feat(transport): add error log for oversized envelopes (HTTP 413)

[jpnurmi]

Per the spec for dealing with network failures, the SDK SHOULD log an error when an envelope is discarded due to a HTTP 413 Content Too Large response so users understand why their data was dropped.

https://develop.sentry.dev/sdk/foundations/transport/offline-caching/#dealing-with-network-failures

A partial solution to #1487, Crashpad needs to be addressed separately.

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[JoshuaMoelans]

LGTM, not sure if it fully closes #1487 because of Crashpad not handling 413's yet IIRC.

[jpnurmi]

LGTM, not sure if it fully closes #1487 because of Crashpad not handling 413's yet IIRC.

Oops, good catch! I'll take a look.

[jpnurmi]

Unlike /envelope/, the /minidump/ endpoint doesn't respond with 413:

[47325:52067264:20260414,181631.861230:ERROR http_transport_mac.mm:259] HTTP status 400, response = "{"detail":"invalid multipart data","causes":["stream size exceeded limit: 209715200 bytes"]}"

Analysis

/envelope/ — returns 413 via Axum's body-limit middleware:

• relay-server/src/endpoints/envelope.rs#L128 —post(handle).route_layer(DefaultBodyLimit::max(config.max_envelope_size())). Oversize is rejected before the handler, so Axum returns the standard 413.

/minidump/ — multipart bypasses the body-limit layer and reports oversize as 400:

• relay-server/src/endpoints/minidump.rs#L264 — multipart path: utils::multipart_from_request(request, state.config().max_attachments_size())
• relay-server/src/endpoints/minidump.rs#L288 — raw-minidump path still uses DefaultBodyLimit::max(config.max_attachment_size()) (this one would return 413)
• relay-server/src/utils/multipart.rs#L283-L288 — limit enforced via multer::Constraints::new().size_limit(...)
• relay-server/src/utils/multipart.rs#L241 — on exceed: return Err(multer::Error::StreamSizeExceeded { ... })

Status-code mapping — the multer error becomes 400, not 413:

• relay-server/src/endpoints/common.rs#L62 — InvalidMultipart(#[from] multer::Error)
• relay-server/src/endpoints/common.rs#L136 — only BadStoreRequest::Overflow maps to PAYLOAD_TOO_LARGE
• relay-server/src/endpoints/common.rs#L140 — everything else, including InvalidMultipart(StreamSizeExceeded), falls through to BAD_REQUEST

Skip Crashpad for now?