fix: validate HTTP status when fetching sitemaps

[anxkhn]

Description

• _fetch_and_process_sitemap never looked at response.status_code. It opened the stream, picked a parser from the content type, parsed whatever body came back, and then broke out of the retry loop. A 503 with an empty body was therefore accepted as a valid, empty sitemap.
• The practical effect is that a transient outage on a sitemap endpoint silently produces zero URLs. SitemapRequestLoader then marks the sitemap processed and reports itself finished, so the crawl looks successful while nothing was crawled. Per RFC 9110 section 15.6, a 5xx response means the server failed to fulfil the request, not that a representation was returned.
• This change validates the status before a parser is selected. 408, 429 and 5xx go through the retry loop that already exists in this function, and other non-success statuses are raised immediately without parsing the body.
• SitemapRequestLoader.is_finished now retrieves the result of the background loading task, so a load that failed is surfaced to the caller instead of being swallowed as a clean completion. Cancellation is still treated as before.

Behaviour change worth flagging: fetch failures already aborted parse_sitemap (a connection error after the retries are exhausted propagates today), and terminal statuses now join that class. That means a stale 404 entry inside a sitemap index will fail the load rather than being parsed as an empty sitemap. If you would prefer terminal statuses to be logged and skipped instead, I am happy to change it.

Issues

• No related issue filed. Happy to open one if you prefer to track it there.

Testing

• tests/unit/_utils/test_sitemap.py: two 503 responses followed by a valid sitemap are retried and the URLs are returned; a persistent 503 raises once the retries are exhausted; a 404 raises immediately without a retry and without parsing the body it carried.
• tests/unit/request_loaders/test_sitemap_request_loader.py: the loader recovers from transient 503s and loads the URLs, and it surfaces the failure instead of finishing empty when the retries are exhausted.
• The existing stream mocks in these files needed a status_code on the mocked response, since the code now reads it.
• Ran uv run pytest tests/unit/_utils/test_sitemap.py tests/unit/request_loaders/test_sitemap_request_loader.py.

Checklist

• CI passed

[Mantisus]

That means a stale 404 entry inside a sitemap index will fail the load rather than being parsed as an empty sitemap. If you would prefer terminal statuses to be logged and skipped instead, I am happy to change it.

Yes. I suggest:

• Server errors trigger a retry. Once all retries are exhausted, log a warning instead of raising.
• The same applies to 429 and 408.
• Other client errors skip the sitemap, treating it as empty.

Also, updating is_finished interrupts the loader's operation, preventing it from handing out URLs that have already been loaded. Checking url_queue and in_progress before retrieving the task result would be enough.

[Copilot]

Pull request overview

Validates sitemap HTTP responses before parsing and propagates background loader failures, preventing failed sitemap fetches from appearing as successful empty loads.

Changes:

• Retry 408, 429, and 5xx sitemap responses; immediately reject other error statuses.
• Surface completed background loading task exceptions from SitemapRequestLoader.is_finished.
• Add coverage for transient, persistent, and terminal HTTP failures.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/crawlee/_utils/sitemap.py	Adds HTTP status validation and retry classification.
src/crawlee/request_loaders/_sitemap_request_loader.py	Propagates background loading failures.
tests/unit/_utils/test_sitemap.py	Tests status retry and rejection behavior.
tests/unit/request_loaders/test_sitemap_request_loader.py	Tests loader recovery and failure propagation.

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[anxkhn]

@Mantisus @vdusek addressed the review feedback: retryable failures are contained per sitemap, exhausted and non-retryable responses are skipped with warnings, successful sources continue draining, and partial-failure coverage was added with the requested cleanup. rebased onto the latest master; 119 focused tests and ruff pass. could you please take another look?