fix: void the cost of rows whose usage is unavailable

失败尝试与终态失败行的 usage_source 由 estimated 改 unavailable(用量确实
不可得),并在 TelemetryEmitter 的成本换算里为 unavailable 短路记 NULL。
短路刻意插在 cache_hit 分支之后: 缓存命中未产生新调用,0.0 是事实而非未知。
附 OCR 成功行的防回归钉(仍为 measured、settle 恒 0,设计 §3.3 剔出决定)。

tests/unit/test_ocr_client.py

@@ -394,6 +394,21 @@ class TestTelemetry:
         assert recorder.rows[1]["error"] is None
         assert recorder.rows[1]["prompt_tokens"] == 0
 
+    async def test_success_row_stays_measured_and_settles_zero(self):
+        """OCR 的 0 token 是**事实**而非未知(est_tokens 解耦设计 §3.3 剔出决定)。
+
+        三态化不得把 OCR 成功行改成 `unavailable`——那会灌水缺口度量
+        `COUNT(*) WHERE usage_source='unavailable'`;settle 恒 0 的差异①同样不动。
+        """
+        recorder = _MemoryRecorder()
+        client, limiter, _ = _client([_src(tpm=1000, est_tokens=400)], ["text"], telemetry=recorder)
+        await client.recognize_text(b"jpg")
+        row = recorder.rows[0]
+        assert row["usage_source"] == "measured"
+        assert row["prompt_tokens"] == 0 and row["completion_tokens"] == 0
+        assert row["error"] is None
+        assert (await limiter.source_stats("m1")).tpm_used == 0  # settle(0) 全额退回预扣
+
 
 class TestAssembly:
     _ENV = {

tests/unit/test_telemetry.py

@@ -9,6 +9,7 @@ import pytest
 
 from polygateway.errors import CircuitOpenError, RequestRejectedError
 from polygateway.middleware.telemetry import TelemetryEmitter, TelemetryMW
+from polygateway.pricing import ModelPrice, PricingTable
 from polygateway.telemetry.sqlite import SQLiteRecorder
 from polygateway.types import ChatRequest, LLMResponse, SourceConfig
 
@@ -68,6 +69,10 @@ def _source():
     )
 
 
+# 输出单价 8 元/百万: 改前 `unavailable` 行按兜底的 0/4000 换算恰好是 0.032
+_PRICING = PricingTable({"m": ModelPrice(input_per_1m=1.0, output_per_1m=8.0)})
+
+
 async def _record_minimal(recorder, call_id="c1", **overrides):
     fields = {
         "call_id": call_id,
@@ -168,7 +173,58 @@ class TestEmitter:
         )
         row = rec.rows[0]
         assert row["error"].startswith("TransientError")
-        assert row["response"] == "" and row["usage_source"] == "estimated"
+        # 失败尝试没有任何用量信息可言 → unavailable(设计 §3.2 #6)
+        assert row["response"] == "" and row["usage_source"] == "unavailable"
+        assert row["cost"] is None
+
+    async def test_terminal_failure_row_is_unavailable(self):
+        rec = _MemoryRecorder()
+        await TelemetryEmitter(rec, pricing=_PRICING).emit_terminal_failure(
+            request=_REQ, call_id="cid-t", latency_ms=5, error="cancelled"
+        )
+        row = rec.rows[0]
+        assert row["usage_source"] == "unavailable" and row["cost"] is None
+
+    @pytest.mark.parametrize(("prompt", "completion"), [(0, 0), (0, 4000)])
+    async def test_unavailable_success_row_has_null_cost(self, prompt, completion):
+        """产生了真实调用但用量不可得 → cost 记 NULL(设计 §3.1 不变式)。
+
+        参数第二组是改前兜底写出的 `0/4000` 形态: 那时换算出 0.032 的假金额。
+        """
+        rec = _MemoryRecorder()
+        await TelemetryEmitter(rec, pricing=_PRICING).emit_attempt(
+            request=_REQ,
+            source=_source(),
+            call_id="cid-u",
+            latency_ms=42,
+            response=_resp(
+                usage_source="unavailable", prompt_tokens=prompt, completion_tokens=completion
+            ),
+            error=None,
+        )
+        assert rec.rows[0]["cost"] is None
+
+    async def test_measured_row_still_priced(self):
+        """对照组: 同一价格表下 measured 行照常换算,证明 None 不是价格表没接上。"""
+        rec = _MemoryRecorder()
+        await TelemetryEmitter(rec, pricing=_PRICING).emit_attempt(
+            request=_REQ,
+            source=_source(),
+            call_id="cid-m",
+            latency_ms=42,
+            response=_resp(prompt_tokens=0, completion_tokens=4000),
+            error=None,
+        )
+        assert rec.rows[0]["cost"] == pytest.approx(0.032)
+
+    async def test_cache_hit_keeps_zero_cost_even_when_unavailable(self):
+        """缓存命中未产生新调用,0.0 是事实而非未知 → 短路必须排在 cache_hit 之后。"""
+        rec = _MemoryRecorder()
+        await TelemetryEmitter(rec, pricing=_PRICING).emit_cache_hit(
+            request=_REQ,
+            response=_resp(cache_hit=True, usage_source="unavailable", completion_tokens=4000),
+        )
+        assert rec.rows[0]["cache_hit"] is True and rec.rows[0]["cost"] == 0.0
 
     async def test_multimodal_messages_digested_before_storage(self):
         rec = _MemoryRecorder()