fix: update tests for CORE_MEMORY_BLOCK_CHAR_LIMIT increase to 100k (#9645)

Tests were failing because they relied on the old default limit of 20,000:

- test_memory.py: "x " * 50000 = 100,000 chars now equals the limit
  instead of exceeding it. Increased to "x " * 60000 (120k chars).

- test_block_manager.py: Block created with default limit (now 100k),
  then 30k char update no longer exceeds it. Set explicit limit=20000
  on the test block to preserve the test intent.

- test_log_context_middleware.py: Removed stale `limit: 20000` from
  dummy frontmatter fixtures to match new serialization behavior.

Related to #9537

Co-authored-by: letta-code <248085862+letta-code@users.noreply.github.com>
Co-authored-by: Kian Jones <kianjones9@users.noreply.github.com>

tests/managers/test_block_manager.py

@@ -562,7 +562,9 @@ async def test_update_block(server: SyncServer, default_user):
 @pytest.mark.asyncio
 async def test_update_block_limit(server: SyncServer, default_user):
     block_manager = BlockManager()
-    block = await block_manager.create_or_update_block_async(PydanticBlock(label="persona", value="Original Content"), actor=default_user)
+    block = await block_manager.create_or_update_block_async(
+        PydanticBlock(label="persona", value="Original Content", limit=20000), actor=default_user
+    )
 
     limit = len("Updated Content") * 2000
     update_data = BlockUpdate(value="Updated Content" * 2000, description="Updated description")

tests/test_log_context_middleware.py

@@ -52,8 +52,8 @@ class TestLogContextMiddleware:
             async def get_files(self, agent_id, org_id, ref):
                 assert ref == "HEAD"
                 return {
-                    "system/human.md": "---\ndescription: human\nlimit: 20000\n---\nname: sarah",
-                    "system/persona.md": "---\ndescription: persona\nlimit: 20000\n---\nbe helpful",
+                    "system/human.md": "---\ndescription: human\n---\nname: sarah",
+                    "system/persona.md": "---\ndescription: persona\n---\nbe helpful",
                 }
 
         class DummyMemoryRepoManager:

tests/test_memory.py

@@ -25,9 +25,9 @@ def test_chat_memory_init_and_utils(chat_memory: Memory):
 
 def test_memory_limit_validation(chat_memory: Memory):
     with pytest.raises(ValueError):
-        ChatMemory(persona="x " * 50000, human="y " * 50000)
+        ChatMemory(persona="x " * 60000, human="y " * 60000)
     with pytest.raises(ValueError):
-        chat_memory.get_block("persona").value = "x " * 50000
+        chat_memory.get_block("persona").value = "x " * 60000
 
 
 def test_get_block_not_found(chat_memory: Memory):