diff --git a/src/harness/providers/openai/mod.rs b/src/harness/providers/openai/mod.rs
index bbefe30..04568c7 100644
--- a/src/harness/providers/openai/mod.rs
+++ b/src/harness/providers/openai/mod.rs
@@ -76,7 +76,7 @@ use convert::*;
 use sse::*;
 #[cfg(test)]
 use transport::{
-    auth_headers, effective_temperature, error_source_chain, glob_match, merge_provider_options,
+    auth_headers, effective_temperature, glob_match, merge_provider_options,
     merge_system_into_user, request_timeout,
 };
 
diff --git a/src/harness/providers/openai/test.rs b/src/harness/providers/openai/test.rs
index 42147e6..5ae6268 100644
--- a/src/harness/providers/openai/test.rs
+++ b/src/harness/providers/openai/test.rs
@@ -1475,33 +1475,3 @@ fn merge_provider_options_prefers_overrides_and_handles_nulls() {
         json!(["top_k", 40])
     );
 }
-
-#[test]
-fn error_source_chain_walks_all_causes() {
-    use std::fmt;
-    // A transport error whose outer Display hides the actionable errno one link
-    // down the `source()` chain (the reqwest/hyper shape).
-    #[derive(Debug)]
-    struct Outer(std::io::Error);
-    impl fmt::Display for Outer {
-        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-            write!(f, "error sending request for url (http://localhost:1234/)")
-        }
-    }
-    impl std::error::Error for Outer {
-        fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-            Some(&self.0)
-        }
-    }
-    let io = std::io::Error::new(
-        std::io::ErrorKind::ConnectionRefused,
-        "connection refused (os error 111)",
-    );
-    let chain = error_source_chain(&Outer(io));
-    assert!(chain.contains("error sending request for url (http://localhost:1234/)"));
-    assert!(chain.contains("connection refused (os error 111)"));
-    assert_eq!(
-        chain,
-        "error sending request for url (http://localhost:1234/): connection refused (os error 111)"
-    );
-}
diff --git a/src/harness/providers/openai/transport.rs b/src/harness/providers/openai/transport.rs
index bb0fb90..92a569f 100644
--- a/src/harness/providers/openai/transport.rs
+++ b/src/harness/providers/openai/transport.rs
@@ -877,12 +877,8 @@ impl OpenAiModel {
         url: &str,
     ) -> Result<reqwest::Response> {
         let response = builder.send().await.map_err(|e| {
-            let error = self.provider_error(
-                format!("{what} to {url} failed: {}", error_source_chain(&e)),
-                None,
-                None,
-                None,
-            );
+            let error =
+                self.provider_error(format!("{what} to {url} failed: {e}"), None, None, None);
             TinyAgentsError::Model(self.provider_failure_message(&error))
         })?;
 
@@ -992,27 +988,6 @@ pub(super) fn request_timeout(timeout_ms: Option<u64>, streaming: bool) -> Optio
     }
 }
 
-/// Renders an error together with its full `source()` cause chain, joined by
-/// `": "`.
-///
-/// `reqwest`/`hyper` transport errors surface only their outermost context in
-/// `Display` (e.g. `error sending request for url (...)`), while the actionable
-/// detail — `connection refused (os error 111)`, a TLS failure, a DNS error —
-/// lives one or more links down the `source()` chain. A plain `{e}` drops it, so
-/// callers that classify on the message (loopback-offline detection, transport
-/// retryability) never see it. Walking the chain here keeps the whole shape in
-/// the `TinyAgentsError::Model` string. Pure, so it is unit-testable.
-pub(super) fn error_source_chain(err: &dyn std::error::Error) -> String {
-    let mut rendered = err.to_string();
-    let mut source = err.source();
-    while let Some(inner) = source {
-        rendered.push_str(": ");
-        rendered.push_str(&inner.to_string());
-        source = inner.source();
-    }
-    rendered
-}
-
 /// Merges baked `defaults` under a request's own `overrides` provider options.
 ///
 /// Keys present in `overrides` win over `defaults`. A `Null` on either side