fix(web): drop tavily from the removed-backend registry after the restore

#100540 added a REMOVED_BACKENDS startup warning keyed on tavily; with the
backend restored, that entry would warn on a working provider. The registry
stays (empty) for future removals; migration tests now pin the machinery via
a synthetic entry plus a guard asserting no live provider is ever listed as
removed.

tests/tools/test_removed_backend_migration.py

@@ -1,54 +1,68 @@
-"""Removed-backend migration warnings (post-#99199 Tavily removal).
+"""Removed-backend migration warnings (registry added in #100540).
 
-A config still pointing at a backend that no longer ships in-tree
-(``web.backend: tavily``) must fail loudly and specifically:
+A config still pointing at a backend registered in
+``tools.tool_backend_helpers.REMOVED_BACKENDS`` must fail loudly and
+specifically:
 
 1. startup — ``validate_config_structure`` emits a warning naming the
    removal, instead of staying silent until the first tool call;
-2. tool call — ``selection_error`` explains the backend was removed and
-   names alternatives, instead of the generic "no registered provider
-   has that name".
+2. tool call — ``selection_error`` explains the backend was removed,
+   instead of the generic "no registered provider has that name".
 
-Regression source: keyed Tavily users upgrading to v0.21.0 saw their
-config silently become invalid with no migration or startup notice
-(reported on PR #99731).
+The registry ships empty on main (the Tavily removal that motivated it,
+#99199, was reverted by the #99731 restore), so these tests inject a
+synthetic ``legacysearch`` entry — they pin the machinery, not any
+specific vendor's membership.
 """
 
+import pytest
+
+import tools.tool_backend_helpers as tbh
 from hermes_cli.config import validate_config_structure
-from tools.tool_backend_helpers import (
-    REMOVED_BACKENDS,
-    removed_backend_note,
-    selection_error,
-)
+from tools.tool_backend_helpers import removed_backend_note, selection_error
+
+_NOTE = "the LegacySearch backend was removed in v0.0.0 (alternatives: exa, parallel)"
+
+
+@pytest.fixture
+def legacy_removed(monkeypatch):
+    monkeypatch.setitem(tbh.REMOVED_BACKENDS, "web", {"legacysearch": _NOTE})
 
 
 class TestRemovedBackendNote:
-    def test_tavily_is_registered_as_removed_web_backend(self):
-        assert "tavily" in REMOVED_BACKENDS["web"]
+    def test_note_lookup_normalizes_quotes_and_case(self, legacy_removed):
+        assert removed_backend_note("web", "legacysearch") == _NOTE
+        assert removed_backend_note("web", "'LegacySearch'") == _NOTE
+        assert removed_backend_note("web", '  "LEGACYSEARCH" ') == _NOTE
 
-    def test_note_lookup_normalizes_quotes_and_case(self):
-        plain = removed_backend_note("web", "tavily")
-        assert plain is not None
-        assert removed_backend_note("web", "'Tavily'") == plain
-        assert removed_backend_note("web", '  "TAVILY" ') == plain
-
-    def test_unknown_names_and_sections_return_none(self):
+    def test_unknown_names_and_sections_return_none(self, legacy_removed):
         assert removed_backend_note("web", "exa") is None
         assert removed_backend_note("web", "") is None
-        assert removed_backend_note("stt", "tavily") is None
+        assert removed_backend_note("stt", "legacysearch") is None
+
+    def test_registry_ships_without_live_backends(self):
+        # Restored/live backends must never sit in REMOVED_BACKENDS — the
+        # startup warning would fire on a working provider. Guards the
+        # #99731 restore against a stale tavily entry reappearing.
+        from agent.web_search_registry import get_provider
+
+        for name in tbh.REMOVED_BACKENDS.get("web", {}):
+            assert get_provider(name) is None, (
+                f"{name!r} is registered as removed but a live web provider "
+                "with that name exists"
+            )
 
 
 class TestSelectionErrorRemovedBackend:
-    def test_removed_backend_gets_specific_explanation(self):
-        msg = selection_error("web", "'tavily'", "no registered web search provider has that name")
-        assert "removed" in msg
-        assert "tavily" in msg.lower()
+    def test_removed_backend_gets_specific_explanation(self, legacy_removed):
+        msg = selection_error("web", "'legacysearch'", "no registered web search provider has that name")
+        assert _NOTE in msg
         # generic failure text replaced, not appended
         assert "no registered web search provider" not in msg
         # still ends with the uniform remediation contract
         assert "Run 'hermes tools' to change it." in msg
 
-    def test_live_backend_keeps_caller_failure_text(self):
+    def test_live_backend_keeps_caller_failure_text(self, legacy_removed):
         msg = selection_error("web", "'exa'", "no registered web search provider has that name")
         assert "no registered web search provider has that name" in msg
         assert "removed" not in msg
@@ -59,26 +73,26 @@ class TestStartupWarningForRemovedWebBackend:
     def _removed_issues(config):
         return [
             i for i in validate_config_structure(config)
-            if "removed" in i.message and "tavily" in i.message
+            if "removed" in i.message and "legacysearch" in i.message
         ]
 
-    def test_stale_web_backend_warns_at_startup(self):
-        issues = self._removed_issues({"web": {"backend": "tavily"}})
+    def test_stale_web_backend_warns_at_startup(self, legacy_removed):
+        issues = self._removed_issues({"web": {"backend": "legacysearch"}})
         assert len(issues) == 1
         assert issues[0].severity == "warning"
         assert "hermes tools" in issues[0].hint
 
-    def test_per_capability_keys_are_checked(self):
-        assert len(self._removed_issues({"web": {"search_backend": "tavily"}})) == 1
-        assert len(self._removed_issues({"web": {"extract_backend": "tavily"}})) == 1
+    def test_per_capability_keys_are_checked(self, legacy_removed):
+        assert len(self._removed_issues({"web": {"search_backend": "legacysearch"}})) == 1
+        assert len(self._removed_issues({"web": {"extract_backend": "legacysearch"}})) == 1
 
-    def test_same_stale_value_warns_once(self):
+    def test_same_stale_value_warns_once(self, legacy_removed):
         issues = self._removed_issues(
-            {"web": {"backend": "tavily", "search_backend": "tavily", "extract_backend": "tavily"}}
+            {"web": {"backend": "legacysearch", "search_backend": "legacysearch", "extract_backend": "legacysearch"}}
         )
         assert len(issues) == 1
 
-    def test_healthy_backend_produces_no_removed_warning(self):
+    def test_healthy_backend_produces_no_removed_warning(self, legacy_removed):
         assert self._removed_issues({"web": {"backend": "exa"}}) == []
         assert self._removed_issues({"web": {}}) == []
         assert self._removed_issues({}) == []

tools/tool_backend_helpers.py

@@ -411,12 +411,10 @@ def selection_exists(section: str) -> bool:
 # happened and what to do. Declared data, one policy — add future removals
 # here, never as one-off string checks at call sites.
 REMOVED_BACKENDS: Dict[str, Dict[str, str]] = {
-    "web": {
-        "tavily": (
-            "the Tavily backend was removed in v0.21.0 "
-            "(keyless alternatives: exa, parallel, firecrawl, keenable)"
-        ),
-    },
+    # Currently empty: the Tavily removal (#99199) that introduced this
+    # registry was reverted by the #99731 restore. Future backend removals
+    # add an entry here, e.g.
+    #   "web": {"<name>": "the <Name> backend was removed in vX.Y.Z (...)"},
 }