diff --git a/.changeset/five-pans-tease.md b/.changeset/five-pans-tease.md
new file mode 100644
index 0000000000..0306eb6ec9
--- /dev/null
+++ b/.changeset/five-pans-tease.md
@@ -0,0 +1,35 @@
+---
+"@objectstack/cli": patch
+---
+
+fix(cli): `OS_APP_NAME` overrides `config.email.defaultTemplateContext.appName` again (#5448)
+
+`resolveEmailCapabilityArg` computed the email template context's `appName`
+first and then spread the whole `config.email.defaultTemplateContext` over it.
+A config that spelled `defaultTemplateContext: { appName: 'Acme Dev' }`
+therefore made `OS_APP_NAME` inert — silently, with nothing logged — even
+though this resolver's stated contract ("`OS_EMAIL_*` environment variables
+override per setting", the header of `EmailServiceConfigSchema` and of the
+generated `references/system/email-config` page) holds for every other key it
+reads: `apiKey`, `defaultFrom`, `retries`, `queueDelivery`, `persist`, SMTP.
+
+One `objectstack.config.ts` deployed to several environments has exactly one
+per-environment lever, and it did nothing: production kept sending mail branded
+with the repo-pinned name, and because the fallback sender is slugged from the
+same value, the envelope said `no-reply@acme-dev.local` too.
+
+`appName` is now resolved after the spread, in the order
+`OS_APP_NAME` > `config.email.appName` >
+`config.email.defaultTemplateContext.appName` > top-level `config.appName` >
+`'ObjectStack'`. Every other key of `defaultTemplateContext` is unchanged — it
+has no env or dedicated-config carrier, so the author's context is still spread
+through wholesale.
+
+**Behaviour change, accepted deliberately.** A deployment that relied on
+`defaultTemplateContext.appName` beating `OS_APP_NAME` will now see the env
+value in mail subjects, bodies and the derived fallback sender. Unset
+`OS_APP_NAME` in that environment, or move the intended name into
+`config.email.appName`, to keep the old result. Note that
+`defaultTemplateContext.appName` stays in the chain rather than losing to the
+two dedicated sources outright: a config that spells only the context form is
+still honoured and is not demoted to `'ObjectStack'`.
diff --git a/packages/cli/src/commands/serve-email-appname-precedence.test.ts b/packages/cli/src/commands/serve-email-appname-precedence.test.ts
new file mode 100644
index 0000000000..ca2da4f582
--- /dev/null
+++ b/packages/cli/src/commands/serve-email-appname-precedence.test.ts
@@ -0,0 +1,228 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+//
+// framework#5448 — `OS_APP_NAME` wins over
+// `config.email.defaultTemplateContext.appName`.
+//
+// `EmailServiceConfigSchema`'s header states the resolution order this file's
+// resolver implements — config first, `OS_EMAIL_*` overriding per setting —
+// and every other key honoured it: apiKey, defaultFrom, retries,
+// queueDelivery, persist, the SMTP family. `appName` was the single exception,
+// and it was an exception nobody could see: the resolved value was computed
+// first and then the whole `defaultTemplateContext` was spread OVER it, so an
+// author who wrote `defaultTemplateContext: { appName: 'Acme Dev' }` made
+// `OS_APP_NAME` inert.
+//
+// That is not a cosmetic ordering detail. One `objectstack.config.ts` deployed
+// to several environments has exactly one per-environment lever — the env var
+// — and it silently did nothing: production sent mail branded "Acme Dev", and
+// because the fallback sender is slugged from the same value, the envelope
+// said `no-reply@acme-dev.local` too. Nothing failed, nothing logged.
+//
+// The chain deliberately keeps `defaultTemplateContext.appName` IN it rather
+// than dropping it behind the two dedicated sources: a config that spells only
+// the context form is a real, existing shape, and demoting it to 'ObjectStack'
+// would trade one silently wrong value for a worse one. Hence the five-level
+// ladder below, one test per rung, plus the anti-demotion case.
+
+import { describe, it, expect, vi } from 'vitest';
+import { EmailServicePlugin } from '@objectstack/plugin-email';
+import { resolveEmailCapabilityArg } from './serve.js';
+
+const appNameOf = (cfgEmail: Record<string, any>, env: NodeJS.ProcessEnv = {}, configAppName?: string) =>
+  (resolveEmailCapabilityArg(cfgEmail, env, configAppName).options
+    .defaultTemplateContext as Record<string, unknown>).appName;
+
+// ── the five-level chain, one rung per test ────────────────────────────────
+
+describe('resolveEmailCapabilityArg — defaultTemplateContext.appName precedence (#5448)', () => {
+  // Every source present at once. This is the case the old code got wrong, and
+  // it is the only one whose expectation changed: it used to answer
+  // 'From The Context'.
+  it('rung 1 — OS_APP_NAME beats every config source', () => {
+    expect(appNameOf(
+      { appName: 'From The Key', defaultTemplateContext: { appName: 'From The Context' } },
+      { OS_APP_NAME: 'From The Env' },
+      'From The Top Level',
+    )).toBe('From The Env');
+  });
+
+  it('rung 2 — config.email.appName takes over when the env says nothing', () => {
+    expect(appNameOf(
+      { appName: 'From The Key', defaultTemplateContext: { appName: 'From The Context' } },
+      {},
+      'From The Top Level',
+    )).toBe('From The Key');
+  });
+
+  it('rung 3 — defaultTemplateContext.appName takes over when the dedicated key is absent', () => {
+    expect(appNameOf(
+      { defaultTemplateContext: { appName: 'From The Context' } },
+      {},
+      'From The Top Level',
+    )).toBe('From The Context');
+  });
+
+  it('rung 4 — top-level config.appName takes over when email says nothing', () => {
+    expect(appNameOf({}, {}, 'From The Top Level')).toBe('From The Top Level');
+  });
+
+  it("rung 5 — 'ObjectStack' when no source says anything", () => {
+    expect(appNameOf({}, {})).toBe('ObjectStack');
+  });
+
+  // ── the anti-demotion case ───────────────────────────────────────────────
+
+  it('does NOT demote a config that spells only defaultTemplateContext.appName', () => {
+    // The trap the fix had to avoid. Resolving `appName` after the spread
+    // without putting the context form back into the chain would have answered
+    // 'ObjectStack' here — a config that used to work would start branding
+    // every mail with the framework's own name. This case is the reason the
+    // chain has five rungs and not four.
+    expect(appNameOf({ defaultTemplateContext: { appName: 'Context Only' } }, {}))
+      .toBe('Context Only');
+    // …and the env still overrides that shape, which is the whole point.
+    expect(appNameOf(
+      { defaultTemplateContext: { appName: 'Context Only' } },
+      { OS_APP_NAME: 'Ops Override' },
+    )).toBe('Ops Override');
+  });
+
+  // ── the blast radius the issue named: the fallback sender ────────────────
+
+  it('slugs the fallback from-address from the resolved appName, not the raw context', () => {
+    // `defaultFrom` is derived from this value when no sender is configured,
+    // so the inverted precedence put the wrong brand in the envelope as well
+    // as the body. Both halves move together or the fix is half done.
+    const { options } = resolveEmailCapabilityArg(
+      { defaultTemplateContext: { appName: 'Acme Dev' } },
+      { OS_APP_NAME: 'Acme' },
+    );
+    expect(options.defaultFrom).toEqual({ name: 'Acme', address: 'no-reply@acme.local' });
+  });
+
+  it('leaves an explicitly configured defaultFrom alone', () => {
+    const { options } = resolveEmailCapabilityArg(
+      { defaultFrom: { name: 'Support', address: 'support@acme.test' },
+        defaultTemplateContext: { appName: 'Acme Dev' } },
+      { OS_APP_NAME: 'Acme' },
+    );
+    expect(options.defaultFrom).toEqual({ name: 'Support', address: 'support@acme.test' });
+  });
+
+  // ── the other context keys are untouched ─────────────────────────────────
+
+  it('changes NOTHING about the other defaultTemplateContext keys', () => {
+    // Only `appName` has env and dedicated-config carriers above it, so only
+    // `appName` is special-cased. Everything else the author wrote is still
+    // spread through wholesale — including keys whose names merely resemble
+    // one of the resolved settings, and including a key deliberately named
+    // after a config setting this resolver reads, to pin that the special case
+    // is exactly one key wide.
+    const { options } = resolveEmailCapabilityArg(
+      {
+        appName: 'Acme',
+        defaultTemplateContext: {
+          appName: 'ignored — the chain decides this one',
+          supportEmail: 'help@acme.test',
+          brandColor: '#0af',
+          provider: 'this is template data, not the transport',
+          year: 2026,
+          nested: { logoUrl: 'https://cdn.acme.test/logo.png' },
+        },
+      },
+      { OS_APP_NAME: 'Acme Prod' },
+    );
+    expect(options.defaultTemplateContext).toEqual({
+      appName: 'Acme Prod',
+      supportEmail: 'help@acme.test',
+      brandColor: '#0af',
+      provider: 'this is template data, not the transport',
+      year: 2026,
+      nested: { logoUrl: 'https://cdn.acme.test/logo.png' },
+    });
+    // …and a context key that shadows a real setting name stayed template
+    // data: the transport is still resolved from its own sources.
+    expect(options.provider).toBe('log');
+  });
+
+  it('still emits a context with only appName when no context was configured', () => {
+    // The shape existing deployments get. Absent config must not start
+    // producing an empty or missing context object.
+    expect(resolveEmailCapabilityArg({}, { OS_APP_NAME: 'Solo' }).options.defaultTemplateContext)
+      .toEqual({ appName: 'Solo' });
+  });
+});
+
+// ── end to end: resolver output -> real plugin -> live EmailService ────────
+
+/**
+ * Minimal ObjectQL stand-in — `start()`'s `kernel:ready` handler needs an
+ * engine before it decides anything, and the stranded-outbox sweep reads
+ * `sys_email` on the persisting path.
+ */
+function fakeEngine() {
+  return {
+    async find() { return []; },
+    async insert(_table: string, data: any) { return { id: data?.id }; },
+    async update() { return {}; },
+    async delete() { return { deleted: 0 }; },
+  };
+}
+
+/**
+ * Boot the real `EmailServicePlugin` the way `os serve` does — through the
+ * resolver — and report the `defaultTemplateContext` the LIVE `EmailService`
+ * ended up holding.
+ *
+ * Reading the service's own options rather than the resolver's return value is
+ * what makes this more than a restatement: `sendTemplate` merges exactly this
+ * object into every template's data (pinned on the plugin side by
+ * `send-template.test.ts`), so what it holds is what an operator's mail
+ * renders with.
+ */
+async function contextReachingTheService(
+  cfgEmail: Record<string, any>,
+  env: NodeJS.ProcessEnv = {},
+): Promise<Record<string, unknown>> {
+  const constructedWith = resolveEmailCapabilityArg(cfgEmail, env).options;
+
+  const services: Record<string, unknown> = { manifest: { register: () => {} }, objectql: fakeEngine() };
+  const hooks: Record<string, Array<() => Promise<void> | void>> = {};
+  const ctx: any = {
+    logger: { info: vi.fn(), warn: vi.fn(), error: vi.fn(), debug: vi.fn() },
+    getService: (name: string) => {
+      if (!(name in services)) throw new Error(`service '${name}' not registered`);
+      return services[name];
+    },
+    registerService: (name: string, svc: unknown) => { services[name] = svc; },
+    hook: (name: string, fn: () => Promise<void> | void) => { (hooks[name] ??= []).push(fn); },
+  };
+
+  const plugin = new EmailServicePlugin(constructedWith as any);
+  await plugin.init(ctx);
+  await plugin.start(ctx);
+  for (const fn of hooks['kernel:ready'] ?? []) await fn();
+
+  const service = services.email as { options: { defaultTemplateContext?: Record<string, unknown> } };
+  return service.options.defaultTemplateContext ?? {};
+}
+
+describe('the resolved appName reaches the service that renders templates (#5448)', () => {
+  it('carries OS_APP_NAME through to the live EmailService over a config-pinned context', async () => {
+    // The reported symptom, end to end: repo config hard-codes the dev brand,
+    // production sets the env var, and the mail that goes out must say 'Acme'.
+    const context = await contextReachingTheService(
+      { defaultTemplateContext: { appName: 'Acme Dev', supportEmail: 'help@acme.test' } },
+      { OS_APP_NAME: 'Acme' },
+    );
+    expect(context).toEqual({ appName: 'Acme', supportEmail: 'help@acme.test' });
+  }, 60_000);
+
+  it('carries the context-only appName when no env or dedicated key exists', async () => {
+    const context = await contextReachingTheService(
+      { defaultTemplateContext: { appName: 'Context Only' } },
+      {},
+    );
+    expect(context).toEqual({ appName: 'Context Only' });
+  }, 60_000);
+});
diff --git a/packages/cli/src/commands/serve.ts b/packages/cli/src/commands/serve.ts
index 2a122f0986..6bf0e06694 100644
--- a/packages/cli/src/commands/serve.ts
+++ b/packages/cli/src/commands/serve.ts
@@ -3040,6 +3040,18 @@ function envBooleanFlag(raw: string | undefined): boolean | undefined {
  * function's own, per setting: env > `config.email.persist` > the plugin
  * default (persist ON) — so a config and an env that say nothing leave the
  * option absent and the plugin's default untouched.
+ *
+ * The template context's `appName` follows the same env-wins rule as every
+ * other setting here (#5448): `OS_APP_NAME` > `config.email.appName` >
+ * `config.email.defaultTemplateContext.appName` > top-level `config.appName` >
+ * `'ObjectStack'`. It used to be the file's one exception — the whole
+ * `defaultTemplateContext` was spread OVER the resolved value, so a config that
+ * spelled `defaultTemplateContext: { appName: … }` made `OS_APP_NAME` inert and
+ * the per-environment override an operator has for a repo-pinned config did
+ * nothing, silently, in the mail body AND in the `no-reply@<slug>.local`
+ * fallback sender derived from it. Every OTHER key of `defaultTemplateContext`
+ * is unchanged: it has no env or dedicated-config carrier, so the author's
+ * context is still spread through wholesale.
  */
 export function resolveEmailCapabilityArg(
   cfgEmail: Record<string, any> = {},
@@ -3075,9 +3087,30 @@ export function resolveEmailCapabilityArg(
   // audit trail. Absent from BOTH sources means the key is left out of the
   // constructor options entirely, so the plugin's own default decides.
   const persist = envBooleanFlag(env.OS_EMAIL_PERSIST_ENABLED) ?? cfgEmail.persist;
+  // `appName` is resolved AFTER the context spread, not before it (#5448).
+  // The other keys of `defaultTemplateContext` are still spread wholesale and
+  // are the only source for themselves; `appName` alone has dedicated carriers
+  // above it, and this file's stated contract — "env overrides per setting" —
+  // has to hold for it like it does for apiKey / defaultFrom / retries /
+  // queueDelivery / persist / SMTP. Spreading the context over the resolved
+  // value inverted exactly that one key: an author who wrote
+  // `defaultTemplateContext: { appName: 'Acme Dev' }` made `OS_APP_NAME`
+  // silently inert, so the one lever an operator has for a repo-pinned config
+  // deployed to several environments did nothing — and since the fallback
+  // sender is slugged from this value, the wrong name reached the envelope as
+  // well as the body.
+  //
+  // `defaultTemplateContext.appName` stays IN the chain rather than losing to
+  // the two dedicated sources and vanishing: dropping it would demote every
+  // config that spells only the context form straight to 'ObjectStack',
+  // trading one silently wrong value for a worse one. Order: env >
+  // `config.email.appName` > `config.email.defaultTemplateContext.appName` >
+  // top-level `config.appName` > 'ObjectStack'.
+  const cfgTemplateContext = cfgEmail.defaultTemplateContext || {};
   const defaultTemplateContext = {
-    appName: env.OS_APP_NAME || cfgEmail.appName || configAppName || 'ObjectStack',
-    ...(cfgEmail.defaultTemplateContext || {}),
+    ...cfgTemplateContext,
+    appName: env.OS_APP_NAME || cfgEmail.appName || cfgTemplateContext.appName
+      || configAppName || 'ObjectStack',
   };
   // Provide a sensible fallback `from` so templates can render even before
   // operators configure SMTP/SaaS. The log transport simply prints to stdout;