agentydragon(tasks): add chat UI textarea overlay and border styling fix task

agentydragon/tasks/18-chat-ui-textarea-overlay-border-fix.md

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+++ # Task 18: Chat UI Textarea Overlay and Border Styling Fix
+++
+---
+id: 18
+title: Chat UI Textarea Overlay and Border Styling Fix
+status: Not started  # one of: Not started, Started, Needs manual review, Done, Cancelled
+summary: Fix overlay of waiting messages and streamline borders between chat window and input area to improve visibility and reclaim terminal space.
+goal: |
+  Adjust the TUI chat interface so that waiting/status messages no longer overlay the first line of the input textarea (ensuring user drafts remain visible), and merge/remove borders as follows:
+    - Merge the bottom border of the chat history window with the top border of the input textarea.
+    - Remove the left, right, and bottom overall borders around the chat interface to reduce wasted space.
+---
+
+> *This task is specific to codex-rs.*
+
+## Acceptance Criteria
+
+- Waiting/status messages (e.g. "Thinking...", "Typing...", etc.) appear above the textarea rather than overlaying the first line of the input area.
+- User draft text remains visible at all times, even when agent messages or status indicators are rendered.
+- The bottom border of the chat history pane and the top border of the textarea are unified into a single border line.
+- The left, right, and bottom borders around the entire chat UI are removed, reclaiming columns/rows in the terminal.
+- Manual or automated visual verification steps demonstrate correct layout in a variety of terminal widths.
+
+## Implementation
+
+**How it was implemented**  
+*(Not implemented yet)*
+
+**How it works**  
+*(Not implemented yet)*
+
+## Notes
+
+- This involves updating the rendering logic in the TUI modules (likely under `tui/src/` in `codex-rs`).
+- Ensure layout changes do not break existing tests or rendering in unusual terminal sizes.
+- Consider writing a simple snapshot test or manual demo script to validate border and overlay behavior.
+
+---
+Run the frontmatter linter to ensure conformance:
+```bash
+python3 agentydragon/tools/check_task_frontmatter.py agentydragon/tasks/18-chat-ui-textarea-overlay-border-fix.md
+```