feat(ruby_llm): capture prompt, completion, and tool I/O when capture_bodies is enabled

CHANGELOG.md

@@ -1,5 +1,23 @@
 # Changelog
 
+## [0.2.0] - 2026-08-14
+
+### Added
+
+- The RubyLLM adapter captures conversation content when the configuration's
+  `capture_bodies` is enabled: `llm.prompt`, `llm.instructions` and
+  `llm.completion` on the root span, and `tool.arguments` / `tool.result` on
+  each tool span. Each value is truncated to 4,000 characters
+  (`RubyLLM::CONTENT_LIMIT`). `llm.instructions` joins every system message,
+  since RubyLLM's `with_instructions` appends by default and reporting only
+  the last one would hide a layered base prompt. A tool span records a result
+  only when the call succeeded; a raised tool reports its truncated error
+  message instead.
+
+  Capture stays **off** by default. Prompts and tool results carry whatever
+  the application sends the model, so enabling this is a data-handling
+  decision — the truncation is a cap on trace size, not a redaction boundary.
+
 ## [Unreleased]
 
 ### Added

README.md

@@ -50,7 +50,8 @@ root   SupportBot.respond              1,240ms   OK
    └─ tool tool.search_docs               310ms   OK
 ```
 
-Tool arguments and results are never sent. Error messages are truncated and
+Prompts, completions, and tool arguments/results are sent only when
+`capture_bodies` is enabled (off by default). Error messages are truncated and
 backtraces are never transmitted.
 
 ## Self-hosting

adapters/ruby_llm/README.md

@@ -48,7 +48,9 @@ enclosing event, 2.x drives a flat `step until complete?` loop whose rounds
 are siblings with tool calls between them. Rounds are accumulated and flushed
 on the round that ends the turn, so both produce the same trace.
 
-Tool arguments and results are never sent; error messages are truncated.
+Prompts, completions, and tool arguments/results are sent only when the
+configuration's `capture_bodies` is enabled (off by default, truncated to
+4,000 characters); error messages are truncated.
 
 ## Naming the traffic
 

adapters/ruby_llm/lib/activeagents/telemetry/ruby_llm.rb

@@ -27,7 +27,9 @@ module Telemetry
     # Tokens are summed per round from the assistant messages that round added,
     # so a repeated event-level count is never double counted.
     #
-    # Tool arguments and results are never sent; error messages are truncated.
+    # Prompts, completions, and tool arguments/results are not sent unless the
+    # configuration's capture_bodies is enabled (they may contain sensitive
+    # data); error messages are truncated.
     module RubyLLM
       AGENT_KEY = :activeagents_telemetry_ruby_llm_agent
       STATE_KEY = :activeagents_telemetry_ruby_llm_state
@@ -36,6 +38,8 @@ module RubyLLM
       # A turn that never reaches a final round (a halted tool call, or an app
       # driving RubyLLM 2.x's `step` by hand) would otherwise accumulate forever.
       MAX_TURN_SECONDS = 600
+      # Captured prompt/completion/tool content is truncated to this many characters.
+      CONTENT_LIMIT = 4_000
 
       DEFAULT_AGENT = { name: "RubyLLM::Chat", action: "chat" }.freeze
 
@@ -139,11 +143,16 @@ def finish_round(payload)
 
         def build_tool_span(payload, started_at, finished_at)
           error = payload[:exception_object]
+          attributes = { "tool.name" => payload[:tool_name].to_s, "tool.call_id" => payload[:tool_call_id].to_s }
+          if configuration.capture_bodies?
+            attributes["tool.arguments"] = tool_io_json(payload[:tool_arguments])
+            attributes["tool.result"] = tool_io_json(payload[:result_content]) unless error
+          end
           span = Span.new(
             "tool.#{payload[:tool_name]}",
             type: "tool",
             start_time: started_at,
-            attributes: { "tool.name" => payload[:tool_name].to_s, "tool.call_id" => payload[:tool_call_id].to_s }
+            attributes: attributes
           )
           span.record_error(error, message_limit: configuration.error_message_limit) if error
           span.finish(at: finished_at)
@@ -163,14 +172,17 @@ def report_turn(payload, turn)
             resource_attributes: configuration.resource_attributes
           )
 
+          root_attributes = {
+            "agent.class" => agent[:name],
+            "agent.action" => agent[:action],
+            "agent.provider" => payload[:provider].to_s,
+            "agent.model" => payload[:model].to_s
+          }
+          root_attributes.merge!(conversation_attributes(payload)) if configuration.capture_bodies?
+
           root = trace.span(
             "#{agent[:name]}.#{agent[:action]}", type: "root", start_time: started_at,
-            attributes: {
-              "agent.class" => agent[:name],
-              "agent.action" => agent[:action],
-              "agent.provider" => payload[:provider].to_s,
-              "agent.model" => payload[:model].to_s
-            }
+            attributes: root_attributes
           )
 
           llm = trace.span(
@@ -215,6 +227,59 @@ def resolve_agent(payload)
           nil
         end
 
+        # The prompt that opened the turn and the answer that closed it — the two
+        # ends a trace is otherwise missing. System instructions are included:
+        # they are the most common cause of a surprising answer.
+        def conversation_attributes(payload)
+          input = Array(payload[:input_messages])
+          new_messages = Array(payload[:messages_after])[input.size..] || []
+
+          attributes = {}
+          if (prompt = last_message_text(input, "user"))
+            attributes["llm.prompt"] = truncate_captured(prompt)
+          end
+          if (instructions = system_instructions(input))
+            attributes["llm.instructions"] = truncate_captured(instructions)
+          end
+          if (completion = last_message_text(new_messages, "assistant"))
+            attributes["llm.completion"] = truncate_captured(completion)
+          end
+          attributes
+        end
+
+        # RubyLLM's `with_instructions` appends by default, so a chat can carry
+        # several system messages and the model sees all of them. Join rather
+        # than taking the last, or an app that layers a base prompt with a
+        # per-request one would report only the fragment.
+        def system_instructions(messages)
+          texts = messages.select do |candidate|
+            candidate.respond_to?(:role) && candidate.role.to_s == "system" &&
+              candidate.respond_to?(:content) && !candidate.content.to_s.empty?
+          end.map { |message| message.content.to_s }
+
+          texts.empty? ? nil : texts.join("\n\n")
+        end
+
+        def last_message_text(messages, role)
+          message = messages.reverse.find do |candidate|
+            candidate.respond_to?(:role) && candidate.role.to_s == role &&
+              candidate.respond_to?(:content) && !candidate.content.to_s.empty?
+          end
+          text = message&.content.to_s
+          text.empty? ? nil : text
+        end
+
+        def tool_io_json(value)
+          json = value.is_a?(String) ? value : JSON.generate(value)
+          truncate_captured(json)
+        rescue StandardError
+          value.inspect[0, CONTENT_LIMIT]
+        end
+
+        def truncate_captured(text)
+          text.to_s[0, CONTENT_LIMIT]
+        end
+
         def token_totals(payload)
           initial_count = Array(payload[:input_messages]).size
           new_messages = Array(payload[:messages_after])[initial_count..] || []

adapters/ruby_llm/lib/activeagents/telemetry/ruby_llm/version.rb

@@ -3,7 +3,7 @@
 module ActiveAgents
   module Telemetry
     module RubyLLM
-      VERSION = "0.1.0"
+      VERSION = "0.2.0"
     end
   end
 end

adapters/ruby_llm/test/test_ruby_llm.rb

@@ -144,6 +144,50 @@ def test_inherits_destination_from_the_shared_configuration
     ActiveAgents::Telemetry.reset!
   end
 
+  ContentMsg = Struct.new(:role, :content, :input_tokens, :output_tokens, :thinking_tokens)
+
+  def test_does_not_capture_content_by_default
+    payload = chat_payload(input_messages: [ ContentMsg.new("user", "what is up?") ])
+    instrument("tool_call.ruby_llm", tool_name: "search", tool_call_id: "t1", tool_arguments: { q: "x" }, result_content: "y") { nil }
+    instrument("chat.ruby_llm", payload) do
+      payload[:messages_after] = payload[:input_messages] + [ ContentMsg.new("assistant", "not much", 1, 1, 0) ]
+    end
+
+    trace = traces.first
+    root_attributes = spans_of(trace, "root").first["attributes"]
+    tool_attributes = spans_of(trace, "tool").first["attributes"]
+    refute_includes root_attributes.keys, "llm.prompt"
+    refute_includes root_attributes.keys, "llm.completion"
+    refute_includes tool_attributes.keys, "tool.arguments"
+    refute_includes tool_attributes.keys, "tool.result"
+  end
+
+  def test_captures_conversation_and_tool_io_when_capture_bodies_enabled
+    ActiveAgents::Telemetry.configure { |config| config.capture_bodies = true }
+    subscribe
+
+    payload = chat_payload(input_messages: [
+      ContentMsg.new("system", "Be terse."),
+      ContentMsg.new("system", "Answer in English."),
+      ContentMsg.new("user", "what is up?" * 1_000)
+    ])
+    instrument("tool_call.ruby_llm", tool_name: "search", tool_call_id: "t1", tool_arguments: { q: "x" }, result_content: "y") { nil }
+    instrument("chat.ruby_llm", payload) do
+      payload[:messages_after] = payload[:input_messages] + [ ContentMsg.new("assistant", "not much", 1, 1, 0) ]
+    end
+
+    trace = traces.first
+    root_attributes = spans_of(trace, "root").first["attributes"]
+    tool_attributes = spans_of(trace, "tool").first["attributes"]
+    assert_equal ActiveAgents::Telemetry::RubyLLM::CONTENT_LIMIT, root_attributes["llm.prompt"].length
+    assert_equal "Be terse.\n\nAnswer in English.", root_attributes["llm.instructions"]
+    assert_equal "not much", root_attributes["llm.completion"]
+    assert_equal '{"q":"x"}', tool_attributes["tool.arguments"]
+    assert_equal "y", tool_attributes["tool.result"]
+  ensure
+    ActiveAgents::Telemetry.reset!
+  end
+
   private
 
   def subscribe_inheriting

lib/activeagents/telemetry/version.rb

@@ -2,6 +2,6 @@
 
 module ActiveAgents
   module Telemetry
-    VERSION = "0.1.0"
+    VERSION = "0.2.0"
   end
 end