diff --git a/src/polygateway/errors.py b/src/polygateway/errors.py
new file mode 100644
index 0000000..57d8aa0
--- /dev/null
+++ b/src/polygateway/errors.py
@@ -0,0 +1,121 @@
+"""错误四分类与 scope 级不可用语义(M1 设计 §3;ARCH §6)。
+
+分类决定治理行为(重试/换源/熔断计数),库内禁止绕过分类做 ad-hoc 判断。
+构造形态承 CHS `app/domain/errors.py` 的 ProviderError 一族。
+"""
+
+SCOPE_REASONS = frozenset(
+    {"circuit_open", "retry_exhausted", "stalled", "quota_exhausted", "no_sources"}
+)
+SOURCE_REASONS = frozenset(
+    {"network_error", "timeout", "rate_limited", "source_dead", "circuit_open", "cooldown"}
+)
+
+
+class PolyGatewayError(Exception):
+    """库内一切领域错误的基类,携带来源上下文便于遥测与日志定位。"""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        source_name: str | None = None,
+        status_code: int | None = None,
+        operation: str | None = None,
+    ) -> None:
+        super().__init__(message)
+        self.source_name = source_name
+        self.status_code = status_code
+        self.operation = operation
+
+
+class TransientError(PolyGatewayError):
+    """瞬时错误(超时/5xx/429/网络抖动/SSE 异常): 退避后可重试、可换源、计熔断。"""
+
+    def __init__(self, message: str, *, retry_after_s: float | None = None, **kwargs) -> None:
+        super().__init__(message, **kwargs)
+        self.retry_after_s = retry_after_s
+
+
+class SourceDeadError(PolyGatewayError):
+    """源死亡(401/403/欠费): 不重试,立即换源,该源 force_open。"""
+
+
+class RequestRejectedError(PolyGatewayError):
+    """请求被拒(400/坏输入): 不重试不换源,直接上抛。"""
+
+
+class ResultInvalidError(PolyGatewayError):
+    """坏结果 ≠ 坏服务: 调用成功但内容不可解析;熔断记成功,不入 transport 重试。"""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        raw_text: str = "",
+        repair_error: str | None = None,
+        validation_errors: tuple[str, ...] = (),
+        **kwargs,
+    ) -> None:
+        super().__init__(message, **kwargs)
+        self.raw_text = raw_text
+        self.repair_error = repair_error
+        self.validation_errors = tuple(validation_errors)
+
+
+class GatewayUnavailableError(PolyGatewayError):
+    """scope 级暂时不可用;业务侧 catch 本类做延期重投(CHS arq 模式)。
+
+    `retry_after_s` 非可选(0 = 可立即重试),承 CHS ProviderUnavailableError。
+    """
+
+    def __init__(
+        self,
+        *,
+        scope: str,
+        reason: str,
+        retry_after_s: float,
+        per_source_reasons: dict[str, str] | None = None,
+        source_name: str | None = None,
+    ) -> None:
+        if not scope.strip():
+            raise ValueError("scope 不能为空")
+        if reason not in SCOPE_REASONS:
+            raise ValueError(f"未知 scope 级 reason: {reason!r}(允许: {sorted(SCOPE_REASONS)})")
+        if retry_after_s < 0:
+            raise ValueError("retry_after_s 不能为负")
+        reasons = dict(per_source_reasons or {})
+        for src, src_reason in reasons.items():
+            if src_reason not in SOURCE_REASONS:
+                raise ValueError(f"源 {src!r} 的 reason 非法: {src_reason!r}(允许: {sorted(SOURCE_REASONS)})")
+        super().__init__(f"{scope.lower()} 网关暂时不可用: {reason}", source_name=source_name)
+        self.scope = scope.lower()
+        self.reason = reason
+        self.retry_after_s = retry_after_s
+        self.per_source_reasons = reasons
+
+
+class CircuitOpenError(GatewayUnavailableError):
+    """全部候选源被熔断门拒绝;reason 恒为 circuit_open。"""
+
+    def __init__(
+        self,
+        *,
+        scope: str,
+        retry_after_s: float,
+        per_source_reasons: dict[str, str] | None = None,
+    ) -> None:
+        super().__init__(
+            scope=scope,
+            reason="circuit_open",
+            retry_after_s=retry_after_s,
+            per_source_reasons=per_source_reasons,
+        )
+
+
+class AllSourcesExhausted(GatewayUnavailableError):  # noqa: N818 — ARCH §6.1 冻结的公共名
+    """重试预算耗尽 / 无可用源 / 配额 fail-fast 等 scope 级失败。"""
+
+
+class GovernanceBackendError(PolyGatewayError):
+    """限流/熔断状态后端自身故障: 必须报错而非放行(防击穿网关,降级方向铁律)。"""
diff --git a/src/polygateway/types.py b/src/polygateway/types.py
new file mode 100644
index 0000000..80cd328
--- /dev/null
+++ b/src/polygateway/types.py
@@ -0,0 +1,186 @@
+"""核心冻结类型(M1 设计 §2;最内层,禁止 import 任何实现)。
+
+`LLMResponse` 前 11 个字段与三参考项目逐字保序——它们的测试按位置构造
+fake,字段顺序即公共承诺;新增字段只增不删且必带默认值。
+"""
+
+from dataclasses import dataclass, field
+from typing import Any
+
+_MISSING_DONE_DOMAIN = frozenset({"retry", "salvage"})
+
+
+@dataclass(frozen=True)
+class LLMResponse:
+    """一次治理调用的统一响应(与三项目超集兼容,ARCH §5.1)。"""
+
+    content: str
+    thinking: str
+    model: str
+    provider: str
+    prompt_tokens: int
+    completion_tokens: int
+    latency_ms: int
+    ttft_ms: float | None
+    max_inter_token_ms: float | None
+    cache_hit: bool
+    call_id: str
+    # —— 库新增(只增不删,必带默认值;迁移兼容硬约束)——
+    source_name: str = ""
+    cost: float | None = None
+    usage_source: str = "measured"
+    structured_data: Any | None = None
+
+
+@dataclass(frozen=True)
+class ChatRequest:
+    """洋葱内部流转的不可变请求;中间件用 dataclasses.replace 派生,禁止原地修改。"""
+
+    messages: list[dict[str, Any]]
+    session_id: str | None = None
+    parent_call_id: str | None = None
+    cache_salt: str | None = None
+    cache_namespace: str | None = None
+    structured: Any | None = None
+    stream: bool = True
+    overlay: dict[str, Any] = field(default_factory=dict)
+
+
+@dataclass(frozen=True)
+class Usage:
+    """token 用量;OCR 等无计费调用填 0。"""
+
+    prompt_tokens: int
+    completion_tokens: int
+    usage_source: str = "measured"
+
+
+@dataclass(frozen=True)
+class SourceStats:
+    """限流后端回读的单源即时指标(CHS ports.py 同款)。"""
+
+    inflight: int
+    rpm_used: int
+    tpm_used: int
+
+
+@dataclass(frozen=True)
+class TransportResult:
+    """transport 单次原始调用的产物;治理字段由 RetryMW 补齐为 LLMResponse。"""
+
+    content: str
+    thinking: str
+    prompt_tokens: int
+    completion_tokens: int
+    usage_source: str
+    ttft_ms: float | None
+    max_inter_token_ms: float | None
+    raw: dict[str, Any]
+
+
+@dataclass(frozen=True)
+class SourceConfig:
+    """单个模型源的完整配置(CHS config.py 超集;不变式在构造期报错)。
+
+    限额闸 0 表示不启用;`enable_thinking` 三态: None=不注入(模型默认)、
+    True=注入开启参数、False=注入关闭参数(统一 VT 与 CHS 相反的现状)。
+    """
+
+    name: str
+    provider: str
+    base_url: str
+    api_key: str
+    model: str
+    timeout_s: float
+    max_concurrency: int = 0
+    rpm: int = 0
+    tpm: int = 0
+    est_tokens: int = 0
+    ttft_timeout_s: float | None = None
+    inter_token_timeout_s: float | None = None
+    enable_thinking: bool | None = None
+    missing_done: str = "retry"
+    trust_env: bool = True
+
+    def __post_init__(self) -> None:
+        self._validate_identity()
+        self._validate_gates()
+        self._validate_watchdog()
+
+    def _validate_identity(self) -> None:
+        for attr in ("name", "provider", "base_url", "api_key", "model"):
+            if not getattr(self, attr).strip():
+                raise ValueError(f"SourceConfig.{attr} 不能为空")
+        if self.missing_done not in _MISSING_DONE_DOMAIN:
+            raise ValueError(f"missing_done 必须是 {sorted(_MISSING_DONE_DOMAIN)}: {self.missing_done!r}")
+
+    def _validate_gates(self) -> None:
+        if self.timeout_s <= 0:
+            raise ValueError("timeout_s 必须 > 0")
+        for attr in ("max_concurrency", "rpm", "tpm", "est_tokens"):
+            if getattr(self, attr) < 0:
+                raise ValueError(f"SourceConfig.{attr} 不能为负(0 表示不启用)")
+        if self.tpm > 0 and self.est_tokens <= 0:
+            raise ValueError("启用 TPM 闸时 est_tokens 必须 > 0(入场预扣依据)")
+
+    def _validate_watchdog(self) -> None:
+        # CHS config.py:66-82: 流式看门狗成对配置且 0 < inter < ttft < timeout_s
+        if (self.ttft_timeout_s is None) != (self.inter_token_timeout_s is None):
+            raise ValueError("ttft_timeout_s 与 inter_token_timeout_s 必须同时设置或同时缺省")
+        if self.ttft_timeout_s is not None and not (
+            0 < self.inter_token_timeout_s < self.ttft_timeout_s < self.timeout_s
+        ):
+            raise ValueError("看门狗不变式要求 0 < inter_token < ttft < timeout_s")
+
+
+@dataclass(frozen=True)
+class RetryPolicy:
+    """重试策略;max_attempts = 总尝试次数(含首次,M1 设计 §2.3 统一语义)。"""
+
+    max_attempts: int
+    backoff_base_s: float
+    backoff_max_s: float
+
+    def __post_init__(self) -> None:
+        if self.max_attempts < 1:
+            raise ValueError("max_attempts 必须 ≥ 1(含首次尝试)")
+        if self.backoff_base_s <= 0 or self.backoff_max_s < self.backoff_base_s:
+            raise ValueError("退避参数要求 0 < backoff_base_s ≤ backoff_max_s")
+
+
+@dataclass(frozen=True)
+class BreakerConfig:
+    """熔断配置;probe_ttl_s 是半开探针租约时长(持有者死亡后自动回收)。"""
+
+    fail_threshold: int
+    cooldown_s: float
+    probe_ttl_s: float
+
+    def __post_init__(self) -> None:
+        if self.fail_threshold < 1 or self.cooldown_s <= 0 or self.probe_ttl_s <= 0:
+            raise ValueError("熔断配置要求 fail_threshold ≥ 1 且 cooldown_s/probe_ttl_s > 0")
+
+
+@dataclass(frozen=True)
+class BackpressurePolicy:
+    """背压配置;M1 仅使用 poll_interval_s,stall 判定 M2 启用。"""
+
+    stall_window_s: float
+    poll_interval_s: float
+
+    def __post_init__(self) -> None:
+        if self.stall_window_s <= 0 or self.poll_interval_s <= 0:
+            raise ValueError("背压参数必须 > 0")
+
+
+@dataclass(frozen=True)
+class GlobalLimits:
+    """scope 级全局限额;0 表示该闸不启用。"""
+
+    max_concurrency: int
+    rpm: int
+    tpm: int
+
+    def __post_init__(self) -> None:
+        if self.max_concurrency < 0 or self.rpm < 0 or self.tpm < 0:
+            raise ValueError("全局限额不能为负(0 表示不启用)")
diff --git a/tests/unit/test_errors.py b/tests/unit/test_errors.py
new file mode 100644
index 0000000..52e004f
--- /dev/null
+++ b/tests/unit/test_errors.py
@@ -0,0 +1,85 @@
+"""errors.py 错误四分类与 scope 级不可用语义测试(M1 设计 §3)。"""
+
+import pytest
+
+from polygateway.errors import (
+    AllSourcesExhausted,
+    CircuitOpenError,
+    GatewayUnavailableError,
+    GovernanceBackendError,
+    PolyGatewayError,
+    RequestRejectedError,
+    ResultInvalidError,
+    SourceDeadError,
+    TransientError,
+)
+
+
+class TestBaseShape:
+    def test_base_carries_source_context(self):
+        exc = PolyGatewayError("boom", source_name="qwen_1", status_code=502, operation="chat")
+        assert exc.source_name == "qwen_1"
+        assert exc.status_code == 502
+        assert exc.operation == "chat"
+
+    def test_four_way_taxonomy_inherits_base(self):
+        for cls in (TransientError, SourceDeadError, RequestRejectedError, ResultInvalidError):
+            assert issubclass(cls, PolyGatewayError)
+
+    def test_transient_retry_after_optional(self):
+        assert TransientError("429").retry_after_s is None
+        assert TransientError("429", retry_after_s=2.5).retry_after_s == 2.5
+
+
+class TestResultInvalid:
+    def test_carries_diagnosis(self):
+        exc = ResultInvalidError(
+            "bad json", raw_text="{oops", repair_error="unterminated",
+            validation_errors=("field x missing",),
+        )
+        assert exc.raw_text == "{oops"
+        assert exc.repair_error == "unterminated"
+        assert exc.validation_errors == ("field x missing",)
+
+
+class TestGatewayUnavailable:
+    def test_fields_and_inheritance(self):
+        exc = AllSourcesExhausted(
+            scope="LLM", reason="retry_exhausted", retry_after_s=4.0,
+            per_source_reasons={"qwen_1": "timeout"},
+        )
+        assert isinstance(exc, GatewayUnavailableError)
+        assert exc.scope == "llm"  # CHS 同款: scope 归一化小写
+        assert exc.reason == "retry_exhausted"
+        assert exc.retry_after_s == 4.0
+        assert exc.per_source_reasons == {"qwen_1": "timeout"}
+
+    def test_circuit_open_reason_fixed(self):
+        exc = CircuitOpenError(scope="LLM", retry_after_s=30.0)
+        assert exc.reason == "circuit_open"
+        assert isinstance(exc, GatewayUnavailableError)
+
+    def test_scope_reason_domain_enforced(self):
+        with pytest.raises(ValueError):
+            AllSourcesExhausted(scope="LLM", reason="bad_reason", retry_after_s=0.0)
+
+    def test_per_source_reason_domain_enforced(self):
+        with pytest.raises(ValueError):
+            AllSourcesExhausted(
+                scope="LLM", reason="no_sources", retry_after_s=0.0,
+                per_source_reasons={"qwen_1": "weird"},
+            )
+
+    def test_retry_after_non_negative_and_scope_non_empty(self):
+        with pytest.raises(ValueError):
+            AllSourcesExhausted(scope="LLM", reason="stalled", retry_after_s=-1.0)
+        with pytest.raises(ValueError):
+            AllSourcesExhausted(scope="  ", reason="stalled", retry_after_s=0.0)
+
+
+class TestBackendFailure:
+    def test_governance_backend_error_is_not_transient(self):
+        """限流/熔断后端故障必须报错不放行,且不落入可重试分类。"""
+        exc = GovernanceBackendError("redis down")
+        assert isinstance(exc, PolyGatewayError)
+        assert not isinstance(exc, TransientError)
diff --git a/tests/unit/test_types.py b/tests/unit/test_types.py
new file mode 100644
index 0000000..c258255
--- /dev/null
+++ b/tests/unit/test_types.py
@@ -0,0 +1,150 @@
+"""types.py 冻结签名的行为测试(M1 设计 §2)。"""
+
+import dataclasses
+
+import pytest
+
+from polygateway.types import (
+    BackpressurePolicy,
+    BreakerConfig,
+    ChatRequest,
+    GlobalLimits,
+    LLMResponse,
+    RetryPolicy,
+    SourceConfig,
+    TransportResult,
+    Usage,
+)
+
+
+def _make_source(**overrides):
+    """构造最小合法 SourceConfig,单点覆盖便于逐条触发不变式。"""
+    base = dict(
+        name="qwen_1",
+        provider="qwen",
+        base_url="https://gw.example/v1",
+        api_key="sk-test",
+        model="qwen-max",
+        timeout_s=120.0,
+    )
+    base.update(overrides)
+    return SourceConfig(**base)
+
+
+class TestLLMResponse:
+    def test_eleven_legacy_fields_positional(self):
+        """三项目 fake 的 11 参位置构造必须零改动成立(迁移兼容硬约束)。"""
+        resp = LLMResponse(
+            "content", "thinking", "qwen-max", "qwen", 10, 20, 300, 50.0, 80.0, False, "cid"
+        )
+        assert resp.content == "content"
+        assert resp.call_id == "cid"
+
+    def test_new_fields_have_defaults(self):
+        resp = LLMResponse("c", "t", "m", "p", 1, 2, 3, None, None, False, "cid")
+        assert resp.source_name == ""
+        assert resp.cost is None
+        assert resp.usage_source == "measured"
+        assert resp.structured_data is None
+
+    def test_frozen(self):
+        resp = LLMResponse("c", "t", "m", "p", 1, 2, 3, None, None, False, "cid")
+        with pytest.raises(dataclasses.FrozenInstanceError):
+            resp.content = "x"
+
+
+class TestChatRequest:
+    def test_defaults_and_frozen(self):
+        req = ChatRequest(messages=[{"role": "user", "content": "hi"}])
+        assert req.session_id is None
+        assert req.parent_call_id is None
+        assert req.cache_salt is None
+        assert req.cache_namespace is None
+        assert req.structured is None
+        assert req.stream is True
+        assert req.overlay == {}
+        with pytest.raises(dataclasses.FrozenInstanceError):
+            req.stream = False
+
+    def test_replace_derivation(self):
+        """中间件用 dataclasses.replace 派生新请求(设计 §4.1 方案 A1)。"""
+        req = ChatRequest(messages=[{"role": "user", "content": "hi"}])
+        derived = dataclasses.replace(req, overlay={"response_format": {"type": "json_object"}})
+        assert derived.overlay and req.overlay == {}
+
+
+class TestSourceConfig:
+    def test_minimal_valid(self):
+        src = _make_source()
+        assert src.max_concurrency == 0 and src.rpm == 0 and src.tpm == 0
+        assert src.est_tokens == 0
+        assert src.enable_thinking is None
+        assert src.missing_done == "retry"
+        assert src.trust_env is True
+
+    @pytest.mark.parametrize("field", ["name", "provider", "base_url", "api_key", "model"])
+    def test_identity_fields_must_be_non_empty(self, field):
+        with pytest.raises(ValueError):
+            _make_source(**{field: "  "})
+
+    def test_timeout_must_be_positive(self):
+        with pytest.raises(ValueError):
+            _make_source(timeout_s=0)
+
+    def test_tpm_requires_est_tokens(self):
+        with pytest.raises(ValueError):
+            _make_source(tpm=10000, est_tokens=0)
+        assert _make_source(tpm=10000, est_tokens=800).est_tokens == 800
+
+    def test_negative_gate_rejected(self):
+        with pytest.raises(ValueError):
+            _make_source(rpm=-1)
+
+    def test_watchdog_invariant_chain(self):
+        """CHS config.py:66-82: 0 < inter < ttft < timeout_s。"""
+        ok = _make_source(ttft_timeout_s=30.0, inter_token_timeout_s=15.0)
+        assert ok.ttft_timeout_s == 30.0
+        with pytest.raises(ValueError):
+            _make_source(ttft_timeout_s=30.0, inter_token_timeout_s=40.0)
+        with pytest.raises(ValueError):
+            _make_source(ttft_timeout_s=200.0, inter_token_timeout_s=15.0)  # ttft >= timeout
+        with pytest.raises(ValueError):
+            _make_source(ttft_timeout_s=30.0)  # 只设其一
+
+    def test_missing_done_domain(self):
+        assert _make_source(missing_done="salvage").missing_done == "salvage"
+        with pytest.raises(ValueError):
+            _make_source(missing_done="ignore")
+
+
+class TestResilienceConfigs:
+    def test_retry_policy_validation(self):
+        assert RetryPolicy(max_attempts=3, backoff_base_s=2.0, backoff_max_s=30.0)
+        with pytest.raises(ValueError):
+            RetryPolicy(max_attempts=0, backoff_base_s=2.0, backoff_max_s=30.0)
+        with pytest.raises(ValueError):
+            RetryPolicy(max_attempts=3, backoff_base_s=30.0, backoff_max_s=2.0)
+
+    def test_breaker_config_validation(self):
+        assert BreakerConfig(fail_threshold=5, cooldown_s=60.0, probe_ttl_s=120.0)
+        with pytest.raises(ValueError):
+            BreakerConfig(fail_threshold=0, cooldown_s=60.0, probe_ttl_s=120.0)
+
+    def test_backpressure_and_global_limits(self):
+        assert BackpressurePolicy(stall_window_s=300.0, poll_interval_s=0.5)
+        with pytest.raises(ValueError):
+            BackpressurePolicy(stall_window_s=300.0, poll_interval_s=0)
+        assert GlobalLimits(max_concurrency=8, rpm=60, tpm=100000)
+        with pytest.raises(ValueError):
+            GlobalLimits(max_concurrency=-1, rpm=0, tpm=0)
+
+
+class TestAuxTypes:
+    def test_usage_and_stats(self):
+        u = Usage(prompt_tokens=10, completion_tokens=20, usage_source="estimated")
+        assert u.prompt_tokens == 10
+        s = TransportResult(
+            content="c", thinking="", prompt_tokens=1, completion_tokens=2,
+            usage_source="measured", ttft_ms=12.5, max_inter_token_ms=30.0, raw={"id": "x"},
+        )
+        assert s.raw["id"] == "x"