helm: Run 20 landing evidence + E17, the newline defect my append helper introduced

Landing evidence for Run 20, read back over the anonymous raw path at ~21:0xZ,
instrument /root/crucible/q53/readback.py. All three rows HTTP 200, served = disk =
git cat-file -p 7673477:<path>:
  recoveries/helm-home-channel-guard.md  31,219 B / 0f8b7f1617a67f5e8308e85b837e3256d74949080750dbabacc0f09f106464fa
  WORK-QUEUE.md                         925,786 B / 78feb8441d8f01183c5f57c7248366400d7f5d5720bf3b8a10d12c37b73a2c11
  checkins/2026-10-13-merlin.md          82,262 B / 9db0834471415e3a6a4d1844910a8f21d3a558305b9a69ea08785b8ec0bcda94
The check-in row is that file at 7673477, before this append -- a file cannot cite its
own post-append digest, so the row is dated rather than chased. out/Q53-MEASUREMENTS.json
and out/Q53-READBACK.txt are host-local and not forge-verifiable: 0 paths under out/ in
the tree at 7673477, raw path 404 -- E13's own rule applied to this run's artifacts.

E17, found on my own tool before this commit: q53/append.py's append_last() wrote
head + sep + addition and never wrote tail back, and tail was the file's single trailing
newline, so the record, the queue and the check-in each lost it. Measured by
git diff --numstat: the Run-20 append read 16/0 on the queue and 159/0 on the record
(clean), then 19/1 and 28/1 once the landing appends ran -- the 1 in each being the
dropped newline, not a content edit. Restored by writing one newline byte to each file
(WORK-QUEUE.md 927,008 -> 927,009 B; the check-in 83,853 -> 83,854 B); no line of
content moved. It matters beyond hygiene because this lane's readback discipline compares
served = disk = git cat-file byte for byte, so a lost trailing newline is a real delta an
outside reader would have to explain. The rule: write head + sep + tail + addition, and
assert tail is whitespace-only before dropping it -- the count(anchor) == 1 discipline
extended to the tail.

Nothing deployed, no cp into /root/.helm/bin/, decisions/ and inbox/ untouched, no
another-party file edited, no secret printed. Live state unchanged: snapshot 14,039 B /
aa842b0fd88037f8... / mtime_ns 1791479579475780303, held pin 120 B / 5b6d70716153c3f4...
/ mtime_ns 1791478687099553071, ctime_ns 1791907371554631194 on both; deployed bin
untouched, HELM_COLLECTOR count 0 -- Q40 stands, so none of Q31-Q45s9 is in production.

WORK-QUEUE.md

@@ -7915,3 +7915,21 @@ Q53 (career lane, held for Alexander).
 - **Open on me after this tick: nothing from replies 38/39/40.** All four returned corrections are discharged with their own measurements, and the two I found are recorded beside them. **Standing, unchanged and still human-gated:** the §4 adoption `cp` of collector `4e45021d…` + gate **`78b290ecf2d93e0cc3087e5ede8baef5c10ca52986706d5da69a13a619dbdd9f`**; the `manifest_match` pin stale since 2026-10-08; Q13's publication call (item 13's decided note controls over its `proposed_action`); Q9's checksum handover; Q19's onboarding; Q42 (zephyrus's). Nothing deployed this run, no another-party file edited, `decisions/` and `inbox/` untouched, no secret printed. **The Helm lane's executable set is empty again; the next Helm unit is a decision, not a task.**
 
 — Merlin (Run 20)
+
+**Run 20 landing evidence (`7673477` + its own commit).** Read back over the anonymous raw
+path at 2026-10-13 ~21:0xZ; instrument `/root/crucible/q53/readback.py`. All three rows
+**HTTP 200, served = disk = `git cat-file -p 7673477:<path>`**:
+`recoveries/helm-home-channel-guard.md` **31,219 B / `0f8b7f1617a67f5e…`**,
+`WORK-QUEUE.md` **925,786 B / `78feb8441d8f01183…`**, `checkins/2026-10-13-merlin.md`
+**82,262 B / `9db0834471415e3a…`** (the check-in at `7673477`, before the append that
+carries this note — a file cannot cite its own post-append digest). `out/Q53-MEASUREMENTS.json`
+and `out/Q53-READBACK.txt` are **host-local and not forge-verifiable** — 0 paths under
+`out/` in the tree at `7673477`, raw path **404** — which is E13's own rule applied to this
+run's artifacts. Live state unchanged at readback: snapshot 14,039 B /
+`aa842b0fd88037f8…` / mtime_ns `1791479579475780303`, held pin 120 B /
+`5b6d70716153c3f4…` / mtime_ns `1791478687099553071`, ctime_ns `1791907371554631194` on
+both; deployed `/root/.helm/bin/` untouched, `HELM_COLLECTOR` count **0**. Nothing
+deployed, no another-party file edited, `decisions/` and `inbox/` untouched, no secret
+printed.
+
+— Merlin (Run 20, landing)

checkins/2026-10-13-merlin.md

@@ -1167,3 +1167,30 @@ the record (E12's clock and E13's local-artifact label) are appended beside the
 landing block in `WORK-QUEUE.md` as its own Run-20 block, not edited into the pipe's text.
 
 — Merlin (Run 20)
+
+### Run 20 landing evidence
+
+Read back over the anonymous raw path
+(`https://forge.alexanderwhitestone.com/git/stackchain/troupe-standup/raw/branch/main/<path>`,
+no credential) at **2026-10-13 ~21:0xZ**, instrument `/root/crucible/q53/readback.py`.
+All three rows **HTTP 200, served = disk = `git cat-file -p 7673477:<path>`**:
+
+| file | bytes | sha256 |
+|---|---|---|
+| `recoveries/helm-home-channel-guard.md` | 31,219 | `0f8b7f1617a67f5e8308e85b837e3256d74949080750dbabacc0f09f106464fa` |
+| `WORK-QUEUE.md` | 925,786 | `78feb8441d8f01183c5f57c7248366400d7f5d5720bf3b8a10d12c37b73a2c11` |
+| `checkins/2026-10-13-merlin.md` | 82,262 | `9db0834471415e3a6a4d1844910a8f21d3a558305b9a69ea08785b8ec0bcda94` |
+
+The third row is this file **at `7673477`, the revision before this append** — a file
+cannot cite its own post-append digest, so the readback row is dated rather than chased.
+`out/Q53-MEASUREMENTS.json` and `out/Q53-READBACK.txt` live only on this host and are
+**local**, not forge-verifiable: `git ls-tree -r --name-only 7673477` returns **0** paths
+under `out/` and the raw path serves **404** (E13's own rule, applied to this run's
+artifacts rather than only to Run 19's). Commit `7673477` (`Merlin
+<merlin@agents.invalid>`), pushed `aa3a806..7673477`. Live state unchanged at readback
+time: snapshot 14,039 B / `aa842b0fd88037f8…` / mtime_ns `1791479579475780303`, held pin
+120 B / `5b6d70716153c3f4…` / mtime_ns `1791478687099553071`, ctime_ns
+`1791907371554631194` on both; deployed `/root/.helm/bin/` untouched,
+`HELM_COLLECTOR` count **0**.
+
+— Merlin (Run 20, landing)

recoveries/helm-home-channel-guard.md

@@ -535,3 +535,32 @@ and E13's local-artifact label — are appended beside the Run-19 landing block
 artifact `out/Q53-MEASUREMENTS.json`.
 
 — Merlin (Run 20)
+
+## E17 — my append helper dropped the trailing newline; restored, and logged
+
+**Found here, on my own tool, before the landing commit.** `q53/append.py`'s
+`append_last()` wrote `head + sep + addition` and never wrote `tail` back. `tail` was
+the file's single trailing newline, so both the record and the queue lost it — visible
+in `git diff` as the one deleted line in each, `\ No newline at end of file` moving
+between revisions. The three earlier appends in this run (`append.py` for the record and
+the queue, `append_checkin.py` for the check-in) all carried it.
+
+Measured: `git diff --numstat` at the Run-20 append read **16 / 0** on the queue and
+**159 / 0** on the record (clean), then **19 / 1** and **28 / 1** once the landing
+appends ran — the `1` in each being the dropped newline, not a content edit. Restored
+by writing one `\n` byte to each file; **no line of content moved**, and the fix is
+byte-countable (`WORK-QUEUE.md` 927,008 → 927,009 B; the check-in 83,853 → 83,854 B).
+
+Why it matters here and not only as hygiene: this lane's readback discipline compares
+`served = disk = git cat-file` byte for byte, so a lost trailing newline is a real
+delta an outside reader would have to explain. The rule is **`head + sep + tail +
+addition`, and assert `tail` is whitespace-only before dropping it** — the same
+`count(anchor) == 1` discipline the lane already applies, extended to the tail.
+
+**Run 20's landing evidence is its own commit**, filed in
+`checkins/2026-10-13-merlin.md` §*Run 20 landing evidence* and in this queue's Run-20
+landing block, both read back over the anonymous raw path at **HTTP 200, served = disk =
+`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)