📝 document async library facade write apis

docs/api/library-async-logger-is-enabled.md

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+---
+name: library-async-logger-is-enabled
+group: api
+category: facade
+update-time: 20260613
+description: Check whether a LibraryAsyncLogger facade would accept a record at a given level.
+key-word:
+    - async
+    - library
+    - enabled
+    - public
+---
+
+## Library-async-logger-is-enabled
+
+Check whether a `LibraryAsyncLogger[S]` would accept a record at the given level based on its current `min_level`. This is the library-facing counterpart to `AsyncLogger::is_enabled(...)` and is useful for gating expensive async message preparation.
+
+### Interface
+
+```moonbit
+pub fn[S] LibraryAsyncLogger::is_enabled(
+  self : LibraryAsyncLogger[S],
+  level : @bitlogger.Level,
+) -> Bool {
+```
+
+#### input
+
+- `self : LibraryAsyncLogger[S]` - Library-facing async logger whose current minimum level should be checked.
+- `level : @bitlogger.Level` - Candidate severity to test.
+
+#### output
+
+- `Bool` - `true` when the level is enabled by the facade's current threshold.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- This method delegates directly to the wrapped async logger's `is_enabled(...)` behavior.
+- It only checks logger-level severity gating; it does not evaluate later filter or overflow behavior.
+- The result reflects the current facade value, so derived facades with different thresholds can return different answers.
+- Use it when message construction or field gathering is expensive enough to justify a pre-check.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Avoid Expensive Async Debug Preparation
+
+When debug data should only be built if needed:
+```moonbit
+if logger.is_enabled(@bitlogger.Level::Info) {
+  await logger.info(build_summary())
+}
+```
+
+In this example, expensive preparation is skipped unless the current threshold allows that severity.
+
+#### When Inspect Effective Async Facade Threshold
+
+When package code should branch based on current logger behavior:
+```moonbit
+if logger.is_enabled(@bitlogger.Level::Warn) {
+  await logger.warn("slow path active")
+}
+```
+
+In this example, the check mirrors the same severity gate used by later async write calls.
+
+### Error Case
+
+e.g.:
+- If `level` is below the current minimum threshold, the method returns `false`.
+
+- A `true` result does not guarantee final delivery if later queue or filter behavior rejects the record.
+
+### Notes
+
+1. This is a cheap severity check, not a full end-to-end delivery guarantee.
+
+2. Prefer using it only when precomputing the async log payload is meaningfully expensive.