosticLabel} response is invalid`;
       return { data: null, error: diagnostic.slice(0, 256) };
     }

web/workspace/src/lib/workspace/api/ticket-browser.test.ts

@@ -2,8 +2,10 @@ declare const Deno: {
   test(name: string, fn: () => Promise<void> | void): void;
 };
 
+import { loadJson } from "./http.ts";
 import { fixturePost } from "../home/dashboard.test-fixtures.ts";
 import {
+  TICKET_BROWSER_API_LOAD_POLICY,
   parseTicketEvent,
   parseMergeRequestDetailResponse,
   parseMergeRequestListResponse,
@@ -64,12 +66,37 @@ Deno.test("Ticket post parser rejects absent safety fields and unknown wire fiel
   }
   assertThrows(() => parseTicketEvent({ ...fixturePost("Post"), editable: "yes" }), "editable");
   assertThrows(() => parseTicketEvent({ ...fixturePost("Post"), edited_by: 7 }), "edited_by");
-  assertThrows(() => parseTicketEvent({ ...fixturePost("Post"), surprise: true }), "unknown field surprise");
+  assertThrows(() => parseTicketEvent({ ...fixturePost("Post"), surprise: true }), "unknown field");
   const detail: Record<string, unknown> = { ...ticketDetailFixture() };
   delete detail.initial_post;
   assertThrows(() => parseTicketDetail(detail), "initial_post");
 });
 
+Deno.test("Ticket load diagnostics retain the failed field without leaking response contents", async () => {
+  const secret = "PRIVATE_RESPONSE_TEXT";
+  const wire: Record<string, unknown> = { ...ticketDetailFixture(), body: secret };
+  delete wire.initial_post;
+  const load = (payload: unknown) => loadJson(
+    (async () => Response.json(payload)) as typeof fetch,
+    "/api/w/workspace-a/tickets/T-1",
+    undefined,
+    parseTicketDetail,
+    TICKET_BROWSER_API_LOAD_POLICY,
+  );
+  const missing = await load(wire);
+  assertEquals(missing.data, null);
+  assertEquals(missing.error, "Ticket Browser API: Ticket detail.initial_post must be an object");
+  assertEquals(missing.status, undefined);
+  const unknown = await load({ ...ticketDetailFixture(), [secret]: true });
+  assertEquals(unknown.error, "Ticket Browser API: Ticket detail contains unknown field");
+  const nested = ticketDetailFixture();
+  const malformed = await load({ ...nested, initial_post: { ...nested.initial_post, attributes: { [secret]: 5 } } });
+  assertEquals(malformed.error, "Ticket Browser API: Ticket detail.initial_post.attributes value must be a string");
+  for (const result of [missing, unknown, malformed]) {
+    assertEquals(result.error?.includes(secret), false);
+  }
+});
+
 Deno.test("Ticket Browser parser accepts the generated Ticket list shape", () => {
   const parsed = parseTicketListResponse({
     workspace_id: "workspace-a",
@@ -105,7 +132,7 @@ Deno.test("Ticket Browser parser rejects unknown fields and out-of-range limits"
   };
   assertThrows(
     () => parseTicketListResponse({ ...fixture, stale: true }),
-    "unknown field stale",
+    "unknown field",
   );
   assertThrows(
     () => parseTicketListResponse({ ...fixture, limit: 1001 }),
@@ -296,7 +323,7 @@ Deno.test("Ticket Browser parser accepts target collections and rejects singular
         repository_key: "main",
         ref_selector: "develop",
       }),
-    "unknown field repository_key",
+    "unknown field",
   );
 });
 
@@ -393,11 +420,11 @@ Deno.test("Merge Request summaries reject missing and malformed tagged source ob
         { status: "unavailable", code: "x".repeat(262_145) },
         "code exceeds its length limit",
       ],
-      [{ status: "observed", code: "stale" }, "unknown field code"],
-      [{ status: "not_required", code: "stale" }, "unknown field code"],
+      [{ status: "observed", code: "stale" }, "unknown field"],
+      [{ status: "not_required", code: "stale" }, "unknown field"],
       [
         { status: "unavailable", code: "missing", extra: true },
-        "unknown field extra",
+        "unknown field",
       ],
     ] as const
   ) {
@@ -529,7 +556,7 @@ Deno.test("Ticket Browser parser validates the canonical Merge Request thread",
         ...parsed,
         thread: [{ ...parsed.thread[0], unexpected: true }],
       }),
-    "unknown field unexpected",
+    "unknown field",
   );
 });
 
@@ -692,7 +719,7 @@ Deno.test("Ticket tag projections reject missing collections and malformed ident
           "last_operation_key must be a string",
         ],
         [{ ...tag, deleted: "false" }, "deleted must be a boolean"],
-        [{ ...tag, state: "closed" }, "unknown field state"],
+        [{ ...tag, state: "closed" }, "unknown field"],
       ] as const
     ) {
       assertThrows(() => parse([value]), message);

web/workspace/src/lib/workspace/api/ticket-browser.ts

@@ -54,10 +54,14 @@ import type {
   WorkspaceTag,
 } from "#lib/generated/ticket-api.ts";
 
+export class TicketBrowserContractError extends Error {}
+
 export const TICKET_BROWSER_API_MAX_RESPONSE_BYTES = 4 * 1024 * 1024;
 export const TICKET_BROWSER_API_LOAD_POLICY = {
   diagnosticLabel: "Ticket Browser API",
   maxResponseBytes: TICKET_BROWSER_API_MAX_RESPONSE_BYTES,
+  describeValidationError: (error: unknown) =>
+    error instanceof TicketBrowserContractError ? error.message : undefined,
 } as const;
 
 const MAX_STRING_LENGTH = 262_144;
@@ -66,7 +70,7 @@ const MAX_MAP_ENTRIES = 4_096;
 
 function object(value: unknown, label: string): Record<string, unknown> {
   if (typeof value !== "object" || value === null || Array.isArray(value)) {
-    throw new Error(`${label} must be an object`);
+    throw new TicketBrowserContractError(`${label} must be an object`);
   }
   return value as Record<string, unknown>;
 }
@@ -78,20 +82,20 @@ function exact(
 ): void {
   const unexpected = Object.keys(value).find((key) => !allowed.includes(key));
   if (unexpected !== undefined) {
-    throw new Error(`${label} contains unknown field ${unexpected}`);
+    throw new TicketBrowserContractError(`${label} contains unknown field`);
   }
 }
 
 function string(value: unknown, label: string): string {
-  if (typeof value !== "string") throw new Error(`${label} must be a string`);
+  if (typeof value !== "string") throw new TicketBrowserContractError(`${label} must be a string`);
   if (value.length > MAX_STRING_LENGTH) {
-    throw new Error(`${label} exceeds its length limit`);
+    throw new TicketBrowserContractError(`${label} exceeds its length limit`);
   }
   return value;
 }
 
 function boolean(value: unknown, label: string): boolean {
-  if (typeof value !== "boolean") throw new Error(`${label} must be a boolean`);
+  if (typeof value !== "boolean") throw new TicketBrowserContractError(`${label} must be a boolean`);
   return value;
 }
 
@@ -105,7 +109,7 @@ function integer(
     typeof value !== "number" || !Number.isSafeInteger(value) ||
     value < minimum || value > maximum
   ) {
-    throw new Error(
+    throw new TicketBrowserContractError(
       `${label} must be an integer from ${minimum} through ${maximum}`,
     );
   }
@@ -128,9 +132,9 @@ function array<T>(
   label: string,
   parse: (item: unknown, label: string) => T,
 ): T[] {
-  if (!Array.isArray(value)) throw new Error(`${label} must be an array`);
+  if (!Array.isArray(value)) throw new TicketBrowserContractError(`${label} must be an array`);
   if (value.length > MAX_COLLECTION_LENGTH) {
-    throw new Error(`${label} exceeds its item limit`);
+    throw new TicketBrowserContractError(`${label} exceeds its item limit`);
   }
   return value.map((item, index) => parse(item, `${label}[${index}]`));
 }
@@ -143,12 +147,12 @@ function stringMap(value: unknown, label: string): Record<string, string> {
   const source = object(value, label);
   const entries = Object.entries(source);
   if (entries.length > MAX_MAP_ENTRIES) {
-    throw new Error(`${label} exceeds its entry limit`);
+    throw new TicketBrowserContractError(`${label} exceeds its entry limit`);
   }
   return Object.fromEntries(
     entries.map(([key, item]) => [
       string(key, `${label} key`),
-      string(item, `${label}.${key}`),
+      string(item, `${label} value`),
     ]),
   );
 }
@@ -199,7 +203,7 @@ function parseInvalidProjectRecord(
 
 function parseTicketState(value: unknown, label: string): BrowserTicketState {
   if (value !== "open" && value !== "closed") {
-    throw new Error(`${label} is invalid`);
+    throw new TicketBrowserContractError(`${label} is invalid`);
   }
   return value;
 }
@@ -226,7 +230,7 @@ function parseCaseAction(value: unknown, label: string): TicketCaseAction {
     return { action: "reopen" };
   }
   if (item.action !== "close" && item.action !== "correct_closure") {
-    throw new Error(`${label}.action is invalid`);
+    throw new TicketBrowserContractError(`${label}.action is invalid`);
   }
   exact(item, ["action", "reason"], label);
   return {
@@ -351,7 +355,7 @@ export function parseWorkspaceTag(
   ], label);
   const id = string(item.id, `${label}.id`);
   if (id.trim().length === 0 || new TextEncoder().encode(id).length > 128) {
-    throw new Error(`${label}.id must be nonempty and at most 128 UTF-8 bytes`);
+    throw new TicketBrowserContractError(`${label}.id must be nonempty and at most 128 UTF-8 bytes`);
   }
   return {
     workspace_id: string(item.workspace_id, `${label}.workspace_id`),
@@ -588,7 +592,7 @@ function parseTicketAssignmentPrincipal(
     exact(item, ["agent_key", "kind"], label);
     return { kind, agent_key: string(item.agent_key, `${label}.agent_key`) };
   }
-  throw new Error(`${label}.kind is invalid`);
+  throw new TicketBrowserContractError(`${label}.kind is invalid`);
 }
 
 function parseTicketAssignmentSummary(
@@ -653,7 +657,7 @@ function parseTicketRoleAssignmentRecord(
   ], label);
   const role = string(item.role, `${label}.role`);
   if (!["orchestrator", "worker", "owner", "contributor"].includes(role)) {
-    throw new Error(`${label}.role is invalid`);
+    throw new TicketBrowserContractError(`${label}.role is invalid`);
   }
   return {
     assigned_at: string(item.assigned_at, `${label}.assigned_at`),
@@ -681,7 +685,7 @@ export function parseAssignmentTracking(
   );
   const status = string(item.status, `${label}.status`);
   if (status !== "waiting" && status !== "inprogress" && status !== "done") {
-    throw new Error(`${label}.status is invalid`);
+    throw new TicketBrowserContractError(`${label}.status is invalid`);
   }
   return {
     status,
@@ -715,7 +719,7 @@ function parseAssignmentRelease(
   ], label);
   const action = string(item.action, `${label}.action`);
   if (action !== "unassigned" && action !== "replaced") {
-    throw new Error(`${label}.action is invalid`);
+    throw new TicketBrowserContractError(`${label}.action is invalid`);
   }
   return {
     action,
@@ -839,7 +843,7 @@ function parseSourceRefObservation(
     exact(item, ["status", "code"], label);
     return { status, code: string(item.code, `${label}.code`) };
   }
-  throw new Error(`${label}.status is invalid`);
+  throw new TicketBrowserContractError(`${label}.status is invalid`);
 }
 
 function parseTicketMergeRequestSummary(
@@ -1085,7 +1089,7 @@ function parseTicketTarget(value: unknown, label: string): TicketTarget {
   exact(item, ["access", "ref_selector", "repository_key"], label);
   const access = string(item.access, `${label}.access`);
   if (access !== "read_only" && access !== "read_write") {
-    throw new Error(`${label}.access is invalid`);
+    throw new TicketBrowserContractError(`${label}.access is invalid`);
   }
   return {
     access,
@@ -1234,7 +1238,7 @@ export function parseTicketRecordRef(value: unknown): TicketRef {
   exact(item, ["id", "resource_key", "slug", "status"], label);
   const status = string(item.status, `${label}.status`);
   if (status !== "Open" && status !== "Closed") {
-    throw new Error(`${label}.status is invalid`);
+    throw new TicketBrowserContractError(`${label}.status is invalid`);
   }
   return {
     id: string(item.id, `${label}.id`),
@@ -1502,7 +1506,7 @@ function parseReviewFinding(value: unknown, label: string): ReviewFinding {
   exact(item, ["body", "code", "line", "path", "severity"], label);
   const severity = string(item.severity, `${label}.severity`);
   if (!["blocker", "major", "minor", "note"].includes(severity)) {
-    throw new Error(`${label}.severity is invalid`);
+    throw new TicketBrowserContractError(`${label}.severity is invalid`);
   }
   return {
     body: string(item.body, `${label}.body`),
@@ -1576,7 +1580,7 @@ function parseMergeRequestThreadEvent(
     ], label);
     const decision = string(item.decision, `${label}.decision`);
     if (!["approve", "request_changes"].includes(decision)) {
-      throw new Error(`${label}.decision is invalid`);
+      throw new TicketBrowserContractError(`${label}.decision is invalid`);
     }
     return {
       ...eventBase,
@@ -1658,10 +1662,10 @@ function parseMergeRequestThreadEvent(
     const strategy = string(item.strategy, `${label}.strategy`);
     const resolution = string(item.resolution, `${label}.resolution`);
     if (!["fast_forward", "merge"].includes(strategy)) {
-      throw new Error(`${label}.strategy is invalid`);
+      throw new TicketBrowserContractError(`${label}.strategy is invalid`);
     }
     if (!["none", "clean", "conflicts_resolved"].includes(resolution)) {
-      throw new Error(`${label}.resolution is invalid`);
+      throw new TicketBrowserContractError(`${label}.resolution is invalid`);
     }
     return {
       ...eventBase,
@@ -1688,7 +1692,7 @@ function parseMergeRequestThreadEvent(
       ),
     };
   }
-  throw new Error(`${label}.kind is invalid`);
+  throw new TicketBrowserContractError(`${label}.kind is invalid`);
 }
 
 function parseMergeRequestRef(
@@ -1743,7 +1747,7 @@ export function parseMergeRequestDetailResponse(
   ], label);
   const state = string(item.state, `${label}.state`);
   if (!["open", "merged", "closed"].includes(state)) {
-    throw new Error(`${label}.state is invalid`);
+    throw new TicketBrowserContractError(`${label}.state is invalid`);
   }
   return {
     created_at: string(item.created_at, `${label}.created_at`),

web/workspace/src/lib/workspace/navigation/DeferredPage.svelte

@@ -13,6 +13,31 @@
   let resolved = $state.raw<{ path: string; value: ResolvedPageData<T> } | null>(null);
   let failure = $state.raw<{ path: string; value: DeferredFailure } | null>(null);
   let loading = $state(true);
+  let renderFailure = $state.raw<{ path: string; error: unknown } | null>(null);
+  let recoveryVersion = $state(0);
+  let retrying = $state(false);
+  let retryFailure = $state<string | null>(null);
+  const errorMessage = (error: unknown) => {
+    // SvelteKit may transform render exceptions into a serialized App.Error.
+    if (error !== null && typeof error === 'object' && 'message' in error && typeof error.message === 'string') {
+      return error.message;
+    }
+    return String(error);
+  };
+
+  async function retry() {
+    if (retrying || loading) return;
+    const requestedPath = path;
+    retrying = true;
+    retryFailure = null;
+    try {
+      await invalidateAll();
+    } catch (error) {
+      if (path === requestedPath) retryFailure = errorMessage(error);
+    } finally {
+      retrying = false;
+    }
+  }
   const path = $derived(identity ?? page.url.pathname);
   const current = $derived(resolved?.path === path ? resolved.value : null);
   const currentFailure = $derived(failure?.path === path ? failure.value : null);
@@ -23,9 +48,14 @@
     let active = true;
     loading = true;
     failure = null;
+    retryFailure = null;
     void resolvePageData(requestedData).then(async (result) => {
       if (!active) return;
       if (result.ok) {
+        // Never reset a failed boundary against stale data, including while Retry
+        // invalidation is pending. Remount only after this load has fresh data.
+        if (renderFailure?.path === requestedPath) recoveryVersion += 1;
+        renderFailure = null;
         resolved = { path: requestedPath, value: result.data };
         loading = false;
       } else if (result.failure.redirect) {
@@ -51,7 +81,7 @@
 </script>
 
 <svelte:head>
-  {#if currentFailure}<title>{title} · Unavailable</title>
+  {#if currentFailure || renderFailure?.path === path}<title>{title} · Error</title>
   {:else if !current}<title>{title} · Loading</title>{/if}
 </svelte:head>
 
@@ -59,11 +89,26 @@
   <section class="workspace-page deferred-page" aria-label={title}>
     <h1>{title}</h1>
     <p role="alert">{currentFailure.message}</p>
-    <button type="button" class="workspace-secondary-button" onclick={() => invalidateAll()}>Retry</button>
+    {#if retryFailure}<p role="alert">{retryFailure}</p>{/if}
+    <button type="button" class="workspace-secondary-button" disabled={retrying || loading} onclick={retry}>Retry</button>
   </section>
 {:else if current}
   {#if loading}<p class="deferred-refresh" role="status">Updating…</p>{/if}
-  {#key path}{@render children(current)}{/key}
+  {#key path}
+    {#key recoveryVersion}
+      <svelte:boundary onerror={(error) => { renderFailure = { path, error }; }}>
+        {@render children(current)}
+        {#snippet failed(error)}
+          <section class="workspace-page deferred-page" aria-label={title}>
+            <h1>{title}</h1>
+            <p role="alert">{errorMessage(error)}</p>
+            {#if retryFailure}<p role="alert">{retryFailure}</p>{/if}
+            <button type="button" class="workspace-secondary-button" disabled={retrying || loading} onclick={retry}>Retry</button>
+          </section>
+        {/snippet}
+      </svelte:boundary>
+    {/key}
+  {/key}
 {:else}
   <section class="workspace-page deferred-page" aria-label={title} aria-busy="true">
     <h1>{title}</h1>

web/workspace/src/lib/workspace/navigation/DeferredPageHarness.svelte

@@ -0,0 +1,31 @@
+<script lang="ts">
+  import DeferredPage from './DeferredPage.svelte';
+  import DeferredPageTestContent from './DeferredPageTestContent.svelte';
+  import type { DeferredResult } from './deferred.ts';
+
+  let { data, identity, onConstruct }: {
+    data: {
+      deferredWorkspace?: Promise<DeferredResult<{ workspace: string }>>;
+      deferredPage: Promise<DeferredResult<{ label: string; message?: string; serializedError?: boolean }>>;
+    };
+    identity: string;
+    onConstruct?: (label: string) => void;
+  } = $props();
+</script>
+
+<svelte:boundary>
+  <header>Valid Workspace</header>
+  <aside aria-label="Workspace sidebar"><a href="/w/team/tickets">Tickets</a></aside>
+  <main>
+    <DeferredPage {data} {identity} title="Ticket">
+      {#snippet children(content)}
+        <DeferredPageTestContent {content} {onConstruct} />
+      {/snippet}
+    </DeferredPage>
+  </main>
+  {#snippet failed()}
+    <h1>Workspace unavailable</h1>
+    <p>Workspace removed</p>
+    <button type="button">Create Workspace</button>
+  {/snippet}
+</svelte:boundary>

web/workspace/src/lib/workspace/navigation/DeferredPageTestContent.svelte

@@ -0,0 +1,19 @@
+<script lang="ts">
+  let { content, onConstruct }: {
+    content: { label: string; message?: string; serializedError?: boolean };
+    onConstruct?: (label: string) => void;
+  } = $props();
+
+  // Model PageContent's constructor check when an ApiResult has null data.
+  function construct() {
+    onConstruct?.(content.label);
+    if (content.message) {
+      if (content.serializedError) throw { message: content.message };
+      throw new Error(content.message);
+    }
+  }
+  construct();
+</script>
+
+<p>{content.label}</p>
+<label>Draft<input aria-label="Draft" /></label>

web/workspace/src/lib/workspace/navigation/deferred-page.browser.spec.ts

@@ -1,8 +1,9 @@
 // @vitest-environment happy-dom
-import { cleanup, fireEvent, render, waitFor } from "@testing-library/svelte";
+import { cleanup, fireEvent, render, screen, waitFor } from "@testing-library/svelte";
 import { afterEach, expect, test, vi } from "vitest";
 import { createRawSnippet, tick } from "svelte";
 import DeferredPage from "./DeferredPage.svelte";
+import DeferredPageHarness from "./DeferredPageHarness.svelte";
 import { type DeferredResult, settle } from "./deferred.ts";
 
 const navigation = vi.hoisted(() => ({
@@ -19,6 +20,7 @@ afterEach(() => {
   cleanup();
   vi.clearAllMocks();
   navigation.to = null;
+  navigation.invalidateAll.mockImplementation(async () => {});
 });
 function gate<T>() {
   let resolve!: (value: T) => void;
@@ -141,3 +143,148 @@ test("old canonical redirect cannot overtake a navigation still loading its rout
   await tick();
   expect(navigation.goto).not.toHaveBeenCalled();
 });
+
+function expectWorkspacePreserved() {
+  expect(screen.getByText("Valid Workspace")).toBeTruthy();
+  expect(screen.getByRole("complementary", { name: "Workspace sidebar" })).toBeTruthy();
+  expect(screen.queryByText("Workspace unavailable")).toBeNull();
+  expect(screen.queryByText("Workspace removed")).toBeNull();
+  expect(screen.queryByRole("button", { name: "Create Workspace" })).toBeNull();
+}
+
+const renderError = 'Ticket lookup failed: <img src=x onerror="throw 1">';
+const brokenData = () => ({ deferredPage: settle({ label: "Broken ticket", message: renderError }) });
+
+test("child constructor error stays local, with the actual message escaped below the page title", async () => {
+  const view = render(DeferredPageHarness, { data: brokenData(), identity: "team:ticket-a" });
+  const alert = await view.findByRole("alert");
+  expect(view.getByRole("heading", { name: "Ticket" })).toBeTruthy();
+  expect(alert.textContent).toBe(renderError);
+  expect(alert.querySelector("img")).toBeNull();
+  expect(view.container.querySelector("main h1 + p")).toBe(alert);
+  expect(view.queryByLabelText("Draft")).toBeNull();
+  expectWorkspacePreserved();
+});
+
+test("serialized SvelteKit App.Error displays its message, not object coercion", async () => {
+  const view = render(DeferredPageHarness, {
+    data: { deferredPage: settle({ label: "Broken ticket", message: renderError, serializedError: true }) },
+    identity: "team:ticket-a",
+  });
+  const alert = await view.findByRole("alert");
+  expect(alert.textContent).toBe(renderError);
+  expect(alert.querySelector("img")).toBeNull();
+  expectWorkspacePreserved();
+});
+
+test("Retry waits for new successful deferred data before remounting a failed child", async () => {
+  const onConstruct = vi.fn();
+  const view = render(DeferredPageHarness, { data: brokenData(), identity: "team:ticket-a", onConstruct });
+  await view.findByRole("alert");
+  const invalidation = gate<void>();
+  navigation.invalidateAll.mockImplementationOnce(() => invalidation.promise);
+  await fireEvent.click(view.getByRole("button", { name: "Retry" }));
+  expect(navigation.invalidateAll).toHaveBeenCalledOnce();
+  expect(onConstruct).toHaveBeenCalledTimes(1);
+  expect((view.getByRole("button", { name: "Retry" }) as HTMLButtonElement).disabled).toBe(true);
+
+  const refresh = gate<DeferredResult<Content>>();
+  await view.rerender({ data: { deferredPage: refresh.promise }, identity: "team:ticket-a", onConstruct });
+  invalidation.resolve();
+  await tick();
+  expect(view.getByRole("alert").textContent).toBe(renderError);
+  expect(onConstruct).toHaveBeenCalledTimes(1);
+  expect((view.getByRole("button", { name: "Retry" }) as HTMLButtonElement).disabled).toBe(true);
+  expectWorkspacePreserved();
+
+  refresh.resolve({ ok: true, data: { label: "Recovered ticket" } });
+  await view.findByText("Recovered ticket");
+  expect(onConstruct).toHaveBeenCalledTimes(2);
+  expect(view.queryByRole("alert")).toBeNull();
+  expect(view.queryByRole("status")).toBeNull();
+  expect(view.getByLabelText("Draft")).toBeTruthy();
+  expectWorkspacePreserved();
+});
+
+test("invalidation without new data never resets the boundary against stale failed data", async () => {
+  const onConstruct = vi.fn();
+  const view = render(DeferredPageHarness, { data: brokenData(), identity: "team:ticket-a", onConstruct });
+  await view.findByRole("alert");
+  await fireEvent.click(view.getByRole("button", { name: "Retry" }));
+  await tick();
+  expect(onConstruct).toHaveBeenCalledTimes(1);
+  expect(view.getByRole("alert").textContent).toBe(renderError);
+  expectWorkspacePreserved();
+});
+
+test("failed replacement data remains local and another fresh result can recover", async () => {
+  const onConstruct = vi.fn();
+  const view = render(DeferredPageHarness, { data: brokenData(), identity: "team:ticket-a", onConstruct });
+  await view.findByRole("alert");
+  await view.rerender({
+    data: { deferredPage: settle({ label: "Still broken", message: "Ticket still missing" }) },
+    identity: "team:ticket-a", onConstruct,
+  });
+  await waitFor(() => expect(view.getByRole("alert").textContent).toBe("Ticket still missing"));
+  expect(onConstruct).toHaveBeenCalledTimes(2);
+  expectWorkspacePreserved();
+  await view.rerender({ data: { deferredPage: settle({ label: "Recovered" }) }, identity: "team:ticket-a", onConstruct });
+  await view.findByText("Recovered");
+  expect(view.queryByRole("alert")).toBeNull();
+});
+
+test("changing route identity clears a failed boundary and rejects late cross-workspace results", async () => {
+  const onConstruct = vi.fn();
+  const view = render(DeferredPageHarness, { data: brokenData(), identity: "team:ticket-a", onConstruct });
+  await view.findByRole("alert");
+  const stale = gate<DeferredResult<Content>>();
+  await view.rerender({ data: { deferredPage: stale.promise }, identity: "team:ticket-a", onConstruct });
+  const workspace = gate<DeferredResult<{ workspace: string }>>();
+  const destination = gate<DeferredResult<Content>>();
+  await view.rerender({
+    data: { deferredWorkspace: workspace.promise, deferredPage: destination.promise },
+    identity: "other-team:ticket-b", onConstruct,
+  });
+  expect(view.queryByRole("alert")).toBeNull();
+  expect(view.getByRole("status").textContent).toBe("Loading…");
+  expect(view.queryByLabelText("Draft")).toBeNull();
+  destination.resolve({ ok: true, data: { label: "Other Workspace ticket" } });
+  stale.resolve({ ok: true, data: { label: "Stale team ticket" } });
+  await tick();
+  expect(onConstruct).toHaveBeenCalledTimes(1);
+  expect(view.queryByText("Stale team ticket")).toBeNull();
+  workspace.resolve({ ok: true, data: { workspace: "other-team" } });
+  await view.findByText("Other Workspace ticket");
+  expect(onConstruct.mock.calls.map(([label]) => label)).toEqual(["Broken ticket", "Other Workspace ticket"]);
+  expect(view.queryByRole("alert")).toBeNull();
+  expectWorkspacePreserved();
+});
+
+test("a failed deferred Retry never reconstructs the old failed child", async () => {
+  const onConstruct = vi.fn();
+  const view = render(DeferredPageHarness, { data: brokenData(), identity: "team:ticket-a", onConstruct });
+  await view.findByRole("alert");
+  await view.rerender({
+    data: { deferredPage: Promise.resolve({ ok: false, failure: { message: "Ticket access denied", status: 403, redirect: null } }) },
+    identity: "team:ticket-a", onConstruct,
+  });
+  await waitFor(() => expect(view.getByRole("alert").textContent).toBe("Ticket access denied"));
+  expect(onConstruct).toHaveBeenCalledTimes(1);
+  expect(view.queryByLabelText("Draft")).toBeNull();
+  expectWorkspacePreserved();
+  await view.rerender({ data: { deferredPage: settle({ label: "Authorized ticket" }) }, identity: "team:ticket-a", onConstruct });
+  await view.findByText("Authorized ticket");
+  expect(onConstruct).toHaveBeenCalledTimes(2);
+  expect(view.queryByRole("alert")).toBeNull();
+});
+
+test("a failed Retry request is handled locally without losing the original render error", async () => {
+  const view = render(DeferredPageHarness, { data: brokenData(), identity: "team:ticket-a" });
+  await view.findByRole("alert");
+  navigation.invalidateAll.mockRejectedValueOnce(new Error("Reload failed"));
+  await fireEvent.click(view.getByRole("button", { name: "Retry" }));
+  await view.findByText("Reload failed");
+  expect(view.getByText(renderError)).toBeTruthy();
+  expect((view.getByRole("button", { name: "Retry" }) as HTMLButtonElement).disabled).toBe(false);
+  expectWorkspacePreserved();
+});

web/workspace/src/routes/w/[workspaceId]/+error.svelte

@@ -1,23 +1,16 @@
 <script lang="ts">
   import { page } from "$app/state";
-  import "#lib/workspace/styles/workspace-catalog.css";
-
-  const workspaceId = $derived(page.params.workspaceId ?? "unknown");
+  import "#lib/workspace/styles/workspace-pages.css";
 </script>
 
-<svelte:head><title>Workspace unavailable · Yoi</title></svelte:head>
+<svelte:head><title>Page error · Yoi</title></svelte:head>
 
-<div class="workspace-catalog-shell">
-  <section class="workspace-empty-state">
-    <p class="workspace-catalog-eyebrow">Workspace unavailable</p>
-    <h1>The selected Workspace cannot be opened</h1>
-    <p>
-      <code>{workspaceId}</code> may have been removed, become inaccessible, or no longer exist on
-      this Backend. No state from a previously selected Workspace was retained.
-    </p>
-    <div class="workspace-switcher-actions">
-      <a href="/">Choose another Workspace</a>
-      <a href="/#workspace-create-title">Create Workspace</a>
+<section class="workspace-page">
+  <h1>Unable to display this page</h1>
+  <p role="alert">{page.error?.message ?? "An unexpected error occurred."}</p>
+  <p>Error {page.status}</p>
+  <div class="workspace-toolbar">
+    <button type="button" class="workspace-secondary-button" onclick={() => window.location.reload()}>Reload page</button>
+    <a href="/">Home</a>
   </div>
 </section>
-</div>

web/workspace/src/routes/w/[workspaceId]/+layout.svelte

@@ -91,13 +91,13 @@
 />
 
 <svelte:head>
-  {#if workspaceError}<title>Workspace · Unavailable</title>
+  {#if workspaceError}<title>Workspace · Load error</title>
   {:else if !workspace}<title>Workspace · Loading</title>{/if}
 </svelte:head>
 
 {#if workspaceError}
   <section class="workspace-page">
-    <h1>Workspace unavailable</h1>
+    <h1>Workspace details could not be loaded</h1>
     <p role="alert">{workspaceError}</p>
     <button type="button" class="workspace-secondary-button" onclick={() => invalidateAll()}>Retry</button>
   </section>

web/workspace/src/routes/w/[workspaceId]/+layout.ts

@@ -25,9 +25,13 @@ async function loadWorkspace(fetch: Parameters<LayoutLoad>[0]["fetch"], workspac
   const workspace = workspaceResult.data;
   const workspaceError = workspaceResult.error;
   if (!workspace) {
-    error(404, {
-      message: workspaceError ?? `Workspace ${workspaceId} is unavailable`,
-    });
+    const message = workspaceError ?? "Workspace details could not be loaded";
+    const status = workspaceResult.status;
+    if (status !== undefined && status >= 400 && status <= 599) {
+      error(status, message);
+    }
+    // Transport/decoding failures do not prove that the Workspace was removed.
+    throw new Error(message);
   }
 
   const repositories = repositoryResult.data;

web/workspace/src/routes/w/[workspaceId]/tickets/[ticketId]/+page.ts

@@ -1,4 +1,4 @@
-import { redirect } from "@sveltejs/kit";
+import { error, redirect } from "@sveltejs/kit";
 import { loadJson, workspaceApiPath } from "#lib/workspace/api/http.ts";
 import { loadWorkspaceRepositoryList } from "#lib/workspace/api/repositories.ts";
 import { parseBrowserWorkspaceOrchestratorResponse } from "#lib/workspace/api/workers.ts";
@@ -36,6 +36,14 @@ export const load = deferPage(async ({ fetch, params }: Parameters<PageLoad>[0])
       parseBrowserWorkspaceOrchestratorResponse,
     ),
   ]);
+  if (!ticket.data) {
+    const message = ticket.error ?? "Ticket details could not be loaded";
+    if (ticket.status !== undefined && ticket.status >= 400 && ticket.status <= 599) {
+      error(ticket.status, message);
+    }
+    // Expected read failures belong to the deferred loader, not component construction.
+    throw new Error(message);
+  }
   if (ticket.data) {
     const canonical = canonicalResourceReference(
       ticket.data.resource_key,

web/workspace/src/routes/w/[workspaceId]/workspace-error.browser.spec.ts

@@ -0,0 +1,58 @@
+// @vitest-environment happy-dom
+import { cleanup, fireEvent, render } from "@testing-library/svelte";
+import { afterEach, expect, test, vi } from "vitest";
+import WorkspaceError from "./+error.svelte";
+import { load } from "./+layout.ts";
+
+const state = vi.hoisted(() => ({
+  page: { params: { workspaceId: "workspace-a" }, status: 500, error: { message: "Ticket Browser API response is invalid" } },
+}));
+vi.mock("$app/state", () => state);
+afterEach(() => { cleanup(); vi.restoreAllMocks(); });
+
+test("a child page error preserves its message and never claims Workspace deletion", async () => {
+  const reload = vi.spyOn(window.location, "reload").mockImplementation(() => {});
+  const view = render(WorkspaceError);
+  expect(view.getByRole("alert").textContent).toBe("Ticket Browser API response is invalid");
+  expect(view.getByText("Error 500")).toBeTruthy();
+  expect(view.queryByText("The selected Workspace cannot be opened")).toBeNull();
+  expect(view.queryByText("Workspace unavailable")).toBeNull();
+  expect(view.queryByText("Create Workspace")).toBeNull();
+  expect(view.queryByText("Choose another Workspace")).toBeNull();
+  await fireEvent.click(view.getByRole("button", { name: "Reload page" }));
+  expect(reload).toHaveBeenCalledOnce();
+});
+
+async function loadFailure(workspaceFetch: () => Promise<Response>) {
+  const fetcher = vi.fn(async (input: RequestInfo | URL) => {
+    if (String(input).endsWith("/workspace")) return await workspaceFetch();
+    return new Response("repository lookup unavailable", { status: 503 });
+  });
+  return await load({ fetch: fetcher, params: { workspaceId: "workspace-a" } } as unknown as Parameters<typeof load>[0]).deferredWorkspace;
+}
+
+test.each([401, 403, 404, 500, 503])("Workspace HTTP %i is not rewritten as 404", async (status) => {
+  const result = await loadFailure(async () => new Response("private backend body", { status }));
+  expect(result.ok).toBe(false);
+  if (result.ok) throw new Error("expected a failed Workspace load");
+  expect(result.failure.status).toBe(status);
+  expect(result.failure.message).toBe(`Workspace API request failed with HTTP ${status}`);
+  expect(result.failure.message).not.toContain("private backend body");
+});
+
+test.each(["network", "json", "contract"] as const)("Workspace %s failures do not imply a missing Workspace", async (kind) => {
+  const result = await loadFailure(async () => {
+    if (kind === "network") throw new TypeError("Failed to fetch");
+    return kind === "json" ? new Response("not json") : Response.json({});
+  });
+  expect(result.ok).toBe(false);
+  if (result.ok) throw new Error("expected a failed Workspace load");
+  expect(result.failure.status).toBeNull();
+  expect(result.failure.message).toBe({
+    network: "Workspace API request could not be completed",
+    json: "Workspace API response could not be decoded as JSON",
+    contract: "Workspace API response is invalid",
+  }[kind]);
+  expect(result.failure.message).not.toContain("removed");
+  expect(result.failure.message).not.toContain("404");
+});