Librarian: stop warning about missing netrc when mailto is set via env

Librarian.__init__ reads the Crossref contact from CONJURER_CROSSREF_MAILTO,
then tries to override it from a 'crossref' netrc entry. When no netrc is
mounted (the normal container setup - default /root/.netrc) the read raises
FileNotFoundError and it logged 'Crossref credentials missing in netrc ...'
on EVERY search, even though the env var was set and used. Pure noise.

Only warn when there is genuinely no contact from either source (env unset
AND netrc unreadable) - which is also the case that then raises. When the
env var is set, a missing netrc is expected and logged at debug.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

conjurer_librarian/conjurer_librarian.py

@@ -212,6 +212,9 @@ class Librarian(object):
         - search_result_from_cr: A dictionary to store the search results from Crossref.
         - done: A flag indicating if the search is done.
         """
+        # Crossref only needs a contact mailto. It can come from
+        # CONJURER_CROSSREF_MAILTO (the usual container setup) OR from a
+        # "crossref" entry in the netrc; netrc takes precedence when present.
         mailto_contact: Optional[str] = os.getenv("CONJURER_CROSSREF_MAILTO")
         if netrc:
             try:
@@ -219,10 +222,22 @@ class Librarian(object):
                 auth_tokens = netrc_mod.authenticators("crossref")
                 if auth_tokens:
                     mailto_contact = auth_tokens[0]
-            except (FileNotFoundError, netrc.NetrcParseError):
-                logging.getLogger("conjurer_librarian").warning(
-                    "Crossref credentials missing in netrc %s", NETRC_FILE
-                )
+            except (FileNotFoundError, netrc.NetrcParseError) as exc:
+                # A missing/unreadable netrc is NORMAL when the mailto is set via
+                # env - don't cry wolf on every single search. Only warn when we
+                # genuinely have no contact from either source.
+                _log = logging.getLogger("conjurer_librarian")
+                if mailto_contact:
+                    _log.debug(
+                        "netrc %s not used (%s) - using CONJURER_CROSSREF_MAILTO",
+                        NETRC_FILE, exc,
+                    )
+                else:
+                    _log.warning(
+                        "Crossref contact not configured: netrc %s unreadable (%s) "
+                        "and CONJURER_CROSSREF_MAILTO unset",
+                        NETRC_FILE, exc,
+                    )
         if not mailto_contact:
             raise RuntimeError(
                 "Crossref credentials not configured. Set CONJURER_CROSSREF_MAILTO or add to netrc."