fix: Fix output handling (#2059)

Author: Bownairo

release-controller/dre_cli.py

@@ -150,10 +150,8 @@ def get_blessed_guestos_versions(self) -> set[str]:
         # `dre get` forwards its arguments verbatim to `ic-admin`, so the
         # output format is dictated by the ic-admin build that matches the
         # currently deployed registry canister (downloaded at runtime), not
-        # by this code.  Newer ic-admin releases ignore `--json` for this
-        # subcommand and print a plain newline-separated list of version IDs;
-        # older ones wrapped it in {"value": {"blessed_version_ids": [...]}}.
-        # Accept both so a registry-canister upgrade can't break us again.
+        # by this code. With the migration away from blessed versions, ic-admin
+        # has had a few formats. Support all of them here.
         output = subprocess.check_output(
             [self.cli, "get", "blessed-replica-versions", "--json"],
             env=self.env,
@@ -163,11 +161,18 @@ def get_blessed_guestos_versions(self) -> set[str]:
             parsed = json.loads(output)
         except json.JSONDecodeError:
             parsed = None
+
+        # Old format
         if isinstance(parsed, dict):
             return set(
                 typing.cast(list[str], parsed["value"]["blessed_version_ids"])
             )
-        return {line.strip() for line in output.splitlines() if line.strip()}
+        # New format, with --json support
+        elif isinstance(parsed, list):
+            return set(parsed)
+        # New format, without --json support
+        else:
+            return {line.strip() for line in output.splitlines() if line.strip()}
 
     def get_blessed_hostos_versions(self) -> set[str]:
         """Query the blessed HostOS versions."""