feat: organize news packages into verified event timelines

Add optional events, evidence-backed timelines, versioned package corrections and bounded historical reprocessing. Keep independent packages readable and isolate retries by failed stage. Configure reasoning effort per model stage and refresh default news Skill drafts without publishing.

backend/src/alphapulse/news_risk/contracts.py

@@ -0,0 +1,51 @@
+"""Structured correction and time contracts shared by news stages."""
+from datetime import datetime
+from typing import Literal
+from pydantic import BaseModel, Field, model_validator
+
+class PackageInput(BaseModel):
+    id: int = Field(gt=0)
+    revision: int = Field(ge=0)
+
+
+class Assignment(BaseModel):
+    analysis_id: int = Field(gt=0)
+    evidence: str = Field(min_length=1, max_length=500)
+
+
+class Replacement(BaseModel):
+    keep_id: int | None
+    title: str = Field(min_length=1, max_length=300)
+    fact: str = Field(min_length=1)
+    category: str = Field(min_length=1, max_length=64)
+    tags: list[str] = Field(min_length=1, max_length=20)
+    content_kind: Literal['report', 'statement', 'data', 'opinion', 'explanation', 'other']
+    assignments: list[Assignment] = Field(min_length=1)
+
+
+class Correction(BaseModel):
+    packages: list[PackageInput] = Field(min_length=1)
+    replacements: list[Replacement] = Field(min_length=1)
+    reason: str = Field(min_length=1)
+
+
+class PackageTimePoint(BaseModel):
+    occurred_at: datetime | None
+    time_precision: Literal['minute', 'day', 'month', 'unknown']
+    time_text: str
+    reported_at: datetime | None
+    description: str = Field(min_length=1)
+    verification: Literal['supported', 'partial', 'conflicting', 'insufficient', 'refuted']
+    evidence_refs: list[dict] = Field(min_length=1)
+
+    @model_validator(mode='after')
+    def time_consistency(self):
+        if (self.occurred_at is None) != (self.time_precision == 'unknown'):
+            raise ValueError('发生时间与精度不一致')
+        if self.occurred_at and self.occurred_at.tzinfo is None:
+            raise ValueError('发生时间必须有时区')
+        if self.reported_at and self.reported_at.tzinfo is None:
+            raise ValueError('报道时间必须有时区')
+        return self
+
+