📝 Add configured logger file policy API docs

docs/api/configured-logger-file-policy-matches-default.md

@@ -0,0 +1,76 @@
+---
+name: configured-logger-file-policy-matches-default
+group: api
+category: runtime
+update-time: 20260512
+description: Read whether the current runtime file policy still matches the configured logger default policy.
+key-word:
+    - logger
+    - runtime
+    - file
+    - public
+---
+
+## Configured-logger-file-policy-matches-default
+
+Read whether the current runtime file policy still matches the default policy of a `ConfiguredLogger`. This helper is useful for detecting operational drift.
+
+### Interface
+
+```moonbit
+pub fn ConfiguredLogger::file_policy_matches_default(self : ConfiguredLogger) -> Bool {}
+```
+
+#### input
+
+- `self : ConfiguredLogger` - Config-driven runtime logger whose runtime policy drift should be checked.
+
+#### output
+
+- `Bool` - Whether the current runtime file policy still matches the default.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- File-backed sinks compare current runtime file policy against their stored defaults.
+- Queued file sinks forward the comparison from the wrapped file sink.
+- Non-file sinks return `false`.
+- This helper is a compact drift signal when callers do not need to compare full policy objects directly.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Drift Detection
+
+When diagnostics should report whether file policy changed after startup:
+```moonbit
+let unchanged = logger.file_policy_matches_default()
+```
+
+In this example, the configured logger exposes whether runtime file policy still matches the baseline.
+
+#### When Gate Reset Logic
+
+When code should only reset policy if drift exists:
+```moonbit
+if !logger.file_policy_matches_default() {
+  ignore(logger.file_reset_policy())
+}
+```
+
+In this example, policy reset only happens when runtime state diverged from defaults.
+
+### Error Case
+
+e.g.:
+- If the configured sink is not file-backed, the method returns `false`.
+
+- If callers need the exact differences instead of a boolean drift signal, they should inspect both `file_policy()` and `file_default_policy()`.
+
+### Notes
+
+1. Use this helper for compact runtime policy drift checks.
+
+2. It is especially useful before calling reset-style operations.