feat(models): 组织、用户、角色、客户、会话与消息模型

按组织边界定义数据关系，补齐仓储层与通用工具，迁移脚本可重复执行。

backend/app/models/guardrail_event.py

@@ -0,0 +1,89 @@
+"""
+Copyright 2024-2026 ChatterMate
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+import uuid
+
+from sqlalchemy import (
+    JSON,
+    TIMESTAMP,
+    Boolean,
+    Column,
+    Float,
+    ForeignKey,
+    Index,
+    Integer,
+    String,
+    UUID,
+    func,
+)
+
+from app.core.encryption import EncryptedText
+from app.database import Base
+
+
+class GuardrailEvent(Base):
+    """One row per guardrail trigger across every surface (widget, channels,
+    workflow, help center).
+
+    Append-only: this is the record that answers "is off-topic abuse actually
+    material?" and "is a rule wrongly refusing real customers?" — the review
+    gate before any detection rule is promoted from counting to blocking.
+
+    `matched` holds rule ids / short match tokens ONLY — the column is plain
+    JSON (unencrypted), so raw visitor text must never land in it. The
+    reviewable text lives in `excerpt`, which is encrypted at rest exactly
+    like ChatHistory.message.
+    """
+
+    __tablename__ = "guardrail_events"
+    __table_args__ = (
+        # Declared here as well as in the migration so autogenerate never
+        # proposes dropping them and the sqlite test schema matches Postgres.
+        Index("ix_guardrail_events_org_created", "organization_id", "created_at"),
+        Index("ix_guardrail_events_rule_created", "rule", "created_at"),
+    )
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    organization_id = Column(
+        UUID(as_uuid=True),
+        ForeignKey("organizations.id", ondelete="CASCADE"),
+        nullable=True,
+    )
+    agent_id = Column(
+        UUID(as_uuid=True), ForeignKey("agents.id", ondelete="SET NULL"), nullable=True
+    )
+    # No FK: a help-center /ask event has no chat session at all.
+    session_id = Column(UUID(as_uuid=True), nullable=True)
+    # widget | channel | workflow | help_center
+    surface = Column(String(20), nullable=False)
+    # inbound | output
+    layer = Column(String(16), nullable=False)
+    # Stable rule id, e.g. injection.frame_tokens, offtopic.model_refused
+    rule = Column(String(64), nullable=False)
+    # blocked | counted | replaced
+    action = Column(String(16), nullable=False)
+    score = Column(Float, nullable=True)
+    # Rule ids / short match tokens only — NEVER raw visitor text (plain JSON).
+    matched = Column(JSON, default=None, nullable=True)
+    # Input length so wasted-token cost is estimable (~ char_len / 4).
+    char_len = Column(Integer, nullable=True)
+    # First 300 chars of the offending text, encrypted at rest; gated by
+    # GUARDRAIL_STORE_EXCERPT.
+    excerpt = Column(EncryptedText, nullable=True)
+    # Review workflow: precision denominator for the strict-mode decision.
+    reviewed = Column(Boolean, default=False, nullable=False)
+    false_positive = Column(Boolean, default=False, nullable=False)
+    created_at = Column(TIMESTAMP(timezone=True), server_default=func.now())