diff --git a/docs/agent-handoff.md b/docs/agent-handoff.md
index 5307799..2c5ca22 100644
--- a/docs/agent-handoff.md
+++ b/docs/agent-handoff.md
@@ -1443,6 +1443,22 @@ round-trip cannot detect a discriminant shift.
 
 ## 5. Hard-won ops lessons
 
+- **A gate summary assembled through a pipe can report success over a
+  failure.** `cmd | tail -2` returns **`tail`'s** exit status, not
+  `cmd`'s — in `fish` and `bash` alike — so a chain of
+  `cargo test ... | tail -2 && cargo test ... | tail -2 && echo "ALL
+  GATES CLEAN"` prints the clean line even when a suite failed. This
+  is not carelessness that closer reading would catch: the failure is
+  **structurally invisible** in the summary the PR then cites. It
+  happened while gating the silent-skip lane, and a `pmacs-gpu`
+  failure was reported as clean.
+
+  Either check `$pipestatus[1]` in fish (`${PIPESTATUS[0]}` in bash),
+  or — better — redirect each gate to a file and read the file
+  afterwards, which also preserves the full log this section already
+  asks you to keep. Same family as the skip-reports-`ok` lesson below
+  and the double-invocation traps: **the thing that summarizes a gate
+  must not be able to lose the gate's verdict.**
 - **A test that skips on a missing precondition reports `ok`, and a gate log
   cannot tell that apart from a pass.** `vterm_stage3_acceptance::a37` — the
   only acceptance driving a real daemon, a real PTY and a real wgpu render
diff --git a/tests/support/mod.rs b/tests/support/mod.rs
index f661b3d..14fbeec 100644
--- a/tests/support/mod.rs
+++ b/tests/support/mod.rs
@@ -1,7 +1,13 @@
 //! Shared test-support helpers.
 //!
 //! Included by `#[path = "support/mod.rs"] mod support;` rather than
-//! copied.
+//! copied. Files under `tests/` subdirectories are not compiled as
+//! their own test binaries, so this costs nothing — and
+//! `m6_8_multi_repl_acceptance.rs` previously carried a comment saying
+//! cross-test-binary sharing "would need a fixture crate", which is not
+//! so. A correct helper in one file and a degraded copy in another is
+//! this suite's most repeated defect shape; sharing removes the way it
+//! happens.
 //!
 //! **Why this is separate from `tests/common/`, which also exists.**
 //! `tests/common/mod.rs` re-exports `daemon` and `pty` — real daemon
@@ -11,13 +17,7 @@
 //! dependency-free half: helpers any test binary can take without
 //! taking a subsystem with them. Two directories is a cost worth
 //! naming rather than leaving to be rediscovered; if a third appears,
-//! consolidate instead of continuing the pattern. Files under `tests/` subdirectories are not compiled as
-//! their own test binaries, so this costs nothing — and
-//! `m6_8_multi_repl_acceptance.rs` previously carried a comment saying
-//! cross-test-binary sharing "would need a fixture crate", which is not
-//! so. A correct helper in one file and a degraded copy in another is
-//! this suite's most repeated defect shape; sharing removes the way it
-//! happens.
+//! consolidate instead of continuing the pattern.
 
 #![allow(dead_code)]