📝 Add logger write API docs

docs/api/logger-debug.md

@@ -0,0 +1,77 @@
+---
+name: logger-debug
+group: api
+category: logging
+update-time: 20260512
+description: Emit a debug-level record through the logger using the debug severity shortcut.
+key-word:
+    - logger
+    - debug
+    - sync
+    - public
+---
+
+## Logger-debug
+
+Emit a debug-level record through the synchronous logger. This is the convenience wrapper for `log(Level::Debug, ...)`.
+
+### Interface
+
+```moonbit
+pub fn[S : Sink] Logger::debug(self : Logger[S], message : String, fields~ : Array[Field] = []) -> Unit {}
+```
+
+#### input
+
+- `self : Logger[S]` - Logger that should emit the debug record.
+- `message : String` - Debug message text.
+- `fields : Array[Field]` - Optional structured fields attached to the record.
+
+#### output
+
+- `Unit` - No return value. The record is handled according to the logger threshold and sink pipeline.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- This helper delegates to `log(Level::Debug, ...)`.
+- Debug logging is useful for development diagnostics that are usually too verbose for normal production visibility.
+- Per-call target override is not exposed here; use `log(...)` for that level of control.
+- All logger wrappers remain active exactly as they would for the base `log(...)` path.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Internal State Diagnostics
+
+When implementation details should be observable during debugging:
+```moonbit
+logger.debug("cache refreshed")
+```
+
+In this example, the call site signals a development-focused diagnostic event.
+
+#### When Attach Structured Debug Fields
+
+When a debug event should carry explicit state:
+```moonbit
+logger.debug("session loaded", fields=[field("user_id", "42")])
+```
+
+In this example, the logger emits structured state without using the fully explicit `log(...)` form.
+
+### Error Case
+
+e.g.:
+- If the logger minimum level is above `Debug`, the call returns without writing a record.
+
+- If the event needs a custom target override, use `log(...)` instead of this shortcut.
+
+### Notes
+
+1. Prefer this helper when debug intent is more readable than a raw `log(Level::Debug, ...)` call.
+
+2. Use `is_enabled(Level::Debug)` when building the debug payload is expensive.
+