refactor(routes): move research domain into routes/research/ subpackage

Move the research route domain into the canonical routes/research/ subpackage while preserving the legacy routes.research_routes import path through a sys.modules compatibility shim.

The moved canonical module is behavior-preserving, app wiring now imports the canonical route setup function, source-introspection tests point at the new canonical path, and shim regression coverage pins legacy/canonical same-object behavior plus string-targeted monkeypatch reach-through.

Refs #4082.
Refs #4071.

tests/test_aux_llm_owner_scope.py

@@ -54,7 +54,7 @@ def test_scheduler_fallbacks_and_research_headers_are_owner_scoped():
 
 
 def test_research_routes_fallbacks_are_owner_scoped():
-    src = _src("routes/research_routes.py")
+    src = _src("routes/research/research_routes.py")
 
     assert 'resolve_endpoint("research", owner=user)' in src
     assert 'resolve_endpoint("utility", owner=user)' in src

tests/test_endpoint_owner_scope_followup.py

@@ -402,7 +402,7 @@ def test_gallery_image_endpoint_lookups_are_owner_scoped():
 
 
 def test_research_endpoint_resolution_passes_owner():
-    body = Path("routes/research_routes.py").read_text(encoding="utf-8")
+    body = Path("routes/research/research_routes.py").read_text(encoding="utf-8")
 
     assert "def _resolve_research_endpoint(sess, owner:" in body
     assert 'resolve_endpoint("research", owner=user)' in body

tests/test_research_routes_shim.py

@@ -0,0 +1,44 @@
+"""Regression test for the research route shim (slice 2b, #4082/#4071).
+
+The backward-compat shim at ``routes/research_routes.py`` uses ``sys.modules``
+replacement so the legacy import path and the canonical ``routes.research.*``
+path resolve to the *same* module object. This is required because
+``test_research_owner_scope_routes.py`` does a string-targeted
+``monkeypatch.setattr("routes.research_routes.DEEP_RESEARCH_DIR", ...)`` which
+must reach the canonical module. This test pins that contract.
+"""
+
+import importlib
+
+import routes.research_routes as _shim_research  # noqa: F401
+
+
+def test_legacy_and_canonical_research_module_are_same_object():
+    """``import routes.research_routes`` must alias the canonical module."""
+    legacy = importlib.import_module("routes.research_routes")
+    canonical = importlib.import_module("routes.research.research_routes")
+    assert legacy is canonical, (
+        "routes.research_routes shim must resolve to the canonical "
+        "routes.research.research_routes module object"
+    )
+
+
+def test_string_targeted_monkeypatch_reaches_canonical(monkeypatch):
+    """String-targeted ``monkeypatch.setattr`` via the legacy path must reach
+    the canonical module.
+
+    ``test_research_owner_scope_routes.py`` patches
+    ``"routes.research_routes.DEEP_RESEARCH_DIR"`` as an autouse fixture; for
+    that to take effect at runtime, the legacy module name and the canonical
+    module must be identical.
+    """
+    legacy = importlib.import_module("routes.research_routes")
+    canonical = importlib.import_module("routes.research.research_routes")
+
+    sentinel = "/tmp/shim-test-sentinel"
+    monkeypatch.setattr("routes.research_routes.DEEP_RESEARCH_DIR", sentinel)
+    assert canonical.DEEP_RESEARCH_DIR == sentinel, (
+        "string-targeted monkeypatch via legacy path did not reach the canonical module"
+    )
+    # restore is handled by monkeypatch fixture teardown
+    assert legacy is canonical