[Bug]: TUI streaming Markdown renders item 2 over item 1 nested bullet points (cursor offset)

Description

While the assistant is streaming a Markdown response containing a numbered list with nested bullet items, the TUI encounters a 1-row cursor offset error. Item 2. is stamped directly on top of the sub-bullet of item 1., overwriting its first 19 characters and completely swallowing the preceding bullet point.

Crucial Observation:
Selecting and copying the corrupted text with the mouse yields 100% complete, intact, and correct text. The raw record in ~/.local/share/opencode/opencode.db (part table) is also completely undamaged. This proves the underlying AST and message buffer are intact—the bug is strictly an ANSI cursor repositioning / line-height calculation error in OpenTUI's differential streaming renderer.

Steps to Reproduce

1. Start OpenCode in interactive TUI mode (tested in both standard and --mini mode):

   opencode
   

2. Send the following prompt (which forces the model to stream the exact Markdown structure):

   Repeat the following Markdown text verbatim without codeblocks or extra text:
   
   1. **Hardware-Optimierungen:**
       * **MLX Engine:** Massive Performance-Verbesserungen für Apple Silicon (Macs).
       * **GGUF-Unterstützung:** Bessere Kompatibilität und schnellere Ausführung von GGUF-Modellen über `llama.cpp`.
   2. **Neue Funktionen:**
       * **Thinking-Modus:** Die Fähigkeit, internen Denkprozessen (Reasoning) bei Modellen zu folgen bzw. diese zu steuern.
       * **Streaming für Tool-Calls:** Verbessertes Streaming von Antworten auch dann, wenn das Modell Werkzeuge (Tools) nutzt.
   3. **Modell-Vielfalt & Integration:**
       * Schnelleres Hinzufügen neuer High-End-Modelle (wie Nemotron, Gemmaerweiterungen).
       * Bessere Unterstützung für Multimodalität (Bild- und Textverarbeitung in einem Flow).
   4. **Stabilität:**
       * Speichermanagement zur Vermeidung von Abstürzen beim Laden sehr großer Modelle auf lokaler Hardware.
   

3. Watch the live terminal streaming output.

Expected Behavior

All 4 numbered sections should render with their respective sub-bullets cleanly indented below them:

1. Hardware-Optimierungen:
   - MLX Engine: Massive Performance-Verbesserungen...
   - GGUF-Unterstützung: Bessere Kompatibilität...
2. Neue Funktionen:
   - Thinking-Modus: ...
   ...

Actual Behavior (Visual Screenshot)

Anatomy of the visual corruption:

1. Under 1. Hardware-Optimierungen:, OpenCode draws a card divider line ────────────────────────.
2. The first sub-bullet (MLX Engine) is swallowed in the blank row.
3. The heading 2. Neue Funktionen: (19 characters) is stamped directly over the first 19 characters of the second sub-bullet (* GGUF-Unterstüt), leaving only the tail zung: Bessere Kompatibilität und schnellere Ausführung von GGUF-Modellen über llama.cpp. trailing in white/green.
4. Once OpenCode enters ordered list mode, items 2., 3., and 4. no longer draw horizontal divider lines, and their respective sub-bullets render properly with -.

Technical Investigation & Root Cause Notes

1. State Transition Glitch:
   At token 1. **...**:, the streaming lexer does not yet know an ordered list is following and renders it as a card/section header with an underlying horizontal separator rule (───).
2. Cursor Offset Miscalculation:
   When token 2. **...**: arrives, the streaming engine recognizes the ordered list context and issues an ANSI cursorUp sequence to re-anchor the layout. However, the calculation does not account for the extra line consumed by the horizontal separator.
3. Overdraw:
   The cursor lands exactly on the line where sub-bullet 2 was just written. It prints 2. Neue Funktionen: at (X=0, Y) without clearing the line, producing the spliced text.
4. Clipboard vs. Screen:
   Selecting the corrupted region with the mouse and copying to clipboard outputs the complete, untruncated text, confirming that the internal DOM/component tree is completely correct and only the terminal cursor coordinates were miscalculated.

Environment Details

• OpenCode Version: 1.18.30 (opencode-ai)
• OS: Linux (x86_64, Kernel 6.x)
• Terminal: GNOME Terminal (xterm-256color, COLORTERM=truecolor)
• Terminal Resolution: Tested on 382 columns × 92 rows
• Provider: Ollama (via local streaming proxy)