📝 document runtime sink file state

docs/api/index.md

@@ -386,6 +386,8 @@ BitLogger API navigation.
 - [runtime-sink-file-policy.md](./runtime-sink-file-policy.md)
 - [runtime-sink-file-default-policy.md](./runtime-sink-file-default-policy.md)
 - [runtime-sink-file-policy-matches-default.md](./runtime-sink-file-policy-matches-default.md)
+- [runtime-sink-file-state.md](./runtime-sink-file-state.md)
+- [runtime-sink-file-runtime-state.md](./runtime-sink-file-runtime-state.md)
 - [configured-logger.md](./configured-logger.md)
 - [configured-logger-flush.md](./configured-logger-flush.md)
 - [configured-logger-drain.md](./configured-logger-drain.md)

docs/api/runtime-sink-file-runtime-state.md

@@ -0,0 +1,77 @@
+---
+name: runtime-sink-file-runtime-state
+group: api
+category: runtime
+update-time: 20260613
+description: Read combined file and queue runtime state from a RuntimeSink when it is backed by a file sink.
+key-word:
+    - runtime
+    - sink
+    - file
+    - public
+---
+
+## Runtime-sink-file-runtime-state
+
+Read combined file and queue runtime state from a `RuntimeSink`. This helper is the richest file-specific diagnostics API on direct runtime sink values.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::file_runtime_state(self : RuntimeSink) -> RuntimeFileState? {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose file runtime state should be inspected.
+
+#### output
+
+- `RuntimeFileState?` - Combined file and queue diagnostics when the runtime sink is file-backed, otherwise `None`.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Plain `File` runtime variants return `Some(RuntimeFileState::new(sink.state()))`, so queue metadata stays at its default non-queued shape.
+- `QueuedFile` runtime variants return `Some(RuntimeFileState)` with the wrapped file state plus `queued=true`, `pending_count=sink.pending_count()`, and `dropped_count=sink.dropped_count()`.
+- Non-file runtime variants return `None`.
+- This helper is richer than `file_state()` because it can also surface queued backlog and dropped counts.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Rich File Runtime Diagnostics
+
+When support output should include both file and queue state:
+```moonbit
+let state = sink.file_runtime_state()
+```
+
+In this example, callers can inspect availability, failure counters, and queue metrics together.
+
+#### When Need To Branch On File-backed Runtime Shape
+
+When code should behave differently for file-backed direct sinks:
+```moonbit
+match sink.file_runtime_state() {
+  Some(state) => ignore(state)
+  None => ()
+}
+```
+
+In this example, the optional return value reflects whether the runtime sink is file-backed.
+
+### Error Case
+
+e.g.:
+- If the runtime sink is not file-backed, the method returns `None`.
+
+- If callers only need raw file status without queue context, `file_state()` may be the simpler API.
+
+### Notes
+
+1. Use this helper for the richest file-backed runtime diagnostics on direct sink values.
+
+2. It is especially useful for queued file sinks where file health and queue state both matter.

docs/api/runtime-sink-file-state.md

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+---
+name: runtime-sink-file-state
+group: api
+category: runtime
+update-time: 20260613
+description: Read the current file sink snapshot from a RuntimeSink.
+key-word:
+    - runtime
+    - sink
+    - file
+    - public
+---
+
+## Runtime-sink-file-state
+
+Read the current file sink snapshot from a `RuntimeSink`. This helper exposes path, availability, policy flags, rotation config, and failure counters as one object.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::file_state(self : RuntimeSink) -> FileSinkState {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose file state snapshot should be inspected.
+
+#### output
+
+- `FileSinkState` - Current file sink snapshot.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Plain `File` runtime variants return a live snapshot from the wrapped `FileSink`.
+- `QueuedFile` runtime variants forward the snapshot from the wrapped inner `FileSink`.
+- Non-file runtime variants return a fallback empty-style state with `path=""`, `available=false`, `append=false`, `auto_flush=false`, `rotation=None`, and all failure counters set to `0`.
+- This helper is broader than individual file counters or policy accessors because it aggregates core file status into one read.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need A Full File Health Snapshot
+
+When diagnostics should inspect direct runtime file state as one object:
+```moonbit
+let state = sink.file_state()
+```
+
+In this example, callers receive a single file-state snapshot instead of querying each property separately.
+
+#### When Need To Export File Runtime Diagnostics
+
+When a support path should serialize current file state:
+```moonbit
+println(stringify_file_sink_state(sink.file_state(), pretty=true))
+```
+
+In this example, the runtime sink snapshot can be exported directly through existing JSON helpers.
+
+### Error Case
+
+e.g.:
+- If the runtime sink is not file-backed, the returned snapshot is a fallback empty-style state rather than a live file view.
+
+- If callers also need queue context for queued file sinks, `file_runtime_state()` is the richer API.
+
+### Notes
+
+1. Use this helper for the main one-shot file status snapshot.
+
+2. Prefer it over individual counters when broader file diagnostics are needed.