feat: Add tool result pruning compactor

[sjrl]

Related Issues

• fixes https://github.com/deepset-ai/haystack-private/issues/511

Proposed Changes:

Added the experimental ToolResultPruningCompactor. It reduces Agent context usage by replacing older, large tool results with short placeholders while preserving tool-call/result structure. Results from a configurable number of recent tool-calling Agent steps remain intact, including parallel results from those steps.

from haystack.hooks.compaction import ContextCompactionHook, ToolResultPruningCompactor

compaction_hook = ContextCompactionHook(
    compactor=ToolResultPruningCompactor(
        min_keep_steps=2,
        min_tokens=200,
    ),
    context_window=400_000,
    compact_at=0.7,
    compact_to=0.4,
)

Also went ahead and added the docs pages for this in the same PR

How did you test it?

New tests

Notes for the reviewer

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have updated the related issue with new insights and changes.
• I have added unit tests and updated the docstrings.
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test: and added ! in case the PR includes breaking changes.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run pre-commit hooks and fixed any issue.

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
haystack-docs	Ignored	Preview	Aug 5, 2026 2:28pm

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
haystack/hooks/compaction
__init__.py
sliding_window.py
tool_result_pruning.py
utils.py
Project Total

This report was generated by python-coverage-comment-action

[anakin87]

I left a few minor comments

[anakin87]

Looks good!

Pushed a fix for my wrong docs suggestion in e7af32f.
For some reason, Docusaurus build was not done in this PR but I saw locally that it broke the build.

[sjrl]

Looks good!

Pushed a fix for my wrong docs suggestion in e7af32f. For some reason, Docusaurus build was not done in this PR but I saw locally that it broke the build.

thanks for the catch! very odd that the docusaurus build was skipped in this PR though ...