adding inverted color commands

AGENTS.md

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+# Agent Guidelines for `eink_api`
+
+These instructions apply to the entire repository.
+
+## Code Style
+- Follow existing Pico SDK patterns in `eink_api.c`; prefer straightforward, readable C without unnecessary abstractions.
+- Match the project logging approach (`printf` for user feedback) and keep messages concise and informative.
+- When modifying command handlers, mimic the `else if` chain style that ensures only one command executes per input.
+- Avoid adding inline comments unless they clarify non-obvious logic.
+
+## Command Handling
+- Use fixed-length comparisons (`strncmp`) with explicit delimiter checks so longer commands do not trigger shorter prefixes (e.g., guard `draw_circle` vs. `draw_circle_fill`).
+- Validate command arguments with `sscanf`, checking return counts before acting.
+- Ensure screen-state guards (`screen_on`, `editor_mode`) remain intact around command logic.
+
+## Display Operations
+- Use the Waveshare `Paint_*` helpers already in use; do not introduce alternative drawing backends without a strong reason.
+- Prefer existing constants (`BLACK`, `WHITE`, `DOT_PIXEL_1X1`, fill enums) for clarity and consistency.
+
+## Build & Tooling
+- Keep the CMake-based build flow unchanged (`cmake -S . -B build` / `cmake --build build`).
+- Scripts under `scripts/` should remain POSIX shell compatible and should surface user-friendly errors tied to README guidance.
+
+## Documentation
+- Update the README table of commands whenever new commands are added or behaviors change.
+- Maintain alignment between serial command descriptions and their implementation details.