Add minimal postcard migration smoke tests

Verify the bincode → postcard migration works correctly with targeted
tests for Value roundtrips and error conversion.

Author: Drew Robinson

libsql-server/src/lib.rs

@@ -87,6 +87,8 @@ mod query;
 mod query_analysis;
 mod query_result_builder;
 mod replication;
+#[cfg(test)]
+mod rpc_postcard_tests;
 mod schema;
 mod stats;
 #[cfg(test)]

libsql-server/src/rpc_postcard_tests.rs

@@ -0,0 +1,52 @@
+#![cfg(test)]
+
+//! Minimal smoke tests for postcard serialisation.
+//! These verify the bincode → postcard migration works correctly.
+
+use crate::query::Value;
+
+/// Verify roundtrip works for all Value variants.
+#[test]
+fn test_value_roundtrip_all_variants() {
+    let values = vec![
+        Value::Null,
+        Value::Integer(0),
+        Value::Integer(i64::MAX),
+        Value::Integer(i64::MIN),
+        Value::Real(std::f64::consts::PI),
+        Value::Real(f64::MAX),
+        Value::Text(String::new()),
+        Value::Text("hello 🦀".to_string()),
+        Value::Blob(vec![]),
+        Value::Blob(vec![0u8, 255u8]),
+    ];
+
+    for value in &values {
+        let encoded = postcard::to_stdvec(value).expect("encode failed");
+        let decoded: Value = postcard::from_bytes(&encoded).expect("decode failed");
+        assert_eq!(format!("{:?}", value), format!("{:?}", decoded));
+    }
+}
+
+/// Verify large blobs don't hit size limits.
+#[test]
+fn test_large_blob_roundtrip() {
+    let value = Value::Blob(vec![42u8; 1_000_000]);
+    let encoded = postcard::to_stdvec(&value).expect("encode failed");
+    let decoded: Value = postcard::from_bytes(&encoded).expect("decode failed");
+    assert!(matches!(decoded, Value::Blob(b) if b.len() == 1_000_000));
+}
+
+/// Verify postcard errors convert correctly to our error type.
+#[test]
+fn test_postcard_error_conversion() {
+    let garbage = vec![0xff, 0xfe];
+    let result: Result<Value, postcard::Error> = postcard::from_bytes(&garbage);
+
+    if let Err(e) = result {
+        let crate_error = crate::error::Error::from(e);
+        assert!(
+            matches!(crate_error, crate::error::Error::Internal(msg) if msg.contains("Unexpected"))
+        );
+    }
+}