Module: Legion::LLM::Inference::Executor::ContextWindow

Included in:
Legion::LLM::Inference::Executor
Defined in:
lib/legion/llm/inference/executor/context_window.rb

Overview

ContextWindow methods extracted from Executor verbatim (P4b §1.5, refactor-under-green). Functional message-list transformations: empty/thinking/tool-result trimming and context-window-aware compaction. Operates on the messages argument; reads

Instance Method Summary collapse

Instance Method Details

#compact_to_fit(messages, target_tokens) ⇒ Object 



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# File 'lib/legion/llm/inference/executor/context_window.rb', line 66

def compact_to_fit(messages, target_tokens)
  return messages if estimate_message_tokens(messages) <= target_tokens

  filtered = messages.reject do |msg|
    role = (msg[:role] || msg['role']).to_s
    role == 'tool' && (msg[:content] || msg['content']).to_s.length > 500
  end
  messages = filtered.map do |msg|
    role = (msg[:role] || msg['role']).to_s
    next msg unless role == 'tool'

    content = (msg[:content] || msg['content']).to_s
    content.length > 200 ? msg.merge(content: "#{content[0, 200]}\n[compacted]") : msg
  end

  return messages if estimate_message_tokens(messages) <= target_tokens

  half = messages.size / 2
  messages.last(half)
end

#empty_assistant_message?(msg) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/legion/llm/inference/executor/context_window.rb', line 182

def empty_assistant_message?(msg)
  return false unless msg.is_a?(Hash)
  return false unless (msg[:role] || msg['role']).to_s == 'assistant'

  content = msg[:content] || msg['content']
  has_content = content.is_a?(String) ? !content.strip.empty? : !content.nil?
  return false if has_content

  tool_calls = msg[:tool_calls] || msg['tool_calls']
  return false if tool_calls.is_a?(Array) && tool_calls.any?

  true
end

#enforce_context_window(messages) ⇒ Object 



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# File 'lib/legion/llm/inference/executor/context_window.rb', line 24

def enforce_context_window(messages)
  context_window = resolved_context_window
  @context_accounting[:component_status][:context_window] = :observed
  return messages unless context_window&.positive?

  threshold = (context_window * 0.90).to_i
  estimated = estimate_message_tokens(messages)
  return messages if estimated <= threshold

  log.warn "[llm][executor] action=context_compaction request_id=#{@request.id} " \
           "estimated_tokens=#{estimated} context_window=#{context_window} threshold=#{threshold}"

  preserve_after = last_user_message_index(messages)
  recent = messages[preserve_after..]
  older = messages[0...preserve_after]

  target_tokens = threshold - estimate_message_tokens(recent)
  compacted = compact_to_fit(older, target_tokens)

  result = compacted + recent
  after_tokens = estimate_message_tokens(result)
  saved = [estimated - after_tokens, 0].max

  @context_accounting[:tokens][:context_window_saved_estimated_tokens] += saved
  @context_accounting[:counts][:context_window_message_count_before] = messages.size
  @context_accounting[:counts][:context_window_message_count_after] = result.size
  @context_accounting[:events] << ContextAccounting.event(
    event_type:    :context_window_enforcement,
    component:     :context_window,
    before_tokens: estimated,
    after_tokens:  after_tokens,
    before_count:  messages.size,
    after_count:   result.size,
    metadata:      { context_window: context_window, threshold: threshold }
  )

  log.info "[llm][executor] action=context_compaction_complete request_id=#{@request.id} " \
           "before=#{messages.size} after=#{result.size} " \
           "tokens_before=#{estimated} tokens_after=#{after_tokens}"
  result
end

#estimate_message_tokens(messages) ⇒ Object 



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# File 'lib/legion/llm/inference/executor/context_window.rb', line 93

def estimate_message_tokens(messages)
  messages.sum { |m| ((m[:content] || m['content']).to_s.length / 4.0).ceil }
end

#last_user_message_index(messages) ⇒ Object 



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# File 'lib/legion/llm/inference/executor/context_window.rb', line 171

def last_user_message_index(messages)
  messages.rindex { |m| (m[:role] || m['role']).to_s == 'user' } || messages.size
end

#native_dispatch_messages ⇒ Object 



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# File 'lib/legion/llm/inference/executor/context_window.rb', line 12

def native_dispatch_messages
  messages = apply_conversation_breakpoint(@request.messages)
  rejected = messages.count { |m| empty_assistant_message?(m) }
  if rejected.positive?
    log.warn "[llm][executor] action=strip_empty_assistants request_id=#{@request.id} removed=#{rejected}"
    messages = messages.reject { |m| empty_assistant_message?(m) }
  end
  messages = strip_thinking_from_history(messages)
  messages = trim_oversized_tool_results(messages)
  enforce_context_window(messages)
end

#resolved_context_window ⇒ Object 



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# File 'lib/legion/llm/inference/executor/context_window.rb', line 87

def resolved_context_window
  @resolved_offering_metadata&.dig(:limits, :context_window) ||
    @resolved_offering_metadata&.dig(:context_window) ||
    @resolved_offering_metadata&.dig('limits', 'context_window')
end

#strip_leading_thinking_block(text) ⇒ Object 



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# File 'lib/legion/llm/inference/executor/context_window.rb', line 136

def strip_leading_thinking_block(text)
  result = text.lstrip
  THINKING_TAG_PAIRS.each do |open_tag, close_tag|
    next unless result.start_with?(open_tag)

    close_idx = result.index(close_tag, open_tag.length)
    return close_idx ? result[(close_idx + close_tag.length)..].lstrip : ''
  end
  text
end

#strip_thinking_from_history(messages) ⇒ Object 



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# File 'lib/legion/llm/inference/executor/context_window.rb', line 97

def strip_thinking_from_history(messages)
  before_tokens = ContextAccounting.estimate_message_tokens(messages)
  preserve_after = last_user_message_index(messages)
  stripped_count = 0
  result = messages.each_with_index.map do |msg, idx|
    next msg if idx >= preserve_after
    next msg unless (msg[:role] || msg['role']).to_s == 'assistant'

    content = msg[:content] || msg['content']
    next msg unless content.is_a?(String)

    cleaned = strip_leading_thinking_block(content)
    next msg if cleaned == content

    stripped_count += 1
    msg.merge(content: cleaned)
  end

  after_tokens = ContextAccounting.estimate_message_tokens(result)
  saved = [before_tokens - after_tokens, 0].max
  @context_accounting[:component_status][:thinking_strip] = :observed
  if saved.positive?
    @context_accounting[:tokens][:stripped_thinking_estimated_tokens] += saved
    @context_accounting[:counts][:stripped_thinking_message_count] += stripped_count
    @context_accounting[:events] << ContextAccounting.event(
      event_type:    :thinking_stripped,
      component:     :stripped_thinking,
      before_tokens: before_tokens,
      after_tokens:  after_tokens,
      before_count:  messages.size,
      after_count:   result.size,
      metadata:      { stripped_count: stripped_count }
    )
  end

  log.info "[llm][executor] action=strip_thinking_history request_id=#{@request.id} stripped=#{stripped_count}" if stripped_count.positive?
  result
end

#tool_result_message?(msg) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/legion/llm/inference/executor/context_window.rb', line 175

def tool_result_message?(msg)
  return false unless msg.is_a?(Hash)

  role = (msg[:role] || msg['role']).to_s
  role == 'tool' || msg.key?(:tool_call_id) || msg.key?('tool_call_id')
end

#trim_oversized_tool_results(messages) ⇒ Object 



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# File 'lib/legion/llm/inference/executor/context_window.rb', line 147

def trim_oversized_tool_results(messages)
  max_chars = Legion::Settings[:llm][:tool_result_max_dispatch_chars].to_i
  return messages unless max_chars.positive?

  preserve_after = last_user_message_index(messages)
  trimmed_count = 0
  result = messages.each_with_index.map do |msg, idx|
    next msg if idx >= preserve_after
    next msg unless tool_result_message?(msg)

    content = msg[:content] || msg['content']
    next msg unless content.is_a?(String) && content.length > max_chars

    trimmed_count += 1
    msg.merge(content: "#{content[0, max_chars]}\n[truncated — #{content.length} chars total]")
  end

  if trimmed_count.positive?
    log.info "[llm][executor] action=trim_tool_results request_id=#{@request.id} trimmed=#{trimmed_count} " \
             "max_chars=#{max_chars} preserved_after=#{preserve_after}"
  end
  result
end