fix(test): two flakes in the tests added today, found by stress.yml

crates/termlens-cli/tests/cli.rs

@@ -363,12 +363,20 @@ fn with_stdin(args: &[&str], input: &str) -> std::process::Output {
         .stderr(Stdio::piped())
         .spawn()
         .expect("spawn termlens");
-    child
-        .stdin
-        .take()
-        .expect("a stdin pipe")
-        .write_all(input.as_bytes())
-        .expect("write to the child's stdin");
+    // A broken pipe here is a *result*, not a failure. `diff - -` refuses its
+    // arguments before reading anything, so the child can exit and close the
+    // pipe before this write lands — the faster the refusal, the likelier it
+    // is. The stress workflow found it on both Linux shards while it never
+    // reproduced locally, because on an idle machine the bytes reach the
+    // pipe buffer first. The child's exit code and stderr are what the
+    // callers assert; whether it read the input is the child's business.
+    let mut pipe = child.stdin.take().expect("a stdin pipe");
+    match pipe.write_all(input.as_bytes()) {
+        Ok(()) => {}
+        Err(e) if e.kind() == std::io::ErrorKind::BrokenPipe => {}
+        Err(e) => panic!("write to the child's stdin: {e}"),
+    }
+    drop(pipe);
     child.wait_with_output().expect("the child's output")
 }
 

crates/termlens/tests/process.rs

@@ -166,6 +166,16 @@ fn a_panicking_child_puts_its_message_on_the_screen() -> termlens::Result<()> {
     // Wide enough that the message is one row: the runtime's own
     // `panicked at <file>:<line>` line wraps on a narrow grid, and a
     // wrapped needle is a test about the width, not about the panic.
+    //
+    // And every wait below names the *message*, never the word "panicked".
+    // The runtime writes the location line and the message as separate
+    // writes, so `contains("panicked")` is true one line before the message
+    // exists — which went red on CI with the grid holding `panicked at
+    // …:281:37:` and nothing under it. Waiting for the message is rule 3 of
+    // the wait-semantics contract (docs/DESIGN.md §2): name the last thing
+    // the application paints, so that its truth implies the rest arrived.
+    // "panicked" is then asserted rather than waited on — it cannot be
+    // absent once the line after it is there.
     let wide = || {
         Terminal::builder()
             .size(100, 10)
@@ -174,8 +184,9 @@ fn a_panicking_child_puts_its_message_on_the_screen() -> termlens::Result<()> {
 
     // 1. A plain child, which is what the README's table is about.
     let mut t = common::spawn_emit(wide(), &["drew this ", "--panic", "plain panic here"])?;
-    t.wait_until(|s| s.contains("panicked"))?;
+    t.wait_until(|s| s.contains("plain panic here"))?;
     let s = t.screen();
+    assert!(s.contains("panicked"), "the word the README promises: {s}");
     assert!(
         s.contains("plain panic here"),
         "the message reaches the grid: {s}"
@@ -201,10 +212,10 @@ fn a_panicking_child_puts_its_message_on_the_screen() -> termlens::Result<()> {
             "boom in the alt screen",
         ],
     )?;
-    t.wait_until(|s| s.contains("panicked"))?;
+    t.wait_until(|s| s.contains("boom in the alt screen"))?;
     let s = t.screen();
+    assert!(s.contains("panicked"), "{s}");
     assert!(s.alternate_screen(), "nothing tore it down: {s}");
-    assert!(s.contains("boom in the alt screen"), "{s}");
     assert!(
         s.contains("TUI drawing here"),
         "the message joins the frame it died on: {s}"
@@ -225,10 +236,10 @@ fn a_panicking_child_puts_its_message_on_the_screen() -> termlens::Result<()> {
             "boom after teardown",
         ],
     )?;
-    t.wait_until(|s| s.contains("panicked"))?;
+    t.wait_until(|s| s.contains("boom after teardown"))?;
     let s = t.screen();
+    assert!(s.contains("panicked"), "{s}");
     assert!(!s.alternate_screen(), "the child left it: {s}");
-    assert!(s.contains("boom after teardown"), "{s}");
     assert!(
         !s.contains("TUI drawing here"),
         "what the alternate screen held went with it: {s}"