feat(librarian): Module C retrieval upgrades (stack base for #1088)

Dual-index retrieval, CRE summaries, prior cage, hub seed, edition remap,
and related librarian defaults. Rewrites #1088 as the reviewable base; later
stacked PRs add harvester, B2 eval, fixtures, mappings, and full-pipeline docs.

Author: northdpole

application/prompt_client/litellm_router.py

@@ -8,15 +8,17 @@
 
 from __future__ import annotations
 
-from cre_logging import get_logger
-
-logger = get_logger(__name__)
-
+import logging
 import os
 import time
 from typing import Any, Callable, List, Optional, Sequence
 
-from application.prompt_client.llm_error_utils import is_rate_limit_error
+from application.prompt_client.llm_error_utils import (
+    is_rate_limit_error,
+    is_transient_llm_error,
+)
+
+logger = logging.getLogger(__name__)
 
 LlmFn = Callable[[str, str], str]
 
@@ -47,21 +49,26 @@ def with_rate_limit_retry(
     max_retries: Optional[int] = None,
     retry_sleep_seconds: Optional[int] = None,
 ) -> Any:
+    """Retry rate limits and transient connection/timeout blips."""
     default_retries, default_sleep = retry_policy()
     retries = default_retries if max_retries is None else max_retries
     sleep_s = default_sleep if retry_sleep_seconds is None else retry_sleep_seconds
     for attempt in range(retries + 1):
         try:
             return fn()
         except Exception as err:
-            if not is_rate_limit_error(err) or attempt >= retries:
+            retriable = is_transient_llm_error(err) or is_rate_limit_error(err)
+            if not retriable or attempt >= retries:
                 raise
+            kind = "rate/quota" if is_rate_limit_error(err) else "transient"
             logger.info(
-                "rate/quota limited during %s; sleeping %ss (attempt %s/%s)",
+                "%s limited during %s; sleeping %ss (attempt %s/%s): %s",
+                kind,
                 context,
                 sleep_s,
                 attempt + 1,
                 retries + 1,
+                type(err).__name__,
             )
             time.sleep(sleep_s)
     raise RuntimeError("unreachable: retry loop exited unexpectedly")

application/prompt_client/llm_error_utils.py

@@ -31,3 +31,38 @@ def is_rate_limit_error(err: BaseException) -> bool:
             if code == 429:
                 return True
     return False
+
+
+def is_transient_llm_error(err: BaseException) -> bool:
+    """Connection / timeout blips that are safe to retry (not model refusal)."""
+    if is_rate_limit_error(err):
+        return True
+    name = type(err).__name__.lower()
+    if any(
+        tok in name
+        for tok in (
+            "connect",
+            "timeout",
+            "apiconnection",
+            "remoteprotocol",
+            "network",
+        )
+    ):
+        return True
+    msg = str(err).lower()
+    return any(
+        tok in msg
+        for tok in (
+            "connection reset",
+            "connection aborted",
+            "connection refused",
+            "temporarily unavailable",
+            "broken pipe",
+            "timed out",
+            "timeout",
+            "errno 54",
+            "errno 104",
+            "server disconnected",
+            "remote end closed",
+        )
+    )