PtcRunner.SubAgent.Compression behaviour (PtcRunner v0.5.1)

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Behaviour for message history compression strategies.

Compression strategies transform turn history into LLM messages at render time. This enables various prompt optimization techniques like coalescing multiple turns into a single USER message.

Strategy Pattern

Strategies implement to_messages/3 which receives:

  • turns - List of completed turns to compress
  • memory - Accumulated definitions from all turns
  • opts - Rendering options (mission, tools, data, limits, etc.)

Configuration

Use normalize/1 to handle the various compression option formats:

# Disabled (default)
normalize(nil)   # => {nil, []}
normalize(false) # => {nil, []}

# Enabled with defaults
normalize(true)  # => {SingleUserCoalesced, [println_limit: 15, tool_call_limit: 20]}

# Custom strategy or options
normalize(MyStrategy)               # => {MyStrategy, [println_limit: 15, ...]}
normalize({MyStrategy, opts})       # => {MyStrategy, merged_opts}

Summary

Types

message()

An LLM message with role and content.

opts()

Options passed to compression strategies.

stats()

Statistics about what compression did.

Callbacks

name()

Human-readable name for this compression strategy.

to_messages(turns, memory, opts)

Render turns into LLM messages with compression statistics.

Functions

default_opts()

Returns the default compression options.

normalize(module)

Normalize compression configuration into {strategy, opts} tuple.

Types

message()

@type message() :: %{role: :system | :user | :assistant, content: String.t()}

An LLM message with role and content.

opts()

@type opts() :: [
  prompt: String.t(),
  system_prompt: String.t(),
  tools: map(),
  data: map(),
  println_limit: non_neg_integer(),
  tool_call_limit: non_neg_integer(),
  turns_left: non_neg_integer()
]

Options passed to compression strategies.

  • mission - The agent's mission/prompt text
  • system_prompt - Static system prompt content
  • tools - Map of available tools
  • data - Input data provided to the agent
  • println_limit - Max println calls to include (default: 15)
  • tool_call_limit - Max tool calls to include (default: 20)
  • turns_left - Remaining turns for the agent

stats()

@type stats() :: %{
  enabled: boolean(),
  strategy: String.t(),
  turns_compressed: non_neg_integer(),
  tool_calls_total: non_neg_integer(),
  tool_calls_shown: non_neg_integer(),
  tool_calls_dropped: non_neg_integer(),
  printlns_total: non_neg_integer(),
  printlns_shown: non_neg_integer(),
  printlns_dropped: non_neg_integer(),
  error_turns_collapsed: non_neg_integer()
}

Statistics about what compression did.

Returned alongside messages to report exactly what was dropped or collapsed.

Callbacks

name()

@callback name() :: String.t()

Human-readable name for this compression strategy.

to_messages(turns, memory, opts)

@callback to_messages(
  turns :: [PtcRunner.Turn.t()],
  memory :: map(),
  opts :: opts()
) :: {[message()], stats()}

Render turns into LLM messages with compression statistics.

Returns a tuple of {messages, stats} where stats reports exactly what the compression did (items dropped, errors collapsed, etc.).

Compression is a pure function - same inputs always produce the same output. Turn count is derived from length(turns), not message count.

Functions

default_opts()

@spec default_opts() :: keyword()

Returns the default compression options.

Examples

iex> PtcRunner.SubAgent.Compression.default_opts()
[println_limit: 15, tool_call_limit: 20]

normalize(module)

@spec normalize(boolean() | module() | {module(), keyword()} | nil) ::
  {module() | nil, keyword()}

Normalize compression configuration into {strategy, opts} tuple.

Handles various configuration formats:

  • nil or false - Compression disabled, returns {nil, []}
  • true - Use default strategy with default options
  • Module - Use custom strategy with default options
  • {Module, opts} - Use custom strategy with merged options

Examples

iex> PtcRunner.SubAgent.Compression.normalize(nil)
{nil, []}

iex> PtcRunner.SubAgent.Compression.normalize(false)
{nil, []}

iex> {strategy, opts} = PtcRunner.SubAgent.Compression.normalize(true)
iex> strategy
PtcRunner.SubAgent.Compression.SingleUserCoalesced
iex> opts[:println_limit]
15
iex> opts[:tool_call_limit]
20

iex> {strategy, _opts} = PtcRunner.SubAgent.Compression.normalize(SomeStrategy)
iex> strategy
SomeStrategy

iex> {strategy, opts} = PtcRunner.SubAgent.Compression.normalize({SomeStrategy, println_limit: 5})
iex> strategy
SomeStrategy
iex> opts[:println_limit]
5
iex> opts[:tool_call_limit]
20