feat: add the {SCOPE}__CIRCUIT_OPEN admission policy key

Limiter rejections have always chosen between waiting and failing fast;
breaker rejections had no such choice. The new key is the missing cell
of that matrix, shaped exactly like QUOTA_FULL so there is nothing new
to learn. It defaults to fail_fast: flipping the default would move
every existing deployment's worst-case wall clock from milliseconds to
the stall window, which is the wrong direction to impose on anyone.
Single-source scopes are the ones that want wait, and they now have a
way to say so.

The two keys stay separate despite sharing a domain, because a full
quota is "queue for your share" (your turn always comes) while an open
circuit is "wait for the source to recover" (it might not).

Policy validation collapses into SourceAdmission, the only consumer.
The three client constructors used to each carry their own copy of the
quota_full check; adding a second key there would have made eight
copies of the same two lines. Rejection timing and message are
unchanged -- admission is built inside those constructors.

This commit only wires the key through; the control flow that reads it
lands next.

src/polygateway/client.py

@@ -134,6 +134,7 @@ class GatewayClient:
         retry: RetryPolicy,
         backpressure: BackpressurePolicy,
         quota_full: str = "wait",
+        circuit_open: str = "fail_fast",
         telemetry: TelemetryRecorder | None = None,
         pricing: PricingTable | None = None,
         text_cap: int | None = None,
@@ -162,6 +163,7 @@ class GatewayClient:
             retry=retry,
             backpressure=backpressure,
             quota_full=quota_full,
+            circuit_open=circuit_open,
             cooldown_memo=SourceCooldownMemo(now=now),
             # AIMD ceiling 尊重源级静态并发上限(独立核验 I1: 不得静默钳制大于 64 的配置)
             pacer=AdaptivePacer(
@@ -313,6 +315,7 @@ class GatewayClient:
             retry=settings.retry,
             backpressure=settings.backpressure,
             quota_full=settings.quota_full,
+            circuit_open=settings.circuit_open,
             telemetry=telemetry if telemetry is not None else _build_telemetry(settings),
             pricing=PricingTable.from_file(settings.pricing_path)
             if settings.pricing_path is not None

src/polygateway/config.py

@@ -50,6 +50,9 @@ _SOURCE_FIELDS: dict[str, tuple[str, str]] = {
 _RESERVED_SEGMENTS = frozenset({"GLOBAL", "RETRY", "BREAKER", "BACKPRESSURE"})
 _SELECTORS = frozenset({"round_robin", "least_inflight", "health_aware"})
 _QUOTA_FULL = frozenset({"wait", "fail_fast"})
+# 熔断全拒时的处置(issue #14);值域与 _QUOTA_FULL 相同但语义不同——配额满是
+# "排队等自己的份额"(必然轮到),熔断开路是"等源恢复"(未必恢复),故分列两键
+_CIRCUIT_OPEN = frozenset({"wait", "fail_fast"})
 # 后端合法域: env 解析与构造期校验共用一份定义,避免两处分叉
 _LIMITER_BACKENDS = frozenset({"memory", "redis"})
 _BREAKER_BACKENDS = frozenset({"memory", "redis"})
@@ -128,6 +131,9 @@ class GatewaySettings:
     backpressure: BackpressurePolicy
     selector: str
     quota_full: str
+    # 熔断全拒时是当场判死还是等冷却过去(issue #14);缺省 fail_fast 保持
+    # 存量下游的控制流不变,单源 scope 应显式配 wait
+    circuit_open: str
     limiter_backend: str
     breaker_backend: str
     cache_backend: str
@@ -203,6 +209,7 @@ class GatewaySettings:
             ("telemetry_backend", _TELEMETRY_BACKENDS),
             ("selector", _SELECTORS),
             ("quota_full", _QUOTA_FULL),
+            ("circuit_open", _CIRCUIT_OPEN),
         ):
             value = getattr(self, field)
             if value not in allowed:
@@ -320,6 +327,9 @@ class GatewaySettings:
             backpressure=_load_backpressure(scope_u, env),
             selector=_load_choice(env, f"{scope_u}__SELECTOR", _SELECTORS, "health_aware"),
             quota_full=_load_choice(env, f"{scope_u}__QUOTA_FULL", _QUOTA_FULL, "wait"),
+            circuit_open=_load_choice(
+                env, f"{scope_u}__CIRCUIT_OPEN", _CIRCUIT_OPEN, "fail_fast"
+            ),
             **_load_pgw(env),
         )
 

src/polygateway/embedding.py

@@ -101,6 +101,7 @@ class EmbeddingClient:
         retry: RetryPolicy,
         backpressure: BackpressurePolicy,
         quota_full: str = "wait",
+        circuit_open: str = "fail_fast",
         telemetry: TelemetryRecorder | None = None,
         pricing: PricingTable | None = None,
         text_cap: int | None = None,
@@ -113,8 +114,6 @@ class EmbeddingClient:
     ) -> None:
         if batch_size < 1:
             raise ValueError("batch_size 必须 ≥ 1")
-        if quota_full not in ("wait", "fail_fast"):
-            raise ValueError(f"quota_full 必须是 wait|fail_fast: {quota_full!r}")
         if expected_dim is not None and expected_dim < 1:
             raise ValueError("expected_dim 必须 ≥ 1")
         self._scope = scope
@@ -145,6 +144,7 @@ class EmbeddingClient:
             breaker=self._breaker,
             backpressure=backpressure,
             quota_full=quota_full,
+            circuit_open=circuit_open,
             now=now,
             sleep=sleep,
             rng=rng,
@@ -500,6 +500,7 @@ class EmbeddingClient:
             retry=gw.retry,
             backpressure=gw.backpressure,
             quota_full=gw.quota_full,
+            circuit_open=gw.circuit_open,
             telemetry=telemetry if telemetry is not None else _build_telemetry(gw),
             pricing=PricingTable.from_file(gw.pricing_path)
             if gw.pricing_path is not None

src/polygateway/middleware/admission.py

@@ -29,6 +29,9 @@ from loguru import logger
 from polygateway.errors import AllSourcesExhausted, CircuitOpenError
 from polygateway.sources import SourceCooldownMemo
 
+# 两个准入策略键共用的值域;校验只此一处,不在各客户端重复
+_POLICIES = frozenset({"wait", "fail_fast"})
+
 if TYPE_CHECKING:
     from collections.abc import Callable
 
@@ -137,6 +140,7 @@ class SourceAdmission:
         breaker: BreakerGate,
         backpressure: BackpressurePolicy,
         quota_full: str,
+        circuit_open: str,
         memo: SourceCooldownMemo | None = None,
         pacer: AdaptivePacer | None = None,
         health_view: Callable[[str], float] | None = None,
@@ -144,8 +148,9 @@ class SourceAdmission:
         sleep: Callable[[float], object] = asyncio.sleep,
         rng: Callable[[], float] = random.random,
     ) -> None:
-        if quota_full not in ("wait", "fail_fast"):
-            raise ValueError(f"quota_full 必须是 wait|fail_fast: {quota_full!r}")
+        for name, value in (("quota_full", quota_full), ("circuit_open", circuit_open)):
+            if value not in _POLICIES:
+                raise ValueError(f"{name} 必须是 wait|fail_fast: {value!r}")
         self._scope = scope
         self._sources = sources
         self._selector = selector
@@ -153,6 +158,7 @@ class SourceAdmission:
         self._breaker = breaker
         self._bp = backpressure
         self._quota_full = quota_full
+        self._circuit_open = circuit_open
         self._memo = memo or SourceCooldownMemo(now=now)
         self._pacer = pacer
         self._health_view = health_view

src/polygateway/middleware/retry.py

@@ -178,6 +178,7 @@ class RetryMW:
         retry: RetryPolicy,
         backpressure: BackpressurePolicy,
         quota_full: str = "wait",
+        circuit_open: str = "fail_fast",
         cooldown_memo: SourceCooldownMemo | None = None,
         pacer: AdaptivePacer | None = None,
         emitter: object | None = None,
@@ -185,8 +186,6 @@ class RetryMW:
         sleep: Callable[[float], Awaitable[None]] = asyncio.sleep,
         rng: Callable[[], float] = random.random,
     ) -> None:
-        if quota_full not in ("wait", "fail_fast"):
-            raise ValueError(f"quota_full 必须是 wait|fail_fast: {quota_full!r}")
         self._scope = scope
         self._sources = list(sources)
         # 记账写回与 pacer 结算仍在 `_attempt` 内,故这三者由本类持有并与
@@ -212,6 +211,7 @@ class RetryMW:
             breaker=self._breaker,
             backpressure=backpressure,
             quota_full=quota_full,
+            circuit_open=circuit_open,
             memo=cooldown_memo,
             pacer=self._pacer,
             health_view=self._outcome_sink.health if self._outcome_sink else None,

src/polygateway/ocr.py

@@ -107,14 +107,13 @@ class OcrClient:
         retry: RetryPolicy,
         backpressure: BackpressurePolicy,
         quota_full: str = "wait",
+        circuit_open: str = "fail_fast",
         telemetry: TelemetryRecorder | None = None,
         text_cap: int | None = None,
         now: Callable[[], float] = time.monotonic,
         sleep: Callable[[float], Awaitable[None]] = asyncio.sleep,
         rng: Callable[[], float] = random.random,
     ) -> None:
-        if quota_full not in ("wait", "fail_fast"):
-            raise ValueError(f"quota_full 必须是 wait|fail_fast: {quota_full!r}")
         self._scope = scope
         # MonkeyOCR 只发 multipart 表单,带 extra_body 的源必须先剥离,否则
         # 遥测会记录一个从未发出的采样参数(issue #4 决策 G)
@@ -139,6 +138,7 @@ class OcrClient:
             breaker=self._breaker,
             backpressure=backpressure,
             quota_full=quota_full,
+            circuit_open=circuit_open,
             now=now,
             sleep=sleep,
             rng=rng,
@@ -513,6 +513,7 @@ class OcrClient:
             retry=gw.retry,
             backpressure=gw.backpressure,
             quota_full=gw.quota_full,
+            circuit_open=gw.circuit_open,
             telemetry=telemetry if telemetry is not None else _build_telemetry(gw),
             # OCR 行与 chat 行写同一张 llm_calls;漏传这一条,同表内就一半受控
             # 一半不受控(issue #12)