fix: address M2.5 verifier findings before merge

AIMD ceiling now respects per-source max_concurrency and the pacer is
assembled explicitly in the client; MIN_CALLS parses as strict int;
acceptance doc corrects source-5 attempt count to 549; design and
migration notes aligned with implemented 429/stall/suppression
semantics and AIMD constants documented.

src/polygateway/client.py

@@ -25,6 +25,7 @@ from polygateway.middleware.telemetry import TelemetryEmitter, TelemetryMW
 from polygateway.pricing import PricingTable
 from polygateway.providers import get_provider
 from polygateway.sources import (
+    AdaptivePacer,
     HealthAwareSelector,
     LeastInflightSelector,
     RoundRobinSelector,
@@ -97,6 +98,10 @@ class GatewayClient:
             backpressure=backpressure,
             quota_full=quota_full,
             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(
+                ceiling=float(max([64, *(s.max_concurrency for s in sources if s.max_concurrency)]))
+            ),
             emitter=emitter,
             now=now,
             sleep=sleep,
@@ -128,6 +133,7 @@ class GatewayClient:
                 )
             )
         self._structured_available = structured_strategy is not None
+        self._terminal = terminal  # 内部引用: 装配自省/测试用
         self._handler = compose(middlewares, terminal)
         self._transport = transport
         self._telemetry = telemetry