feat: compact

[bobrykov]

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[coderabbitai]

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• src/compact.rs
• src/lib.rs

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📝 Walkthrough

Walkthrough

A new context compaction module is introduced to manage and reduce agent conversation memory. It defines a pluggable async ContextCompactor trait, supporting types for metadata and telemetry, a built-in TruncatingCompactor implementation, utilities for splitting messages at turn boundaries, and a ContextManager that orchestrates compaction based on token thresholds and emergency zones.

Changes

Context Compaction System

Layer / File(s)	Summary
Architecture & Compactor Trait Contract src/compact.rs	Module documentation establishes "when to compact" vs "how to compact" separation. ContextCompactor trait defines the async object-safe contract for pluggable compaction strategies.
Data Contracts & Telemetry src/compact.rs	CompactionContext, CompactReason, and CompactionOutcome define data shapes. Telemetry structures (CompactTelemetry, PreCompactStats, PostCompactStats) capture observability metadata.
Truncating Compactor Implementation src/compact.rs	TruncatingCompactor implements ContextCompactor, dropping oldest messages while preserving a configurable number of recent messages and enforcing minimum message count.
Token Splitting Utility src/compact.rs	TokenSplitter and SplitResult segment message histories at coherent turn boundaries (assistant→user transitions) into compactable and preserved segments with token accounting.
Error & Result Types src/compact.rs	ContextOverflow terminal error contains token usage, window/message counts, and trigger reason. EnsureContextResult represents compaction outcome or no-action results.
Context Manager Orchestration src/compact.rs	ContextManager estimates tokens, determines compaction triggers (threshold + emergency zone), and orchestrates compaction via configured ContextCompactor. Async ensure_context_fits and compact_manual methods return EnsureContextResult or ContextOverflow.
Tests & Module Export src/compact.rs, src/lib.rs	Extensive unit tests verify token estimation, thresholds, splitting, truncation, compaction flows, and telemetry. Module is exported via pub mod compact; and documented in crate overview.

🚥 Pre-merge checks | ✅ 3 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Title check	❓ Inconclusive	The title 'feat: compact' is overly vague and generic. While it references a real part of the changeset, it fails to clearly convey the primary purpose or main functionality being introduced.	Replace with a more descriptive title such as 'feat: add context compaction system for managing agent conversation history' to clearly indicate the main feature being introduced.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 50.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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• Commit unit tests in branch feat/compact

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/compact.rs`:
- Around line 253-265: The compacted constructor currently computes tokens_saved
incorrectly (tokens_after.saturating_sub(tokens_after)) and needs a real
tokens_before value; update pub fn compacted(messages: Vec<Message>,
tokens_after: u64) -> Self to accept a tokens_before: u64 parameter and set
tokens_saved = tokens_before.saturating_sub(tokens_after), leaving
messages_compacted = 0 (caller will set) and preserving success: true and error:
None; alternatively, if you prefer leaving tokens_saved to callers, remove the
tokens_saved field initialization here and document that callers must set it,
but the preferred fix is adding the tokens_before parameter and computing
tokens_saved in compacted.
- Around line 330-336: The docstring claims the compactor preserves the first
system prompt but the current compaction logic simply keeps the last
preserve_recent messages; modify the compaction routine (the code that currently
slices to keep the last preserve_recent messages) to also include the first
message when it has the expected role: check messages.first().map(|m| m.role)
and if it matches the prompt role (as described in the docstring) prepend that
first message to the preserved list and then append the last preserve_recent
messages without duplicating it (use preserve_recent, messages, and the
compaction function/logic identifiers to locate where to change the
slice/collection code); alternatively if you prefer the simpler fix, update the
docstring text to remove the claim about preserving the system prompt so it
matches the existing behavior.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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Configuration used: Organization UI

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📥 Commits

Reviewing files that changed from the base of the PR and between ad7e6cd and 5523916.

📒 Files selected for processing (2)

• src/compact.rs
• src/lib.rs