diff --git a/webui/.agents/skills/migrate-to-tanstack/SKILL.md b/webui/.agents/skills/migrate-to-tanstack/SKILL.md
index a27f593de..80686465f 100644
--- a/webui/.agents/skills/migrate-to-tanstack/SKILL.md
+++ b/webui/.agents/skills/migrate-to-tanstack/SKILL.md
@@ -11,15 +11,16 @@ description: Migrate a data-fetching endpoint from the legacy ExtensionRegistryS
 
 `src/extension-registry-service.ts` (`ExtensionRegistryService`, plus `service.admin.*`) holds every server call. Legacy, un-migrated consumers call these methods straight from a component, passing an `AbortController` and relying on `fetch-retry`'s 10-attempt backoff inside `sendRequest`. That drags along per-component `AbortController` refs, `useEffect` fetch-on-mount wiring, and hand-rolled loading/error state.
 
-Migrated endpoints instead go through a `use*` hook wrapping `useQuery`/`useMutation`, and retries move to the shared query client (`src/query-client.ts`). Roughly half the service is migrated — grep before assuming either state.
+Migrated endpoints instead go through a `use*` hook wrapping `useQuery`/`useMutation`, retries move to the shared query client (`src/query-client.ts`), and error handling moves into the transport via `sendStrictRequest`. Roughly half the service is migrated — grep before assuming either state.
 
 ## Steps
 
 1. **Find every consumer** of the method you're migrating: `grep -rn "service\.<method>\|\.<method>(" src`. List them — you'll migrate all of them or a named subset.
 
-2. **Decide the retry scope — ask if unsure.** Ideally the service method flips from `sendRequest` (retriable) to `sendNonRetriableRequest`, handing retries to TanStack. Only do that when **every** consumer is moving to a hook — a legacy consumer still calling the method directly would silently lose its retry. If you're migrating just one of several consumers, either leave the method retriable (the query then double-retries, tolerated in the interim) or confirm scope with the user. When the request doesn't make the consumer scope clear, ask.
+2. **Decide the retry scope — ask if unsure.** Ideally the service method flips from `sendRequest` (retriable) to `sendStrictRequest`, handing retries to TanStack. Only do that when **every** consumer is moving to a hook — a legacy consumer still calling the method directly would silently lose its retry *and* start seeing rejections where it used to get a resolved error result. If you're migrating just one of several consumers, either leave the method retriable (the query then double-retries, tolerated in the interim) or confirm scope with the user. When the request doesn't make the consumer scope clear, ask.
 
 3. **Adjust the service method.**
+   - Switch it to `sendStrictRequest` and **drop `| ErrorResult` from its return type** (`Promise<Readonly<SuccessResult | ErrorResult>>` → `Promise<Readonly<SuccessResult>>`). The method now resolves with data or rejects; the hook needs no `isError` check, and consumers lose their `as SuccessResult` casts.
    - Query methods: keep the `AbortController` param — the hook passes `controllerFromSignal(signal)`.
    - Mutation methods: **drop the `AbortController` param** — we no longer abort writes.
 
@@ -27,7 +28,9 @@ Migrated endpoints instead go through a `use*` hook wrapping `useQuery`/`useMuta
 
 5. **Update the consumers.** Replace the `AbortController` / `useEffect` / manual-state boilerplate with the hook, destructuring and renaming its result (`const { data: user, error: userError } = ...`; `const { mutateAsync, isPending } = ...`). Delete the dead boilerplate.
 
-6. **Finish per the `write-code` skill:** add or update tests (`write-tests`), add a changelog entry, and pass `yarn lint`.
+6. **Fix the tests that stubbed the old contract.** A spec stubbing the service method with `mockResolvedValue({ error: '…' })` was standing in for the old resolve-an-error-result behaviour — flip it to `mockRejectedValue({ error: '…' })`. `sendStrictRequest` itself is covered once, in `test/unit/server-request.spec.ts`; don't re-test it per endpoint.
+
+7. **Finish per the `write-code` skill:** add or update tests (`write-tests`), add a changelog entry, and pass `yarn lint`.
 
 ## Don't
 
diff --git a/webui/.agents/skills/tanstack-query-conventions/SKILL.md b/webui/.agents/skills/tanstack-query-conventions/SKILL.md
index b769eaef5..a93992a00 100644
--- a/webui/.agents/skills/tanstack-query-conventions/SKILL.md
+++ b/webui/.agents/skills/tanstack-query-conventions/SKILL.md
@@ -18,15 +18,13 @@ export const useUserExtension = (target: UserExtensionTarget) => {
     const { service } = useContext(MainContext);
     return useQuery({
         queryKey: ['user', 'extension', target.namespace, target.extension],
-        queryFn: async ({ signal }) => {
-            const result = await service.getExtension(controllerFromSignal(signal), target.namespace, target.extension);
-            if (isError(result)) throw result; // let errors reach TanStack
-            return result;
-        }
+        queryFn: ({ signal }) =>
+            service.getExtension(controllerFromSignal(signal), target.namespace, target.extension)
     });
 };
 ```
 
+- The `queryFn` is a one-liner because the service method rejects on failure — see "Errors belong to the service" below. Never re-check `isError` in a hook.
 - `controllerFromSignal(signal)` (`query-client.ts`) bridges TanStack's `AbortSignal` to the `AbortController` the service expects — service signatures stay untouched, component-level `AbortController` refs go away.
 - `useQuery` forbids `undefined`; normalise a "no result" case to `null`.
 - Query keys are hierarchical arrays (`['admin', 'namespace', name]`). When a key is reused for invalidation, export a small `*Keys` helper next to the hook.
@@ -46,12 +44,28 @@ export const useCreateNamespace = () => {
 
 - **No `AbortController` / signal in mutations** — we don't abort writes anymore.
 - Mutations don't retry (TanStack's default `retry: 0`), which is correct for non-idempotent writes.
-- `throw` on an error result when the caller relies on a `catch` / `onError` path.
+- The `mutationFn` forwards the service call directly; the service rejects on failure, so `mutateAsync` callers get their `catch` / `onError` path for free.
 - Invalidate or remove affected queries in `onSuccess`.
 
+## Errors belong to the service, not the hook
+
+The registry answers some failures with a `200` carrying an `{ error: '…' }` body instead of a non-2xx status. `sendStrictRequest` (`server-request.ts`) is the single place that normalises this: it is non-retriable *and* rejects on such a body, so a migrated service method resolves with data or rejects — never both.
+
+```ts
+// extension-registry-service.ts — migrated methods
+async getNamespace(abortController: AbortController, name: string): Promise<Readonly<Namespace>> {
+    return sendStrictRequest({ abortController, credentials: true, endpoint: /* … */ });
+}
+```
+
+- A migrated method's return type **drops `| ErrorResult`** — that union is what forced the `isError` check on every caller.
+- Hooks therefore never contain `if (isError(result)) throw result`. If you find yourself writing one, the service method still needs migrating.
+- `sendRequest` / `sendNonRetriableRequest` keep resolving error bodies; legacy, un-migrated consumers check `isError` themselves. Don't change their behaviour.
+- Same rule in tests: stub a failing service method with `mockRejectedValue({ error: '…' })`, not `mockResolvedValue`.
+
 ## Retries and caching are owned by the shared client
 
-- One singleton `queryClient` (`query-client.ts`) retries network/5xx with backoff, never 4xx; 429s are waited out inside `sendRequest`. Migrated service methods use `sendNonRetriableRequest`, so this is the only retry layer.
+- One singleton `queryClient` (`query-client.ts`) retries network/5xx with backoff, never 4xx; 429s are waited out inside `sendRequest`. Migrated service methods use `sendStrictRequest` (fetch-retry disabled for non-429 responses), so TanStack should remain the only layer retrying network/5xx.
 - Defaults: `refetchOnWindowFocus: false`, `staleTime: 60s`. Override per hook only with reason — `staleTime: 0` / `gcTime: 0` when data must always be fresh (right after publish/delete), `retry: false` to let a 404 surface immediately.
 
 ## Options objects, not positional flags
diff --git a/webui/CHANGELOG.md b/webui/CHANGELOG.md
index 6dd2f5341..c18d9f6b6 100644
--- a/webui/CHANGELOG.md
+++ b/webui/CHANGELOG.md
@@ -30,6 +30,7 @@ This change log covers only the frontend library (webui) of Open VSX.
 - Fix the admin dashboard Scan tab getting stuck on the loading spinner after switching tabs, even though the new tab's data had already loaded successfully
 - Fix the page jumping to the top whenever a menu, select or dialog opens.
 - Fix the extension detail page's download menu so each target-platform option is clickable across its whole row, not just its text: the option was an inline link nested inside a non-interactive menu item, rather than the menu item itself being the link
+- Fix `sendRequest` re-enabling fetch-retry's own retries for the request that follows a 429 wait, because the recursive call didn't forward the original `retry` flag. A `sendStrictRequest`/`sendNonRetriableRequest` call that hit a 429 could end up having its follow-up request retried twice - once by fetch-retry and once by the query client
 - Fix the create-namespace dialog acting on Enter when its button is disabled: an empty or over-long name was submitted anyway, and a held key sent the request more than once
 
 ### Dependencies
diff --git a/webui/src/extension-registry-service.ts b/webui/src/extension-registry-service.ts
index b506ecfd2..17a8faaef 100644
--- a/webui/src/extension-registry-service.ts
+++ b/webui/src/extension-registry-service.ts
@@ -148,10 +148,7 @@ export class ExtensionRegistryService {
         });
     }
 
-    async search(
-        abortController: AbortController,
-        filter?: ExtensionFilter
-    ): Promise<Readonly<SearchResult | ErrorResult>> {
+    async search(abortController: AbortController, filter?: ExtensionFilter): Promise<Readonly<SearchResult>> {
         const query: { key: string; value: string | number }[] = [];
         if (filter) {
             if (filter.query) query.push({ key: 'query', value: filter.query });
@@ -162,8 +159,8 @@ export class ExtensionRegistryService {
             if (filter.sortOrder) query.push({ key: 'sortOrder', value: filter.sortOrder });
         }
         const endpoint = createAbsoluteURL([this.serverUrl, 'api', '-', 'search'], query);
-        // Non-retriable: retries are owned by the TanStack query that calls this.
-        return sendNonRetriableRequest({ abortController, endpoint });
+        // Retries are owned by the TanStack query that calls this.
+        return sendStrictRequest({ abortController, endpoint });
     }
 
     async getExtensionDetail(
@@ -613,7 +610,7 @@ export class ExtensionRegistryService {
     ): Promise<Readonly<Extension>> {
         const headers: Record<string, string> = {};
 
-        return sendNonRetriableRequest<Extension>({
+        return sendStrictRequest<Extension>({
             abortController,
             method: 'GET',
             credentials: true,
@@ -626,7 +623,7 @@ export class ExtensionRegistryService {
         namespace: string;
         extension: string;
         targetPlatformVersions?: object[];
-    }): Promise<Readonly<SuccessResult | ErrorResult>> {
+    }): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.getCsrfToken();
         const headers: Record<string, string> = {
             'Content-Type': 'application/json;charset=UTF-8'
@@ -636,7 +633,7 @@ export class ExtensionRegistryService {
             headers[csrfToken.header] = csrfToken.value;
         }
 
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'POST',
             credentials: true,
             endpoint: createAbsoluteURL([this.serverUrl, 'user', 'extension', req.namespace, req.extension, 'delete']),
@@ -657,21 +654,21 @@ export interface AdminService {
         namespace: string;
         extension: string;
         targetPlatformVersions?: object[];
-    }): Promise<Readonly<SuccessResult | ErrorResult>>;
+    }): Promise<Readonly<SuccessResult>>;
     purgeExtensions(req: {
         namespace: string;
         extension: string;
         targetPlatformVersions?: object[];
-    }): Promise<Readonly<SuccessResult | ErrorResult>>;
+    }): Promise<Readonly<SuccessResult>>;
     getNamespace(abortController: AbortController, name: string): Promise<Readonly<Namespace>>;
-    createNamespace(namespace: { name: string }): Promise<Readonly<SuccessResult | ErrorResult>>;
-    deleteNamespace(namespace: { name: string }): Promise<Readonly<SuccessResult | ErrorResult>>;
+    createNamespace(namespace: { name: string }): Promise<Readonly<SuccessResult>>;
+    deleteNamespace(namespace: { name: string }): Promise<Readonly<SuccessResult>>;
     changeNamespace(req: {
         oldNamespace: string;
         newNamespace: string;
         removeOldNamespace: boolean;
         mergeIfNewNamespaceAlreadyExists: boolean;
-    }): Promise<Readonly<SuccessResult | ErrorResult>>;
+    }): Promise<Readonly<SuccessResult>>;
     getPublisherInfo(
         abortController: AbortController,
         provider: string,
@@ -685,10 +682,10 @@ export interface AdminService {
         provider: string,
         login: string,
         role: 'admin' | 'privileged' | 'none'
-    ): Promise<Readonly<SuccessResult | ErrorResult>>;
-    revokePublisherContributions(provider: string, login: string): Promise<Readonly<SuccessResult | ErrorResult>>;
-    revokeAccessTokens(provider: string, login: string): Promise<Readonly<SuccessResult | ErrorResult>>;
-    forgetUser(provider: string, login: string): Promise<Readonly<SuccessResult | ErrorResult>>;
+    ): Promise<Readonly<SuccessResult>>;
+    revokePublisherContributions(provider: string, login: string): Promise<Readonly<SuccessResult>>;
+    revokeAccessTokens(provider: string, login: string): Promise<Readonly<SuccessResult>>;
+    forgetUser(provider: string, login: string): Promise<Readonly<SuccessResult>>;
     getAllScans(
         abortController: AbortController,
         params?: {
@@ -745,15 +742,15 @@ export interface AdminService {
     getTiers(abortController: AbortController): Promise<Readonly<TierList>>;
     createTier(tier: Tier): Promise<Readonly<Tier>>;
     updateTier(name: string, tier: Tier): Promise<Readonly<Tier>>;
-    deleteTier(name: string): Promise<Readonly<SuccessResult | ErrorResult>>;
+    deleteTier(name: string): Promise<Readonly<SuccessResult>>;
     getCustomers(abortController: AbortController): Promise<Readonly<CustomerList>>;
     getCustomer(abortController: AbortController, name: string): Promise<Readonly<Customer>>;
     createCustomer(customer: Customer): Promise<Readonly<Customer>>;
     updateCustomer(name: string, customer: Customer): Promise<Readonly<Customer>>;
-    deleteCustomer(name: string): Promise<Readonly<SuccessResult | ErrorResult>>;
+    deleteCustomer(name: string): Promise<Readonly<SuccessResult>>;
     getCustomerMembers(abortController: AbortController, name: string): Promise<Readonly<CustomerMembershipList>>;
-    addCustomerMember(name: string, user: UserData): Promise<Readonly<SuccessResult | ErrorResult>>;
-    removeCustomerMember(name: string, user: UserData): Promise<Readonly<SuccessResult | ErrorResult>>;
+    addCustomerMember(name: string, user: UserData): Promise<Readonly<SuccessResult>>;
+    removeCustomerMember(name: string, user: UserData): Promise<Readonly<SuccessResult>>;
     getUsageStats(
         abortController: AbortController,
         customerName: string,
@@ -770,7 +767,7 @@ export interface AdminService {
         customerName: string
     ): Promise<Readonly<RateLimitToken[]>>;
     createCustomerRateLimitToken(customerName: string, description: string): Promise<Readonly<RateLimitToken>>;
-    deleteCustomerRateLimitToken(customerName: string, tokenId: number): Promise<Readonly<SuccessResult | ErrorResult>>;
+    deleteCustomerRateLimitToken(customerName: string, tokenId: number): Promise<Readonly<SuccessResult>>;
     getSettings(abortController: AbortController): Promise<Readonly<Settings>>;
     updateSettings(settings: Settings): Promise<Readonly<Settings>>;
     getConsistencyChecks(abortController: AbortController): Promise<Readonly<ConsistencyCheckList>>;
@@ -778,8 +775,8 @@ export interface AdminService {
         abortController: AbortController,
         checkId: string
     ): Promise<Readonly<ConsistencyFindingList>>;
-    fixConsistencyFindings(checkId: string): Promise<Readonly<SuccessResult | ErrorResult>>;
-    fixConsistencyFinding(checkId: string, entityId: number): Promise<Readonly<SuccessResult | ErrorResult>>;
+    fixConsistencyFindings(checkId: string): Promise<Readonly<SuccessResult>>;
+    fixConsistencyFinding(checkId: string, entityId: number): Promise<Readonly<SuccessResult>>;
 }
 
 export interface AdminServiceConstructor {
@@ -794,7 +791,7 @@ export class AdminServiceImpl implements AdminService {
         namespace: string,
         extension: string
     ): Promise<Readonly<Extension>> {
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             abortController,
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'extension', namespace, extension])
@@ -805,7 +802,7 @@ export class AdminServiceImpl implements AdminService {
         namespace: string;
         extension: string;
         targetPlatformVersions?: object[];
-    }): Promise<Readonly<SuccessResult | ErrorResult>> {
+    }): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {
             'Content-Type': 'application/json;charset=UTF-8'
@@ -815,7 +812,7 @@ export class AdminServiceImpl implements AdminService {
             headers[csrfToken.header] = csrfToken.value;
         }
 
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'POST',
             credentials: true,
             endpoint: createAbsoluteURL([
@@ -835,7 +832,7 @@ export class AdminServiceImpl implements AdminService {
         namespace: string;
         extension: string;
         targetPlatformVersions?: object[];
-    }): Promise<Readonly<SuccessResult | ErrorResult>> {
+    }): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {
             'Content-Type': 'application/json;charset=UTF-8'
@@ -845,7 +842,7 @@ export class AdminServiceImpl implements AdminService {
             headers[csrfToken.header] = csrfToken.value;
         }
 
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'POST',
             credentials: true,
             endpoint: createAbsoluteURL([
@@ -862,14 +859,14 @@ export class AdminServiceImpl implements AdminService {
     }
 
     async getNamespace(abortController: AbortController, name: string): Promise<Readonly<Namespace>> {
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             abortController,
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'namespace', name])
         });
     }
 
-    async createNamespace(namespace: { name: string }): Promise<Readonly<SuccessResult | ErrorResult>> {
+    async createNamespace(namespace: { name: string }): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {
             'Content-Type': 'application/json;charset=UTF-8'
@@ -878,7 +875,7 @@ export class AdminServiceImpl implements AdminService {
             const csrfToken = csrfResponse as CsrfTokenJson;
             headers[csrfToken.header] = csrfToken.value;
         }
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'create-namespace']),
             method: 'POST',
@@ -887,7 +884,7 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async deleteNamespace(namespace: { name: string }): Promise<Readonly<SuccessResult | ErrorResult>> {
+    async deleteNamespace(namespace: { name: string }): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {
             'Content-Type': 'application/json;charset=UTF-8'
@@ -896,7 +893,7 @@ export class AdminServiceImpl implements AdminService {
             const csrfToken = csrfResponse as CsrfTokenJson;
             headers[csrfToken.header] = csrfToken.value;
         }
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'namespace', namespace.name]),
             method: 'DELETE',
@@ -908,7 +905,7 @@ export class AdminServiceImpl implements AdminService {
         newNamespace: string;
         removeOldNamespace: boolean;
         mergeIfNewNamespaceAlreadyExists: boolean;
-    }): Promise<Readonly<SuccessResult | ErrorResult>> {
+    }): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {
             'Content-Type': 'application/json;charset=UTF-8'
@@ -917,7 +914,7 @@ export class AdminServiceImpl implements AdminService {
             const csrfToken = csrfResponse as CsrfTokenJson;
             headers[csrfToken.header] = csrfToken.value;
         }
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'change-namespace']),
             method: 'POST',
@@ -968,7 +965,7 @@ export class AdminServiceImpl implements AdminService {
         provider: string,
         login: string,
         role: 'admin' | 'privileged' | 'none'
-    ): Promise<Readonly<SuccessResult | ErrorResult>> {
+    ): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {};
         if (!isError(csrfResponse)) {
@@ -976,7 +973,7 @@ export class AdminServiceImpl implements AdminService {
             headers[csrfToken.header] = csrfToken.value;
         }
         const query = [{ key: 'role', value: role }];
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'POST',
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'user', provider, login, 'role'], query),
@@ -984,17 +981,14 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async revokePublisherContributions(
-        provider: string,
-        login: string
-    ): Promise<Readonly<SuccessResult | ErrorResult>> {
+    async revokePublisherContributions(provider: string, login: string): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {};
         if (!isError(csrfResponse)) {
             const csrfToken = csrfResponse as CsrfTokenJson;
             headers[csrfToken.header] = csrfToken.value;
         }
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'POST',
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'publisher', provider, login, 'revoke']),
@@ -1002,14 +996,14 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async revokeAccessTokens(provider: string, login: string): Promise<Readonly<SuccessResult | ErrorResult>> {
+    async revokeAccessTokens(provider: string, login: string): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {};
         if (!isError(csrfResponse)) {
             const csrfToken = csrfResponse as CsrfTokenJson;
             headers[csrfToken.header] = csrfToken.value;
         }
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'POST',
             credentials: true,
             endpoint: createAbsoluteURL([
@@ -1025,14 +1019,14 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async forgetUser(provider: string, login: string): Promise<Readonly<SuccessResult | ErrorResult>> {
+    async forgetUser(provider: string, login: string): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {};
         if (!isError(csrfResponse)) {
             const csrfToken = csrfResponse as CsrfTokenJson;
             headers[csrfToken.header] = csrfToken.value;
         }
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'POST',
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'publisher', provider, login, 'delete']),
@@ -1302,7 +1296,7 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async deleteTier(name: string): Promise<SuccessResult | ErrorResult> {
+    async deleteTier(name: string): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {
             'Content-Type': 'application/json;charset=UTF-8'
@@ -1311,7 +1305,7 @@ export class AdminServiceImpl implements AdminService {
             const csrfToken = csrfResponse as CsrfTokenJson;
             headers[csrfToken.header] = csrfToken.value;
         }
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'DELETE',
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'ratelimit', 'tiers', name]),
@@ -1371,7 +1365,7 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async deleteCustomer(name: string): Promise<SuccessResult | ErrorResult> {
+    async deleteCustomer(name: string): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {
             'Content-Type': 'application/json;charset=UTF-8'
@@ -1380,7 +1374,7 @@ export class AdminServiceImpl implements AdminService {
             const csrfToken = csrfResponse as CsrfTokenJson;
             headers[csrfToken.header] = csrfToken.value;
         }
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'DELETE',
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'ratelimit', 'customers', name]),
@@ -1399,7 +1393,7 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async addCustomerMember(name: string, user: UserData): Promise<Readonly<SuccessResult | ErrorResult>> {
+    async addCustomerMember(name: string, user: UserData): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {};
         if (!isError(csrfResponse)) {
@@ -1410,7 +1404,7 @@ export class AdminServiceImpl implements AdminService {
             { key: 'user', value: user.loginName },
             { key: 'provider', value: user.provider }
         ];
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             headers,
             method: 'POST',
             credentials: true,
@@ -1421,7 +1415,7 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async removeCustomerMember(name: string, user: UserData): Promise<Readonly<SuccessResult | ErrorResult>> {
+    async removeCustomerMember(name: string, user: UserData): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {};
         if (!isError(csrfResponse)) {
@@ -1432,7 +1426,7 @@ export class AdminServiceImpl implements AdminService {
             { key: 'user', value: user.loginName },
             { key: 'provider', value: user.provider }
         ];
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             headers,
             method: 'POST',
             credentials: true,
@@ -1528,10 +1522,7 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async deleteCustomerRateLimitToken(
-        customerName: string,
-        tokenId: number
-    ): Promise<Readonly<SuccessResult | ErrorResult>> {
+    async deleteCustomerRateLimitToken(customerName: string, tokenId: number): Promise<Readonly<SuccessResult>> {
         const csrfResponse = await this.registry.getCsrfToken();
         const headers: Record<string, string> = {
             'Content-Type': 'application/json;charset=UTF-8'
@@ -1540,7 +1531,7 @@ export class AdminServiceImpl implements AdminService {
             const csrfToken = csrfResponse as CsrfTokenJson;
             headers[csrfToken.header] = csrfToken.value;
         }
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'DELETE',
             credentials: true,
             endpoint: createAbsoluteURL([
@@ -1602,9 +1593,9 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async fixConsistencyFindings(checkId: string): Promise<Readonly<SuccessResult | ErrorResult>> {
+    async fixConsistencyFindings(checkId: string): Promise<Readonly<SuccessResult>> {
         const headers = await this.csrfHeaders();
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'POST',
             credentials: true,
             endpoint: createAbsoluteURL([this.registry.serverUrl, 'admin', 'consistency', checkId, 'fix']),
@@ -1612,9 +1603,9 @@ export class AdminServiceImpl implements AdminService {
         });
     }
 
-    async fixConsistencyFinding(checkId: string, entityId: number): Promise<Readonly<SuccessResult | ErrorResult>> {
+    async fixConsistencyFinding(checkId: string, entityId: number): Promise<Readonly<SuccessResult>> {
         const headers = await this.csrfHeaders();
-        return sendNonRetriableRequest({
+        return sendStrictRequest({
             method: 'POST',
             credentials: true,
             endpoint: createAbsoluteURL([
diff --git a/webui/src/hooks/use-infinite-search.ts b/webui/src/hooks/use-infinite-search.ts
index 98bf61464..bfb8dcd3c 100644
--- a/webui/src/hooks/use-infinite-search.ts
+++ b/webui/src/hooks/use-infinite-search.ts
@@ -14,7 +14,7 @@
 import { useContext } from 'react';
 import { keepPreviousData, useInfiniteQuery } from '@tanstack/react-query';
 import { MainContext } from '../context';
-import { isError, SearchResult } from '../extension-registry-types';
+import { SearchResult } from '../extension-registry-types';
 import { ExtensionFilter } from '../extension-registry-service';
 import { controllerFromSignal } from '../query-client';
 
@@ -37,20 +37,15 @@ export const useInfiniteSearch = (filter: ExtensionFilter) => {
     const { query, category, size, sortBy, sortOrder } = filter;
     return useInfiniteQuery({
         queryKey: searchKeys.list({ query, category, size, sortBy, sortOrder }),
-        queryFn: async ({ pageParam, signal }): Promise<SearchResult> => {
-            const result = await service.search(controllerFromSignal(signal), {
+        queryFn: ({ pageParam, signal }): Promise<SearchResult> =>
+            service.search(controllerFromSignal(signal), {
                 query,
                 category,
                 size,
                 sortBy,
                 sortOrder,
                 offset: pageParam
-            });
-            if (isError(result)) {
-                throw result;
-            }
-            return result as SearchResult;
-        },
+            }),
         initialPageParam: 0,
         getNextPageParam: (lastPage, allPages) => {
             const loaded = allPages.reduce((sum, page) => sum + page.extensions.length, 0);
diff --git a/webui/src/pages/admin-dashboard/customers/use-customers.ts b/webui/src/pages/admin-dashboard/customers/use-customers.ts
index 6ebec6081..3df68311c 100644
--- a/webui/src/pages/admin-dashboard/customers/use-customers.ts
+++ b/webui/src/pages/admin-dashboard/customers/use-customers.ts
@@ -14,7 +14,7 @@
 import { useContext } from 'react';
 import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
 import { MainContext } from '../../../context';
-import { type Customer, isError, type UserData } from '../../../extension-registry-types';
+import { type Customer, type UserData } from '../../../extension-registry-types';
 import { controllerFromSignal } from '../../../query-client';
 
 export const customerKeys = {
@@ -123,13 +123,7 @@ export const useDeleteCustomerToken = (name: string) => {
     const { service } = useContext(MainContext);
     const queryClient = useQueryClient();
     return useMutation({
-        mutationFn: async (tokenId: number) => {
-            const result = await service.admin.deleteCustomerRateLimitToken(name, tokenId);
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        },
+        mutationFn: (tokenId: number) => service.admin.deleteCustomerRateLimitToken(name, tokenId),
         onSuccess: () => {
             queryClient.invalidateQueries({ queryKey: customerKeys.tokens(name) });
         }
@@ -154,13 +148,7 @@ export const useAddCustomerMember = (name: string) => {
     const { service } = useContext(MainContext);
     const queryClient = useQueryClient();
     return useMutation({
-        mutationFn: async (user: UserData) => {
-            const result = await service.admin.addCustomerMember(name, user);
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        },
+        mutationFn: (user: UserData) => service.admin.addCustomerMember(name, user),
         onSuccess: () => {
             queryClient.invalidateQueries({ queryKey: customerKeys.members(name) });
         }
@@ -174,13 +162,7 @@ export const useRemoveCustomerMember = (name: string) => {
     const { service } = useContext(MainContext);
     const queryClient = useQueryClient();
     return useMutation({
-        mutationFn: async (user: UserData) => {
-            const result = await service.admin.removeCustomerMember(name, user);
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        },
+        mutationFn: (user: UserData) => service.admin.removeCustomerMember(name, user),
         onSuccess: () => {
             queryClient.invalidateQueries({ queryKey: customerKeys.members(name) });
         }
diff --git a/webui/src/pages/admin-dashboard/namespace-change-dialog.tsx b/webui/src/pages/admin-dashboard/namespace-change-dialog.tsx
index 34296670c..4498d6e18 100644
--- a/webui/src/pages/admin-dashboard/namespace-change-dialog.tsx
+++ b/webui/src/pages/admin-dashboard/namespace-change-dialog.tsx
@@ -21,7 +21,7 @@ import {
     TextField
 } from '@mui/material';
 import { ButtonWithProgress } from '../../components/button-with-progress';
-import { Namespace, SuccessResult } from '../../extension-registry-types';
+import { Namespace } from '../../extension-registry-types';
 import { MainContext } from '../../context';
 import { InfoDialog } from '../../components/info-dialog';
 import { useChangeNamespace } from './use-namespace-admin';
@@ -78,10 +78,9 @@ export const NamespaceChangeDialog: FunctionComponent<NamespaceChangeDialogProps
                 mergeIfNewNamespaceAlreadyExists
             });
 
-            const successResult = result as SuccessResult;
             props.setLoadingState(false);
             setInfoDialogIsOpen(true);
-            setInfoDialogMessage(successResult.success);
+            setInfoDialogMessage(result.success);
         } catch (err) {
             props.setLoadingState(false);
             handleError(err);
diff --git a/webui/src/pages/admin-dashboard/publisher-details.tsx b/webui/src/pages/admin-dashboard/publisher-details.tsx
index 3c8973c46..0284571a3 100644
--- a/webui/src/pages/admin-dashboard/publisher-details.tsx
+++ b/webui/src/pages/admin-dashboard/publisher-details.tsx
@@ -31,7 +31,7 @@ import FolderSharedIcon from '@mui/icons-material/FolderShared';
 import VpnKeyIcon from '@mui/icons-material/VpnKey';
 import ExtensionIcon from '@mui/icons-material/Extension';
 import GavelIcon from '@mui/icons-material/Gavel';
-import { UserRelationships, SuccessResult } from '../../extension-registry-types';
+import { UserRelationships } from '../../extension-registry-types';
 import { ErrorResponse } from '../../server-request';
 import { MainContext } from '../../context';
 import { ExtensionCardList } from '../../components/extension/extension-card-list';
@@ -197,7 +197,7 @@ export const PublisherDetails: FunctionComponent<{ entry: UserRelationships }> =
 
             {updateRole.isSuccess && (
                 <Alert severity='success' sx={{ mb: 2 }}>
-                    {(updateRole.data as Partial<SuccessResult>).success ?? ''}
+                    {updateRole.data.success}
                 </Alert>
             )}
 
diff --git a/webui/src/pages/admin-dashboard/use-extension-admin.ts b/webui/src/pages/admin-dashboard/use-extension-admin.ts
index c71b3bb72..afe3c95aa 100644
--- a/webui/src/pages/admin-dashboard/use-extension-admin.ts
+++ b/webui/src/pages/admin-dashboard/use-extension-admin.ts
@@ -14,7 +14,6 @@
 import { useContext } from 'react';
 import { useMutation, useQuery } from '@tanstack/react-query';
 import { MainContext } from '../../context';
-import { isError } from '../../extension-registry-types';
 import { controllerFromSignal } from '../../query-client';
 
 interface ExtensionTarget {
@@ -37,17 +36,8 @@ export const useAdminExtension = (target: ExtensionTarget | null) => {
     const { service } = useContext(MainContext);
     return useQuery({
         queryKey: ['admin', 'extension', target?.namespace ?? '', target?.extension ?? ''],
-        queryFn: async ({ signal }) => {
-            const result = await service.admin.getExtension(
-                controllerFromSignal(signal),
-                target!.namespace,
-                target!.extension
-            );
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        },
+        queryFn: ({ signal }) =>
+            service.admin.getExtension(controllerFromSignal(signal), target!.namespace, target!.extension),
         enabled: !!target,
         retry: false,
         staleTime: 0
@@ -55,9 +45,7 @@ export const useAdminExtension = (target: ExtensionTarget | null) => {
 };
 
 /**
- * Deletes extension versions. Mirrors the previous behaviour of not throwing on
- * an error result; thrown (network/server) errors reject so the caller's catch
- * path runs.
+ * Deletes extension versions.
  */
 export const useDeleteExtension = () => {
     const { service } = useContext(MainContext);
diff --git a/webui/src/pages/admin-dashboard/use-namespace-admin.ts b/webui/src/pages/admin-dashboard/use-namespace-admin.ts
index dab0ee74e..ec848338d 100644
--- a/webui/src/pages/admin-dashboard/use-namespace-admin.ts
+++ b/webui/src/pages/admin-dashboard/use-namespace-admin.ts
@@ -14,7 +14,6 @@
 import { useContext } from 'react';
 import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
 import { MainContext } from '../../context';
-import { isError } from '../../extension-registry-types';
 import { controllerFromSignal } from '../../query-client';
 
 interface ChangeNamespaceRequest {
@@ -37,13 +36,7 @@ export const useAdminNamespace = (name: string) => {
     const { service } = useContext(MainContext);
     return useQuery({
         queryKey: namespaceAdminKeys.detail(name),
-        queryFn: async ({ signal }) => {
-            const namespace = await service.admin.getNamespace(controllerFromSignal(signal), name);
-            if (isError(namespace)) {
-                throw namespace;
-            }
-            return namespace;
-        },
+        queryFn: ({ signal }) => service.admin.getNamespace(controllerFromSignal(signal), name),
         enabled: !!name,
         retry: false,
         staleTime: 0
@@ -65,36 +58,22 @@ export const useCreateNamespace = () => {
 };
 
 /**
- * Renames (and optionally merges) a namespace. Throws on an error result so the
- * caller's catch / onError path runs.
+ * Renames (and optionally merges) a namespace.
  */
 export const useChangeNamespace = () => {
     const { service } = useContext(MainContext);
     return useMutation({
-        mutationFn: async (req: ChangeNamespaceRequest) => {
-            const result = await service.admin.changeNamespace(req);
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        }
+        mutationFn: (req: ChangeNamespaceRequest) => service.admin.changeNamespace(req)
     });
 };
 
 /**
- * Deletes a namespace. Throws on an error result so the caller's catch /
- * onError path runs.
+ * Deletes a namespace.
  */
 export const useDeleteNamespace = () => {
     const { service } = useContext(MainContext);
     return useMutation({
-        mutationFn: async (name: string) => {
-            const result = await service.admin.deleteNamespace({ name });
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        }
+        mutationFn: (name: string) => service.admin.deleteNamespace({ name })
     });
 };
 
diff --git a/webui/src/pages/admin-dashboard/use-publisher-admin.ts b/webui/src/pages/admin-dashboard/use-publisher-admin.ts
index 35356716e..096971874 100644
--- a/webui/src/pages/admin-dashboard/use-publisher-admin.ts
+++ b/webui/src/pages/admin-dashboard/use-publisher-admin.ts
@@ -14,7 +14,6 @@
 import { useContext } from 'react';
 import { keepPreviousData, useInfiniteQuery, useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
 import { MainContext } from '../../context';
-import { isError } from '../../extension-registry-types';
 import { controllerFromSignal } from '../../query-client';
 
 export type PublisherRole = 'admin' | 'privileged' | 'none';
@@ -67,20 +66,15 @@ export const useInfinitePublishers = (search: string, role: string) => {
 
 /**
  * Updates a publisher's role and refreshes the publisher list on success so the
- * new role is reflected. Throws on an error result so the caller's catch path runs.
+ * new role is reflected.
  */
 export const useUpdatePublisherRole = () => {
     const { service } = useContext(MainContext);
     const queryClient = useQueryClient();
     return useMutation({
         mutationKey: [...publisherMutationKey, 'role'],
-        mutationFn: async ({ provider, login, role }: { provider: string; login: string; role: PublisherRole }) => {
-            const result = await service.admin.updateUserRole(provider, login, role);
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        },
+        mutationFn: ({ provider, login, role }: { provider: string; login: string; role: PublisherRole }) =>
+            service.admin.updateUserRole(provider, login, role),
         onSuccess: () => {
             queryClient.invalidateQueries({ queryKey: ['admin', 'publishers'] });
         }
@@ -88,55 +82,37 @@ export const useUpdatePublisherRole = () => {
 };
 
 /**
- * Revokes all contributions of a publisher. Throws on an error result so the
- * caller's catch path runs.
+ * Revokes all contributions of a publisher.
  */
 export const useRevokePublisherContributions = () => {
     const { service } = useContext(MainContext);
     return useMutation({
         mutationKey: [...publisherMutationKey, 'revoke-contributions'],
-        mutationFn: async ({ provider, login }: { provider: string; login: string }) => {
-            const result = await service.admin.revokePublisherContributions(provider, login);
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        }
+        mutationFn: ({ provider, login }: { provider: string; login: string }) =>
+            service.admin.revokePublisherContributions(provider, login)
     });
 };
 
 /**
- * Revokes the access tokens of a publisher. Throws on an error result so the
- * caller's catch path runs.
+ * Revokes the access tokens of a publisher.
  */
 export const useRevokeAccessTokens = () => {
     const { service } = useContext(MainContext);
     return useMutation({
         mutationKey: [...publisherMutationKey, 'revoke-tokens'],
-        mutationFn: async ({ provider, login }: { provider: string; login: string }) => {
-            const result = await service.admin.revokeAccessTokens(provider, login);
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        }
+        mutationFn: ({ provider, login }: { provider: string; login: string }) =>
+            service.admin.revokeAccessTokens(provider, login)
     });
 };
 
 /**
- * Forgets a user in response to a data-protection erasure request. Throws on
- * an error result so the caller's catch path runs.
+ * Forgets a user in response to a data-protection erasure request.
  */
 export const useForgetUser = () => {
     const { service } = useContext(MainContext);
     return useMutation({
         mutationKey: [...publisherMutationKey, 'forget-user'],
-        mutationFn: async ({ provider, login }: { provider: string; login: string }) => {
-            const result = await service.admin.forgetUser(provider, login);
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        }
+        mutationFn: ({ provider, login }: { provider: string; login: string }) =>
+            service.admin.forgetUser(provider, login)
     });
 };
diff --git a/webui/src/pages/home/use-home-data.ts b/webui/src/pages/home/use-home-data.ts
index 435dc441d..fd718611d 100644
--- a/webui/src/pages/home/use-home-data.ts
+++ b/webui/src/pages/home/use-home-data.ts
@@ -14,7 +14,7 @@
 import { useContext, useMemo } from 'react';
 import { useQueries } from '@tanstack/react-query';
 import { MainContext } from '../../context';
-import { SearchEntry, SearchResult, SortOrder, isError } from '../../extension-registry-types';
+import { SearchEntry, SortOrder } from '../../extension-registry-types';
 import { ExtensionCategory } from '../../extension-registry-types';
 import { useCategories } from '../../components/categories';
 import { HomeCuratedSection } from '../../page-settings';
@@ -80,10 +80,7 @@ export function useCuratedRows(curatedSections: HomeCuratedSection[]): CuratedRo
                     sortBy: section.sortBy,
                     sortOrder: 'desc' as SortOrder
                 });
-                if (isError(result)) {
-                    throw result;
-                }
-                return (result as SearchResult).extensions;
+                return result.extensions;
             }
         }))
     });
diff --git a/webui/src/pages/user/extensions/use-user-extension.ts b/webui/src/pages/user/extensions/use-user-extension.ts
index 6d77da1e8..69d229e03 100644
--- a/webui/src/pages/user/extensions/use-user-extension.ts
+++ b/webui/src/pages/user/extensions/use-user-extension.ts
@@ -14,7 +14,6 @@
 import { useContext } from 'react';
 import { useMutation, useQuery } from '@tanstack/react-query';
 import { MainContext } from '../../../context';
-import { isError } from '../../../extension-registry-types';
 import { controllerFromSignal, NO_CACHE } from '../../../query-client';
 
 interface UserExtensionTarget {
@@ -35,21 +34,13 @@ export const useUserExtension = (target: UserExtensionTarget) => {
     const { service } = useContext(MainContext);
     return useQuery({
         queryKey: ['user', 'extension', target.namespace, target.extension],
-        queryFn: async ({ signal }) => {
-            const result = await service.getExtension(controllerFromSignal(signal), target.namespace, target.extension);
-            if (isError(result)) {
-                throw result;
-            }
-            return result;
-        },
+        queryFn: ({ signal }) => service.getExtension(controllerFromSignal(signal), target.namespace, target.extension),
         ...NO_CACHE
     });
 };
 
 /**
- * Deletes extension versions. Mirrors the previous behaviour of not throwing on
- * an error result; thrown (network/server) errors reject so the caller's catch
- * path runs.
+ * Deletes extension versions.
  */
 export const useDeleteUserExtensionVersions = () => {
     const { service } = useContext(MainContext);
diff --git a/webui/src/server-request.ts b/webui/src/server-request.ts
index bc2fcb26e..b15b6a717 100644
--- a/webui/src/server-request.ts
+++ b/webui/src/server-request.ts
@@ -93,7 +93,7 @@ export async function sendRequest<Res>(req: ServerAPIRequest, retry: boolean = t
         const jitter = Math.floor(Math.random() * 100);
         const timeoutMillis = (Number(retrySeconds) + 1) * 1000 + jitter;
         return new Promise<ServerAPIRequest>(resolve => setTimeout(resolve, timeoutMillis, req)).then(request =>
-            sendRequest(request)
+            sendRequest(request, retry)
         );
     } else {
         let err: ErrorResponse;
diff --git a/webui/test/unit/components/extension/extension-version-delete-dialog.spec.tsx b/webui/test/unit/components/extension/extension-version-delete-dialog.spec.tsx
new file mode 100644
index 000000000..63147c000
--- /dev/null
+++ b/webui/test/unit/components/extension/extension-version-delete-dialog.spec.tsx
@@ -0,0 +1,82 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ ********************************************************************************/
+
+import { describe, expect, it, vi } from 'vitest';
+import { screen, waitFor } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { renderWithProviders } from '../../support/test-providers';
+import { DeleteVersionDialog } from '../../../../src/components/extension/extension-version-delete-dialog';
+import { Extension, VersionTargetPlatforms } from '../../../../src/extension-registry-types';
+
+const extension = { name: 'bar', namespace: 'foo', displayName: 'Bar Tools' } as unknown as Extension;
+
+const version: VersionTargetPlatforms = {
+    version: '1.0.0',
+    targetPlatforms: [{ targetPlatform: 'universal', removed: false }]
+} as unknown as VersionTargetPlatforms;
+
+// MUI's Dialog transition trips a jsdom getComputedStyle bug that every getByRole query
+// walks into while the dialog is open - query the dialog's buttons by text instead.
+const removeButton = () => screen.getByText('Remove', { selector: 'button' });
+
+function renderDialog(onRemove: () => Promise<unknown>) {
+    const onDeleted = vi.fn();
+    const onClose = vi.fn();
+    const handleError = vi.fn();
+    renderWithProviders(
+        <DeleteVersionDialog
+            open
+            onClose={onClose}
+            extension={extension}
+            version={version}
+            onRemove={onRemove}
+            onDeleted={onDeleted}
+        />,
+        { mainContext: { handleError } }
+    );
+    return { onDeleted, onClose, handleError };
+}
+
+describe('DeleteVersionDialog', () => {
+    it('closes and notifies the page when the removal succeeds', async () => {
+        const { onDeleted, onClose, handleError } = renderDialog(vi.fn().mockResolvedValue({ success: 'ok' }));
+
+        await userEvent.click(removeButton());
+
+        await waitFor(() => expect(onDeleted).toHaveBeenCalled());
+        expect(onClose).toHaveBeenCalled();
+        expect(handleError).not.toHaveBeenCalled();
+    });
+
+    it('reports a rejected removal instead of reporting success', async () => {
+        const { onDeleted, onClose, handleError } = renderDialog(vi.fn().mockRejectedValue({ error: 'boom' }));
+
+        await userEvent.click(removeButton());
+
+        await waitFor(() => expect(handleError).toHaveBeenCalledWith({ error: 'boom' }));
+        expect(onDeleted).not.toHaveBeenCalled();
+        expect(onClose).not.toHaveBeenCalled();
+    });
+
+    it('defers closing to the error dialog when the versions are stale (409)', async () => {
+        const { onDeleted, onClose, handleError } = renderDialog(vi.fn().mockRejectedValue({ status: 409 }));
+
+        await userEvent.click(removeButton());
+
+        await waitFor(() => expect(handleError).toHaveBeenCalled());
+        expect(onDeleted).not.toHaveBeenCalled();
+        expect(onClose).not.toHaveBeenCalled();
+
+        // The page refreshes and the dialog closes only once the user acknowledges the error.
+        handleError.mock.calls[0][1].onClose();
+        expect(onDeleted).toHaveBeenCalled();
+        expect(onClose).toHaveBeenCalled();
+    });
+});
diff --git a/webui/test/unit/pages/admin-dashboard/publisher-forget-user-button.spec.tsx b/webui/test/unit/pages/admin-dashboard/publisher-forget-user-button.spec.tsx
index 31ec40dbf..9b907d249 100644
--- a/webui/test/unit/pages/admin-dashboard/publisher-forget-user-button.spec.tsx
+++ b/webui/test/unit/pages/admin-dashboard/publisher-forget-user-button.spec.tsx
@@ -84,8 +84,9 @@ describe('PublisherForgetUserButton', () => {
         expect(handleUserDeleted).toHaveBeenCalled();
     });
 
-    it('reports an error result to the page and leaves the dialog open', async () => {
-        const forgetUser = vi.fn().mockResolvedValue({ error: 'boom' });
+    it('reports a rejected request to the page and leaves the dialog open', async () => {
+        // The service rejects on failure (`sendStrictRequest`), including a 200 carrying an error body.
+        const forgetUser = vi.fn().mockRejectedValue({ error: 'boom' });
         const handleError = vi.fn();
         const handleUserDeleted = vi.fn();
         renderWithProviders(
diff --git a/webui/test/unit/server-request.spec.ts b/webui/test/unit/server-request.spec.ts
new file mode 100644
index 000000000..c10be978e
--- /dev/null
+++ b/webui/test/unit/server-request.spec.ts
@@ -0,0 +1,96 @@
+/********************************************************************************
+ * Copyright (c) 2026 Contributors to the Eclipse Foundation
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0.
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ ********************************************************************************/
+
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { sendNonRetriableRequest, sendStrictRequest } from '../../src/server-request';
+
+function jsonResponse(body: unknown, status = 200): Response {
+    return new Response(JSON.stringify(body), {
+        status,
+        headers: { 'Content-Type': 'application/json' }
+    });
+}
+
+function stubFetch(...responses: Response[]) {
+    const fetchMock = vi.fn();
+    responses.forEach(response => fetchMock.mockResolvedValueOnce(response));
+    vi.stubGlobal('fetch', fetchMock);
+    return fetchMock;
+}
+
+afterEach(() => {
+    vi.unstubAllGlobals();
+});
+
+describe('sendStrictRequest', () => {
+    it('resolves with the parsed body of a successful response', async () => {
+        stubFetch(jsonResponse({ name: 'redhat' }));
+
+        await expect(sendStrictRequest({ endpoint: 'https://open-vsx.org/api/redhat' })).resolves.toEqual({
+            name: 'redhat'
+        });
+    });
+
+    it('rejects with the error result when the server answers 200 with an error body', async () => {
+        stubFetch(jsonResponse({ error: 'Namespace not found' }));
+
+        await expect(sendStrictRequest({ endpoint: 'https://open-vsx.org/api/nope' })).rejects.toEqual({
+            error: 'Namespace not found'
+        });
+    });
+
+    it('rejects with the error response of a failed request', async () => {
+        stubFetch(jsonResponse({ error: 'Forbidden', message: 'no access' }, 403));
+
+        await expect(sendStrictRequest({ endpoint: 'https://open-vsx.org/admin/namespace/x' })).rejects.toMatchObject({
+            error: 'Forbidden',
+            status: 403
+        });
+    });
+
+    it('does not retry a server error - retries are owned by the query client', async () => {
+        const fetchMock = stubFetch(jsonResponse({ error: 'boom' }, 500));
+
+        await expect(sendStrictRequest({ endpoint: 'https://open-vsx.org/api/-/search' })).rejects.toMatchObject({
+            status: 500
+        });
+        expect(fetchMock).toHaveBeenCalledTimes(1);
+    });
+
+    // Regression test: sendRequest re-invokes itself on 429 without forwarding the original `retry`
+    // flag, so it used to fall back to the default `retry = true` - re-enabling fetch-retry's own
+    // retries for the follow-up request even though sendStrictRequest asked for none. A 500 after the
+    // 429 would then be retried by fetch-retry itself instead of surfacing as a single rejection.
+    it('does not re-enable retries for the request that follows a 429', async () => {
+        vi.useFakeTimers();
+        const fetchMock = stubFetch(jsonResponse({}, 429), jsonResponse({ error: 'boom' }, 500));
+
+        // Attach the rejection assertion before letting the fake 429 delay elapse, so the rejection it
+        // triggers is never briefly unhandled.
+        const assertion = expect(
+            sendStrictRequest({ endpoint: 'https://open-vsx.org/api/-/search' })
+        ).rejects.toMatchObject({ status: 500 });
+        await vi.runAllTimersAsync();
+        await assertion;
+
+        expect(fetchMock).toHaveBeenCalledTimes(2);
+        vi.useRealTimers();
+    });
+});
+
+describe('sendNonRetriableRequest', () => {
+    it('resolves an error body instead of rejecting', async () => {
+        stubFetch(jsonResponse({ error: 'Namespace not found' }));
+
+        await expect(sendNonRetriableRequest({ endpoint: 'https://open-vsx.org/api/nope' })).resolves.toEqual({
+            error: 'Namespace not found'
+        });
+    });
+});