feat: expose bare generation time and hedge flags in CallStats

CallStats gains hedges/generation_ms/hedge_won (all defaulted, appended
after total_latency_ms); _CallContext counts them via record_generation
(overwrite for chat/OCR, accumulate for embedding batches) and
register_hedge, and snapshot carries them out. All three _attempt
implementations time only the transport call itself on the same injected
clock as total_latency_ms; the chat sink is recorded by the orchestrator
so hedge winner attribution stays with T3. Hedge counters stay 0/False
until the T3 orchestration lands.

Red-green evidence: tests/outputs/137/t2/ (10 new tests AttributeError
red, then green; full unit+contracts 1621 passed).

tests/unit/test_retry.py

@@ -93,6 +93,39 @@ class FakeTransport:
         return action
 
 
+class _GenClockTransport:
+    """委托 FakeTransport 的薄包装: 每次调用返回前按脚本推进注入钟(1.3.7 批次 C)。
+
+    generation_ms 的口径是"只计 transport 调用本身",故推进必须发生在被包
+    transport 内部;退避耗时由用例自带的 sleep 闭包推进,与本包装无关。
+    """
+
+    def __init__(self, script, advances, clock):
+        self._inner = FakeTransport(script)
+        self._advances = list(advances)
+        self._clock = clock
+
+    @property
+    def calls(self):
+        return self._inner.calls
+
+    async def complete(
+        self, *, messages, source, stream, overlay, call_id, reasoning_effort, first_token_event
+    ):
+        advance = self._advances.pop(0)
+        result = await self._inner.complete(
+            messages=messages,
+            source=source,
+            stream=stream,
+            overlay=overlay,
+            call_id=call_id,
+            reasoning_effort=reasoning_effort,
+            first_token_event=first_token_event,
+        )
+        self._clock.advance(advance)
+        return result
+
+
 class HangingGate(InMemoryGate):
     """在指定记账写回处永久挂起的门控: 把"取消落在某个 await 上"变成确定性事件。
 
@@ -141,6 +174,8 @@ def _harness(
     selector=None,
     pacer=None,
     gate=None,
+    transport=None,
+    sleep=None,
 ):
     clock = clock or FakeClock()
     limiter = InMemoryLimiter(
@@ -151,8 +186,8 @@ def _harness(
         now=clock,
     )
     gate = gate if gate is not None else InMemoryGate(config=_BREAKER, now=clock)
-    transport = FakeTransport(script)
-    sleep = FakeSleep()
+    transport = transport if transport is not None else FakeTransport(script)
+    sleep = sleep if sleep is not None else FakeSleep()
     mw = RetryMW(
         scope="llm",
         sources=sources,
@@ -916,6 +951,54 @@ class TestRateLimitPushback:
         assert len(transport.calls) == 3
 
 
+class TestGenerationMs:
+    """裸生成时间(1.3.7 H8): 只计 transport 调用本身,不含退避/准入/遥测收尾。"""
+
+    def _ctx(self, clock):
+        from polygateway.types import _CallContext
+
+        return _CallContext(now=clock)
+
+    async def test_generation_ms_excludes_backoff_and_admission(self):
+        """[Transient, ok] 脚本: 退避推进 5s、成功次 transport 推进 0.25s。
+
+        generation_ms 恒等于成功次 transport 的 250ms;若口径混入了退避,
+        它会涨到 5250ms 量级——与 total_latency_ms 的下界断言互为对偶。
+        推进量取二进制可精确表示值(0.25/5.0): int 截断下 0.2 之类会因浮点
+        误差落到 199,断言随之抖动(同 test_types 既有用例只用 1.5/2.0 的惯例)。
+        """
+        clock = FakeClock()
+
+        async def advancing_sleep(seconds):
+            clock.advance(seconds)
+
+        transport = _GenClockTransport(
+            [TransientError("boom", source_name="a"), _ok()], [0.0, 0.25], clock
+        )
+        mw, *_ = _harness(
+            [_src("a")],
+            [],
+            clock=clock,
+            transport=transport,
+            sleep=advancing_sleep,
+            rng=lambda: 2.0,  # backoff = 2.0 * (0.5 + 2.0) = 5.0s
+        )
+        ctx = self._ctx(clock)
+        resp = await mw(dataclasses.replace(_REQ, call_context=ctx))
+        assert resp.content == "ok" and len(transport.calls) == 2
+        stats = ctx.snapshot()
+        assert stats.generation_ms == 250
+        assert stats.total_latency_ms >= 5250
+
+    async def test_generation_ms_zero_hedge_flags_without_hedging(self):
+        """无对冲时 hedges/hedge_won 恒 0/False(对冲登记是 T3 的事)。"""
+        mw, *_ = _harness([_src("a")], [_ok()])
+        ctx = self._ctx(FakeClock())
+        await mw(dataclasses.replace(_REQ, call_context=ctx))
+        stats = ctx.snapshot()
+        assert stats.hedges == 0 and stats.hedge_won is False
+
+
 class TestLogicalAttemptCounting:
     """尝试登记在 transport 调用**之前**(1.3.5 设计 §4)。