fix: add field validators to Block schema for int32 limit and null bytes (#9185)

- Add `validate_limit_int32` validator (mode=after) to reject limit values
  exceeding PostgreSQL INTEGER max (2147483647)
- Add `sanitize_value_null_bytes` validator (mode=before) to strip null bytes
  from block values, preventing asyncpg CharacterNotInRepertoireError

Fixes DB errors:
- "value out of int32 range" on block.limit
- "invalid byte sequence for encoding UTF8: 0x00" on block.value

🤖 Generated with [Letta Code](https://letta.com)

Co-authored-by: Letta <noreply@letta.com>

letta/schemas/block.py

@@ -1,12 +1,14 @@
 from datetime import datetime
 from typing import Any, List, Optional
 
-from pydantic import ConfigDict, Field, model_validator
+from pydantic import ConfigDict, Field, field_validator, model_validator
 
 from letta.constants import CORE_MEMORY_BLOCK_CHAR_LIMIT, DEFAULT_HUMAN_BLOCK_DESCRIPTION, DEFAULT_PERSONA_BLOCK_DESCRIPTION
 from letta.schemas.enums import PrimitiveType
 from letta.schemas.letta_base import LettaBase
 
+INT32_MAX = 2147483647
+
 # block of the LLM context
 
 
@@ -48,6 +50,22 @@ class BaseBlock(LettaBase, validate_assignment=True):
 
     model_config = ConfigDict(extra="ignore")  # Ignores extra fields
 
+    @field_validator("limit", mode="after")
+    @classmethod
+    def validate_limit_int32(cls, v: int) -> int:
+        """Ensure limit is within PostgreSQL INTEGER (int32) range."""
+        if v > INT32_MAX:
+            raise ValueError(f"limit must be <= {INT32_MAX} (int32 max), got {v}")
+        return v
+
+    @field_validator("value", mode="before")
+    @classmethod
+    def sanitize_value_null_bytes(cls, v):
+        """Remove null bytes from value to prevent PostgreSQL encoding errors."""
+        if isinstance(v, str):
+            return v.replace("\x00", "")
+        return v
+
     @model_validator(mode="before")
     @classmethod
     def verify_char_limit(cls, data: Any) -> Any: