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PolyGateway/research-wiki/designs/settings-invariants-round-2.md
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iomgaa 8c9e1179bc docs: design second round of settings validation consolidation
The independent verifier found 15 more checks still living only in from_env:
six enum domains, seven conditional-required pairs and two scalar ranges.
More severe than round one because client.py has five asserts that claim
config already validated the redis_url and telemetry paths, which is false on
the from_settings path.

Also records a normalisation gap the verifier missed: _load_pg_dsn strips the
SQLAlchemy +asyncpg suffix, so a hand-built DSN reaches asyncpg unstripped.
2026-07-30 00:46:44 -04:00

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---
type: design
node_id: design:settings-invariants-round-2
title: "GatewaySettings 装配校验补齐(第二轮)"
date: 2026-07-30
---
# GatewaySettings 装配校验补齐(第二轮)
全文见 [2026-07-30-settings-invariants-round-2-design.md](2026-07-30-settings-invariants-round-2-design.md)。第一轮见 [settings-invariant-guards](settings-invariant-guards.md)。
- **缘起**: 第一轮交付后独立 verifier 发现 `from_env` 上还留着 15 条同族校验(枚举合法域 6、条件必填 7、标量域 2),`from_settings` 与直接构造全部放行。
- **严重性高于第一轮**: `client.py:262/282/302/312/316` 有 5 处 `assert ... # 内部不变量: config 已校验` 明文依赖这个前提;实测断言开启抛裸 `AssertionError`,`python -O` 下退化为 redis 库天书。
- **方案**: 沿用第一轮已批准的方案 A,不重新论证;新增 `_validate_backends/_validate_cache/_validate_telemetry`,枚举合法域上提为模块级常量供 `_load_pgw` 与构造期共用。
- **assert 处置**: **保留不改**——前提一旦由构造期保证,它就是 CLAUDE.md §4.3 认可的内部不变量用法且给类型检查器收窄 `str | None`;只改那句会变成谎言的注释,点明由哪个方法保证。
- **本轮唯一新决策**: `_load_pg_dsn``+asyncpg` 驱动后缀是**规范化**不是校验,直接构造那条路不会剥。选校验拒绝(显式)而非构造期 `object.__setattr__` 剥后缀(在用户背后改 frozen 字段)。两条路接受度不同是有意的:env 路要吃三项目历史遗留的 SQLAlchemy DSN 写法,代码构造路没有历史包袱。
- **版本**: 1.0.2(patch),CHANGELOG 单列"行为收紧"小节。