📝 document file sink state constructor

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

@@ -0,0 +1,108 @@
+---
+name: file-sink-state-new
+group: api
+category: runtime
+update-time: 20260613
+description: Construct a FileSinkState snapshot from explicit file availability, policy, and failure-counter values.
+key-word:
+    - file
+    - state
+    - diagnostics
+    - public
+---
+
+## File-sink-state-new
+
+Construct a `FileSinkState` snapshot from explicit file availability, policy, and failure-counter values. This is the low-level constructor behind the public file sink state shape used in diagnostics.
+
+### Interface
+
+```moonbit
+pub fn FileSinkState::new(
+  path : String,
+  available~ : Bool = false,
+  append~ : Bool = true,
+  auto_flush~ : Bool = true,
+  rotation~ : FileRotation? = None,
+  open_failures~ : Int = 0,
+  write_failures~ : Int = 0,
+  flush_failures~ : Int = 0,
+  rotation_failures~ : Int = 0,
+) -> FileSinkState {
+```
+
+#### input
+
+- `path : String` - File path represented by the snapshot.
+- `available : Bool` - Whether the file sink currently reports an available file handle.
+- `append : Bool` - Current append-mode policy.
+- `auto_flush : Bool` - Current auto-flush policy.
+- `rotation : FileRotation?` - Current optional rotation policy.
+- `open_failures : Int` - Current open-failure counter.
+- `write_failures : Int` - Current write-failure counter.
+- `flush_failures : Int` - Current flush-failure counter.
+- `rotation_failures : Int` - Current rotation-failure counter.
+
+#### output
+
+- `FileSinkState` - File sink snapshot containing the supplied path, availability, policy, and failure-counter values.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Omitting optional arguments uses a conservative baseline snapshot: unavailable, append enabled, auto-flush enabled, no rotation, and zeroed counters.
+- This constructor simply packages the supplied fields into one public snapshot value.
+- It does not inspect a live `FileSink` by itself.
+- `FileSink::state()` and `ConfiguredLogger::file_state()` are the higher-level APIs that read these values from concrete runtime objects.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need A Hand-built File State Snapshot
+
+When tests or adapters should construct file diagnostics explicitly:
+```moonbit
+let state = FileSinkState::new(
+  "app.log",
+  available=true,
+  append=false,
+  auto_flush=false,
+  rotation=Some(file_rotation(2048, max_backups=2)),
+)
+```
+
+In this example, the file state snapshot is built directly without querying a live sink.
+
+#### When Need Structured Diagnostics Input Before Serialization
+
+When code should prepare a typed file state value for later export:
+```moonbit
+let state = FileSinkState::new(
+  sink.path(),
+  available=sink.is_available(),
+  append=sink.append_mode(),
+  auto_flush=sink.auto_flush_enabled(),
+  rotation=sink.rotation_config(),
+  open_failures=sink.open_failures(),
+  write_failures=sink.write_failures(),
+  flush_failures=sink.flush_failures(),
+  rotation_failures=sink.rotation_failures(),
+)
+```
+
+In this example, callers still use the direct constructor while making each diagnostic input explicit.
+
+### Error Case
+
+e.g.:
+- This constructor itself does not have a normal failure mode; it only packages the provided values.
+
+- If callers want a snapshot directly from a live file sink or configured logger, `state()` or `file_state()` is the simpler API.
+
+### Notes
+
+1. Use this helper when code should construct a `FileSinkState` value explicitly.
+
+2. Pair it with `file_sink_state_to_json(...)` or `stringify_file_sink_state(...)` when the snapshot should be exported.

docs/api/index.md

@@ -179,6 +179,7 @@ BitLogger API navigation.
 - [file-sink-policy-to-json.md](./file-sink-policy-to-json.md)
 - [file-sink-policy.md](./file-sink-policy.md)
 - [stringify-file-sink-policy.md](./stringify-file-sink-policy.md)
+- [file-sink-state-new.md](./file-sink-state-new.md)
 - [file-sink-state-to-json.md](./file-sink-state-to-json.md)
 - [file-sink-state.md](./file-sink-state.md)
 - [stringify-file-sink-state.md](./stringify-file-sink-state.md)