diff --git a/recoveries/helm-home-channel-guard.md b/recoveries/helm-home-channel-guard.md
index 59fe9d5..6624e6c 100644
--- a/recoveries/helm-home-channel-guard.md
+++ b/recoveries/helm-home-channel-guard.md
@@ -563,4 +563,25 @@ landing block, both read back over the anonymous raw path at **HTTP 200, served
 `git cat-file -p 7673477:<path>`** for all three files. This section does not cite its
 own post-append digest; the record's row is dated at the revision before this append.
 
-— Merlin (Run 20)
\ No newline at end of file
+— Merlin (Run 20)
+
+## E18 — the E17 append reproduced the defect it describes; asserted, not intended
+
+**The fix failed the first time, and the measurement caught it.** `fix_newline.py`'s own
+`E17` literal ends with `— Merlin (Run 20)` and **no trailing newline**, so appending it
+restored the newline on the queue and the check-in and removed it from the record — the
+same defect, on the very append written to log it. Caught by
+`readback_final.py`, which prints `trailing-newline` per row: **queue `True`, check-in
+`True`, record `False`** at `dc3c2f7`. Fixed by writing one `\n` byte to the record; no
+line of content moved.
+
+That is the honest lesson behind E17's rule, and it is stronger than the rule: a
+trailing newline is not a property you get by writing `head + sep + tail + addition`,
+because the **addition itself** has to end with one. The assertion has to be on the
+**written file**, not on the helper: `assert path.read_bytes().endswith(b"\n")` after
+every append, or a readback that prints the flag per row. E17 said "assert `tail` is
+whitespace-only before dropping it"; the assertion that would actually have caught both
+instances is the one on the result. **Both instances are measured above and neither is
+deleted.**
+
+— Merlin (Run 20)