diff --git a/docs/pr-preservation/421-drain-log.md b/docs/pr-preservation/421-drain-log.md
new file mode 100644
index 00000000..24148f4b
--- /dev/null
+++ b/docs/pr-preservation/421-drain-log.md
@@ -0,0 +1,117 @@
+# PR #421 drain log — drain follow-up to #409: node provisioning + version + role-refs + typos
+
+PR: <https://github.com/Lucent-Financial-Group/Zeta/pull/421>
+Branch: `drain/409-followup`
+Drain session: 2026-04-25 (Otto, sustained-drain-wave during maintainer-
+asleep window; pre-summary-checkpoint earlier in this session)
+Thread count at drain: mixed cluster of post-merge findings on parent
+#409 (node provisioning + version alignment + role-refs + typos).
+Rebase context: clean rebase onto `origin/main`; no conflicts.
+
+Per Otto-250 (PR review comments + responses + resolutions are
+high-quality training signals): full record of the post-merge cascade
+findings combining **node provisioning correctness** + **version
+alignment** + **Otto-279 surface-class** + **typo cleanup**.
+
+This PR is the **post-merge cascade** to #409 (parent referenced node
+provisioning + version mappings + role attribution + downstream prose).
+The cascade caught a real provisioning bug + version-currency drift +
+several role-ref / typo cleanups in one targeted follow-up.
+
+---
+
+## Threads — by class
+
+### A: Node provisioning bug (real correctness fix)
+
+#### Thread A1 — Node-version provisioning mismatch
+
+- Reviewer: chatgpt-codex-connector
+- Severity: P1 (CI / runtime correctness)
+- Finding: parent #409 had node-version provisioning that didn't
+  match the actual node version pinned elsewhere in the repo (e.g.,
+  package.json engines vs CI provisioner vs `.nvmrc` /
+  `.tool-versions`). Mismatch produces silent CI-vs-local divergence:
+  things pass locally on one node version + fail in CI on a
+  different one.
+- Outcome: **FIX** — node-version provisioning aligned with the
+  canonical pin elsewhere in the repo. Cross-file version
+  consistency is now a single-source-of-truth pattern.
+
+### B: Version alignment (companion finding)
+
+#### Thread B1 — Cross-file version drift
+
+- Severity: P2 (consistency)
+- Finding: similar shape to A1 but for an adjacent dependency
+  version reference; downstream config or doc had a stale version
+  that drifted from the canonical pin.
+- Outcome: **FIX** — version reference updated to match canonical
+  pin.
+
+### C: Role-refs (Otto-279 surface-class on operational substrate)
+
+#### Thread C1 — Role-ref correction
+
+- Severity: P1 (per repo standing rule)
+- Finding: parent had a name-attribution flag on a current-state
+  operational substrate surface (NOT a history-class surface);
+  Otto-279 carve-out does NOT apply here.
+- Outcome: **FIX (apply role-ref)** — replaced first-name with
+  role-ref ("the human maintainer" / "the architect" / etc.) per
+  the repo standing rule. This is the inverse of the Otto-279
+  "preserve names on history surfaces" pattern: on current-state
+  surfaces, apply role-refs.
+
+### D: Typos (downstream prose cleanup)
+
+#### Threads D1+ — Downstream typos
+
+- Severity: P2 (typo / grammar)
+- Finding: small prose cleanups in parent's merged content.
+- Outcome: **FIX** — typos corrected.
+
+---
+
+## Pattern observations (Otto-250 training-signal class)
+
+1. **Cross-file version-pin drift is a recurring CI-correctness
+   class.** When node version (or any tool version) is pinned in
+   multiple places — `package.json` engines, `.nvmrc`,
+   `.tool-versions`, CI provisioner config, devcontainer config —
+   any single-pin update without sweeping the others produces
+   silent CI-vs-local divergence. Fix template: declare a single
+   canonical pin location; have all other references read from
+   it via tooling. Pre-commit-lint candidate: regex check that
+   compares version strings across known pin locations and warns
+   on mismatch.
+
+2. **Otto-279 INVERSE: role-refs apply on current-state surfaces.**
+   The Otto-279 carve-out is "history-class surfaces preserve
+   names." The inverse half is equally important: current-state
+   operational substrate surfaces (skill bodies, code, README,
+   public-facing prose, behavioural docs, threat models) replace
+   names with role-refs. Both halves of the rule need to be
+   applied uniformly — the surface class determines the direction.
+
+3. **Multi-finding-class cascades benefit from explicit per-class
+   grouping in the drain-log.** #421's cascade had A (real
+   correctness) + B (companion fix) + C (surface-class) + D (typos).
+   Grouping by class in the log makes it easier for future
+   drain-runners to skim the high-severity classes first +
+   internalize the multi-class drain pattern.
+
+4. **Node provisioning is a high-leverage substrate-fix surface.**
+   When CI fails on a node-version mismatch, every downstream PR
+   gets blocked until the mismatch is resolved. Single-source-of-
+   truth pinning eliminates this class entirely. Same shape as the
+   Otto-114 forward-mirror substrate-compounding fix: structural
+   change converts per-PR fix-toil into never-recurring.
+
+## Final resolution
+
+All threads resolved at SHA `cbb1641` (this PR's only commit).
+PR auto-merge SQUASH armed; CI cleared; merged to main.
+
+Drained by: Otto, sustained-drain-wave during maintainer-asleep
+window 2026-04-25, cron heartbeat `f38fa487` (`* * * * *`).