diff --git a/server/src/engagement/templateSeeds.js b/server/src/engagement/templateSeeds.js
index ea44d64..d77e0f0 100644
--- a/server/src/engagement/templateSeeds.js
+++ b/server/src/engagement/templateSeeds.js
@@ -44,6 +44,27 @@ const AMBIENT_VARIABLES = Object.freeze([
   { name: 'year', type: 'string', required: true, example: '2026' },
 ])
 
+
+// The per-DELIVERY additions, which are a different thing from the ambient set
+// above and are declared separately because they apply to a different set of
+// templates.
+//
+// `emailChannel.deliver` computes an unsubscribe token per recipient and merges
+// it LAST over the projection, so a body may always reference it — but a template
+// bound to a TRIGGER takes its variable list from that trigger's declaration
+// (`variablesFor`), and a trigger has no business declaring a fact about how the
+// mail was delivered. Without these, `{{unsubscribeUrl}}` renders correctly and
+// then the save-time undeclared-variable check refuses the first operator who
+// tries to EDIT the body around it.
+//
+// Found in Phase 11b, where module-uo's sixteen in-universe bodies are the first
+// trigger-bound templates in the system to carry an unsubscribe line of their
+// own: core's generic `notify.event` declares it in its own seed and is bound to
+// no trigger, so nothing had ever taken this path.
+const DELIVERY_VARIABLES = Object.freeze([
+  { name: 'unsubscribeUrl', type: 'string', required: false, example: 'https://example.com/unsubscribe/abc123' },
+])
+
 // A tiny helper so the block arrays below read as content rather than as JSON.
 const text = (id, body, opts = {}) => ({
   id,
@@ -296,4 +317,4 @@ function seedByKey(key) {
   return SEEDS.find((s) => s.key === key) || null
 }
 
-module.exports = { SEEDS, AMBIENT_VARIABLES, seedByKey }
+module.exports = { SEEDS, AMBIENT_VARIABLES, DELIVERY_VARIABLES, seedByKey }
diff --git a/server/src/engagement/templates.js b/server/src/engagement/templates.js
index 1b01205..4964be3 100644
--- a/server/src/engagement/templates.js
+++ b/server/src/engagement/templates.js
@@ -18,7 +18,7 @@ const templatesDb = require('../model/engagement/engagementTemplates.db')
 const settings = require('../model/settings/settings.model')
 const brand = require('../config/brand')
 const emailBlocks = require('../emailBlocks')
-const { SEEDS, AMBIENT_VARIABLES, seedByKey } = require('./templateSeeds')
+const { SEEDS, AMBIENT_VARIABLES, DELIVERY_VARIABLES, seedByKey } = require('./templateSeeds')
 // The trigger registry lives with the module registries, not here — a trigger is
 // something a MODULE declares (see engagement/index.js's header).
 const { eventTrigger } = require('../modules/registries')
@@ -84,6 +84,11 @@ function variablesFor(template) {
   if (template && template.trigger_id) {
     const declared = eventTrigger(template.trigger_id)
     if (declared && Array.isArray(declared.variables)) own.push(...declared.variables)
+    // A trigger-bound body is engagement mail, and engagement mail always carries
+    // an unsubscribe the channel computes per recipient. A trigger declares what
+    // HAPPENED and has no business declaring how the mail was sent, so the
+    // delivery facts are added here rather than to every declaration.
+    own.push(...DELIVERY_VARIABLES)
   } else if (template && template.seed_key) {
     const seed = seedByKey(template.seed_key)
     if (seed) own.push(...seed.variables)