fix: Align fact field naming and add description

- Change extraction rule to reference 'fact' instead of 'fact_text'
- Add descriptive text for fact field in Edge model

graphiti_core/prompts/extract_edges.py

@@ -30,7 +30,10 @@ class Edge(BaseModel):
     target_entity_id: int = Field(
         ..., description='The id of the target entity from the ENTITIES list'
     )
-    fact: str = Field(..., description='')
+    fact: str = Field(
+        ...,
+        description='A natural language description of the relationship between the entities, paraphrased from the source text',
+    )
     valid_at: str | None = Field(
         None,
         description='The date and time when the relationship described by the edge fact became true or was established. Use ISO 8601 format (YYYY-MM-DDTHH:MM:SS.SSSSSSZ)',
@@ -116,7 +119,7 @@ You may use information from the PREVIOUS MESSAGES only to disambiguate referenc
 2. Each fact must involve two **distinct** entities.
 3. Use a SCREAMING_SNAKE_CASE string as the `relation_type` (e.g., FOUNDED, WORKS_AT).
 4. Do not emit duplicate or semantically redundant facts.
-5. The `fact_text` should closely paraphrase the original source sentence(s). Do not verbatim quote the original text.
+5. The `fact` should closely paraphrase the original source sentence(s). Do not verbatim quote the original text.
 6. Use `REFERENCE_TIME` to resolve vague or relative temporal expressions (e.g., "last week").
 7. Do **not** hallucinate or infer temporal bounds from unrelated events.