Struct Microcompactor 

pub struct Microcompactor {
    pub trigger_tool_count: usize,
    pub keep_recent: usize,
}

Configuration for count-based proactive pruning of old tool results.

Unlike crate::compact::Compactor (LLM-driven), this compactor requires no provider access — it simply replaces the content of old tool-result messages with a placeholder string when the total number of tool messages exceeds a threshold.

Pairing safety (invariant #8)

This compactor never removes messages — only replaces the content field of Role::Tool messages. The tool-call ↔ tool-result pairing is preserved because every Role::Tool message stays at its index, immediately after the Role::Assistant message whose tool_calls list its id.

Fields

trigger_tool_count: usize

Prune when the number of Role::Tool messages exceeds this.

keep_recent: usize

Keep this many most-recent tool results verbatim.

Implementations

impl Microcompactor

pub fn new(trigger_tool_count: usize, keep_recent: usize) -> Self

Create a new Microcompactor with explicit trigger and keep counts.

pub fn prune(&self, messages: &mut [Message]) -> usize

Prune oldest tool-result contents in place. Returns the number pruned.

Does NOT remove messages — only replaces content of Role::Tool messages older than keep_recent when total tool count exceeds trigger_tool_count. Tool messages shorter than MIN_PRUNE_LENGTH are left untouched (not worth the placeholder swap).

Logic

1. Collect indices of all Role::Tool messages.
2. If count <= self.trigger_tool_count, return 0.
3. Otherwise, the candidates for pruning are all tool messages except the last self.keep_recent. Iterate them oldest-first; for each whose content.len() > MIN_PRUNE_LENGTH and whose content is not already the placeholder, replace content with MICROCOMPACT_PLACEHOLDER. Stop once count - pruned <= self.trigger_tool_count (prune only enough to get back under the trigger — don’t prune everything eligible).
4. Return the number pruned.

Trait Implementations

impl Clone for Microcompactor

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Microcompactor

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Microcompactor

fn default() -> Self

Returns the “default value” for a type.