fix(compaction): failures carry the real error, with endpoint credentials redacted

The pager rendered "Compaction failed." with the error dropped, and the
shell's unsuppressed auto-compaction failure sent an empty error. Both
now carry the decoded first line of the failure (retry guidance plus the
detail), decoded from the ACP data rather than its JSON-escaped Display,
propagated unchanged through the compact extension, capped for a banner.

Endpoint credentials never reach the banner: the sampler redacts the
parsed endpoint (userinfo, sensitive query values, fragment via the
repository sanitizer) in every 401 message and the appended request URL,
and the shell redacts every URL in the error text before line selection,
including URLs whose password holds whitespace or that follow a
multi-byte delimiter.

Ported from upstream 1.0.13 (grok-build dispatch/prompt.rs,
session/compaction.rs), extended with the redaction.

Claude-Session: https://claude.ai/code/session_01RUqV8HVGXcAETyYbZ2tPQ4

crates/codegen/kigi-sampler/src/client.rs

@@ -193,6 +193,16 @@ fn extract_context_total(value: &serde_json::Value) -> Option<u32> {
     Some(i.saturating_add(o))
 }
 
+/// The endpoint as the HTTP client parses it, minus userinfo, sensitive query values and fragment; an unparseable one is not echoed.
+fn redacted_endpoint(endpoint: &str) -> String {
+    match reqwest::Url::parse(endpoint) {
+        Ok(mut url) => {
+            kigi_secrets::redact_url(&mut url);
+            url.to_string()
+        }
+        Err(_) => "<unparseable endpoint>".to_owned(),
+    }
+}
 /// Record `success=false` + `error` on the active inference span when a stream
 /// request fails before any response (transport/connect/TLS errors). Without
 /// this the `#[instrument]` span closes with both fields Empty, so an outage
@@ -806,7 +816,7 @@ impl SamplingClient {
         let server_message_lower = server_message.to_lowercase();
 
         let mut context_parts = vec![server_message.to_string()];
-        context_parts.push(format!("\nRequest URL: {}", endpoint));
+        context_parts.push(format!("\nRequest URL: {}", redacted_endpoint(endpoint)));
 
         // Show headers if error mentions headers
         if server_message_lower.contains("header") {
@@ -1006,7 +1016,8 @@ impl SamplingClient {
                 let endpoint = self.endpoint("chat/completions");
                 let server_message = response.text().await.unwrap_or_default();
                 return Err(SamplingError::Auth(format!(
-                    "Unauthorized (401) from {endpoint}: {server_message}"
+                    "Unauthorized (401) from {}: {server_message}",
+                    redacted_endpoint(&endpoint)
                 )));
             }
 
@@ -1196,7 +1207,8 @@ impl SamplingClient {
                 let endpoint = self.endpoint("responses");
                 let server_message = parse_error_bytes(bytes.as_ref());
                 return Err(SamplingError::Auth(format!(
-                    "Unauthorized (401) from {endpoint}: {server_message}"
+                    "Unauthorized (401) from {}: {server_message}",
+                    redacted_endpoint(&endpoint)
                 )));
             }
 
@@ -1363,7 +1375,8 @@ impl SamplingClient {
                 let endpoint = self.endpoint("responses");
                 let server_message = response.text().await.unwrap_or_default();
                 return Err(SamplingError::Auth(format!(
-                    "Unauthorized (401) from {endpoint}: {server_message}"
+                    "Unauthorized (401) from {}: {server_message}",
+                    redacted_endpoint(&endpoint)
                 )));
             }
             let model_metadata = extract_model_metadata(response.headers());
@@ -1542,7 +1555,8 @@ impl SamplingClient {
                 let endpoint = self.endpoint("messages");
                 let server_message = parse_error_bytes(bytes.as_ref());
                 return Err(SamplingError::Auth(format!(
-                    "Unauthorized (401) from {endpoint}: {server_message}"
+                    "Unauthorized (401) from {}: {server_message}",
+                    redacted_endpoint(&endpoint)
                 )));
             }
 
@@ -1657,7 +1671,8 @@ impl SamplingClient {
                 let endpoint = self.endpoint("messages");
                 let server_message = response.text().await.unwrap_or_default();
                 return Err(SamplingError::Auth(format!(
-                    "Unauthorized (401) from {endpoint}: {server_message}"
+                    "Unauthorized (401) from {}: {server_message}",
+                    redacted_endpoint(&endpoint)
                 )));
             }
             let model_metadata = extract_model_metadata(response.headers());
@@ -3048,3 +3063,31 @@ mod tests {
         ));
     }
 }
+
+#[cfg(test)]
+mod redacted_endpoint_tests {
+    /// Every spelling the client accepts (LF inside, one slash, no slash) loses its userinfo.
+    #[test]
+    fn redacted_endpoint_drops_userinfo_in_every_accepted_spelling() {
+        for spelling in [
+            "http://u:TEST_PASSWORD@127.0.0.1:1/v1/chat/completions",
+            "http://u:TEST PASSWORD@127.0.0.1:1/v1/chat/completions",
+            "http://u:TEST_PASSWORD\n@127.0.0.1:1/v1/chat/completions",
+            "http://u:TEST_PASSWORD\r\n@127.0.0.1:1/v1/chat/completions",
+            "http:/u:TEST_PASSWORD@127.0.0.1:1/v1/chat/completions",
+            "http:u:TEST_PASSWORD@127.0.0.1:1/v1/chat/completions",
+            "http:\\u:TEST_PASSWORD@127.0.0.1:1/v1/chat/completions",
+        ] {
+            let redacted = super::redacted_endpoint(spelling);
+            assert_eq!(
+                redacted, "http://127.0.0.1:1/v1/chat/completions",
+                "{spelling:?}"
+            );
+        }
+        let gateway = super::redacted_endpoint(
+            "http://127.0.0.1:1/?access_token=TEST_QUERY_TOKEN&route=x#frag",
+        );
+        assert!(!gateway.contains("TEST_QUERY_TOKEN"), "{gateway}");
+        assert!(gateway.contains("route=x"), "{gateway}");
+    }
+}