Adding a hook that already exists replaces it instead of running it twice

A hook is a command or function that Claude Code runs automatically at a set point, for example before or after a tool runs. Each hook sits under a matcher, the pattern that decides which actions it applies to.

When a hook is added under a matcher, Claude Code now looks for the same hook already registered there. If it finds one, it replaces that hook's settings and keeps its onHookSuccess handler, instead of adding a second copy. Before, only function hooks that carried an id were replaced this way. Every other kind of hook was added again as a new entry.