[Bug] Terminal Rendering Fails for [Label]:Key Patterns

Bug Description
Claude Code Terminal Fails to Render [Label]:Key Pattern

Summary

The Claude Code terminal interface fails to display any assistant message that consists exclusively of a string matching the [Label]:Key pattern. The assistant generates the correct output, but the client does not render it.

Regex of Non-Rendering Pattern

The bug is triggered by any message that is a complete and exact match for the following regex:

^\[[^\]]+\]:[^ ]+$

Where:

^\[ → Starts with [

[^\]]+ → The Label: one or more of any character except ]

\]: → A literal closing bracket and colon

[^ ]+ → The Key: one or more of any character except a space

$ → End of the string

Observed Behavior (Rendering Failure)

Any message from the assistant that perfectly matches the structure above fails to display. Examples include:

User Prompt: just reply [TEST]:TEST

Assistant's (Hidden) Reply: [TEST]:TEST

User Prompt: just reply [TE ST]:TEST

Assistant's (Hidden) Reply: [TE ST]:TEST

User Prompt: just reply [123]:abc

Assistant's (Hidden) Reply: [123]:abc

User Prompt: just reply [key]:value123

Assistant's (Hidden) Reply: [key]:value123

Correctly Rendered Cases

The terminal correctly displays the assistant's output as long as it does not exclusively match the pattern.

When additional text is present:

Prompt: just reply [TEST]:TEST HELLO

Displayed Reply: [TEST]:TEST HELLO

When the string does not match the pattern:

Prompt: just reply HELLO

Displayed Reply: HELLO

Expected Behavior

All outputs generated by the assistant should be rendered correctly in the terminal, regardless of whether they conform to the [Label]:Key structure.

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 1.0.123
• Feedback ID: 6cf6fd4a-f30d-4cb4-bf8c-04b729660dda

Errors

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