Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/Elastic.Documentation.Configuration/ReleaseNotes/CdnChangelogFetcher.cs`:
- Around line 65-67: The current code memoizes any result from FetchUncached
(var bundles = FetchUncached(...); _ = Cache.TryAdd(cacheKey, bundles);) which
can store empty or partial results; change this to only cache a clean, non-empty
fetch: update FetchUncached to return a result type (e.g., a struct/class or
tuple) that includes the bundles plus a success/hasWarnings flag (or throw on
registry failures), then in the caller check that result.Bundles is not empty
and result.HasWarnings is false (or result.Success is true) before calling
Cache.TryAdd(cacheKey, result.Bundles); otherwise skip caching to avoid
persisting transient CDN/404 failures.

In `@src/infra/docs-lambda-changelog-scrubber/README.md`:
- Around line 33-35: Update the README wording to clarify that the handler does
not copy arbitrary .json files: change the second bullet to state that only
registry manifests (keys matching RegistryKey.IsRegistry(...)) are passed
through by the handler; mention that other .json objects are skipped. Reference
the handler and the RegistryKey.IsRegistry(...) predicate to make the behavior
explicit.

In `@src/services/Elastic.Changelog/Uploading/RegistryBuilder.cs`:
- Around line 251-256: The catch-all that logs "Existing manifest ... could not
be parsed" is swallowing transient I/O/S3 errors and allowing a conditional
If-Match PUT (using the captured etag) to overwrite a valid manifest; change the
catch to only handle manifest parse-related exceptions (e.g., JsonException,
FormatException, InvalidDataException) or explicitly detect a parse failure, log
and return the rebuilt manifest as before, but rethrow or let other exceptions
(IOException, AmazonS3Exception/HttpRequestException, etc.) bubble up so
transient read errors are not treated as a corrupt manifest; locate the
try/catch around the response parsing in RegistryBuilder (the block that reads
response.ETag and parses the manifest, uses _logger.LogWarning and returns ([],
etag)) and update the exception handling accordingly.

In `@tests/Elastic.Markdown.Tests/Directives/ChangelogBasicTests.cs`:
- Around line 339-372: This test mutates the process-wide env var EnvVar via
Environment.SetEnvironmentVariable inside InitializeAsync(), causing flakiness;
instead either serialize the test or remove the global mutation by using an
injectable seam: change the test to call
CdnChangelogFetcher.PrimeCacheForTesting with a configurable base (add an
overload or setter on CdnChangelogFetcher to accept the CdnBase/Uri directly)
and stop setting Environment.SetEnvironmentVariable(EnvVar, CdnBase) (or restore
via a test-scoped lock); locate InitializeAsync(), the
Environment.SetEnvironmentVariable calls, and the PrimeCacheForTesting call and
update the test to pass the CDN base via the new injection point (or wrap the
env change in a process-wide test lock) so no global env var is mutated for
other tests.

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@docs/development/changelog-bundle-registry.md`:
- Line 182: The markdown document has a forward-reference link that points to an
anchor defined later in the file, which violates markdown linting rules. In the
changelog-bundle-registry.md file, the link reference to [Declaration and
prefetch](`#declaration-and-prefetch`) appears before its corresponding anchor
definition. Resolve this by either reorganizing the document structure to place
the "Declaration and prefetch" section before the reference, or alternatively
use an inline anchor syntax (if your markdown flavor supports it) to define the
anchor at the point of reference before the link is used.

In `@docs/syntax/changelog.md`:
- Line 168: The description text for product bundles contains a forward
reference link to the anchor declaring-cdn-backed-products, which is defined
later in the document at line 196. To fix this markdown linting issue (MD051),
either move the section that defines the declaring-cdn-backed-products anchor to
appear before the line containing the forward reference, or reorder the content
so that the anchor is defined before it is referenced in the link.

In `@src/services/Elastic.Documentation.Assembler/AssembleSources.cs`:
- Around line 79-80: The await on releaseNotesFetcher.FetchAsync is missing
ConfigureAwait(false), which violates the library code async guideline. Add
ConfigureAwait(false) to the end of the FetchAsync call chain so that the
continuation does not capture the current synchronization context, which is
required for all library code async operations according to the repo's C# coding
standards.

---

Outside diff comments:
In `@src/Elastic.Documentation.Configuration/ReleaseNotes/CdnChangelogFetcher.cs`:
- Around line 103-106: The exception filter in the catch block at the
CdnChangelogFetcher catch statement uses `when (ex is not
OperationCanceledException)` which silently suppresses TaskCanceledException
(raised on timeout) since it's a subclass of OperationCanceledException. To fix
this, modify the exception filter to differentiate between timeouts and
cancellations by checking the inner exception. Instead of filtering out all
OperationCanceledException types, allow TaskCanceledException through so
emitError is invoked for timeout scenarios. Apply the same fix to the second
occurrence also mentioned in the comment (lines 172-175).