fix(logging): enforce single-writer sinks and bound tracing (#4765)

* fix(obs): prevent rolling log stdout aliasing

* fix(ecstore): bound hot-path tracing payloads

* test(logging): guard service and disk log invariants

* fix(obs): silence useless_conversion on st_dev for Linux clippy

rustix's Stat.st_dev is u64 on Linux/glibc, making u64::try_from a no-op
that trips clippy::useless_conversion under -D warnings. The conversion is
still needed on macOS/BSD where st_dev is a signed dev_t, so suppress the
lint on that line rather than dropping the portable fallible conversion.

* fix(logging): keep stdout sink validation portable (#4769)

* fix(obs): keep stdout device conversion portable

* docs(logging): update single-writer plan status

---------

Co-authored-by: overtrue <anzhengchao@gmail.com>
Co-authored-by: houseme <housemecn@gmail.com>

crates/obs/src/telemetry/rolling.rs

@@ -133,10 +133,22 @@ impl RollingAppender {
         Ok(appender)
     }
 
-    fn active_file_path(&self) -> PathBuf {
+    pub(crate) fn active_file_path(&self) -> PathBuf {
         self.dir.join(&self.filename)
     }
 
+    #[cfg(unix)]
+    pub(crate) fn active_file_identity(&self) -> io::Result<(u64, u64)> {
+        use std::os::unix::fs::MetadataExt;
+
+        let metadata = self
+            .file
+            .as_ref()
+            .ok_or_else(|| io::Error::other("rolling log file is not open"))?
+            .metadata()?;
+        Ok((metadata.dev(), metadata.ino()))
+    }
+
     fn open_file(&mut self) -> io::Result<()> {
         if self.file.is_some() {
             return Ok(());