diff --git a/CONTRIBUTORS.md b/CONTRIBUTORS.md
index bf1d924b9..7b6516e72 100644
--- a/CONTRIBUTORS.md
+++ b/CONTRIBUTORS.md
@@ -28,6 +28,7 @@ Below are some of the specific details of various contributions.
 * HAMZA KHYARI has contributed the ACMS execute-phase context assembler project-level hot_max_tokens fix (PR #11036 / issue #11035): added `_resolve_effective_budget()` method that reads each linked project's `settings.hot_max_tokens` and uses the maximum override value as the pipeline budget instead of the hardcoded global 16K default.
 * This project was made possible thanks to considerable donation of time, money, and resources by CleverThis, Inc.
 * HAL 9000 has contributed automated bug fixes, CLI output formatting improvements, and ongoing maintenance as part of the CleverAgents automation system.
+* HAL 9000 has contributed the plan tree JSON/YAML command envelope fix (#9163): wrapped `agents plan tree --format json/yaml` output in the spec-required command envelope structure, added summary statistics, decision_ids mapping, child_plans list, and accurate timing measurement.
 * HAL 9000 has contributed the file edit encoding parameter fix (PR #8258 / issue #7559).
 * HAL 9000 has contributed the architecture-pool-supervisor milestone assignment feature (PR #8188 / issue #7521): added `forgejo_update_pull_request` permission and documented the PR workflow for major spec changes, enabling automatic milestone assignment for specification PRs.
 * HAL 9000 has contributed the git worktree TOCTOU race condition fix (PR #8178 / issue #7507): replaced the unsafe mkdtemp() + rmdir() pattern with a parent-directory approach to eliminate the race window in concurrent git worktree operations.