diff --git a/contracts/oracles/tests/err_stab.rs b/contracts/oracles/tests/err_stab.rs
new file mode 100644
index 00000000..9f1d8997
--- /dev/null
+++ b/contracts/oracles/tests/err_stab.rs
@@ -0,0 +1,68 @@
+//! Oracle client-facing error-code stability tests.
+//!
+//! These assertions intentionally freeze the numeric values exposed by the
+//! contract's oracle errors. Client applications may persist or branch on
+//! these values, so changing one is a visible API change and requires an
+//! explicit migration or versioning decision.
+
+use oracles::Error;
+
+/// Oracle error codes are reserved for the 200-series range.
+///
+/// Keep this table explicit rather than deriving values from enum ordering:
+/// the numeric assignments are part of the client-facing contract.
+#[test]
+fn oracle_error_codes_are_stable() {
+    let oracle_errors = [
+        (Error::OracleUnavailable, 200u32),
+        (Error::InvalidOracleConfig, 201u32),
+        (Error::OracleStale, 202u32),
+        (Error::OracleNoConsensus, 203u32),
+        (Error::OracleVerified, 204u32),
+        (Error::MarketNotReady, 205u32),
+        (Error::FallbackOracleUnavailable, 206u32),
+        (Error::ResolutionTimeoutReached, 207u32),
+        (Error::OracleConfidenceTooWide, 208u32),
+        (Error::InvalidOracleFeed, 209u32),
+        (Error::OracleCallbackAuthFailed, 210u32),
+        (Error::OracleCallbackUnauthorized, 211u32),
+        (Error::OracleCallbackInvalidSignature, 212u32),
+        (Error::OracleCallbackReplayDetected, 213u32),
+        (Error::OracleCallbackTimeout, 214u32),
+    ];
+
+    for (error, expected_code) in oracle_errors {
+        assert_eq!(
+            error as u32,
+            expected_code,
+            "oracle error code changed for {error:?}; this is a client-facing API change"
+        );
+    }
+}
+
+/// Oracle error codes remain contiguous and contain no duplicates.
+#[test]
+fn oracle_error_codes_are_unique_and_contiguous() {
+    let codes = [
+        Error::OracleUnavailable as u32,
+        Error::InvalidOracleConfig as u32,
+        Error::OracleStale as u32,
+        Error::OracleNoConsensus as u32,
+        Error::OracleVerified as u32,
+        Error::MarketNotReady as u32,
+        Error::FallbackOracleUnavailable as u32,
+        Error::ResolutionTimeoutReached as u32,
+        Error::OracleConfidenceTooWide as u32,
+        Error::InvalidOracleFeed as u32,
+        Error::OracleCallbackAuthFailed as u32,
+        Error::OracleCallbackUnauthorized as u32,
+        Error::OracleCallbackInvalidSignature as u32,
+        Error::OracleCallbackReplayDetected as u32,
+        Error::OracleCallbackTimeout as u32,
+    ];
+
+    for (index, code) in codes.iter().enumerate() {
+        assert_eq!(*code, 200u32 + index as u32);
+        assert!(!codes[..index].contains(code));
+    }
+}