✨ Add explicit append policy setter

bitlogger/BitLogger_test.mbt

@@ -243,8 +243,11 @@ test "configured logger file setters update file sink policy state" {
       queue=Some(QueueConfig::new(2, overflow=QueueOverflowPolicy::DropNewest)),
     ),
   )
+  inspect(logger.file_append_mode(), content="true")
   inspect(logger.file_auto_flush(), content="true")
   inspect(logger.file_rotation_enabled(), content="false")
+  inspect(logger.file_set_append_mode(false), content="true")
+  inspect(logger.file_append_mode(), content="false")
   inspect(logger.file_set_auto_flush(false), content="true")
   inspect(logger.file_auto_flush(), content="false")
   inspect(logger.file_set_rotation(Some(file_rotation(48, max_backups=4))), content="true")
@@ -259,6 +262,8 @@ test "configured logger file setters update file sink policy state" {
   inspect(logger.file_clear_rotation(), content="true")
   inspect(logger.file_rotation_enabled(), content="false")
   inspect(logger.file_rotation_config() is None, content="true")
+  inspect(logger.file_reopen(), content=if logger.file_available() { "true" } else { "false" })
+  inspect(logger.file_append_mode(), content="false")
   ignore(logger.close())
 }
 

bitlogger/BitLogger_wbtest.mbt

@@ -124,8 +124,11 @@ test "file sink rotation config normalizes invalid inputs" {
 
 test "file sink setters update auto flush and rotation state" {
   let sink = file_sink("bitlogger-setters.log")
+  inspect(sink.append_mode(), content="true")
   inspect(sink.auto_flush_enabled(), content="true")
   inspect(sink.rotation_enabled(), content="false")
+  sink.set_append_mode(false)
+  inspect(sink.append_mode(), content="false")
   sink.set_auto_flush(false)
   inspect(sink.auto_flush_enabled(), content="false")
   sink.set_rotation(Some(file_rotation(32, max_backups=2)))
@@ -140,6 +143,8 @@ test "file sink setters update auto flush and rotation state" {
   sink.clear_rotation()
   inspect(sink.rotation_enabled(), content="false")
   inspect(sink.rotation_config() is None, content="true")
+  inspect(sink.reopen(), content=if sink.is_available() { "true" } else { "false" })
+  inspect(sink.append_mode(), content="false")
 }
 
 test "file sink tracks rotation failures on unavailable backend" {

bitlogger/README.mbt.md

@@ -222,9 +222,10 @@ test {
 - 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
+- `set_append_mode(...)` updates the stored append policy without forcing an immediate reopen / `set_append_mode(...)` 可直接更新保存的 append 策略，但不会强制立即 reopen
 - `path()` and `auto_flush_enabled()` expose core file sink policy state / `path()` 与 `auto_flush_enabled()` 可读取 file sink 的基础策略状态
 - `rotation_enabled()` and `rotation_config()` expose whether rotation is active and which settings are currently applied / `rotation_enabled()` 与 `rotation_config()` 可读取 rotation 是否启用及当前配置参数
 - `set_auto_flush(...)`, `set_rotation(...)`, and `clear_rotation()` allow runtime tuning of core file sink policies / `set_auto_flush(...)`、`set_rotation(...)`、`clear_rotation()` 可在运行期调整 file sink 的基础策略
 - `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, append-mode, path, auto-flush, rotation-config, setter, 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、path、auto-flush、rotation 配置、setter 与失败计数访问器
+- `ConfiguredLogger` also forwards file reopen, flush, close, append-mode, path, auto-flush, rotation-config, append setter, policy setter, 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、path、auto-flush、rotation 配置、append setter、策略 setter 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

@@ -239,6 +239,20 @@ pub fn RuntimeSink::file_append_mode(self : RuntimeSink) -> Bool {
   }
 }
 
+pub fn RuntimeSink::file_set_append_mode(self : RuntimeSink, append : Bool) -> Bool {
+  match self {
+    File(sink) => {
+      sink.set_append_mode(append)
+      true
+    }
+    QueuedFile(sink) => {
+      sink.sink.set_append_mode(append)
+      true
+    }
+    _ => false
+  }
+}
+
 pub fn RuntimeSink::file_path(self : RuntimeSink) -> String {
   match self {
     File(sink) => sink.path()
@@ -401,6 +415,10 @@ pub fn ConfiguredLogger::file_append_mode(self : ConfiguredLogger) -> Bool {
   self.sink.file_append_mode()
 }
 
+pub fn ConfiguredLogger::file_set_append_mode(self : ConfiguredLogger, append : Bool) -> Bool {
+  self.sink.file_set_append_mode(append)
+}
+
 pub fn ConfiguredLogger::file_path(self : ConfiguredLogger) -> String {
   self.sink.file_path()
 }

bitlogger/sinks.mbt

@@ -118,6 +118,10 @@ pub fn FileSink::append_mode(self : FileSink) -> Bool {
   self.append.val
 }
 
+pub fn FileSink::set_append_mode(self : FileSink, append : Bool) -> Unit {
+  self.append.val = append
+}
+
 pub fn FileSink::path(self : FileSink) -> String {
   self.path
 }