diff --git a/crates/kingfisher-rules/data/rules/airbrake.yml b/crates/kingfisher-rules/data/rules/airbrake.yml
index e755027..e94c488 100644
--- a/crates/kingfisher-rules/data/rules/airbrake.yml
+++ b/crates/kingfisher-rules/data/rules/airbrake.yml
@@ -33,9 +33,7 @@ rules:
             - status:
                 - 200
               type: StatusMatch
-            - words:
-                - '"id"'
-              type: WordMatch
+            - type: JsonValid
             - words:
                 - '"type":"Unauthorized"'
               type: WordMatch
diff --git a/src/reporter.rs b/src/reporter.rs
index e4b0623..b38a45e 100644
--- a/src/reporter.rs
+++ b/src/reporter.rs
@@ -506,6 +506,22 @@ pub fn run(
     ds: Arc<Mutex<findings_store::FindingsStore>>,
     args: &cli::commands::scan::ScanArgs,
     audit_context: Option<ScanAuditContext>,
+) -> Result<()> {
+    let writer = args.output_args.get_writer()?;
+    run_with_writer(global_args, ds, args, audit_context, writer)
+}
+
+/// Same as [`run`], but writes into a caller-provided `Write` instead of
+/// constructing one from `args.output_args`. Useful when the caller wants
+/// to render into an in-memory buffer first (e.g. so a stdout lock can be
+/// held only around the final atomic emit, not around the report's CPU
+/// work).
+pub fn run_with_writer<W: std::io::Write>(
+    global_args: &GlobalArgs,
+    ds: Arc<Mutex<findings_store::FindingsStore>>,
+    args: &cli::commands::scan::ScanArgs,
+    audit_context: Option<ScanAuditContext>,
+    writer: W,
 ) -> Result<()> {
     global_args.use_color(std::io::stdout());
     let stdout_is_tty = std::io::stdout().is_terminal();
@@ -513,11 +529,8 @@ pub fn run(
     let styles = Styles::new(use_color);
 
     let ds_clone = Arc::clone(&ds);
-    // Initialize the reporter
     let reporter =
         DetailsReporter { datastore: ds_clone, styles, only_valid: args.only_valid, audit_context };
-    let writer = args.output_args.get_writer()?;
-    // Generate and write the report in the specified format
     reporter.report(args.output_args.format, writer, args)
 }
 pub struct DetailsReporter {
diff --git a/src/reporter/json_format.rs b/src/reporter/json_format.rs
index 8843fdc..c796383 100644
--- a/src/reporter/json_format.rs
+++ b/src/reporter/json_format.rs
@@ -12,8 +12,22 @@ impl DetailsReporter {
             // scan path: one envelope per repo) concatenate into valid
             // JSONL that `kingfisher view` can parse. Pipe through `jq .`
             // for human-readable pretty output.
-            serde_json::to_writer(&mut writer, &envelope)?;
-            writeln!(writer)?;
+            //
+            // Serialize into a single buffer and emit via a single
+            // `write_all` so callers that need cross-thread atomicity
+            // (e.g. the parallel scan path emitting one envelope per repo
+            // to stdout) can synchronize at the call site by holding
+            // `std::io::stdout().lock()` around this call. We intentionally
+            // do NOT acquire the stdout lock here because this method is
+            // generic over any `Write` and is also called with file
+            // writers and `Cursor<Vec<u8>>` in tests. Flushing is the
+            // caller's responsibility — flushing here would defeat
+            // upstream `BufWriter` buffering and turn an otherwise-benign
+            // BrokenPipe into a hard error.
+            let mut buf = Vec::with_capacity(8 * 1024);
+            serde_json::to_writer(&mut buf, &envelope)?;
+            buf.push(b'\n');
+            writer.write_all(&buf)?;
         }
         Ok(())
     }
diff --git a/src/scanner/runner.rs b/src/scanner/runner.rs
index c9a034b..384e0d0 100644
--- a/src/scanner/runner.rs
+++ b/src/scanner/runner.rs
@@ -941,13 +941,42 @@ async fn run_parallel_scan(
                         }
 
                         if !output_to_file {
-                            crate::reporter::run(
+                            // Per-repo emit goes to stdout from many rayon
+                            // threads in parallel. Render the report into
+                            // an in-memory buffer first (CPU work, no
+                            // contention), then take the stdout lock only
+                            // around the final atomic write+flush so two
+                            // threads' envelopes can't interleave and
+                            // corrupt JSONL output.
+                            let mut buf: Vec<u8> = Vec::with_capacity(8 * 1024);
+                            crate::reporter::run_with_writer(
                                 global_args,
                                 Arc::clone(&repo_datastore),
                                 &args,
                                 None,
+                                &mut buf,
                             )
                             .context("Failed to run report command")?;
+                            if !buf.is_empty() {
+                                use std::io::Write;
+                                let mut stdout = std::io::stdout().lock();
+                                // Treat a closed downstream pipe (e.g.
+                                // `kingfisher scan ... | head`) as a normal
+                                // early exit, matching `summary.rs::safe_println!`.
+                                // Any other I/O error is a real failure.
+                                if let Err(err) = stdout.write_all(&buf) {
+                                    if err.kind() == std::io::ErrorKind::BrokenPipe {
+                                        std::process::exit(0);
+                                    }
+                                    return Err(err.into());
+                                }
+                                if let Err(err) = stdout.flush() {
+                                    if err.kind() == std::io::ErrorKind::BrokenPipe {
+                                        std::process::exit(0);
+                                    }
+                                    return Err(err.into());
+                                }
+                            }
                         }
 
                         {