feat(fetch): one ESPN scoreboard cache key and a max-age response cache (fetch service stage 2) (#728)

Fetch service stage 2: one ESPN scoreboard cache key shared across the sports base classes (legacy keys still read), and a max-age response cache in the fetch service.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/common/api_helper.py

@@ -10,7 +10,12 @@ import logging
 import time
 from datetime import datetime
 from types import MappingProxyType
-from src.common.espn_dates import ESPN_MAX_LIMIT
+from src.common.espn_dates import (
+    ESPN_MAX_LIMIT,
+    espn_scoreboard_cache_key,
+    read_espn_scoreboard_cache,
+    store_espn_scoreboard_cache,
+)
 from src.common.fetch_service import fetch_get, fetch_post, share_connection_pool
 from typing import TYPE_CHECKING, Any, Dict, Mapping, Optional, cast
 
@@ -117,6 +122,14 @@ class APIHelper:
         Returns:
             Response data as dictionary or None if request fails
         """
+        return self._get(url, params, headers, timeout, cache_key, cache_ttl,
+                         cache_ttl if cache_key else None)
+
+    def _get(self, url: str, params: Optional[Dict], headers: Optional[Dict],
+             timeout: Optional[int], cache_key: Optional[str], cache_ttl: int,
+             cache_max_age: Optional[float]) -> Optional[Dict]:
+        """:meth:`get`, saying how old a response the fetch service's short
+        response cache may hand back (``cache_max_age``, the caller's TTL)."""
         if cache_key and self.cache_manager:
             cached = self._get_from_cache(cache_key, cache_ttl)
             if cached is not None:
@@ -138,7 +151,8 @@ class APIHelper:
                 url, 
                 params=params,
                 headers=request_headers,
-                timeout=timeout or self.default_timeout
+                timeout=timeout or self.default_timeout,
+                cache_max_age=cache_max_age,
             )
             response.raise_for_status()
             
@@ -167,22 +181,23 @@ class APIHelper:
             sport: Sport name (e.g., 'basketball', 'football')
             league: League name (e.g., 'nba', 'nfl')
             date: Date in YYYYMMDD format (defaults to today)
-            cache_key: Cache key for response
-            cache_ttl: Cache time-to-live in seconds
-            
+            cache_key: Cache key for response. By default the canonical
+                ``espn_scoreboard_cache_key(sport, league, date)``, shared
+                with every other consumer of this scoreboard, with the key
+                this used before (``espn_{sport}_{league}_{date}``) read as a
+                fallback for one release. An explicit key works as before.
+            cache_ttl: Cache time-to-live in seconds. A shared entry is
+                returned only while it is at most this old.
+
         Returns:
             ESPN API response data or None if request fails
         """
         if date is None:
             date = datetime.now().strftime('%Y%m%d')
-        
+
         # Build URL
         url = f"https://site.api.espn.com/apis/site/v2/sports/{sport}/{league}/scoreboard"
-        
-        # Build cache key if not provided
-        if cache_key is None:
-            cache_key = f"espn_{sport}_{league}_{date}"
-        
+
         # Set parameters
         # limit above 500 makes ESPN truncate instead of erroring: college
         # football came back with 25 of 68 games. See src/common/espn_dates.py.
@@ -190,8 +205,26 @@ class APIHelper:
             'dates': date,
             'limit': ESPN_MAX_LIMIT
         }
-        
-        return self.get(url, params=params, cache_key=cache_key, cache_ttl=cache_ttl)
+
+        if cache_key is not None:
+            return self.get(url, params=params, cache_key=cache_key, cache_ttl=cache_ttl)
+
+        legacy_key = f"espn_{sport}_{league}_{date}"
+        try:
+            shared_key = espn_scoreboard_cache_key(sport, league, date)
+        except ValueError:
+            # Not a path or date the canonical key covers: the old key.
+            return self.get(url, params=params, cache_key=legacy_key, cache_ttl=cache_ttl)
+        if self.cache_manager:
+            cached = read_espn_scoreboard_cache(
+                self.cache_manager, shared_key, cache_ttl, legacy_keys=(legacy_key,))
+            if cached is not None:
+                self.logger.debug(f"Using cached response for {shared_key}")
+                return cast(Dict[Any, Any], cached)
+        data = self._get(url, params, None, None, None, cache_ttl, cache_ttl)
+        if data is not None and self.cache_manager:
+            store_espn_scoreboard_cache(self.cache_manager, shared_key, data)
+        return data
     
     def fetch_espn_standings(self, sport: str, league: str,
                             cache_key: Optional[str] = None,

src/common/espn_dates.py

@@ -30,15 +30,34 @@ Once a range has been rejected, later ranges skip straight to chunks for
 ``RANGE_RETRY_SECONDS`` instead of spending a doomed request first -- live
 scoreboards ask every 30 seconds. After that the range is tried again, so the
 workaround retires itself if ESPN reverts.
+
+ONE CACHE KEY PER SCOREBOARD
+----------------------------
+The same ESPN scoreboard used to be cached under a different key by every
+consumer: odds-ticker as ``scoreboard_data_{sport}_{league}_{date}``,
+``APIHelper`` as ``espn_{sport}_{league}_{date}``, the scoreboards as
+``{sport_key}_schedule_{window}`` -- so two plugins showing the same league
+fetched and stored it twice. :func:`espn_scoreboard_cache_key` is the one
+name for "this sport/league scoreboard for these dates", and
+:func:`get_espn_scoreboard` (or :func:`read_espn_scoreboard_cache` and
+:func:`store_espn_scoreboard_cache` around :func:`fetch_espn_scoreboard`)
+is the cache-through read every consumer can share. A read never returns an
+entry older than the reader's own ``max_age``, whoever wrote it and whatever
+ttl they stored with it. Old keys are passed as ``legacy_keys`` and read
+after the canonical one, so an upgrade does not refetch everything at once;
+they can go one release after the one that added this.
 """
 
 import contextvars
+import logging
+import math
+import re
 import threading
 import time
 from concurrent.futures import ThreadPoolExecutor
-from datetime import date, timedelta
+from datetime import date, datetime, timedelta
 from functools import partial
-from typing import Any, Dict, List, Optional, Tuple, cast
+from typing import Any, Callable, Dict, Iterable, List, Optional, Tuple, cast
 
 try:
     from src.common.json_body import response_json
@@ -51,18 +70,23 @@ except ImportError:
 try:
     # The core fetch service: counts, per-host budget, merging of identical
     # requests. Same call, same result and errors as ``session.get``.
-    from src.common.fetch_service import fetch_get, pinned_caller
+    from src.common.fetch_service import fetch_get, get_fetch_service, pinned_caller
+    _COUNTS_FETCHES = True
 except ImportError:
     # Bundled copies on cores without it call the session directly.
     import contextlib
 
     def fetch_get(session: Any, url: str, *, share_in_flight: bool = True,
-                  **kwargs: Any) -> Any:
+                  cache_max_age: Optional[float] = None, **kwargs: Any) -> Any:
         return session.get(url, **kwargs)
 
     def pinned_caller() -> Any:
         return contextlib.nullcontext()
 
+    _COUNTS_FETCHES = False
+
+_logger = logging.getLogger(__name__)
+
 # Above this, ESPN returns a truncated list instead of an error. See module
 # docstring: 500 is the largest value measured to return complete data.
 ESPN_MAX_LIMIT = 500
@@ -89,8 +113,23 @@ __all__ = [
     "merge_scoreboard_payloads",
     "fetch_espn_date_chunks",
     "fetch_espn_scoreboard",
+    "ESPN_SCOREBOARD_URL",
+    "espn_scoreboard_url",
+    "espn_scoreboard_cache_key",
+    "espn_scoreboard_cache_key_for_url",
+    "read_espn_scoreboard_cache",
+    "store_espn_scoreboard_cache",
+    "get_espn_scoreboard",
 ]
 
+#: The site-API scoreboard every sport and league shares.
+ESPN_SCOREBOARD_URL = "https://site.api.espn.com/apis/site/v2/sports/{sport}/{league}/scoreboard"
+_ESPN_HOST_URL = "https://site.api.espn.com/"
+
+_PATH_PART = re.compile(r"^[a-z0-9][a-z0-9.\-]*$")
+_DATES = re.compile(r"^\d{4}(?:\d{2}(?:\d{2})?)?$|^\d{8}-\d{8}$")
+_SCOREBOARD_PATH = re.compile(r"/sports/([^/?#]+)/([^/?#]+)/scoreboard/?$")
+
 
 def clamp_espn_limit(params: Optional[Dict[str, Any]]) -> Dict[str, Any]:
     """Return a copy of ``params`` with any ``limit`` over 500 pulled back to 500."""
@@ -129,6 +168,12 @@ def parse_espn_date_range(dates: Any) -> Optional[Tuple[date, date]]:
     return start, end
 
 
+def _memo_kwargs(cache_max_age: Optional[float]) -> Dict[str, Any]:
+    """``cache_max_age`` for fetch_get, only when the caller gave one, so a
+    call that did not say is the call it always was."""
+    return {} if cache_max_age is None else {"cache_max_age": cache_max_age}
+
+
 def _ranges_known_rejected() -> bool:
     with _range_lock:
         return time.monotonic() < _ranges_rejected_until
@@ -204,6 +249,7 @@ def merge_scoreboard_payloads(payloads: List[Any]) -> Dict[str, Any]:
 
 def _fetch_one_chunk(
     session, url: str, params: Dict[str, Any], headers, timeout, logger, chunk: str,
+    cache_max_age: Optional[float] = None,
 ) -> Optional[Dict[str, Any]]:
     """GET a single ``dates=`` chunk, or None when it failed.
 
@@ -217,6 +263,7 @@ def _fetch_one_chunk(
             params=dict(params, dates=chunk, limit=ESPN_MAX_LIMIT),
             headers=headers,
             timeout=timeout,
+            **_memo_kwargs(cache_max_age),
         )
         response.raise_for_status()
         return cast(Optional[Dict[str, Any]], response_json(response))
@@ -228,7 +275,7 @@ def _fetch_one_chunk(
 
 def _fetch_chunks(
     session, url: str, params: Dict[str, Any], headers, timeout, logger,
-    chunks: List[str],
+    chunks: List[str], cache_max_age: Optional[float] = None,
 ) -> List[Optional[Dict[str, Any]]]:
     """Fetch every chunk, returning payloads positionally aligned with ``chunks``.
 
@@ -246,6 +293,7 @@ def _fetch_chunks(
         return []
     fetch = partial(
         _fetch_one_chunk, session, url, params, headers, timeout, logger,
+        cache_max_age=cache_max_age,
     )
     if len(chunks) == 1:
         return [fetch(chunks[0])]
@@ -268,6 +316,7 @@ def fetch_espn_date_chunks(
     headers: Optional[Dict[str, str]] = None,
     timeout: int = 15,
     logger=None,
+    cache_max_age: Optional[float] = None,
 ) -> Optional[Dict[str, Any]]:
     """Fetch a ``YYYYMMDD-YYYYMMDD`` window as month and day chunks.
 
@@ -299,7 +348,7 @@ def fetch_espn_date_chunks(
         )
 
     results = _fetch_chunks(
-        session, url, params, headers, timeout, logger, chunks,
+        session, url, params, headers, timeout, logger, chunks, cache_max_age,
     )
     attempted = len(chunks)
 
@@ -331,7 +380,7 @@ def fetch_espn_date_chunks(
         days = [day for index in sorted(capped) for day in capped[index]]
         attempted += len(days)
         by_day = dict(zip(days, _fetch_chunks(
-            session, url, params, headers, timeout, logger, days,
+            session, url, params, headers, timeout, logger, days, cache_max_age,
         )))
         for index, month_days in capped.items():
             slots[index] = [by_day.get(day) for day in month_days]
@@ -364,6 +413,7 @@ def fetch_espn_scoreboard(
     headers: Optional[Dict[str, str]] = None,
     timeout: int = 15,
     logger=None,
+    cache_max_age: Optional[float] = None,
 ) -> Dict[str, Any]:
     """GET an ESPN scoreboard, re-asking in month/day chunks if a range 400s.
 
@@ -373,6 +423,10 @@ def fetch_espn_scoreboard(
     and later ranges go straight to chunks for ``RANGE_RETRY_SECONDS``. A 400 on
     a non-range request, any other error, and a range whose every chunk fails
     all raise as before.
+
+    ``cache_max_age`` is the oldest response, in seconds, the caller takes
+    from the fetch service's short response cache (its own TTL; 0 always
+    asks ESPN). None leaves it to the service default.
     """
     params = clamp_espn_limit(params)
     is_range = parse_espn_date_range(params.get("dates")) is not None
@@ -381,7 +435,7 @@ def fetch_espn_scoreboard(
     if is_range and _ranges_known_rejected():
         data = fetch_espn_date_chunks(
             session, url, params=params, headers=headers,
-            timeout=timeout, logger=logger,
+            timeout=timeout, logger=logger, cache_max_age=cache_max_age,
         )
         if data is not None:
             return data
@@ -389,7 +443,8 @@ def fetch_espn_scoreboard(
         # real error to log, without spending the chunks a second time.
         chunks_tried = True
 
-    response = fetch_get(session, url, params=params, headers=headers, timeout=timeout)
+    response = fetch_get(session, url, params=params, headers=headers, timeout=timeout,
+                         **_memo_kwargs(cache_max_age))
     if is_range and response.status_code == 400 and not chunks_tried:
         _note_range_rejected()
         if logger:
@@ -400,9 +455,225 @@ def fetch_espn_scoreboard(
             )
         data = fetch_espn_date_chunks(
             session, url, params=params, headers=headers,
-            timeout=timeout, logger=logger,
+            timeout=timeout, logger=logger, cache_max_age=cache_max_age,
         )
         if data is not None:
             return data
     response.raise_for_status()
     return cast(Dict[str, Any], response_json(response))
+
+
+# --- one cache key per scoreboard --------------------------------------------------
+
+def espn_scoreboard_url(sport: str, league: str) -> str:
+    """The site-API scoreboard URL for an ESPN ``sport`` / ``league`` path."""
+    return ESPN_SCOREBOARD_URL.format(sport=_path_part(sport, "sport"),
+                                      league=_path_part(league, "league"))
+
+
+def _path_part(value: Any, what: str) -> str:
+    text = str(value or "").strip().lower()
+    if not _PATH_PART.match(text):
+        raise ValueError(f"not an ESPN {what} path segment: {value!r}")
+    return text
+
+
+def _day(value: Any) -> str:
+    if isinstance(value, (date, datetime)):
+        return value.strftime("%Y%m%d")
+    text = str(value).strip()
+    if len(text) != 8 or not text.isdigit():
+        raise ValueError(f"not an ESPN day (YYYYMMDD): {value!r}")
+    return text
+
+
+def _dates_part(dates: Any) -> str:
+    """``dates`` as ESPN spells it, or ``current`` for no ``dates`` at all."""
+    if dates is None or dates == "":
+        return "current"
+    if isinstance(dates, (date, datetime)):
+        return _day(dates)
+    if isinstance(dates, (tuple, list)):
+        if len(dates) != 2:
+            raise ValueError(f"a date range is (start, end): {dates!r}")
+        start, end = _day(dates[0]), _day(dates[1])
+        return start if start == end else f"{start}-{end}"
+    text = str(dates).strip()
+    if isinstance(dates, bool) or not _DATES.match(text):
+        raise ValueError(
+            f"not an ESPN dates value (YYYY, YYYYMM, YYYYMMDD or "
+            f"YYYYMMDD-YYYYMMDD): {dates!r}")
+    return text
+
+
+def espn_scoreboard_cache_key(sport: str, league: str, dates: Any = None) -> str:
+    """The one cache key for an ESPN scoreboard, whoever caches it.
+
+    ``sport`` and ``league`` are ESPN's own path segments -- ``football`` /
+    ``college-football``, ``soccer`` / ``eng.1`` -- not a plugin's
+    ``sport_key``, so every plugin showing a league names it the same way.
+    ``dates`` is what the request sends as ``dates=``: ``"YYYYMMDD"``,
+    ``"YYYYMM"``, ``"YYYY"``, ``"YYYYMMDD-YYYYMMDD"``, a ``date``, or a
+    ``(start, end)`` pair of either; None is the undated "current"
+    scoreboard. Anything else raises ValueError rather than invent a key.
+
+    The key says nothing about ``limit``: a cached copy is meant to be a
+    whole one (the helpers here always ask for ``ESPN_MAX_LIMIT``).
+    """
+    return (f"espn_scoreboard_{_path_part(sport, 'sport')}_"
+            f"{_path_part(league, 'league')}_{_dates_part(dates)}")
+
+
+def espn_scoreboard_cache_key_for_url(url: str, dates: Any = None) -> Optional[str]:
+    """:func:`espn_scoreboard_cache_key` for a scoreboard URL, or None when
+    ``url`` is not ``.../sports/{sport}/{league}/scoreboard``."""
+    match = _SCOREBOARD_PATH.search(str(url or "").split("?", 1)[0])
+    if match is None:
+        return None
+    try:
+        return espn_scoreboard_cache_key(match.group(1), match.group(2), dates)
+    except ValueError:
+        return None
+
+
+def _note_cache_hit(legacy: bool, avoided_request: bool = True) -> None:
+    if not _COUNTS_FETCHES:
+        return
+    try:
+        get_fetch_service().note_cache_hit(
+            _ESPN_HOST_URL, legacy=legacy, avoided_request=avoided_request)
+    except Exception:  # noqa: BLE001 - counting never breaks a read
+        _logger.debug("could not count a scoreboard cache hit", exc_info=True)
+
+
+def _fresh_cached(cache_manager: Any, key: str, max_age: Optional[float],
+                  now: float) -> Tuple[Optional[Dict[str, Any]], Optional[float]]:
+    """The data cached under ``key`` if it is at most ``max_age`` seconds
+    old, and its age (None when the cache does not say).
+
+    The age is the stored record's own timestamp, checked here: CacheManager
+    lets a ttl stored by the writer override the reader's max_age, and its
+    memory tier times an entry from when it was loaded, not written. A key
+    shared by readers with different TTLs can rely on neither.
+    """
+    reader = getattr(cache_manager, "get_cached_data", None)
+    limit = None if max_age is None else max(1, int(math.ceil(max_age)))
+    if not callable(reader):
+        # A cache without records (a test double, a plugin's own store).
+        value = cache_manager.get(key, max_age=limit)
+        return (value if isinstance(value, dict) else None), None
+    record = reader(key, max_age=limit, memory_ttl=limit)
+    if not isinstance(record, dict):
+        return None, None
+    if "data" not in record:
+        return record, None  # unwrapped; the cache already judged it by mtime
+    stamp = record.get("timestamp")
+    age: Optional[float] = None
+    if not isinstance(stamp, bool) and isinstance(stamp, (int, float)):
+        age = max(0.0, now - float(stamp))
+    if max_age is not None and (age is None or age > max_age):
+        return None, None
+    data = record["data"]
+    return (data if isinstance(data, dict) else None), age
+
+
+def read_espn_scoreboard_cache(
+    cache_manager: Any,
+    key: str,
+    max_age: Optional[float],
+    legacy_keys: Iterable[str] = (),
+    now: Optional[float] = None,
+    accept: Optional[Callable[[Dict[str, Any], Optional[float]], bool]] = None,
+) -> Optional[Dict[str, Any]]:
+    """The cached scoreboard under ``key``, or under the first of
+    ``legacy_keys`` that has one, if it is at most ``max_age`` seconds old.
+
+    None on a miss, a stale entry, ``max_age`` of 0 or less, no cache
+    manager, or any cache error -- a read never raises. ``max_age=None``
+    takes an entry of any age. ``accept(data, age_seconds)`` can turn down
+    an entry the age alone would allow (a payload holding a live game wants
+    a shorter limit); ``age_seconds`` is None when the cache cannot say. A
+    hit is counted in the fetch statistics (``cache_hits``;
+    ``legacy_cache_hits`` too for an old key).
+    """
+    if cache_manager is None:
+        return None
+    if max_age is not None and max_age <= 0:
+        return None
+    clock = time.time() if now is None else now
+    for index, candidate in enumerate([key, *legacy_keys]):
+        if not candidate:
+            continue
+        try:
+            data, age = _fresh_cached(cache_manager, candidate, max_age, clock)
+            if data is not None and accept is not None and not accept(data, age):
+                data = None
+        except Exception:  # noqa: BLE001 - a broken cache is a miss
+            _logger.debug("scoreboard cache read failed for %s", candidate, exc_info=True)
+            continue
+        if data is not None:
+            _note_cache_hit(legacy=index > 0)
+            return data
+    return None
+
+
+def store_espn_scoreboard_cache(cache_manager: Any, key: str, data: Any) -> None:
+    """Cache a fetched scoreboard under ``key``. Never raises.
+
+    No ttl is stored: each reader applies its own ``max_age`` (a live
+    reader 30 s, a schedule reader an hour), and a stored ttl would
+    override theirs in CacheManager.
+    """
+    if cache_manager is None or data is None:
+        return
+    try:
+        cache_manager.set(key, data)
+    except Exception:  # noqa: BLE001 - the caller still has its data
+        _logger.warning("Could not cache scoreboard %s", key, exc_info=True)
+
+
+def get_espn_scoreboard(
+    session: Any,
+    sport: str,
+    league: str,
+    dates: Any = None,
+    *,
+    cache_manager: Any = None,
+    max_age: Optional[float] = 300,
+    legacy_keys: Iterable[str] = (),
+    headers: Optional[Dict[str, str]] = None,
+    timeout: int = 15,
+    logger: Any = None,
+) -> Dict[str, Any]:
+    """An ESPN scoreboard through the shared cache, fetched on a miss.
+
+    Reads :func:`espn_scoreboard_cache_key` (then ``legacy_keys``) and
+    returns an entry at most ``max_age`` seconds old. Otherwise it fetches
+    with :func:`fetch_espn_scoreboard` -- ``limit=ESPN_MAX_LIMIT``, ranges
+    split as ESPN needs -- caches the result under the canonical key and
+    returns it. ``max_age=0`` always fetches (and still caches, for other
+    readers). Errors raise exactly as :func:`fetch_espn_scoreboard` does,
+    and nothing is cached then. ``session=None`` uses the fetch service's
+    pooled session for the ESPN host.
+    """
+    key = espn_scoreboard_cache_key(sport, league, dates)
+    cached = read_espn_scoreboard_cache(cache_manager, key, max_age, legacy_keys)
+    if cached is not None:
+        return cast(Dict[str, Any], cached)
+    params: Dict[str, Any] = {"limit": ESPN_MAX_LIMIT}
+    spelled = _dates_part(dates)
+    if spelled != "current":
+        params["dates"] = spelled
+    data = fetch_espn_scoreboard(
+        session,
+        espn_scoreboard_url(sport, league),
+        params=params,
+        headers=headers,
+        timeout=timeout,
+        logger=logger,
+        # The response cache must not hand back anything older than the
+        # cache read above would have accepted.
+        cache_max_age=None if max_age is None else max(0.0, float(max_age)),
+    )
+    store_espn_scoreboard_cache(cache_manager, key, data)
+    return data

src/common/fetch_service.py

@@ -46,9 +46,25 @@ own conditional headers gets the raw answer. (ESPN sent no validators when
 this was written -- see the PR that added this module -- so on ESPN the store
 stays empty and costs nothing.)
 
+**Response cache (stage 2).** A 200 that says ``Cache-Control: max-age=N``
+is kept in memory for those N seconds (less its ``Age``), and an identical
+GET inside that window is answered from it without a request. ESPN sends
+max-age (1-496 s measured on 2026-10-02, most of it under 10 s) and no
+validators, so this is the only revalidation-free reuse ESPN allows. It
+never hands a caller a response older than the caller accepts: a caller
+says how old with ``cache_max_age`` (``fetch_get(..., cache_max_age=ttl)``;
+0 skips the cache), and one that does not say gets at most
+``response_cache.default_max_age`` (30 s). ``no-store``, ``no-cache``,
+``private``, ``Vary: *`` and ``Set-Cookie`` responses are never kept.
+Identical means what the validator store keys on: URL, query, effective
+headers and, for a session with cookies or auth, the session.
+
 **Counters.** Requests, merged requests, bytes, 304s, errors, HTTP errors,
-adapter retries, throttled requests and seconds waited, per plugin and per
-host. :class:`FetchStatsPublisher` publishes them for the web interface
+adapter retries, throttled requests and seconds waited, plus requests
+answered without the network: ``memo_hits`` (the response cache) and
+``cache_hits`` / ``legacy_cache_hits`` (a shared ESPN scoreboard cache entry,
+counted by ``src/common/espn_dates.py``). Per plugin and per host.
+:class:`FetchStatsPublisher` publishes them for the web interface
 (``GET /api/v3/plugins/fetch-stats``).
 
 CALLER IDENTITY
@@ -68,7 +84,8 @@ Counters are kept per plugin without plugins saying who they are:
 3. Otherwise the request is the core's own (``"core"``).
 
 Nothing here raises on account of bookkeeping: a failure in counting,
-keying or the validator store falls back to a plain ``session.get``.
+keying, the validator store or the response cache falls back to a plain
+``session.get``.
 
 Core-internal for now (stage 1). Plugins reach it through ``APIHelper`` and
 ``espn_dates``; a plugin-facing API comes with stage 3.
@@ -143,8 +160,22 @@ DEFAULT_CONFIG: Mapping[str, Any] = {
         "max_bytes": 4 * 1024 * 1024,
         "max_entry_bytes": 1024 * 1024,
     },
+    # Stage 2: responses ESPN calls fresh (Cache-Control: max-age), reused
+    # for identical GETs. A college-football Saturday is ~1 MB decoded, so
+    # one entry may be 2 MB; months (5-7 MB) are never kept.
+    "response_cache": {
+        "enabled": True,
+        "default_max_age": 30,
+        "max_entries": 64,
+        "max_bytes": 6 * 1024 * 1024,
+        "max_entry_bytes": 2 * 1024 * 1024,
+    },
 }
 
+#: However long a server says a response stays fresh, it is not kept longer
+#: than this: the cache is for requests that coincide, not for storage.
+_RESPONSE_CACHE_CEILING = 600.0
+
 #: Connection pools kept per shared adapter (one per host) and connections
 #: kept per pool. Larger than requests' 10 because one adapter now serves
 #: every core Session with its retry policy: three background workers each
@@ -171,6 +202,9 @@ _COUNTER_FIELDS = (
     "overruns",      # requests that went after max_wait_seconds anyway
     "bytes",         # decoded response body bytes received
     "wait_seconds",  # time spent waiting for host budgets
+    "memo_hits",     # answered from the response cache (max-age); nothing sent
+    "cache_hits",    # scoreboard fetches answered from a shared ESPN cache entry
+    "legacy_cache_hits",  # cache reads answered from a pre-stage-2 key (any helper)
 )
 
 
@@ -393,6 +427,117 @@ class _ValidatorStore:
             return {"entries": len(self._entries), "bytes": self._bytes}
 
 
+# --- response cache (Cache-Control: max-age) --------------------------------------
+
+@dataclass
+class _Fresh:
+    response: requests.Response
+    stored_at: float
+    #: Seconds after stored_at the server said the response stays fresh.
+    lifetime: float
+    size: int
+
+
+class _ResponseCache:
+    """LRU of finished 200 responses, each kept for its server max-age.
+
+    :meth:`get` answers only while the entry is younger than both its own
+    lifetime and the caller's limit, so nobody is handed a response older
+    than they asked for. Expired entries are dropped as they are met and on
+    every insert, so the cache holds only what is still fresh.
+    """
+
+    def __init__(self, max_entries: int, max_bytes: int, max_entry_bytes: int,
+                 clock: Callable[[], float]) -> None:
+        self.max_entries = max_entries
+        self.max_bytes = max_bytes
+        self.max_entry_bytes = max_entry_bytes
+        self._clock = clock
+        self._entries: "OrderedDict[Any, _Fresh]" = OrderedDict()
+        self._bytes = 0
+        self._lock = threading.Lock()
+
+    def get(self, key: Any, max_age: float) -> Optional[requests.Response]:
+        with self._lock:
+            entry = self._entries.get(key)
+            if entry is None:
+                return None
+            age = self._clock() - entry.stored_at
+            if age < 0 or age >= entry.lifetime:
+                self._drop_locked(key)
+                return None
+            if age > max_age:
+                return None  # fresh for someone less strict; kept
+            self._entries.move_to_end(key)
+            clone: requests.Response = _clone_response(entry.response)
+            return clone
+
+    def put(self, key: Any, response: requests.Response, lifetime: float,
+            size: int) -> None:
+        with self._lock:
+            self._drop_locked(key)
+            if size > self.max_entry_bytes or self.max_entries <= 0 or lifetime <= 0:
+                return
+            now = self._clock()
+            for old_key in [k for k, e in self._entries.items()
+                            if now - e.stored_at >= e.lifetime]:
+                self._drop_locked(old_key)
+            self._entries[key] = _Fresh(_clone_response(response), now, lifetime, size)
+            self._bytes += size
+            while self._entries and (len(self._entries) > self.max_entries
+                                     or self._bytes > self.max_bytes):
+                _, old = self._entries.popitem(last=False)
+                self._bytes -= old.size
+
+    def _drop_locked(self, key: Any) -> None:
+        old = self._entries.pop(key, None)
+        if old is not None:
+            self._bytes -= old.size
+
+    def clear(self) -> None:
+        with self._lock:
+            self._entries.clear()
+            self._bytes = 0
+
+    def stats(self) -> Dict[str, int]:
+        with self._lock:
+            return {"entries": len(self._entries), "bytes": self._bytes}
+
+
+def _cache_directives(value: Optional[str]) -> Dict[str, Optional[str]]:
+    directives: Dict[str, Optional[str]] = {}
+    for part in (value or "").split(","):
+        name, _, arg = part.strip().partition("=")
+        if name:
+            directives[name.strip().lower()] = arg.strip().strip('"') if arg else None
+    return directives
+
+
+def _fresh_for(response: Any) -> Optional[float]:
+    """Seconds a finished response stays fresh by its own headers, or None
+    when it must not be reused: not a 200 with its body read, ``no-store``,
+    ``no-cache``, ``private``, ``Vary: *``, ``Set-Cookie``, or no max-age."""
+    if _status_of(response) != 200 or _body_of(response) is None:
+        return None
+    directives = _cache_directives(_str_header(response, "Cache-Control"))
+    if {"no-store", "no-cache", "private"} & set(directives):
+        return None
+    if (_str_header(response, "Vary") or "").strip() == "*":
+        return None
+    if _str_header(response, "Set-Cookie"):
+        return None
+    try:
+        max_age = int(directives.get("max-age") or "")
+    except ValueError:
+        return None
+    try:
+        age = int(_str_header(response, "Age") or 0)
+    except ValueError:
+        age = 0
+    fresh = float(min(max_age - max(age, 0), _RESPONSE_CACHE_CEILING))
+    return fresh if fresh > 0 else None
+
+
 # --- helpers ------------------------------------------------------------------------
 
 def _host_of(url: Any) -> str:
@@ -580,6 +725,9 @@ class FetchService:
         self.max_wait_seconds = 2.0
         self._rate_limits: Dict[str, Tuple[float, float]] = {}
         self._validators = _ValidatorStore(0, 0, 0)
+        self.response_cache = True
+        self.default_max_age = 30.0
+        self._fresh = _ResponseCache(0, 0, 0, clock)
         self._applied: Optional[str] = None
         self.configure(config)
 
@@ -635,6 +783,14 @@ class FetchService:
         store = merged.get("validator_store")
         store = store if isinstance(store, Mapping) else {}
         default_store = DEFAULT_CONFIG["validator_store"]
+        fresh = merged.get("response_cache")
+        if fresh is not None and not isinstance(fresh, Mapping):
+            logger.warning("fetch_service.response_cache is not an object; using the defaults")
+        fresh = fresh if isinstance(fresh, Mapping) else {}
+        default_fresh = DEFAULT_CONFIG["response_cache"]
+        self.response_cache = fresh.get("enabled") is not False
+        self.default_max_age = _as_float(fresh.get("default_max_age"),
+                                         float(default_fresh["default_max_age"]))
         with self._lock:
             self._rate_limits = limits
             self._buckets.clear()
@@ -643,6 +799,12 @@ class FetchService:
                 _as_int(store.get("max_bytes"), default_store["max_bytes"]),
                 _as_int(store.get("max_entry_bytes"), default_store["max_entry_bytes"]),
             )
+            self._fresh = _ResponseCache(
+                _as_int(fresh.get("max_entries"), default_fresh["max_entries"]),
+                _as_int(fresh.get("max_bytes"), default_fresh["max_bytes"]),
+                _as_int(fresh.get("max_entry_bytes"), default_fresh["max_entry_bytes"]),
+                self._clock,
+            )
             self.change_count += 1
 
     def describe_config(self) -> Dict[str, Any]:
@@ -655,6 +817,8 @@ class FetchService:
             "conditional_get": self.conditional_get,
             "max_wait_seconds": self.max_wait_seconds,
             "rate_limits": limits,
+            "response_cache": self.response_cache,
+            "default_max_age": self.default_max_age,
         }
 
     def _limit_for(self, host: str) -> Optional[Tuple[float, float]]:
@@ -723,7 +887,7 @@ class FetchService:
     # -- requests --
 
     def get(self, session: Any, url: str, *, share_in_flight: bool = True,
-            **kwargs: Any) -> Any:
+            cache_max_age: Optional[float] = None, **kwargs: Any) -> Any:
         """``session.get(url, **kwargs)`` through the service.
 
         Same return value, same exceptions, and ``session.get`` is called
@@ -734,6 +898,11 @@ class FetchService:
         than joining an identical one in flight -- for a caller that may
         retry *because* an earlier request hung (BackgroundDataService
         cancels and replaces a fetch) and must not be handed that one.
+
+        ``cache_max_age`` is the oldest response, in seconds, the caller
+        will take from the response cache (its own TTL); 0 always asks the
+        network. None means ``response_cache.default_max_age``. A response
+        is never reused past the max-age its server gave it either.
         """
         transport = session if session is not None else self.session_for(url)
         if not self.enabled:
@@ -744,8 +913,24 @@ class FetchService:
             logger.debug("fetch_service could not key a request to %s", url, exc_info=True)
             request = _Request(plugin=self._caller(), host=_host_of(url))
 
+        reusable = (self.response_cache and request.representation is not None
+                    and not _has_conditional_headers(kwargs.get("headers")))
+        if reusable:
+            try:
+                limit = self._accepted_age(cache_max_age)
+                cached = self._fresh.get(request.representation, limit) if limit > 0 else None
+            except Exception:
+                logger.debug("fetch_service response cache lookup failed", exc_info=True)
+                cached = None
+            if cached is not None:
+                self._count(request.plugin, request.host, memo_hits=1)
+                return cached
+
         if request.flight is None or not self.single_flight or not share_in_flight:
-            return self._send_get(transport, url, kwargs, request)
+            response = self._send_get(transport, url, kwargs, request)
+            if reusable:
+                self._remember(request, response)
+            return response
 
         with self._lock:
             flight = self._inflight.get(request.flight)
@@ -764,6 +949,8 @@ class FetchService:
         try:
             response = self._send_get(transport, url, kwargs, request)
             flight.response = response
+            if reusable:
+                self._remember(request, response)
             return response
         except BaseException as error:
             flight.error = error
@@ -790,6 +977,40 @@ class FetchService:
         except Exception:
             logger.debug("fetch_service could not count a merged request", exc_info=True)
 
+    def note_cache_hit(self, url: Any = None, *, legacy: bool = False,
+                       avoided_request: bool = True,
+                       plugin_id: Optional[str] = None) -> None:
+        """Count a read answered from a shared cache entry instead of the
+        network (``espn_dates``). ``legacy`` marks a read from a key that
+        predates the canonical one; ``avoided_request=False`` counts only
+        that, for a read that was never going to fetch on a miss."""
+        try:
+            self._count(plugin_id or self._caller(), _host_of(url),
+                        cache_hits=int(avoided_request), legacy_cache_hits=int(legacy))
+        except Exception:
+            logger.debug("fetch_service could not count a cache hit", exc_info=True)
+
+    def _accepted_age(self, cache_max_age: Any) -> float:
+        """The oldest cached response this call accepts, in seconds."""
+        if cache_max_age is None:
+            return self.default_max_age
+        if isinstance(cache_max_age, bool) or not isinstance(cache_max_age, (int, float)):
+            return self.default_max_age
+        value = float(cache_max_age)
+        return value if math.isfinite(value) and value > 0 else 0.0
+
+    def _remember(self, request: _Request, response: Any) -> None:
+        """Keep a finished response for its server max-age. Never raises."""
+        try:
+            lifetime = _fresh_for(response)
+            if lifetime is None:
+                return
+            body = _body_of(response)
+            self._fresh.put(request.representation, response, lifetime,
+                            len(body) if body is not None else 0)
+        except Exception:
+            logger.debug("fetch_service could not keep a response", exc_info=True)
+
     def _caller(self) -> str:
         return current_plugin_id() or CORE
 
@@ -927,10 +1148,11 @@ class FetchService:
                 per_plugin[name] += value
                 per_host[name] += value
                 self._totals[name] += value
-            if changes.get("requests") or changes.get("merged"):
+            asked = int(changes.get("requests", 0) + changes.get("merged", 0)
+                        + changes.get("memo_hits", 0) + changes.get("cache_hits", 0))
+            if asked:
                 hosts = self._plugin_hosts.setdefault(plugin, {})
-                hosts[host] = hosts.get(host, 0) + int(changes.get("requests", 0)
-                                                       + changes.get("merged", 0))
+                hosts[host] = hosts.get(host, 0) + asked
             self.change_count += 1
 
     def reset_counters(self) -> None:
@@ -942,12 +1164,14 @@ class FetchService:
             self.change_count += 1
 
     def reset(self) -> None:
-        """Counters, validators, budgets and in-flight table (tests)."""
+        """Counters, validators, response cache, budgets and in-flight
+        table (tests)."""
         self.reset_counters()
         with self._lock:
             self._buckets.clear()
             self._inflight.clear()
         self._validators.clear()
+        self._fresh.clear()
 
     def snapshot(self) -> Dict[str, Any]:
         """Counters since the service started, JSON-ready."""
@@ -971,6 +1195,7 @@ class FetchService:
             "plugins": plugins,
             "hosts": hosts,
             "validators": self._validators.stats(),
+            "response_cache": self._fresh.stats(),
             "config": self.describe_config(),
         }
 
@@ -1005,10 +1230,11 @@ def configure_fetch_service(config: Any) -> FetchService:
 
 
 def fetch_get(session: Any, url: str, *, share_in_flight: bool = True,
-              **kwargs: Any) -> Any:
-    """``session.get(url, **kwargs)`` through the process's FetchService."""
+              cache_max_age: Optional[float] = None, **kwargs: Any) -> Any:
+    """``session.get(url, **kwargs)`` through the process's FetchService.
+    ``cache_max_age``: see :meth:`FetchService.get`."""
     return get_fetch_service().get(session, url, share_in_flight=share_in_flight,
-                                   **kwargs)
+                                   cache_max_age=cache_max_age, **kwargs)
 
 
 def fetch_post(session: Any, url: str, **kwargs: Any) -> Any:

src/common/sports_fetch.py

@@ -40,6 +40,20 @@ listed here.
 - ``live_games``, read with ``getattr`` -- ``_needs_previous_day``.
 - ``background_service``, read with ``getattr`` --
   ``_background_fetches_espn_ranges``.
+- ``sport`` and ``league`` (ESPN's path segments, e.g. ``football`` /
+  ``nfl``) -- ``_schedule_cache_key``, and ``_fetch_season_directly`` when
+  it is given no key and cannot read one from its URL.
+
+THE SCHEDULE CACHE KEY (fetch service stage 2)
+----------------------------------------------
+``_schedule_cache_key`` names a schedule window with the canonical
+``espn_scoreboard_cache_key`` instead of a plugin-built
+``{sport_key}_schedule_{window}``, and ``_cached_schedule`` reads it with the
+old key as a fallback for one release, so an upgrade serves the copy already
+on disk instead of refetching every league at once. The canonical key
+carries the window's dates, so it moves on a day as the window slides; a
+miss on it also deletes the copy for the day before, so a league keeps one
+window file instead of a week of them.
 
 Add it as a base of the plugin's ``SportsCore``, e.g.
 ``class SportsCore(SportsFetchMixin, SportsCoreSharedMixin,
@@ -50,9 +64,31 @@ constant on the plugin's own class still wins over the mixin's.
 import logging
 import threading
 from datetime import datetime, timedelta
-from typing import Any, ClassVar, Dict, Optional
+from typing import Any, ClassVar, Dict, Iterable, Optional
 
-from src.common.espn_dates import ESPN_MAX_LIMIT, fetch_espn_scoreboard
+from src.common.espn_dates import (
+    ESPN_MAX_LIMIT,
+    espn_scoreboard_cache_key,
+    espn_scoreboard_cache_key_for_url,
+    fetch_espn_scoreboard,
+    parse_espn_date_range,
+)
+from src.common.fetch_service import get_fetch_service
+
+_ESPN_SITE = "https://site.api.espn.com/"
+
+
+def _previous_window_key(cache_key: str) -> Optional[str]:
+    """The canonical key of the same window one day earlier, or None when
+    ``cache_key`` is not a canonical day-range key."""
+    head, sep, dates = cache_key.rpartition("_")
+    if not sep or not head.startswith("espn_scoreboard_"):
+        return None
+    span = parse_espn_date_range(dates)
+    if span is None:
+        return None
+    start, end = (day - timedelta(days=1) for day in span)
+    return f"{head}_{start.strftime('%Y%m%d')}-{end.strftime('%Y%m%d')}"
 
 
 class SportsFetchMixin:
@@ -65,6 +101,8 @@ class SportsFetchMixin:
     cache_manager: Any
     logger: logging.Logger
     _games_lock: threading.RLock
+    sport: str
+    league: str
 
     #: How many games past the one on screen keep their odds warm. One is
     #: enough for the line to be ready when the rotation advances; more just
@@ -154,18 +192,66 @@ class SportsFetchMixin:
         service = getattr(self, "background_service", None)
         return bool(getattr(service, "handles_espn_date_ranges", False))
 
+    def _schedule_cache_key(self, datestring: str) -> str:
+        """The canonical cache key for this league's schedule over
+        ``datestring`` (``espn_scoreboard_cache_key``)."""
+        return espn_scoreboard_cache_key(self.sport, self.league, datestring)
+
+    def _cached_schedule(self, cache_key: str, legacy_keys: Iterable[str] = ()) -> Any:
+        """What ``self.cache_manager.get(cache_key)`` returns, falling back
+        to each of ``legacy_keys`` (the plugin's pre-canonical keys) in turn.
+
+        The same read the managers made before -- same default max age, a
+        stored ttl still wins -- so moving to the canonical key changes
+        where a schedule is cached, not for how long. A read from an old key
+        is counted (``legacy_cache_hits``) so it is visible when the
+        fallback can go. A miss on the canonical key also deletes the same
+        window's copy from the day before (see the module docstring).
+        """
+        cached = self.cache_manager.get(cache_key)
+        if cached:
+            return cached
+        self._retire_previous_window(cache_key)
+        for legacy in legacy_keys:
+            if not legacy or legacy == cache_key:
+                continue
+            cached = self.cache_manager.get(legacy)
+            if cached:
+                try:
+                    get_fetch_service().note_cache_hit(
+                        _ESPN_SITE, legacy=True, avoided_request=False)
+                except Exception:  # noqa: BLE001 - counting never breaks a read
+                    pass
+                return cached
+        return None
+
+    def _retire_previous_window(self, cache_key: str) -> None:
+        previous = _previous_window_key(cache_key)
+        delete = getattr(self.cache_manager, "delete", None)
+        if previous is None or not callable(delete):
+            return
+        try:
+            delete(previous)
+        except Exception as e:  # noqa: BLE001 - housekeeping only
+            self.logger.debug(f"Could not delete old schedule copy {previous}: {e}")
+
     def _fetch_season_directly(
         self,
         url: str,
         datestring: str,
-        cache_key: str,
+        cache_key: Optional[str],
         label: str,
         ttl: Optional[int] = None,
     ) -> Optional[Dict]:
         """Fetch a season schedule on this thread, in chunks ESPN accepts, and cache it.
 
         ``label`` names the schedule in log lines, e.g. ``"2026 season"``.
+        ``cache_key=None`` caches it under the canonical key
+        (``espn_scoreboard_cache_key`` for ``url``'s sport and league).
         """
+        if cache_key is None:
+            cache_key = (espn_scoreboard_cache_key_for_url(url, datestring)
+                         or self._schedule_cache_key(datestring))
         try:
             data = fetch_espn_scoreboard(
                 self.session,