Classify pinned Copilot admission failures without echoing provider data

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/paperclip-runner/runner/crates/runner-core/src/acpx_sidecar_transport.rs

@@ -694,6 +694,9 @@ fn response_error_classification(error: &ResponseError) -> &'static str {
         "AGENT_STARTUP_FAILED.OTHER" => return "agent_startup_other",
         "AGENT_DISCONNECTED" => return "agent_disconnected",
         "AUTH_REQUIRED" => return "authentication_required",
+        "COPILOT_AUTH_REQUIRED" => return "authentication_required",
+        "COPILOT_ENTITLEMENT_DENIED" => return "provider_entitlement_denied",
+        "COPILOT_MODEL_UNAVAILABLE" => return "requested_model_unsupported",
         "SESSION_RESUME_REQUIRED" => return "session_resume_required",
         "SESSION_MODE_REPLAY_FAILED" => return "session_mode_replay_failed",
         "SESSION_MODEL_REPLAY_FAILED" => return "session_model_replay_failed",
@@ -804,6 +807,30 @@ mod tests {
         }
     }
 
+    #[test]
+    fn candidate_auth_diagnostics_use_only_closed_codes_and_never_provider_text() {
+        for (code, expected) in [
+            ("COPILOT_AUTH_REQUIRED", "authentication_required"),
+            ("COPILOT_ENTITLEMENT_DENIED", "provider_entitlement_denied"),
+            ("COPILOT_MODEL_UNAVAILABLE", "requested_model_unsupported"),
+            ("COPILOT_AUTH_REQUIRED_EXTRA", "unclassified"),
+            ("COPILOT_REQUEST_FAILED", "unclassified"),
+            ("UNKNOWN_CANDIDATE_FAILURE", "unclassified"),
+        ] {
+            let error = ResponseError {
+                code: code.to_owned(),
+                message:
+                    "private-token-canary COPILOT_AUTH_REQUIRED https://user:secret@example.invalid"
+                        .to_owned(),
+                retryable: false,
+            };
+            let classification = response_error_classification(&error);
+            assert_eq!(classification, expected);
+            assert!(!classification.contains("canary"));
+            assert!(!classification.contains("secret"));
+        }
+    }
+
     #[test]
     fn classifies_only_allowlisted_internal_sidecar_failures() {
         let error = |code: &str, message: &str| ResponseError {