zlog: Ensure log file is flushed (#28923)

Closes #ISSUE

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/zed/src/reliability.rs

@@ -130,6 +130,7 @@ pub fn init_panic_hook(
         if let Some(panic_data_json) = serde_json::to_string_pretty(&panic_data).log_err() {
             log::error!("{}", panic_data_json);
         }
+        zlog::flush();
 
         if !is_pty {
             if let Some(panic_data_json) = serde_json::to_string(&panic_data).log_err() {

crates/zlog/src/sink.rs

@@ -152,7 +152,18 @@ pub fn submit(record: Record) {
 }
 
 pub fn flush() {
-    _ = std::io::stdout().lock().flush();
+    if unsafe { ENABLED_SINKS_STDOUT } {
+        _ = std::io::stdout().lock().flush();
+    }
+    let mut file = ENABLED_SINKS_FILE.lock().unwrap_or_else(|handle| {
+        ENABLED_SINKS_FILE.clear_poison();
+        handle.into_inner()
+    });
+    if let Some(file) = file.as_mut() {
+        if let Err(err) = file.flush() {
+            eprintln!("Failed to flush log file: {}", err);
+        }
+    }
 }
 
 struct ScopeFmt(Scope);

crates/zlog/src/zlog.rs

@@ -5,7 +5,7 @@ mod env_config;
 pub mod filter;
 pub mod sink;
 
-pub use sink::{init_output_file, init_output_stdout};
+pub use sink::{flush, init_output_file, init_output_stdout};
 
 pub const SCOPE_DEPTH_MAX: usize = 4;