diff --git a/src/app/debug_log.rs b/src/app/debug_log.rs
index 1314994..b043cde 100644
--- a/src/app/debug_log.rs
+++ b/src/app/debug_log.rs
@@ -237,8 +237,21 @@ mod tests {
                 .expect("write oversized log");
         }
 
+        // Cross-test interference is expected here and the retry loop below MUST
+        // NOT be collapsed into a single attempt. Production `log()` relies on
+        // PROCESS-GLOBAL statics: `CHECK_COUNTER` (AtomicU32), `LOG_FILE` (Mutex)
+        // and the `TEST_CACHE_HOME` redirect. `TEST_MUTEX` only serializes the two
+        // debug_log tests against each other; it does NOT exclude the hundreds of
+        // other tests running on parallel threads, many of which invoke the
+        // production `debug_log!`/`log()` macro. Once this test installs its
+        // tempdir into the process-global `TEST_CACHE_HOME`, those concurrent
+        // `log()` calls (a) bump the shared `CHECK_COUNTER` and (b) write to
+        // `log_path()`, which now points at THIS test's tempdir. So concurrent
+        // appends and counter bumps can perturb the careful size dance below.
+        // The retry loop tolerates that interference: we keep trying until one of
+        // our own `reset_for_test()` + `log()` cycles wins the size check.
         let mut truncated = false;
-        for attempt in 0..20 {
+        for attempt in 0..50 {
             reset_for_test();
             log(format_args!("attempt {attempt}"));
             let len = std::fs::metadata(&path).map(|m| m.len()).unwrap_or(0);
@@ -258,7 +271,7 @@ mod tests {
         reset_for_test();
         assert!(
             truncated,
-            "log() never acquired mutex to truncate oversized file after 20 retries"
+            "log() never acquired mutex to truncate oversized file after 50 retries"
         );
     }
 }
diff --git a/src/ui/viewer/tests.rs b/src/ui/viewer/tests.rs
index c931ef7..d4643ae 100644
--- a/src/ui/viewer/tests.rs
+++ b/src/ui/viewer/tests.rs
@@ -19,7 +19,6 @@ use std::thread;
 use tempfile::NamedTempFile;
 
 const DEFAULT_PAGE_HEIGHT: usize = 20;
-const TEST_CHANNEL_TIMEOUT_SECS: u64 = 1;
 
 fn create_test_file(content: &str) -> NamedTempFile {
     let mut file = NamedTempFile::new().unwrap();
@@ -89,9 +88,12 @@ fn test_viewer_loader_drop_cancels_worker() {
     drop(loader);
 
     assert!(cancel.load(Ordering::Relaxed));
+    // Drop sets `cancel`, so the worker is guaranteed to send once it observes it.
+    // A blocking recv removes the arbitrary 1s deadline that made this test fail
+    // under heavy CPU load when the detached yield-looping worker got starved.
     done_rx
-        .recv_timeout(std::time::Duration::from_secs(TEST_CHANNEL_TIMEOUT_SECS))
-        .unwrap();
+        .recv()
+        .expect("worker should send done after observing cancel");
 }
 
 #[test]