✨ Make file append mode observable and persistent

bitlogger/BitLogger_test.mbt

@@ -202,6 +202,7 @@ test "configured logger exposes file sink observability helpers" {
     ),
   )
   inspect(logger.file_available() == native_files_supported(), content="true")
+  inspect(logger.file_append_mode(), content="true")
   inspect(logger.file_open_failures(), content=if logger.file_available() { "0" } else { "1" })
   inspect(logger.file_write_failures(), content="0")
   inspect(logger.file_flush_failures(), content="0")
@@ -219,16 +220,24 @@ test "configured logger can reopen built file sink" {
     inspect(logger.close(), content="true")
     inspect(logger.file_reopen(), content="true")
     inspect(logger.file_available(), content="true")
+    inspect(logger.file_append_mode(), content="true")
     inspect(logger.file_open_failures(), content="0")
     logger.info("reopened from config")
     inspect(logger.file_write_failures(), content="0")
+    inspect(logger.file_reopen(append=Some(false)), content="true")
+    inspect(logger.file_append_mode(), content="false")
+    inspect(logger.file_reopen(), content="true")
+    inspect(logger.file_append_mode(), content="false")
     inspect(logger.close(), content="true")
   } else {
+    inspect(logger.file_append_mode(), content="true")
     inspect(logger.file_open_failures(), content="1")
     logger.info("dropped")
     inspect(logger.file_write_failures(), content="1")
     inspect(logger.file_reopen(), content="false")
     inspect(logger.file_open_failures(), content="2")
+    inspect(logger.file_reopen(append=Some(false)), content="false")
+    inspect(logger.file_append_mode(), content="false")
   }
 }
 

bitlogger/BitLogger_wbtest.mbt

@@ -90,6 +90,7 @@ test "native file support flag is queryable" {
 test "file sink availability reflects backend support" {
   let sink = file_sink("bitlogger-test.log")
   inspect(sink.is_available() == native_files_supported(), content="true")
+  inspect(sink.append_mode(), content="true")
   inspect(sink.open_failures(), content=if sink.is_available() { "0" } else { "1" })
   inspect(sink.write_failures(), content="0")
   inspect(sink.flush_failures(), content="0")
@@ -124,23 +125,32 @@ test "file sink tracks rotation failures on unavailable backend" {
 test "file sink reopen and failure counters reflect backend state" {
   let sink = file_sink("bitlogger-reopen.log")
   if sink.is_available() {
+    inspect(sink.append_mode(), content="true")
     inspect(sink.open_failures(), content="0")
     inspect(sink.close(), content="true")
     inspect(sink.reopen(), content="true")
     inspect(sink.is_available(), content="true")
+    inspect(sink.append_mode(), content="true")
     inspect(sink.open_failures(), content="0")
     sink.write(record(Level::Info, "reopened"))
     inspect(sink.write_failures(), content="0")
     inspect(sink.flush_failures(), content="0")
+    inspect(sink.reopen(append=Some(false)), content="true")
+    inspect(sink.append_mode(), content="false")
+    inspect(sink.reopen(), content="true")
+    inspect(sink.append_mode(), content="false")
     inspect(sink.close(), content="true")
     ignore(remove_file_internal("bitlogger-reopen.log"))
   } else {
+    inspect(sink.append_mode(), content="true")
     inspect(sink.open_failures(), content="1")
     sink.write(record(Level::Info, "dropped"))
     inspect(sink.write_failures(), content="1")
     inspect(sink.reopen(), content="false")
     inspect(sink.open_failures(), content="2")
     inspect(sink.flush_failures(), content="0")
+    inspect(sink.reopen(append=Some(false)), content="false")
+    inspect(sink.append_mode(), content="false")
   }
 }
 

bitlogger/README.mbt.md

@@ -221,6 +221,7 @@ test {
 - `file_rotation(max_bytes, max_backups=...)` controls threshold and retained backups / `file_rotation(max_bytes, max_backups=...)` 控制触发阈值和保留备份数
 - JSON config uses `sink.rotation.max_bytes` and `sink.rotation.max_backups` / JSON 配置使用 `sink.rotation.max_bytes` 与 `sink.rotation.max_backups`
 - `FileSink::reopen()` can explicitly reopen the current file handle / `FileSink::reopen()` 可显式重开当前文件句柄
+- `append_mode()` exposes the current append policy, and `reopen(append=...)` updates that policy for later reopen calls / `append_mode()` 可读取当前 append 策略，`reopen(append=...)` 会更新后续 reopen 复用的 append 策略
 - `open_failures()`、`write_failures()`、`flush_failures()`、`rotation_failures()` expose basic sink health counters / `open_failures()`、`write_failures()`、`flush_failures()`、`rotation_failures()` 可用于观察基础 sink 健康状态
-- `ConfiguredLogger` also forwards file reopen, flush, close, and failure-counter helpers for config-built file sinks / `ConfiguredLogger` 也会为配置生成的 file sink 转发 reopen、flush、close 与失败计数访问器
+- `ConfiguredLogger` also forwards file reopen, flush, close, append-mode, and failure-counter helpers for config-built file sinks / `ConfiguredLogger` 也会为配置生成的 file sink 转发 reopen、flush、close、append-mode 与失败计数访问器
 - current scope is observability-first, not a full self-healing sink runtime / 当前定位仍以可观测性优先，不是完整自愈型 sink runtime

bitlogger/config.mbt

@@ -231,6 +231,14 @@ pub fn RuntimeSink::file_reopen(self : RuntimeSink, append~ : Bool? = None) -> B
   }
 }
 
+pub fn RuntimeSink::file_append_mode(self : RuntimeSink) -> Bool {
+  match self {
+    File(sink) => sink.append_mode()
+    QueuedFile(sink) => sink.sink.append_mode()
+    _ => false
+  }
+}
+
 pub fn RuntimeSink::file_flush(self : RuntimeSink) -> Bool {
   match self {
     File(sink) => sink.flush()
@@ -315,6 +323,10 @@ pub fn ConfiguredLogger::file_reopen(self : ConfiguredLogger, append~ : Bool? =
   self.sink.file_reopen(append=append)
 }
 
+pub fn ConfiguredLogger::file_append_mode(self : ConfiguredLogger) -> Bool {
+  self.sink.file_append_mode()
+}
+
 pub fn ConfiguredLogger::file_flush(self : ConfiguredLogger) -> Bool {
   self.sink.file_flush()
 }

bitlogger/sinks.mbt

@@ -46,7 +46,7 @@ pub impl Sink for JsonConsoleSink with write(self, rec) {
 
 pub struct FileSink {
   path : String
-  append : Bool
+  append : Ref[Bool]
   handle : Ref[FileHandle?]
   formatter : RecordFormatter
   auto_flush : Bool
@@ -85,7 +85,7 @@ pub fn file_sink(
   let handle = open_file_handle_internal(path, append)
   {
     path,
-    append,
+    append: Ref::new(append),
     handle: Ref::new(handle),
     formatter,
     auto_flush,
@@ -114,6 +114,10 @@ pub fn FileSink::flush(self : FileSink) -> Bool {
   }
 }
 
+pub fn FileSink::append_mode(self : FileSink) -> Bool {
+  self.append.val
+}
+
 pub fn FileSink::close(self : FileSink) -> Bool {
   match self.handle.val {
     None => false
@@ -142,7 +146,8 @@ pub fn FileSink::flush_failures(self : FileSink) -> Int {
 }
 
 pub fn FileSink::reopen(self : FileSink, append~ : Bool? = None) -> Bool {
-  let append_mode = append.unwrap_or(self.append)
+  let append_mode = append.unwrap_or(self.append.val)
+  self.append.val = append_mode
   match self.handle.val {
     None => ()
     Some(handle) => {