📝 Add logger write API docs

docs/api/logger-error.md

@@ -0,0 +1,77 @@
+---
+name: logger-error
+group: api
+category: logging
+update-time: 20260512
+description: Emit an error-level record through the logger using the highest built-in severity shortcut.
+key-word:
+    - logger
+    - error
+    - sync
+    - public
+---
+
+## Logger-error
+
+Emit an error-level record through the synchronous logger. This is the convenience wrapper for `log(Level::Error, ...)`.
+
+### Interface
+
+```moonbit
+pub fn[S : Sink] Logger::error(self : Logger[S], message : String, fields~ : Array[Field] = []) -> Unit {}
+```
+
+#### input
+
+- `self : Logger[S]` - Logger that should emit the error record.
+- `message : String` - Error 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::Error, ...)`.
+- `Error` is the highest built-in severity in this sync logger API.
+- Per-call target override is not exposed here; use `log(...)` when explicit target control is required.
+- Sink composition, filtering, patching, and queue wrappers still apply normally.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Report A Failing Operation
+
+When an operation should emit a high-severity failure event:
+```moonbit
+logger.error("worker execution failed")
+```
+
+In this example, the call site clearly communicates failure severity.
+
+#### When Attach Structured Error Context
+
+When an error event should include diagnostic fields:
+```moonbit
+logger.error("dispatch failed", fields=[field("job_id", "42")])
+```
+
+In this example, the record carries machine-readable context without dropping to the generic `log(...)` form.
+
+### Error Case
+
+e.g.:
+- If the logger minimum level is above `Error`, the call still returns without writing, though this configuration is unusual.
+
+- If a target override is required, use `log(...)` instead of this severity shortcut.
+
+### Notes
+
+1. Use this helper for high-severity application failures.
+
+2. Emitting an error record is separate from throwing or handling program exceptions.
+