lurker: say in the ROOM when a model swap happened, not only in the journal (#118, lurker half)

The lurker falls back from claude to opencode on any dead end — right, since posting a
failure verbatim helps nobody. But the reply then carried only the SECOND model's name,
so a thin answer read as "the configured model had little to say" when the configured
model had in fact never finished.

Live on 2026-08-02: a Fable architecture run for @reviewer died on error_max_turns, the
lurker fell back to opencode/deepseek, deepseek burned its own budget on the same search
and answered nothing useful. That Fable had run at all appeared solely in
`journalctl --user -u bullpen-lurker@reviewer` — exactly where nobody looks while reading
a disappointing reply. Same defect idea #118 fixed for the grinder: report the model that
actually served, and say so when it was not the one asked for.

The banner only appears on an actual swap; the common case stays as quiet as before.

tests/test_lurker_fallback_visible.py pins all three: the banner names both models on a
swap, no banner when the configured model answers, and a double dead-end still returns a
real diagnosis rather than a banner wrapped around nothing. Mutation-checked — cutting the
announcement fails exactly the first test and leaves the other two green. (The first
attempt at that mutation silently did not apply, which made three green tests meaningless;
redone via a file with an explicit marker assertion.)

lurker/bullpen-lurker

@@ -325,7 +325,14 @@ def run_agent(prompt):
         # If opencode ALSO dead-ends, hand back the more informative of the two so the room at
         # least sees a real diagnosis instead of two layers of "(no result)".
         if oc and not oc.lstrip().startswith(f"(@{NICK}"):
-            return oc
+            # SAY IT IN THE ROOM, not only on stderr. The reply carries the second model's
+            # name, so a thin answer reads as "the configured model had little to say" when
+            # what actually happened is that the configured model never finished. On
+            # 2026-08-02 a Fable architecture run died on max_turns, deepseek answered
+            # instead, and the only trace was journalctl. Same defect bullpen idea #118 fixed
+            # for the grinder: report what SERVED you, and say so when it was not what you asked.
+            return (f"⚠ answered by the fallback: {MODEL or 'claude'} {why}, "
+                    f"served by opencode {_ocmodel()}\n\n{oc}")
         return ans if (ans and not ok) else oc
     return ans
 

tests/test_lurker_fallback_visible.py

@@ -0,0 +1,77 @@
+"""A model swap must be visible in the ROOM, not only in the journal (#118, lurker half).
+
+The lurker falls back from claude to opencode on any dead end — a good behaviour, since
+posting a failure verbatim helps nobody. But the reply then carried only the SECOND
+model's name, so a thin answer read as "the configured model had little to say" when what
+really happened was that the configured model never finished.
+
+Live on 2026-08-02: a Fable architecture run for @reviewer died on `error_max_turns`, the
+lurker silently fell back to opencode/deepseek, and deepseek burned its own budget on the
+same search and answered nothing. The only record that Fable had run at all was
+`journalctl --user -u bullpen-lurker@reviewer` — exactly where nobody looks when reading a
+disappointing reply. Same defect bullpen idea #118 fixed for the grinder: report the model
+that actually served you, and say so when it was not the one you asked for.
+"""
+import importlib.machinery
+import importlib.util
+import os
+import sys
+
+import pytest
+
+REPO = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+
+
+@pytest.fixture
+def lurk(monkeypatch, tmp_path):
+    monkeypatch.setenv("HOME", str(tmp_path))
+    (tmp_path / "spec_lurker").mkdir()
+    sys.modules.pop("lurk", None)
+    argv, sys.argv = sys.argv, ["bullpen-lurker", "spec"]
+    try:
+        ld = importlib.machinery.SourceFileLoader(
+            "lurk", os.path.join(REPO, "lurker", "bullpen-lurker"))
+        mod = importlib.util.module_from_spec(importlib.util.spec_from_loader("lurk", ld))
+        ld.exec_module(mod)
+    finally:
+        sys.argv = argv
+    return mod
+
+
+def test_fallback_announces_itself_in_the_reply(lurk, monkeypatch):
+    monkeypatch.setattr(lurk, "RUNTIME", "claude", raising=False)
+    monkeypatch.setattr(lurk, "MODEL", "fable", raising=False)
+    monkeypatch.setattr(lurk, "run_claude", lambda p: ("(no result, rc 1)", False))
+    monkeypatch.setattr(lurk, "run_opencode", lambda p: "here is the architecture verdict")
+    monkeypatch.setattr(lurk, "_ocmodel", lambda: "bosch/deepseek")
+
+    out = lurk.run_agent("some prompt")
+    assert "architecture verdict" in out, "the fallback's answer must still come through"
+    assert "fable" in out, "the reply must name the model that was ASKED for and failed"
+    assert "deepseek" in out, "…and the model that actually served"
+
+
+def test_no_banner_when_the_configured_model_answers(lurk, monkeypatch):
+    """The common case must not get noisier — same posture as the grinder's model tag."""
+    monkeypatch.setattr(lurk, "RUNTIME", "claude", raising=False)
+    monkeypatch.setattr(lurk, "MODEL", "fable", raising=False)
+    monkeypatch.setattr(lurk, "run_claude", lambda p: ("a fine answer", True))
+    monkeypatch.setattr(lurk, "run_opencode", lambda p: pytest.fail("must not fall back"))
+
+    out = lurk.run_agent("some prompt")
+    assert out == "a fine answer"
+    assert "⚠" not in out
+
+
+def test_double_dead_end_still_returns_a_diagnosis(lurk, monkeypatch):
+    """When BOTH runtimes fail there is nothing to announce — the room needs the error,
+    not a banner wrapped around an empty string."""
+    monkeypatch.setattr(lurk, "RUNTIME", "claude", raising=False)
+    monkeypatch.setattr(lurk, "MODEL", "fable", raising=False)
+    monkeypatch.setattr(lurk, "NICK", "spec", raising=False)
+    monkeypatch.setattr(lurk, "run_claude", lambda p: ("(@spec: claude API error)", False))
+    monkeypatch.setattr(lurk, "run_opencode", lambda p: "(@spec: opencode gave nothing)")
+    monkeypatch.setattr(lurk, "_ocmodel", lambda: "bosch/deepseek")
+
+    out = lurk.run_agent("some prompt")
+    assert "spec" in out and "error" in out.lower()