fix(gate-b): fresh-db install path - conditional guards on plugin-table migrations + dual-path convergence migrations

alembic/versions/0121_agent_run_steps.py

@@ -14,7 +14,24 @@ branch_labels = None
 depends_on = None
 
 
+def _table_exists(conn, table_name: str) -> bool:
+    """True when the table exists (dual-path convergence, Gate B).
+
+    On a fresh install the automation plugin SQL migration has not run yet
+    when Alembic reaches this revision — skip instead of failing. The
+    plugin-side convergence migration creates the same table.
+    """
+    row = conn.execute(
+        sa.text("SELECT to_regclass(:tname) IS NOT NULL"),
+        {"tname": f"public.{table_name}"},
+    ).scalar()
+    return bool(row)
+
+
 def upgrade() -> None:
+    conn = op.get_bind()
+    if not _table_exists(conn, "automation_agent_runs"):
+        return
     op.create_table(
         "automation_agent_run_steps",
         sa.Column("id", PGUUID(as_uuid=True), primary_key=True),