refactor: unify LLM gateway policy

backend/database/migrations/__init__.py

@@ -1,7 +1,8 @@
 from .m0001_adopt_legacy import MIGRATION as M0001_ADOPT_LEGACY
 from .m0002_job_runs import MIGRATION as M0002_JOB_RUNS
+from .m0003_llm_audit import MIGRATION as M0003_LLM_AUDIT
 from .runner import Migration, MigrationError, MigrationRunner
 
-MIGRATIONS = (M0001_ADOPT_LEGACY, M0002_JOB_RUNS)
+MIGRATIONS = (M0001_ADOPT_LEGACY, M0002_JOB_RUNS, M0003_LLM_AUDIT)
 
 __all__ = ["MIGRATIONS", "Migration", "MigrationError", "MigrationRunner"]

backend/database/migrations/m0003_llm_audit.py

@@ -0,0 +1,32 @@
+from __future__ import annotations
+
+import sqlite3
+
+from backend.database.migrations.runner import Migration
+
+
+def extend_llm_audit(connection: sqlite3.Connection) -> None:
+    columns = {
+        str(row["name"])
+        for row in connection.execute("PRAGMA table_info(llm_usage)")
+    }
+    additions = (
+        ("role", "TEXT NOT NULL DEFAULT ''"),
+        ("prompt_version", "TEXT NOT NULL DEFAULT ''"),
+        ("error_code", "TEXT NOT NULL DEFAULT ''"),
+        ("input_tokens", "INTEGER NOT NULL DEFAULT 0"),
+        ("output_tokens", "INTEGER NOT NULL DEFAULT 0"),
+    )
+    for name, declaration in additions:
+        if name not in columns:
+            connection.execute(
+                f"ALTER TABLE llm_usage ADD COLUMN {name} {declaration}"
+            )
+
+
+MIGRATION = Migration(
+    version="0003",
+    name="extend_llm_audit",
+    action=extend_llm_audit,
+    signature="llm-audit:v1:role,prompt-version,error-code,input-tokens,output-tokens",
+)