feat: preserve governed OpenAI tool messages in 1.4.0

Add faithful single-choice chat results, tool stream activity, error-frame retries, and isolated protocol caching.

Reject empty cached completions with the same value predicate as transport, add regression coverage, and adopt Apache-2.0.

tests/unit/test_stall_hedge.py

@@ -78,6 +78,7 @@ class StallHedgeTransport:
         reasoning_effort,
         first_token_event,
         content_event,
+        response_mode,
     ):
         self.calls.append(source.name)
         self.ft_events.append(first_token_event)
@@ -271,9 +272,7 @@ class TestStallHedgeTrigger:
         """参数化四格(设计 §5.2 逐字): 两阈值独立生效,各格触发语义不串。"""
         # 格 1: 仅 AFTER_S + 流式 pre-TTFT 挂起 → AFTER_S 触发(1.3.7 语义不变)
         s1, s2 = _src("s1"), _src("s2")
-        transport = StallHedgeTransport(
-            {"s1": [("hang",), ("ok", "late")], "s2": [("ok", "fast")]}
-        )
+        transport = StallHedgeTransport({"s1": [("hang",), ("ok", "late")], "s2": [("ok", "fast")]})
         mw, _, _ = _harness([s1, s2], transport, hedge_after_s=_STALL_AFTER_S)
         ctx = _ctx()
         resp = await asyncio.wait_for(mw(_req(ctx=ctx)), timeout=5)
@@ -312,9 +311,7 @@ class TestStallHedgeTrigger:
 
         # 格 3b: 两者皆设 + pre-TTFT 挂起 → 阶段 1 AFTER_S 触发(两阶段各管一段)
         s1, s2 = _src("s1"), _src("s2")
-        transport = StallHedgeTransport(
-            {"s1": [("hang",), ("ok", "late")], "s2": [("ok", "fast")]}
-        )
+        transport = StallHedgeTransport({"s1": [("hang",), ("ok", "late")], "s2": [("ok", "fast")]})
         mw, _, _ = _harness(
             [s1, s2], transport, hedge_after_s=_STALL_AFTER_S, stall_after_s=_STALL_AFTER_S
         )
@@ -340,9 +337,7 @@ class TestStallHedgeTrigger:
     async def test_stall_only_non_stream_degrades_to_single_leg(self):
         """仅 stall 已设 + `stream=False` → 逐字单路(中段沉默无非流式概念,入口门)。"""
         s1, s2 = _src("s1"), _src("s2")
-        transport = StallHedgeTransport(
-            {"s1": [("hang",), ("ok", "x")], "s2": [("ok", "other")]}
-        )
+        transport = StallHedgeTransport({"s1": [("hang",), ("ok", "x")], "s2": [("ok", "other")]})
         mw, _, _ = _harness([s1, s2], transport, stall_after_s=_STALL_AFTER_S)
         ctx = _ctx()
         task = asyncio.ensure_future(mw(_req(stream=False, ctx=ctx)))