Rendered KaTeX also shows a garbled plaintext duplicate of the formula

[exAClior]

Before filing

• I searched open and closed issues for duplicates.
• I reproduced this on the latest release (v0.6.2).
• This is one bug, not several bundled together.

Closest existing issue

none found

Split from the same session as a second, independent bug: TeX \(...\) / \[...\] and single-dollar $...$ never become math at all. Filed separately.

What's broken

When chat math does render, the typeset formula is accompanied by extra text. Inline $$\Omega$$ becomes ΩΩ. Display $$ and fenced math show the real equation plus leftover Ω = n=1Σ∞ n21.

Steps to reproduce

1. Launch Berd 0.6.2.

2. New chat. Goose, Grok 4.6 via xAI (xai_oauth).

3. Display $$\Omega$$ on its own line of prose.

4. Display a block:

   $$
   \Omega = \sum_{n=1}^{\infty} \frac{1}{n^2}
   $$
   

5. Display the same equation in a fenced math code block.

What you expected to happen

One typeset formula. No second copy, no doubled glyph.

What actually happened

From a screenshot of the live bubble:

• Inline $$\Omega$$ rendered as ΩΩ (two omegas, not one).
• Display $$ showed a correct centered KaTeX formula and leftover Ω = n=1Σ∞ n21.
• Fenced math did the same: correct KaTeX plus the same leftover string.

Observation only, not claimed root cause: the leftover string looks like the TeX with commands stripped, which is how unhidden KaTeX MathML often appears.

How often does it happen?

Every time — reliably reproducible

Berd version

0.6.2

Operating system

macOS (Apple Silicon)

Model and provider

Grok 4.6 via xAI (Goose / xai_oauth)

Relevant log output

no relevant log output

Looked at ~/Library/Logs/xyz.block.berd/berd.log around the turn. Nothing about KaTeX / math / Streamdown.

Screenshots, recordings, or other context

Screenshot of this session’s live delimiter matrix (same capture as the companion issue):

[exAClior]

Companion delimiter-coverage bug (TeX / single-dollar never parse): #239