docs: correct how a wait-mode call actually dies on a dead source

Branch review caught the docs claiming something the code does not do.
CHANGELOG, README and the design's behaviour matrix all said a
force-opened source under circuit_open=wait waits out the full stall
window. It does not: the probe let through after each cooldown is a
real attempt, so it burns a max_attempts slot like any other, and a
401 source usually runs out of retry budget first -- reason is
retry_exhausted, not stalled. Which budget wins depends on
max_attempts against the cooldowns and the stall window.

The behaviour is right; only the prose was wrong. Charging the probe
to the retry budget is exactly the split issue #8 settled: the
question is who spends max_attempts, and a probe does send a real
request. A test now pins it so the claim cannot drift again.

Also drops the planned "woke up" log line. Each wait round already
logs on entry with its duration, and a still-blocked wake-up logs the
next round immediately, so a second line would only double the volume.

CHANGELOG.md

@@ -4,7 +4,7 @@
 
 熔断开路时,调用方第一次可以选择**等**而不是当场失败(issue #14)。此前准入侧有一格是空的:限流闸满时库允许排队(`{SCOPE}__QUOTA_FULL=wait|fail_fast`,缺省 `wait`),熔断门拒绝时**只有 fail-fast 一档且不可配**——而两者在准入语义上是同构的,都没发出请求、都带着"稍后再来"的提示。新键 `{SCOPE}__CIRCUIT_OPEN=fail_fast|wait` 补上这一格,形状与 `QUOTA_FULL` 逐项对齐。
 
-**缺省是 `fail_fast`,即今天的行为**,存量部署无需改动任何配置。要改的是单源 scope:熔断的设计前提是"这个源坏了,把流量导到别的源",只配了一个源时这个前提不成立,同一段代码做的事就变成"这个源坏了,所以整个 scope 停止服务"。提交方实测:中转抖动 36 秒(22 次尝试 / 19 次 503)触发失败率通道开路,随后 30 次调用全部在 7-74 毫秒内失败,`MAX_ATTEMPTS=8` 一格没用上,一条跑了 3 小时 18 分钟的实验臂当场报废。配 `wait` 之后,熔断对配额和钱包的保护完整保留(等待期照样一个请求都不发),改变的只是调用方当场死还是排队等;代价是单次调用最坏墙钟被拉长到 `STALL_WINDOW_S`(缺省 300 秒),密钥失效这类一击即熔的情形同样要等满——库无法区分"密钥坏了"和"中转抖了",选 `wait` 就是声明"宁可等也不当场死"。
+**缺省是 `fail_fast`,即今天的行为**,存量部署无需改动任何配置。要改的是单源 scope:熔断的设计前提是"这个源坏了,把流量导到别的源",只配了一个源时这个前提不成立,同一段代码做的事就变成"这个源坏了,所以整个 scope 停止服务"。提交方实测:中转抖动 36 秒(22 次尝试 / 19 次 503)触发失败率通道开路,随后 30 次调用全部在 7-74 毫秒内失败,`MAX_ATTEMPTS=8` 一格没用上,一条跑了 3 小时 18 分钟的实验臂当场报废。配 `wait` 之后,熔断对配额和钱包的保护完整保留(等待期照样一个请求都不发),改变的只是调用方当场死还是排队等;代价是单次调用最坏墙钟被拉长——上限是 `STALL_WINDOW_S`(缺省 300 秒)。**但 `wait` 并不豁免重试预算**: 冷却结束后放行的探针是一次真实尝试,失败照样烧一格 `MAX_ATTEMPTS`,所以密钥失效(401/403)这类一击即熔的源通常更早以 `reason=retry_exhausted` 失败,而不是等满窗口后的 `stalled`;两者哪个先到取决于 `MAX_ATTEMPTS` 与冷却时长、`STALL_WINDOW_S` 的相对大小。库无法区分"密钥坏了"和"中转抖了",选 `wait` 就是声明"宁可等也不当场死"。
 
 ### 请先读这一条: `retry_after_s` 在半开状态下的取值变了(缺省档同样生效)