gate: the rebuke turn is not a ground — second examination uses the caller's sources

The live round trip showed the second examination listing the gate's own
rebuke as source user_2. The rebuke is the gate's turn, not something the
caller gave the model; the second reply is now examined against the
caller's original body (same sources and query as the first). Test pins
it. Elixir gate 15/0.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

vav_pipeline/test/gate_test.exs

@@ -207,6 +207,9 @@ defmodule VavPipeline.GateTest do
     assert pass.first.verdict == :lo_tov
     assert pass.bedikah.verdict == :tov
     assert pass.bedikah.rebukes == pass.first.bedikah_ref
+    # The rebuke turn is the gate's, not the caller's: not a source for the second examination.
+    assert Enum.map(pass.bedikah.sources, & &1.id) == ["system", "user_1", "user_2"]
+    assert pass.bedikah.sources == pass.first.sources
     [%{"text" => text}] = pass.reply["content"]
     assert String.starts_with?(text, "CLEAN:")
     assert text =~ "— shorashim #{pass.bedikah.bedikah_ref}: tov (after rebuke of #{pass.first.bedikah_ref}: lo_tov)"