feat: add usage columns to steps table (#9270)

* feat: add usage columns to steps table

Adds denormalized usage fields to the steps table for easier querying:
- model_handle: The model handle (e.g., "openai/gpt-4o-mini")
- cached_input_tokens: Tokens served from cache
- cache_write_tokens: Tokens written to cache (Anthropic)
- reasoning_tokens: Reasoning/thinking tokens

These fields mirror LettaUsageStatistics and are extracted from the
existing prompt_tokens_details and completion_tokens_details JSON columns.

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

Co-Authored-By: Letta <noreply@letta.com>

* chore: regenerate OpenAPI specs and SDK for usage columns

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

Co-authored-by: Sarah Wooders <sarahwooders@users.noreply.github.com>

---------

Co-authored-by: Letta <noreply@letta.com>
Co-authored-by: letta-code <248085862+letta-code@users.noreply.github.com>
Co-authored-by: Sarah Wooders <sarahwooders@users.noreply.github.com>

alembic/versions/3e54e2fa2f7e_add_usage_columns_to_steps.py

@@ -0,0 +1,33 @@
+"""add_usage_columns_to_steps
+
+Revision ID: 3e54e2fa2f7e
+Revises: a1b2c3d4e5f8
+Create Date: 2026-02-03 16:35:51.327031
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "3e54e2fa2f7e"
+down_revision: Union[str, None] = "a1b2c3d4e5f8"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column("steps", sa.Column("model_handle", sa.String(), nullable=True))
+    op.add_column("steps", sa.Column("cached_input_tokens", sa.Integer(), nullable=True))
+    op.add_column("steps", sa.Column("cache_write_tokens", sa.Integer(), nullable=True))
+    op.add_column("steps", sa.Column("reasoning_tokens", sa.Integer(), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("steps", "reasoning_tokens")
+    op.drop_column("steps", "cache_write_tokens")
+    op.drop_column("steps", "cached_input_tokens")
+    op.drop_column("steps", "model_handle")