Function apply_to_s3_config_builder 

pub fn apply_to_s3_config_builder(
    flags: &CompatFlags,
    builder: Builder,
) -> CompatFlagApply

Apply all v1 compat flags from flags onto builder and return the updated builder together with any warnings.

Forward-compat contract

• If flags.flags_schema != CURRENT_FLAGS_SCHEMA, a warning is added but the known fields are still applied — the function always returns Ok.
• Each key in flags.unknown (written by a newer schema version) produces a single “ignored” warning rather than an error.

Flags wiring summary

Flag	Wiring
endpoint_url	SDK loader (applied before S3ConfigBuilder) — caller must handle
region_override	SDK loader — caller must handle
addressing_style	force_path_style(true/false/unset)
signature_version	V4 always (V2 unsupported by aws-sdk-s3 v1; emits warning)
checksum_mode	request_checksum_calculation(WhenRequired) when Disabled
accept_invalid_tls	feature-gated; caller injects a custom HTTP connector
expect_continue	caller injects a custom HTTP connector
chunked_upload	stored; not yet wired to SDK (open-ended, see comment)
bucket_name_validation	Lax noted in warning (no SDK-level hook in v1)