[DOCS] `MessageDisplay` hook event missing from Claude Code hooks documentation

Documentation Type

Missing documentation (feature not documented)

Documentation Location

https://code.claude.com/docs/en/hooks

Section/Topic

Hook events and event-specific reference coverage for MessageDisplay

Current Documentation

The hooks reference currently lists the available events as:

SessionStart, Setup, UserPromptSubmit, UserPromptExpansion, PreToolUse, PermissionRequest, PermissionDenied, PostToolUse, PostToolUseFailure, PostToolBatch, Notification, SubagentStart, SubagentStop, TaskCreated, TaskCompleted, Stop, StopFailure, TeammateIdle, InstructionsLoaded, ConfigChange, CwdChanged, FileChanged, WorktreeCreate, WorktreeRemove, PreCompact, PostCompact, Elicitation, ElicitationResult, SessionEnd

The changelog for v2.1.152 says:

Added a MessageDisplay hook event that lets hooks transform or hide assistant message text as it is displayed

The Agent SDK hooks page also lists available hook events, but that table currently ends with:

TaskCompleted, ConfigChange, WorktreeCreate, WorktreeRemove

What's Wrong or Missing?

MessageDisplay appears to be a new Claude Code hook event in v2.1.152, but the main hooks reference does not list it or document its matcher behavior, input schema, or output fields.

That leaves users without any reference documentation for how to configure the event or what a hook can return to transform or hide assistant message text.

The same gap appears in the Agent SDK hooks page, which still omits MessageDisplay from its available-hooks table.

Suggested Improvement

Add MessageDisplay to the https://code.claude.com/docs/en/hooks event list and give it a full event section covering:

1. When the event fires during assistant message rendering
2. Whether it supports matchers, and what field the matcher applies to if so
3. The full input payload schema
4. The output fields a hook can return to transform displayed text or suppress/hide it
5. A minimal configuration example

Also update https://code.claude.com/docs/en/agent-sdk/hooks so the available-hooks table includes MessageDisplay and links readers back to the main hooks reference for the event schema.

Impact

Medium - Makes feature difficult to understand

Additional Context

Affected Pages:

| Page | Context |
|------|---------|
| https://code.claude.com/docs/en/hooks | Primary hooks reference lists available events, but MessageDisplay is missing even though v2.1.152 announces it |
| https://code.claude.com/docs/en/agent-sdk/hooks | Agent SDK available-hooks table also omits MessageDisplay |
| https://code.claude.com/docs/en/changelog | v2.1.152 changelog announces MessageDisplay as a new hook event |

Total scope: 3 pages affected

Version context: the feature is announced in changelog entry v2.1.152.