[bug] Kafka client creation errors print the rejected rdkafka value

[MarcusKainth]

Where

Kafka sink (spate-kafka)

Version

main (8d023b6)

Cargo features

kafka

Rust version and platform

rustc 1.96, any platform

What happened

When librdkafka rejects an rdkafka: passthrough value, the Kafka sink's startup error prints that value. build (crates/spate-kafka/src/sink/config.rs) formats the error as sink.kafka: producer creation failed: {e}, and the probe producer's error takes the same form. rdkafka's KafkaError::ClientConfig displays as Client config error: {desc} {key} {value}, and librdkafka's own desc quotes it again for an enumerated property. The Kafka source's consumer creation (crates/spate-kafka/src/source.rs, fatal("create consumer")) carries the same error.

${VAR} interpolation runs before parsing, so a secret placed in the wrong property, or in a property with a typed value, ends up in the message. #764 removes values from config type errors in spate-core. This path does not go through that code.

What you expected instead

The error names the property and why librdkafka rejected it, and does not print the value.

Reproduction

// In crates/spate-kafka/src/sink/config.rs tests:
let body = format!("{}  rdkafka:\n    compression.type: hunter2\n", minimal());
let err = build(parse(&body).unwrap()).unwrap_err().to_string();
assert!(!err.contains("hunter2"), "{err}");
// fails: invalid configuration: sink.kafka: producer creation failed: Client config error:
// Invalid value "hunter2" for configuration property "compression.codec" compression.type hunter2