chore(docs): add #1500 entry to CHANGELOG.md and CONTRIBUTORS.md

- Added CHANGELOG.md entry under [Unreleased]/Fixed for actor add --update flag enforcement (#1500)
- Updated CONTRIBUTORS.md with HAL 9000 contribution detail for issue #1500 BDD coverage
ISSUES CLOSED: #1500

CHANGELOG.md

@@ -5,6 +5,10 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
 
+### Fixed
+
+- **`agents actor add` enforces `--update` flag for existing actors** (#1500): Added regression tests to `features/actor_add_update_enforcement.feature` and step definitions in `features/steps/actor_add_update_enforcement_steps.py` verifying that re-adding an existing actor without `--update` fails, while re-adding with `--update` succeeds.
+
 ### Changed
 
 - **Diagnostics spec examples expanded to all 9 providers** (#5320): Updated the

CONTRIBUTORS.md

@@ -20,7 +20,8 @@ Below are some of the specific details of various contributions.
 * HAL 9000 has contributed the bug-hunt-pool-supervisor non-blocking tracking fix: updated step 5 to be best-effort and added rule 9 to prevent the automation-tracking-manager call from blocking the main supervisor loop.
 * HAL 9000 has contributed the plugin entry point security hardening fix (#7476): enforced entry point allowlist validation before importing plugin modules to prevent malicious plugin loading.
 * HAL 9000 has contributed the benchmark workflow separation (#9040): moved the benchmark-regression job out of the default PR workflow into a dedicated scheduled workflow, reducing median PR CI turnaround time from 99-132 minutes to under 30 minutes.
-* HAL 9000 has contributed automated bug fixes, security improvements, and migration safety enhancements including the migration prompt safe-default fix (#7503).
+* HAL 9000 has contributed automated bug fixes, security improvements, and migration safety enhancements including the migration prompt safe-default fix (#7503).* HAL 9000 has contributed the actor add --update flag enforcement tests and BDD coverage for issue #1500: added regression scenario tests verifying that re-adding an existing actor without `--update` fails, while re-adding with `--update` succeeds.
+
 * 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 file edit encoding parameter fix (PR #8258 / issue #7559).