fix(ai): sanitize Langfuse warn logs, normalize tool_use.input, dedup history fetch

Addresses three open CodeRabbit findings on PR #1983.

- Provider::Anthropic Langfuse rescue branches no longer include
  `e.full_message` in `Rails.logger.warn`. `full_message` bundles the
  backtrace + cause chain and on some SDK error types includes the
  serialized request/response payload (prompt, model output). Logs
  now report `#{e.class}: #{e.message}` only. Three sites:
  create_langfuse_trace, log_langfuse_generation, upsert_langfuse_trace.
  Note: Provider::Openai has the same pattern (copy-pasted source) —
  harmonization deferred to a follow-up cleanup PR; this commit fixes
  only the Anthropic provider to keep PR scope tight.

- MessageFormatter#parse_arguments now coerces any non-Hash parsed
  result to `{}`. Anthropic's Messages API requires `tool_use.input`
  to be a JSON object (map); a stored ToolCall::Function record whose
  arguments parse to a scalar, bool, or array (corrupt row, legacy
  data, cross-provider bleed) would otherwise produce a payload the
  API rejects. Normal flow stores Hash arguments end-to-end so the
  fix is defensive — adds 2 tests covering scalar/array JSON strings
  and non-String non-Hash inputs.

- Assistant::Responder dedups the chat-history fetch. The previous
  layout fired two near-identical `chat.messages.where(...).includes(
  :tool_calls).ordered` queries per LLM turn (one for the OpenAI-shape
  payload, one for the raw-records kwarg). A new memoized
  `complete_chat_messages` fetches once; `chat_message_records` filters
  out the current message via `Array#reject`, `openai_messages_payload`
  iterates the cached array unchanged. One SQL query per turn instead
  of two. Memoization scope = single Responder instance (per LLM call),
  so cache invalidation is not a concern.

All 4370 tests pass (1 pre-existing libvips env error unrelated).
Rubocop + brakeman clean.

test/models/provider/anthropic/message_formatter_test.rb

@@ -171,6 +171,45 @@ class Provider::Anthropic::MessageFormatterTest < ActiveSupport::TestCase
     assert_equal "", messages[2][:content].first[:content]
   end
 
+  # Anthropic's tool_use.input MUST be a JSON object (map). If a stored
+  # ToolCall::Function record carries arguments that parse to a scalar or
+  # array (corrupt row, legacy data, OpenAI cross-bleed), the formatter
+  # must coerce them to `{}` so we don't ship an invalid payload.
+  test "coerces non-Hash parsed arguments to empty Hash" do
+    [ '"hello"', "123", "true", "[1,2,3]" ].each do |non_object_json|
+      formatter = Provider::Anthropic::MessageFormatter.new(
+        prompt: "go",
+        function_results: [ {
+          call_id: "toolu_x",
+          name: "noop",
+          arguments: non_object_json,
+          output: nil
+        } ]
+      )
+
+      messages = formatter.build
+
+      assert_equal({}, messages[1][:content].first[:input],
+        "expected empty Hash for arguments=#{non_object_json.inspect}")
+    end
+  end
+
+  test "coerces non-Hash non-String arguments to empty Hash" do
+    formatter = Provider::Anthropic::MessageFormatter.new(
+      prompt: "go",
+      function_results: [ {
+        call_id: "toolu_x",
+        name: "noop",
+        arguments: [ 1, 2, 3 ],
+        output: nil
+      } ]
+    )
+
+    messages = formatter.build
+
+    assert_equal({}, messages[1][:content].first[:input])
+  end
+
   private
     def stub_user_message(content)
       msg = UserMessage.new(content: content, ai_model: "claude-sonnet-4-6")