docs: remote files after the adversarial review

CHANGELOG, the clawhdf5-remote and h5rs READMEs and the remote-files
known issues: redirect rules, scaled timeouts (min_speed), URL redaction,
claimed lengths never allocated (download, --max-download), a 200 for a
small file accepted, and ObjectStoreStorage from any thread.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

docs/known-issues.md

@@ -829,11 +829,23 @@ cache, but:
   ETag (`W/"…"`) cannot be sent as `If-Match`, so it counts as none.
 - **Credentials:** HTTP takes extra headers (`HttpOptions::headers`, e.g.
   `Authorization`); `h5rs` has no option for them. The cloud stores read
-  credentials from the environment only.
+  credentials from the environment only. Messages and `Debug` output show
+  URLs through `redact_url` (no userinfo, query values `REDACTED`);
+  `HttpStorage::url()` returns the URL as given and must not be logged.
+- **Redirects:** at most `HttpOptions::max_redirects` (5) per request,
+  never from `https` to `http`, and the custom headers are not sent once a
+  redirect leaves the URL's origin. The redirect target is not remembered:
+  every request of a redirected file costs its hops again.
+- **Timeouts:** ureq has no idle timeout, only a total one for the body,
+  so the body's budget is `timeout + size / min_speed` (30 s + 16 KiB/s
+  by default). A connection that stalls mid-body is detected only when
+  that budget runs out (94 s for a 1 MiB block, 9 min for an 8 MiB run).
 - Each `ObjectStoreStorage` owns a tokio runtime with two worker threads.
-- `h5rs check` downloads a remote file whole (it validates every byte), and
-  a URL cannot carry a `FILE/OBJECT` suffix; `h5rs` uses the default cache
-  settings.
+  A read called from inside another runtime blocks that runtime's thread
+  for its duration (it works, but `spawn_blocking` is the better place).
+- `h5rs check` downloads a remote file whole (it validates every byte), up
+  to `--max-download` (1 GiB by default), and a URL cannot carry a
+  `FILE/OBJECT` suffix; `h5rs` uses the default cache settings.
 - The zero-copy methods and `File::as_bytes` are unavailable on a remote
   file (see the range-read limits above).