fix(ocaml): diff_report must not abort the batch on one malformed fixture

ocaml/bin/diff_report.ml

@@ -10,8 +10,20 @@ let () =
       let any =
         List.fold_left
           (fun acc f ->
-            let diverged = Diff_report.bundle_if_divergent ~out_dir f in
-            if diverged then Printf.eprintf "divergence: %s -> bundle in %s\n" f out_dir;
+            (* Guard each fixture: a malformed or unreadable one must not raise out of the fold and
+               abort the whole batch, which would silently lose the divergence bundles for every
+               later fixture -- exactly when CI needs them. Surface it as a failure (diverged=true)
+               so the missing comparison forces a non-zero exit instead of disappearing. Matches the
+               explicit Parse_error/Sys_error handling in verify_replay.ml and replay_snapshot.ml. *)
+            let diverged =
+              try
+                let d = Diff_report.bundle_if_divergent ~out_dir f in
+                if d then Printf.eprintf "divergence: %s -> bundle in %s\n" f out_dir;
+                d
+              with Stream_parser.Parse_error msg | Sys_error msg ->
+                Printf.eprintf "cannot compare %s: %s\n" f msg;
+                true
+            in
             acc || diverged)
           false fixtures
       in

ocaml/test/test_diff_report.ml

@@ -24,4 +24,17 @@ let () =
     prerr_endline "FAIL: unexpected divergence for stream_seed7.txt";
     exit 1);
 
+  (* A malformed fixture must raise a catchable Stream_parser.Parse_error, not some other exception:
+     the diff_report bin relies on catching exactly this (and Sys_error) to guard each fixture in
+     the batch so one bad file cannot abort the whole run and silently lose later bundles. *)
+  let bad = Filename.concat out "malformed.txt" in
+  let oc = open_out bad in
+  output_string oc "version 1\ncmd reg S0\n" (* no meta line *);
+  close_out oc;
+  (match Diff_report.bundle_if_divergent ~out_dir:out bad with
+  | _ ->
+      prerr_endline "FAIL: expected Parse_error for malformed fixture";
+      exit 1
+  | exception Stream_parser.Parse_error _ -> ());
+
   print_endline "diff_report: all tests passed"