From 885c250b12bd3c6f3ccf6ecc3cc6c3db13e5a252 Mon Sep 17 00:00:00 2001
From: Matsu <huhta.matias@gmail.com>
Date: Thu, 9 Jul 2026 12:49:39 +0300
Subject: [PATCH] ci: Set up v3 branch sync and nightly build workflows
 (no-changelog) (#33678)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 .github/CLAUDE.md                             |   1 +
 .github/DEVELOPING_V3.md                      | 161 +++++++++++++++++
 .github/WORKFLOWS.md                          |  18 +-
 .github/scripts/docker/docker-tags.mjs        |  25 ++-
 .github/scripts/sync-conflict-owners.mjs      | 139 ++++++++++++++
 .github/scripts/sync-conflict-owners.test.mjs |  81 +++++++++
 .github/scripts/sync-master-to-3x.mjs         | 171 ++++++++++++++++++
 .github/scripts/sync-master-to-3x.test.mjs    | 142 +++++++++++++++
 .github/workflows/build-v3-nightly.yml        |  46 +++++
 .github/workflows/clean-stale-branches.yml    |   4 +-
 .github/workflows/docker-build-push.yml       |  64 ++++++-
 .github/workflows/util-sync-master-to-3x.yml  | 105 +++++++++++
 AGENTS.md                                     |   3 +
 13 files changed, 952 insertions(+), 8 deletions(-)
 create mode 100644 .github/DEVELOPING_V3.md
 create mode 100644 .github/scripts/sync-conflict-owners.mjs
 create mode 100644 .github/scripts/sync-conflict-owners.test.mjs
 create mode 100644 .github/scripts/sync-master-to-3x.mjs
 create mode 100644 .github/scripts/sync-master-to-3x.test.mjs
 create mode 100644 .github/workflows/build-v3-nightly.yml
 create mode 100644 .github/workflows/util-sync-master-to-3x.yml

diff --git a/.github/CLAUDE.md b/.github/CLAUDE.md
index d9c1a35054e..111d7a23aad 100644
--- a/.github/CLAUDE.md
+++ b/.github/CLAUDE.md
@@ -9,6 +9,7 @@ This folder contains n8n's GitHub Actions infrastructure.
 | File/Folder | Purpose |
 |-------------|---------|
 | `WORKFLOWS.md` | Complete CI/CD documentation |
+| `DEVELOPING_V3.md` | How to develop v3 features (master + 3.x branch model, opt-in flags) |
 | `workflows/` | GitHub Actions workflows |
 | `actions/` | Reusable composite actions |
 | `scripts/` | Release & Docker automation |
diff --git a/.github/DEVELOPING_V3.md b/.github/DEVELOPING_V3.md
new file mode 100644
index 00000000000..56071163655
--- /dev/null
+++ b/.github/DEVELOPING_V3.md
@@ -0,0 +1,161 @@
+# Developing v3 features
+
+n8n is preparing a **v3 major release** (~October 2026). v3 is an *operational*
+release: breaking changes, removals, and legacy cleanup — not a big-bang feature
+launch. From July until release we keep **two long-lived branches alive at once**,
+and this guide explains how to develop against them without friction.
+
+> **TL;DR**
+> - Normal feature work → land on **`master`**, behind an **opt-in feature flag**.
+> - Breaking changes → a separate PR targeting **`3.x`** directly. **Never on `master`.**
+> - `master` is synced into `3.x` **daily**, automatically.
+
+## The branch model
+
+`3.x` is not a divergent fork — it is simply **"whatever is on `master`, plus the
+breaking-change commits"**. Their histories stay in lockstep via a daily sync, so
+merging `3.x` back into `master` at release time is painless.
+
+```mermaid
+flowchart LR
+    subgraph master["master (v2 line)"]
+        F["Feature work<br/>(behind opt-in flags)"]
+        D["Deprecation notices"]
+    end
+    subgraph threex["3.x (v3 line)"]
+        B["Breaking-change PRs"]
+    end
+    F --> master
+    D --> master
+    master -- "daily sync (util-sync-master-to-3x.yml)" --> threex
+    B --> threex
+    threex -. "merged to master at v3 release" .-> master
+```
+
+| You want to… | Where it goes | How |
+|--------------|---------------|-----|
+| Ship a new feature/behavior | `master` | Behind an **opt-in flag** (see below) |
+| Warn engineers a function is going away | `master` | Add a **deprecation notice** so usage drops before v3 |
+| Create a migration | `master` | Create a non-destructive migration in master. After the release of v3, you can create the destructive part of migration if needed |
+| Remove/change something in a breaking way | `3.x` | A **separate PR targeting `3.x`** directly |
+
+## Developing a normal feature on `master` (behind an opt-in flag)
+
+Land new implementations on `master` disabled by default, so they ride the daily
+sync into `3.x` and can be trialed without affecting v2 users. n8n uses **PostHog**
+for flags, evaluated server-side and bootstrapped to the frontend.
+
+### Frontend (editor-ui)
+
+1. Register the experiment in
+   [`packages/frontend/editor-ui/src/app/constants/experiments.ts`](../packages/frontend/editor-ui/src/app/constants/experiments.ts)
+   with `createExperiment`, using the next numeric index prefix:
+   ```ts
+   export const MY_V3_FEATURE_EXPERIMENT = createExperiment('0XX_my_v3_feature');
+   ```
+   Add its name to `EXPERIMENTS_TO_TRACK` if it should emit exposure telemetry.
+2. Gate the code via the PostHog store — for a boolean opt-in flag use
+   `isFeatureEnabled`:
+   ```ts
+   const posthog = usePostHogStore();
+   if (posthog.isFeatureEnabled(MY_V3_FEATURE_EXPERIMENT.name)) {
+     // new v3 behavior
+   }
+   ```
+3. Put per-experiment code in its own folder under
+   `packages/frontend/editor-ui/src/experiments/<name>/`.
+
+The **`n8n:experiments` skill** ([`.agents/skills/experiments/`](../.agents/skills/experiments/SKILL.md))
+is the authoritative, step-by-step procedure — including creating the disabled
+PostHog flags in Staging/Production first.
+
+### Backend (cli / config)
+
+A backend opt-in flag is three small pieces (worked example: the
+`084_eval_collections` flag):
+
+1. **Flag key** constant in `@n8n/api-types`
+   (e.g. `EVAL_COLLECTIONS_FLAG = '084_eval_collections'` in
+   `packages/@n8n/api-types/src/schemas/eval-collections.schema.ts`).
+2. **Env toggle** — an `@Env('N8N_...')` boolean defaulting to `false` in a
+   `@n8n/config` config class
+   (e.g. `N8N_EVAL_COLLECTIONS_ENABLED` in
+   `packages/@n8n/config/src/configs/evaluation.config.ts`).
+3. **Override wiring** in `PostHogClient.applyEnvOverrides()`
+   ([`packages/cli/src/posthog/index.ts`](../packages/cli/src/posthog/index.ts)) —
+   force-enable the flag when the env toggle is on:
+   ```ts
+   if (this.globalConfig.evaluation.collectionsEnabled) {
+     overrides[EVAL_COLLECTIONS_FLAG] = true;
+   }
+   ```
+   The override is **force-enable only**; `false` defers to PostHog.
+
+Evaluated flags flow to the frontend through the login / current-user response,
+so a single flag key can gate both backend and frontend behavior.
+
+### Testing behind a flag
+
+Override flags locally without touching PostHog:
+- **Browser:** `window.featureFlags.override('0XX_my_v3_feature', true)`.
+- **Playwright:** set the storage override in `TestRequirements`:
+  ```ts
+  test.use({ requirements: {
+    storage: { N8N_EXPERIMENT_OVERRIDES: JSON.stringify({ '0XX_my_v3_feature': true }) },
+  } });
+  ```
+
+## Introducing a breaking change (on `3.x`)
+
+Breaking changes go **only on `3.x`**, via a PR that targets `3.x` directly
+(branch off the latest `3.x`, open the PR against `3.x`). Do not land breaking
+changes on `master` — the sync guarantees `master` stays releasable as v2.
+
+- Track the change in the [v3 breaking-changes tracker](https://www.notion.so/n8n/1a75b6e0c94f802caca3ce378d0d8046)
+  and the [Release v3 Linear project](https://linear.app/n8n/project/release-v3-7d7032bebbec/activity).
+- Follow the `BREAKING CHANGE:` PR-title convention (see
+  [`pull_request_title_conventions.md`](./pull_request_title_conventions.md)).
+
+**Deprecations land on `master`.** If you plan to remove a function/class in v3,
+add a deprecation notice on `master` first so other engineers reduce usage ahead
+of the breaking removal on `3.x`.
+
+## How the daily sync works
+
+[`util-sync-master-to-3x.yml`](./workflows/util-sync-master-to-3x.yml) runs daily
+and merges `master` into `3.x`:
+
+1. **Fast-forward** when `3.x` hasn't diverged.
+2. **Three-way merge** when it has.
+3. On a **merge conflict** it opens a **draft conflict PR** (labeled
+   `automation:v3-sync`) and posts to the **`#alerts-v3-sync`** Slack channel.
+   **Syncs pause until that PR is resolved and merged** — so conflicts never pile
+   up silently.
+
+**Who gets pinged.** The conflict is attributed to the authors of the `3.x`
+breaking commits touching the conflicted files (computed by
+`.github/scripts/sync-conflict-owners.mjs`: the `master..HEAD` commits per
+conflicted file, mapped to GitHub accounts). Those authors are **requested as
+reviewers** on the conflict PR and listed in the `#alerts-v3-sync` message. So if you
+authored the breaking commit that caused a conflict, you'll be nudged to resolve
+it: fix the conflict markers on the `sync/master-to-3x` branch and merge the PR;
+the next daily run then resumes normally.
+
+## Trialing v3
+
+`3.x` publishes nightly Docker images (see
+[`build-v3-nightly.yml`](./workflows/build-v3-nightly.yml)):
+
+```bash
+docker pull n8nio/n8n:v3-nightly              # latest v3 nightly
+docker pull n8nio/n8n:v3-nightly-20260625     # a specific build date
+```
+
+Use these to trial v3 in docker/kubernetes before release. Do **not** use them in
+production.
+
+## See also
+
+- [`.github/WORKFLOWS.md`](./WORKFLOWS.md) — full CI/CD + release lifecycle.
+- Root [`AGENTS.md`](../AGENTS.md) — general repo guidance.
+- [Branching strategy & releases (Notion)](https://www.notion.so/n8n/Major-Release-v3-Branching-strategy-and-releases-38a5b6e0c94f800881deeb11e515f543).
diff --git a/.github/WORKFLOWS.md b/.github/WORKFLOWS.md
index cdfacf79cbd..15eae5c8287 100644
--- a/.github/WORKFLOWS.md
+++ b/.github/WORKFLOWS.md
@@ -410,12 +410,28 @@ Push to master/1.x
 | Daily 01:30, 02:30, 03:30 | `test-benchmark-nightly.yml`      | Performance benchmarks   |
 | Daily 04:00               | `test-e2e-vm-expressions-nightly.yml`| VM expression E2E     |
 | Daily 05:00               | `test-benchmark-destroy-nightly.yml`| Cleanup benchmark env  |
+| Daily 06:00               | `util-sync-master-to-3x.yml`      | Sync master → 3.x (v3)   |
+| Daily 08:00               | `build-v3-nightly.yml`            | Nightly v3 Docker images |
 | Monday 00:00              | `util-update-node-popularity.yml` | Node usage stats         |
 | Monday 02:00              | `test-e2e-coverage-weekly.yml`    | Weekly E2E coverage      |
 | Saturday 22:00            | `test-evals-ai.yml`               | AI workflow evals        |
 
 ---
 
+## v3 development (master + 3.x)
+
+During the v3 release window, `master` carries normal feature work (behind opt-in
+flags) and the long-lived `3.x` branch carries breaking changes. `master` is
+synced into `3.x` daily by `util-sync-master-to-3x.yml` (conflicts open a draft PR
+labeled `automation:v3-sync`, request the breaking-commit authors as reviewers via
+`sync-conflict-owners.mjs`, post to `#alerts-v3-sync`, and pause further syncs).
+`build-v3-nightly.yml` publishes `n8nio/n8n:v3-nightly[-<date>]` images from `3.x`
+by calling `docker-build-push.yml` with `ref: 3.x` + `date_tag`.
+
+See **[`DEVELOPING_V3.md`](./DEVELOPING_V3.md)** for the full model.
+
+---
+
 ## Custom Actions
 
 Composite actions in `.github/actions/`:
@@ -455,7 +471,7 @@ Workflows with `workflow_call` trigger:
 | `test-linting-reusable.yml`        | `ref`, `nodeVersion`                          | ESLint                |
 | `test-e2e-reusable.yml`            | `branch`, `test-mode`, `shards`, `runner`     | Core E2E executor     |
 | `test-workflows-callable.yml`      | `git_ref`, `compare_schemas`                  | Workflow tests        |
-| `docker-build-push.yml`            | `n8n_version`, `release_type`, `push_enabled` | Docker build          |
+| `docker-build-push.yml`            | `n8n_version`, `release_type`, `push_enabled`, `ref`, `date_tag` | Docker build |
 | `sec-ci-reusable.yml`              | `ref`                                         | Security orchestrator |
 | `sec-poutine-reusable.yml`         | `ref`                                         | Poutine scanner       |
 | `security-trivy-scan-callable.yml` | `image_ref`                                   | Trivy scan            |
diff --git a/.github/scripts/docker/docker-tags.mjs b/.github/scripts/docker/docker-tags.mjs
index a6a2841653b..7d73b07408d 100644
--- a/.github/scripts/docker/docker-tags.mjs
+++ b/.github/scripts/docker/docker-tags.mjs
@@ -9,7 +9,7 @@ class TagGenerator {
 		this.githubOutput = process.env.GITHUB_OUTPUT || null;
 	}
 
-	generate({ image, version, platform, includeDockerHub = false, sha = '' }) {
+	generate({ image, version, platform, includeDockerHub = false, sha = '', date = '' }) {
 		let imageName = image;
 		let versionSuffix = '';
 
@@ -42,6 +42,20 @@ class TagGenerator {
 			tags.shaPrimaryTag = shaGhcr[0].replace(/-amd64$|-arm64$/, '');
 		}
 
+		// Generate additional date-based tags (e.g. v3-nightly-20260625) for nightly builds
+		if (date) {
+			const dateVersion = `${version}-${date}`;
+			const datePlatformTag = `${dateVersion}${versionSuffix}${platformSuffix}`;
+			const dateGhcr = [`ghcr.io/${this.githubOwner}/${imageName}:${datePlatformTag}`];
+			const dateDocker = includeDockerHub
+				? [`${this.dockerUsername}/${imageName}:${datePlatformTag}`]
+				: [];
+			tags.all = [...tags.all, ...dateGhcr, ...dateDocker];
+			tags.ghcr = [...tags.ghcr, ...dateGhcr];
+			tags.docker = [...tags.docker, ...dateDocker];
+			tags.datePrimaryTag = dateGhcr[0].replace(/-amd64$|-arm64$/, '');
+		}
+
 		return tags;
 	}
 
@@ -58,18 +72,21 @@ class TagGenerator {
 			if (tags.shaPrimaryTag) {
 				outputs.push(`${prefixStr}sha_primary_tag=${tags.shaPrimaryTag}`);
 			}
+			if (tags.datePrimaryTag) {
+				outputs.push(`${prefixStr}date_primary_tag=${tags.datePrimaryTag}`);
+			}
 			appendFileSync(this.githubOutput, outputs.join('\n') + '\n');
 		} else {
 			console.log(JSON.stringify(tags, null, 2));
 		}
 	}
 
-	generateAll({ version, platform, includeDockerHub = false, sha = '' }) {
+	generateAll({ version, platform, includeDockerHub = false, sha = '', date = '' }) {
 		const images = ['n8n', 'runners', 'runners-distroless'];
 		const results = {};
 
 		for (const image of images) {
-			const tags = this.generate({ image, version, platform, includeDockerHub, sha });
+			const tags = this.generate({ image, version, platform, includeDockerHub, sha, date });
 			const prefix = image.replace('-distroless', '_distroless');
 			results[prefix] = tags;
 
@@ -105,6 +122,7 @@ if (import.meta.url === `file://${process.argv[1]}`) {
 				platform: getArg('platform'),
 				includeDockerHub: hasFlag('include-docker'),
 				sha: getArg('sha') || '',
+				date: getArg('date') || '',
 			});
 			if (!generator.githubOutput) {
 				console.log(JSON.stringify(results, null, 2));
@@ -121,6 +139,7 @@ if (import.meta.url === `file://${process.argv[1]}`) {
 				platform: getArg('platform'),
 				includeDockerHub: hasFlag('include-docker'),
 				sha: getArg('sha') || '',
+				date: getArg('date') || '',
 			});
 			generator.output(tags);
 		}
diff --git a/.github/scripts/sync-conflict-owners.mjs b/.github/scripts/sync-conflict-owners.mjs
new file mode 100644
index 00000000000..88300cb4414
--- /dev/null
+++ b/.github/scripts/sync-conflict-owners.mjs
@@ -0,0 +1,139 @@
+#!/usr/bin/env node
+/**
+ * Attributes a master→3.x sync conflict to the authors of the breaking commits.
+ *
+ * Since 3.x = master + breaking commits, the commits that diverged 3.x are exactly
+ * `<base>..HEAD` (where <base> is the fetched master SHA). Scoped to the conflicted
+ * files, those are the commits responsible for the conflict; their GitHub authors are
+ * who to nudge. Must run while the merge is unresolved — HEAD still at the pre-merge
+ * 3.x tip and unmerged paths present in the index.
+ *
+ * git log gives only the author name/email, and ~2/3 of n8n authors commit with a
+ * non-noreply email that carries no GitHub username. So the conflicted files → breaking
+ * SHAs analysis is done locally, and a SINGLE GraphQL call maps those few SHAs to GitHub
+ * logins. Bot- and unlinked-account commits resolve to a null user and are skipped.
+ *
+ * Emits a JSON object to stdout: { ownersCsv, slack, body }.
+ *
+ * Usage:
+ *   node .github/scripts/sync-conflict-owners.mjs --base <masterSha> --sync-branch <name>
+ *
+ * Env: GITHUB_REPOSITORY (owner/repo), GH_TOKEN or GITHUB_TOKEN (for the GraphQL API).
+ * Requires Node 18+ (global fetch).
+ */
+
+import { execFileSync } from 'node:child_process';
+import { parseArgs } from 'node:util';
+
+export function runGit(args) {
+	return execFileSync('git', args, { encoding: 'utf8' }).trim();
+}
+
+// Files with unresolved conflicts in the current (in-progress) merge.
+export function conflictedFiles(git = runGit) {
+	const out = git(['diff', '--name-only', '--diff-filter=U']);
+	return out ? out.split('\n').filter(Boolean) : [];
+}
+
+// Unique SHAs of the 3.x-only (breaking) commits that touched the given files.
+export function breakingShas(base, files, git = runGit) {
+	const shas = new Set();
+	for (const file of files) {
+		const out = git(['log', `${base}..HEAD`, '--format=%H', '--', file]);
+		for (const sha of out.split('\n').filter(Boolean)) shas.add(sha);
+	}
+	return [...shas];
+}
+
+// Resolve commit SHAs to GitHub logins in one GraphQL call. Commits whose author has
+// no linked account (unverified email, bots) resolve to a null user and are dropped.
+export async function resolveLogins(repo, shas, token, fetchFn = fetch) {
+	if (shas.length === 0) return [];
+	const [owner, name] = repo.split('/');
+	const aliases = shas
+		.map((sha, i) => `c${i}: object(oid: "${sha}") { ... on Commit { author { user { login } } } }`)
+		.join('\n');
+	const query = `query($owner: String!, $name: String!) { repository(owner: $owner, name: $name) { ${aliases} } }`;
+
+	const res = await fetchFn('https://api.github.com/graphql', {
+		method: 'POST',
+		headers: {
+			Authorization: `Bearer ${token}`,
+			'Content-Type': 'application/json',
+			'User-Agent': 'n8n-sync-conflict-owners',
+		},
+		body: JSON.stringify({ query, variables: { owner, name } }),
+	});
+	if (!res.ok) throw new Error(`GitHub GraphQL request failed: ${res.status}`);
+	const json = await res.json();
+	if (json.errors) throw new Error(`GitHub GraphQL error: ${JSON.stringify(json.errors)}`);
+
+	const repository = json.data?.repository ?? {};
+	const logins = new Set();
+	for (const node of Object.values(repository)) {
+		const login = node?.author?.user?.login;
+		if (login) logins.add(login);
+	}
+	return [...logins].sort();
+}
+
+// Build the conflict-PR body, reviewer CSV, and Slack owner line.
+export function buildOutputs({ syncBranch, files, owners }) {
+	const filesMd = files.map((f) => `- \`${f}\``).join('\n') || '_none detected_';
+	const ownersMd = owners.length
+		? owners.map((o) => `- @${o}`).join('\n')
+		: '_Could not auto-attribute — review the conflicted files manually._';
+	const slack = owners.length
+		? `Likely owners (GitHub): ${owners.map((o) => `@${o}`).join(' ')}`
+		: 'Could not auto-attribute owners.';
+	const body = [
+		`Automated \`master\`→\`3.x\` sync hit a merge conflict. Resolve the conflict markers on \`${syncBranch}\`, then merge this PR. **Daily syncs are paused until it is merged.**`,
+		'',
+		'### Conflicted files',
+		filesMd,
+		'',
+		'### Likely owners',
+		'Authors of the 3.x commits touching the conflicted files, requested as reviewers:',
+		ownersMd,
+	].join('\n');
+	return { ownersCsv: owners.join(','), slack, body };
+}
+
+async function main() {
+	const { values } = parseArgs({
+		options: {
+			base: { type: 'string' },
+			'sync-branch': { type: 'string', default: 'sync/master-to-3x' },
+		},
+	});
+
+	const base = values.base;
+	const syncBranch = values['sync-branch'];
+	const repo = process.env.GITHUB_REPOSITORY;
+	const token = process.env.GH_TOKEN || process.env.GITHUB_TOKEN;
+
+	if (!base) throw new Error('--base <masterSha> is required');
+	if (!repo) throw new Error('GITHUB_REPOSITORY env var is required');
+	if (!token) throw new Error('GH_TOKEN / GITHUB_TOKEN env var is required');
+
+	const files = conflictedFiles();
+	const shas = breakingShas(base, files);
+
+	// Degrade gracefully: a transient API failure should still open the PR
+	// (unattributed) rather than fail the whole sync.
+	let owners = [];
+	try {
+		owners = await resolveLogins(repo, shas, token);
+	} catch (error) {
+		console.error(`warning: could not resolve owners: ${error.message}`);
+	}
+
+	process.stdout.write(JSON.stringify(buildOutputs({ syncBranch, files, owners })));
+}
+
+if (import.meta.url === `file://${process.argv[1]}`) {
+	main().catch((error) => {
+		console.error(`Error: ${error.message}`);
+		process.exit(1);
+	});
+}
diff --git a/.github/scripts/sync-conflict-owners.test.mjs b/.github/scripts/sync-conflict-owners.test.mjs
new file mode 100644
index 00000000000..8f0bceb8810
--- /dev/null
+++ b/.github/scripts/sync-conflict-owners.test.mjs
@@ -0,0 +1,81 @@
+import assert from 'node:assert/strict';
+import { test } from 'node:test';
+
+import { breakingShas, resolveLogins, buildOutputs } from './sync-conflict-owners.mjs';
+
+test('breakingShas collects unique SHAs across the conflicted files only', () => {
+	const calls = [];
+	const git = (args) => {
+		calls.push(args);
+		// args: ['log', 'BASE..HEAD', '--format=%H', '--', <file>]
+		const file = args.at(-1);
+		if (file === 'a.ts') return 'sha1\nsha2\n';
+		if (file === 'b.ts') return 'sha2\nsha3'; // sha2 shared -> deduped
+		return '';
+	};
+	const shas = breakingShas('BASE', ['a.ts', 'b.ts'], git);
+	assert.deepEqual(shas, ['sha1', 'sha2', 'sha3']);
+	assert.equal(calls.length, 2);
+	assert.deepEqual(calls[0], ['log', 'BASE..HEAD', '--format=%H', '--', 'a.ts']);
+});
+
+test('resolveLogins maps SHAs to logins in one call, dropping unlinked/bot authors', async () => {
+	let calls = 0;
+	const fetchFn = async (url, opts) => {
+		calls++;
+		assert.equal(url, 'https://api.github.com/graphql');
+		const query = JSON.parse(opts.body).query;
+		assert.match(query, /c0: object\(oid: "sha1"\)/);
+		assert.match(query, /c2: object\(oid: "sha3"\)/);
+		return {
+			ok: true,
+			json: async () => ({
+				data: {
+					repository: {
+						c0: { author: { user: { login: 'bob' } } },
+						c1: { author: { user: { login: 'alice' } } },
+						c2: { author: { user: null } }, // unlinked / bot -> dropped
+					},
+				},
+			}),
+		};
+	};
+	const owners = await resolveLogins('n8n-io/n8n', ['sha1', 'sha2', 'sha3'], 't', fetchFn);
+	assert.equal(calls, 1); // single batched request
+	assert.deepEqual(owners, ['alice', 'bob']); // sorted, deduped, null dropped
+});
+
+test('resolveLogins makes no request when there are no SHAs', async () => {
+	let calls = 0;
+	const fetchFn = async () => {
+		calls++;
+		return { ok: true, json: async () => ({ data: { repository: {} } }) };
+	};
+	assert.deepEqual(await resolveLogins('r', [], 't', fetchFn), []);
+	assert.equal(calls, 0);
+});
+
+test('resolveLogins throws on API/GraphQL errors (caller degrades gracefully)', async () => {
+	const httpError = async () => ({ ok: false, status: 502, json: async () => ({}) });
+	const gqlError = async () => ({ ok: true, json: async () => ({ errors: [{ message: 'bad' }] }) });
+	await assert.rejects(resolveLogins('r', ['s'], 't', httpError), /502/);
+	await assert.rejects(resolveLogins('r', ['s'], 't', gqlError), /GraphQL error/);
+});
+
+test('buildOutputs formats reviewers, slack line, and PR body with owners', () => {
+	const out = buildOutputs({ syncBranch: 'sync/master-to-3x', files: ['packages/cli/x.ts'], owners: ['alice', 'bob'] });
+	assert.equal(out.ownersCsv, 'alice,bob');
+	assert.equal(out.slack, 'Likely owners (GitHub): @alice @bob');
+	assert.match(out.body, /### Conflicted files/);
+	assert.match(out.body, /- `packages\/cli\/x\.ts`/);
+	assert.match(out.body, /- @alice/);
+	assert.match(out.body, /- @bob/);
+	assert.match(out.body, /Daily syncs are paused until it is merged/);
+});
+
+test('buildOutputs degrades gracefully when nothing could be attributed', () => {
+	const out = buildOutputs({ syncBranch: 'sync/master-to-3x', files: ['x.ts'], owners: [] });
+	assert.equal(out.ownersCsv, '');
+	assert.equal(out.slack, 'Could not auto-attribute owners.');
+	assert.match(out.body, /Could not auto-attribute/);
+});
diff --git a/.github/scripts/sync-master-to-3x.mjs b/.github/scripts/sync-master-to-3x.mjs
new file mode 100644
index 00000000000..befc86832ea
--- /dev/null
+++ b/.github/scripts/sync-master-to-3x.mjs
@@ -0,0 +1,171 @@
+#!/usr/bin/env node
+/**
+ * Syncs the master branch into the long-lived 3.x branch.
+ *
+ * During the v3 development window, master carries normal feature work (behind
+ * opt-in flags) and 3.x is "master + breaking-change commits". This script
+ * fast-forwards 3.x when possible, falls back to a three-way merge when 3.x has
+ * diverged, and — when a merge conflict occurs — opens a draft conflict PR,
+ * attributing it to the authors of the breaking commits. No further syncs run
+ * until that PR is resolved and merged (see the halt gate below).
+ *
+ * Runs from a checkout of the 3.x branch (fetch-depth 0). Assumes credentials
+ * are NOT persisted by checkout — pushes go through an explicit token URL.
+ *
+ * On conflict, emits `conflict_pr` and `conflict_owners` to $GITHUB_OUTPUT so a
+ * downstream job can post to Slack.
+ *
+ * Env: GH_TOKEN (installation token with contents/pull-requests/issues write),
+ *      GITHUB_REPOSITORY (owner/repo, auto-provided by Actions).
+ * Requires Node 18+ (global fetch) and the `gh` CLI on PATH.
+ *
+ * See .github/DEVELOPING_V3.md for the full v3 development model.
+ */
+
+import { execFileSync } from 'node:child_process';
+import { appendFileSync } from 'node:fs';
+
+import { conflictedFiles, breakingShas, resolveLogins, buildOutputs } from './sync-conflict-owners.mjs';
+
+export const TARGET_BRANCH = '3.x';
+export const SYNC_BRANCH = 'sync/master-to-3x';
+export const CONFLICT_LABEL = 'automation:v3-sync';
+
+const BOT_NAME = 'n8n-assistant[bot]';
+const BOT_EMAIL = 'n8n-assistant[bot]@users.noreply.github.com';
+
+// Real command runners. Each takes an args array and returns trimmed stdout,
+// throwing on a non-zero exit (mirrors `set -e`). Injectable for tests.
+const runGit = (args, opts = {}) => execFileSync('git', args, { encoding: 'utf8', ...opts }).trim();
+const runGh = (args, opts = {}) => execFileSync('gh', args, { encoding: 'utf8', ...opts }).trim();
+
+// True when a previous conflict PR is still open — the halt gate.
+export function hasOpenConflictPr(gh, label = CONFLICT_LABEL) {
+	const out = gh(['pr', 'list', '--state', 'open', '--label', label, '--json', 'number']);
+	return JSON.parse(out || '[]').length > 0;
+}
+
+// Attempt the merge. `git merge` fast-forwards when 3.x has not diverged and
+// does a three-way merge otherwise; a non-zero exit means a conflict.
+export function tryMerge(git, masterSha, log = console.log) {
+	try {
+		git(['merge', '--no-edit', masterSha]);
+		return true;
+	} catch (error) {
+		// Surface the merge output (conflict summary) before falling back.
+		if (error.stdout) log(String(error.stdout).trim());
+		return false;
+	}
+}
+
+// Append key=value lines to $GITHUB_OUTPUT (no-op when running outside Actions).
+export function writeGithubOutput(obj, env = process.env) {
+	const path = env.GITHUB_OUTPUT;
+	if (!path) return;
+	const lines = Object.entries(obj)
+		.map(([k, v]) => `${k}=${v ?? ''}`)
+		.join('\n');
+	appendFileSync(path, lines + '\n', 'utf8');
+}
+
+/**
+ * Record the conflicted state on the sync branch and open a draft PR, attributing
+ * it to the authors of the 3.x breaking commits touching the conflicted files.
+ * Runs while the merge is unresolved (HEAD still at the pre-merge 3.x tip,
+ * unmerged paths present) — before committing below.
+ *
+ * @returns {Promise<{ prUrl: string, ownersSlack: string }>}
+ */
+export async function openConflictPr({ git, gh, repo, token, masterSha, pushUrl, fetchFn = fetch, log = console.log }) {
+	const files = conflictedFiles(git);
+	const shas = breakingShas(masterSha, files, git);
+
+	// Degrade gracefully: a transient API failure should still open the PR
+	// (unattributed) rather than fail the whole sync.
+	let owners = [];
+	try {
+		owners = await resolveLogins(repo, shas, token, fetchFn);
+	} catch (error) {
+		log(`warning: could not resolve owners: ${error.message}`);
+	}
+
+	const { ownersCsv, slack, body } = buildOutputs({ syncBranch: SYNC_BRANCH, files, owners });
+
+	// Record the conflicted state (with markers) on the PR branch so it can be
+	// resolved in review, mirroring the backport conflict convention.
+	git(['add', '-A']);
+	git(['commit', '--no-edit']);
+	git(['push', '--force', pushUrl, `HEAD:refs/heads/${SYNC_BRANCH}`]);
+
+	// Ensure the label exists (idempotent), then open the draft conflict PR.
+	gh(['label', 'create', CONFLICT_LABEL, '--color', 'B60205', '--description', 'master→3.x sync conflict', '--force']);
+	const prUrl = gh([
+		'pr', 'create', '--draft',
+		'--base', TARGET_BRANCH,
+		'--head', SYNC_BRANCH,
+		'--label', CONFLICT_LABEL,
+		'--title', 'chore: Resolve master→3.x sync conflict',
+		'--body', body,
+	]);
+
+	// Request owners as reviewers (best-effort: the API rejects the PR author
+	// and non-collaborators, so a failure here must not fail the sync).
+	if (ownersCsv) {
+		try {
+			gh(['pr', 'edit', prUrl, '--add-reviewer', ownersCsv]);
+		} catch {
+			log(`::warning::could not request some reviewers: ${ownersCsv}`);
+		}
+	}
+
+	return { prUrl, ownersSlack: slack };
+}
+
+export async function sync({
+	git = runGit,
+	gh = runGh,
+	env = process.env,
+	fetchFn = fetch,
+	log = console.log,
+} = {}) {
+	const token = env.GH_TOKEN || env.GITHUB_TOKEN;
+	const repo = env.GITHUB_REPOSITORY;
+	if (!token) throw new Error('GH_TOKEN / GITHUB_TOKEN env var is required');
+	if (!repo) throw new Error('GITHUB_REPOSITORY env var is required');
+
+	// Authenticated push URL (credentials are not persisted by checkout).
+	const pushUrl = `https://x-access-token:${token}@github.com/${repo}.git`;
+
+	// Halt gate: if a previous conflict PR is still open, do nothing until it is
+	// resolved and merged.
+	if (hasOpenConflictPr(gh)) {
+		log(`An open '${CONFLICT_LABEL}' conflict PR exists; skipping sync until it is resolved and merged.`);
+		return;
+	}
+
+	git(['config', 'user.name', BOT_NAME]);
+	git(['config', 'user.email', BOT_EMAIL]);
+
+	git(['fetch', 'origin', 'master']);
+	// Pin to the fetched SHA — a command-line refspec doesn't reliably update the
+	// origin/master tracking ref, so FETCH_HEAD is the unambiguous target.
+	const masterSha = git(['rev-parse', 'FETCH_HEAD']);
+
+	if (tryMerge(git, masterSha, log)) {
+		git(['push', pushUrl, `HEAD:${TARGET_BRANCH}`]);
+		log('Synced master into 3.x.');
+		return;
+	}
+
+	log('Merge conflict encountered — attributing owners and opening a conflict PR.');
+	const { prUrl, ownersSlack } = await openConflictPr({ git, gh, repo, token, masterSha, pushUrl, fetchFn, log });
+	writeGithubOutput({ conflict_pr: prUrl, conflict_owners: ownersSlack }, env);
+}
+
+// Only run when executed directly, not when imported by tests.
+if (import.meta.url === `file://${process.argv[1]}`) {
+	sync().catch((error) => {
+		console.error(`Error: ${error.message}`);
+		process.exit(1);
+	});
+}
diff --git a/.github/scripts/sync-master-to-3x.test.mjs b/.github/scripts/sync-master-to-3x.test.mjs
new file mode 100644
index 00000000000..ff823274b98
--- /dev/null
+++ b/.github/scripts/sync-master-to-3x.test.mjs
@@ -0,0 +1,142 @@
+import assert from 'node:assert/strict';
+import { test } from 'node:test';
+
+import {
+	hasOpenConflictPr,
+	tryMerge,
+	openConflictPr,
+	sync,
+	CONFLICT_LABEL,
+	SYNC_BRANCH,
+	TARGET_BRANCH,
+} from './sync-master-to-3x.mjs';
+
+// A git/gh stub: routes calls by a matcher, records every invocation.
+function makeStub(routes = []) {
+	const calls = [];
+	const fn = (args) => {
+		calls.push(args);
+		for (const [match, result] of routes) {
+			if (match(args)) return typeof result === 'function' ? result(args) : result;
+		}
+		return '';
+	};
+	fn.calls = calls;
+	return fn;
+}
+
+const okFetch = (logins) => async () => ({
+	ok: true,
+	json: async () => ({ data: { repository: Object.fromEntries(logins.map((l, i) => [`c${i}`, { author: { user: { login: l } } }])) } }),
+});
+
+test('hasOpenConflictPr reflects the open-PR count from gh', () => {
+	const empty = makeStub([[() => true, '[]']]);
+	assert.equal(hasOpenConflictPr(empty), false);
+	assert.deepEqual(empty.calls[0], ['pr', 'list', '--state', 'open', '--label', CONFLICT_LABEL, '--json', 'number']);
+
+	const one = makeStub([[() => true, JSON.stringify([{ number: 42 }])]]);
+	assert.equal(hasOpenConflictPr(one), true);
+});
+
+test('tryMerge returns true when the merge succeeds', () => {
+	const git = makeStub([[(a) => a[0] === 'merge', '']]);
+	assert.equal(tryMerge(git, 'MASTER', () => {}), true);
+	assert.deepEqual(git.calls[0], ['merge', '--no-edit', 'MASTER']);
+});
+
+test('tryMerge returns false and logs merge output on conflict', () => {
+	const logged = [];
+	const git = () => {
+		const err = new Error('merge failed');
+		err.stdout = 'CONFLICT (content): x.ts\n';
+		throw err;
+	};
+	assert.equal(tryMerge(git, 'MASTER', (m) => logged.push(m)), false);
+	assert.match(logged.join('\n'), /CONFLICT/);
+});
+
+test('sync fast-forwards and pushes to 3.x on a clean merge', async () => {
+	const git = makeStub([
+		[(a) => a[0] === 'rev-parse', 'MASTERSHA'],
+		[(a) => a[0] === 'merge', ''],
+	]);
+	const gh = makeStub([[(a) => a[0] === 'pr' && a[1] === 'list', '[]']]);
+	const env = { GH_TOKEN: 'tok', GITHUB_REPOSITORY: 'n8n-io/n8n' };
+
+	await sync({ git, gh, env, log: () => {} });
+
+	const push = git.calls.find((a) => a[0] === 'push');
+	assert.ok(push, 'expected a push');
+	assert.equal(push[1], 'https://x-access-token:tok@github.com/n8n-io/n8n.git');
+	assert.equal(push[2], `HEAD:${TARGET_BRANCH}`);
+	// No PR created on a clean merge.
+	assert.equal(gh.calls.some((a) => a[0] === 'pr' && a[1] === 'create'), false);
+});
+
+test('sync halts (no fetch/merge) when a conflict PR is already open', async () => {
+	const git = makeStub();
+	const gh = makeStub([[(a) => a[0] === 'pr' && a[1] === 'list', JSON.stringify([{ number: 7 }])]]);
+
+	await sync({ git, gh, env: { GH_TOKEN: 't', GITHUB_REPOSITORY: 'n8n-io/n8n' }, log: () => {} });
+
+	assert.equal(git.calls.length, 0, 'must not touch git while halted');
+});
+
+test('sync opens a conflict PR and writes outputs on merge conflict', async () => {
+	const git = makeStub([
+		[(a) => a[0] === 'rev-parse', 'MASTERSHA'],
+		[(a) => a[0] === 'merge', () => { const e = new Error('conflict'); e.status = 1; throw e; }],
+		[(a) => a[0] === 'diff', 'packages/cli/x.ts'],
+		[(a) => a[0] === 'log', 'sha1'],
+	]);
+	const gh = makeStub([
+		[(a) => a[0] === 'pr' && a[1] === 'list', '[]'],
+		[(a) => a[0] === 'pr' && a[1] === 'create', 'https://github.com/n8n-io/n8n/pull/99'],
+	]);
+	// No GITHUB_OUTPUT set → writeGithubOutput no-ops; assert on the gh/git calls instead.
+	const env = { GH_TOKEN: 'tok', GITHUB_REPOSITORY: 'n8n-io/n8n' };
+
+	await sync({ git, gh, env, fetchFn: okFetch(['alice']), log: () => {} });
+
+	const create = gh.calls.find((a) => a[0] === 'pr' && a[1] === 'create');
+	assert.ok(create, 'expected a PR to be created');
+	assert.ok(create.includes('--draft'));
+	assert.equal(create[create.indexOf('--base') + 1], TARGET_BRANCH);
+	assert.equal(create[create.indexOf('--head') + 1], SYNC_BRANCH);
+
+	// Owner requested as reviewer.
+	const edit = gh.calls.find((a) => a[0] === 'pr' && a[1] === 'edit');
+	assert.ok(edit, 'expected reviewers to be requested');
+	assert.equal(edit[edit.indexOf('--add-reviewer') + 1], 'alice');
+
+	// Conflicted state force-pushed to the sync branch.
+	const push = git.calls.find((a) => a[0] === 'push' && a.includes('--force'));
+	assert.ok(push, 'expected a force push to the sync branch');
+	assert.equal(push.at(-1), `HEAD:refs/heads/${SYNC_BRANCH}`);
+});
+
+test('openConflictPr degrades gracefully when owner resolution fails', async () => {
+	const git = makeStub([
+		[(a) => a[0] === 'diff', 'x.ts'],
+		[(a) => a[0] === 'log', 'sha1'],
+	]);
+	const gh = makeStub([[(a) => a[0] === 'pr' && a[1] === 'create', 'https://github.com/n8n-io/n8n/pull/1']]);
+	const failingFetch = async () => ({ ok: false, status: 500, json: async () => ({}) });
+
+	const { prUrl, ownersSlack } = await openConflictPr({
+		git,
+		gh,
+		repo: 'n8n-io/n8n',
+		token: 't',
+		masterSha: 'MASTER',
+		pushUrl: 'https://push',
+		fetchFn: failingFetch,
+		log: () => {},
+	});
+
+	assert.equal(prUrl, 'https://github.com/n8n-io/n8n/pull/1');
+	assert.equal(ownersSlack, 'Could not auto-attribute owners.');
+	// No reviewer request when there are no owners.
+	assert.equal(gh.calls.some((a) => a[0] === 'pr' && a[1] === 'edit'), false);
+});
diff --git a/.github/workflows/build-v3-nightly.yml b/.github/workflows/build-v3-nightly.yml
new file mode 100644
index 00000000000..9889579707a
--- /dev/null
+++ b/.github/workflows/build-v3-nightly.yml
@@ -0,0 +1,46 @@
+# Builds and publishes nightly Docker images for the v3 (3.x) branch.
+#
+# Produces n8nio/n8n:v3-nightly and a timestamped n8nio/n8n:v3-nightly-<date>
+# (plus the matching runners images) so v3 can be trialed in docker/kubernetes
+# before release. Reuses the shared docker-build-push.yml pipeline, pointing it
+# at the 3.x branch via the `ref` input.
+#
+# Lives on master so the schedule fires (scheduled runs only trigger on the
+# default branch), but builds the 3.x branch's code.
+
+name: 'Build: v3 Nightly Docker Images'
+
+on:
+  schedule:
+    # 08:00 UTC — after the master→3.x sync (06:00) so the image reflects the latest sync
+    - cron: '0 8 * * *'
+  workflow_dispatch:
+
+jobs:
+  prepare:
+    name: Compute date tag
+    if: github.repository == 'n8n-io/n8n'
+    runs-on: ubuntu-latest
+    permissions: {}
+    outputs:
+      date_tag: ${{ steps.date.outputs.date }}
+    steps:
+      - name: Compute date tag
+        id: date
+        run: echo "date=$(date -u +%Y%m%d)" >> "$GITHUB_OUTPUT"
+
+  build:
+    name: Build and push v3-nightly images
+    needs: prepare
+    # No permissions/secrets caps here on purpose: this mirrors the proven
+    # release-publish.yml caller so docker-build-push.yml runs with the permissions
+    # (its own per-job blocks + repo defaults) and org secrets it already relies on.
+    # Capping here risks starving its sub-jobs (SLSA/attestation/scan/push).
+    uses: ./.github/workflows/docker-build-push.yml # zizmor: ignore[excessive-permissions,secrets-inherit]
+    with:
+      ref: '3.x'
+      n8n_version: 'v3-nightly'
+      release_type: 'nightly'
+      date_tag: ${{ needs.prepare.outputs.date_tag }}
+      push_enabled: true
+    secrets: inherit
diff --git a/.github/workflows/clean-stale-branches.yml b/.github/workflows/clean-stale-branches.yml
index c89adb63e58..016a8a2a15e 100644
--- a/.github/workflows/clean-stale-branches.yml
+++ b/.github/workflows/clean-stale-branches.yml
@@ -41,5 +41,7 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ github.token }}
           STALE_DAYS: ${{ inputs.days || '100' }}
-          EXCLUDE_BRANCHES: ${{ inputs.exclude || '' }}
+          # Long-lived major branches are also protected by their deletion rulesets;
+          # this static keep-list is a safety net for scheduled runs (which pass no exclude input).
+          EXCLUDE_BRANCHES: ${{ inputs.exclude || '1.x,3.x' }}
         run: node .github/scripts/stale/clean-stale-branches.mjs --days="$STALE_DAYS" ${{ !inputs.dry-run && '--execute' || '--dry-run' }}
diff --git a/.github/workflows/docker-build-push.yml b/.github/workflows/docker-build-push.yml
index cb8867a11a7..487ce21b6a4 100644
--- a/.github/workflows/docker-build-push.yml
+++ b/.github/workflows/docker-build-push.yml
@@ -29,6 +29,16 @@ on:
         required: false
         type: boolean
         default: true
+      ref:
+        description: 'Git ref (branch/tag/sha) to build from. Empty checks out the triggering ref.'
+        required: false
+        type: string
+        default: ''
+      date_tag:
+        description: 'Optional date suffix for an extra <version>-<date> tag (e.g. 20260625)'
+        required: false
+        type: string
+        default: ''
 
   workflow_dispatch:
     inputs:
@@ -52,9 +62,18 @@ jobs:
       push_enabled: ${{ steps.context.outputs.push_enabled }}
       push_to_docker: ${{ steps.context.outputs.push_to_docker }}
       build_matrix: ${{ steps.context.outputs.build_matrix }}
+      short_sha: ${{ steps.sha.outputs.short_sha }}
     steps:
       - name: Checkout code
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          ref: ${{ inputs.ref }}
+
+      - name: Resolve built commit SHA
+        id: sha
+        # From the checked-out working tree (honours `ref`), not GITHUB_SHA — which
+        # is the triggering ref (e.g. master) and would mislabel a ref-override build.
+        run: echo "short_sha=$(git rev-parse --short=7 HEAD)" >> "$GITHUB_OUTPUT"
 
       - name: Determine build context
         id: context
@@ -87,10 +106,14 @@ jobs:
       n8n_sha_manifest_tag: ${{ steps.determine-tags.outputs.n8n_sha_primary_tag }}
       runners_sha_manifest_tag: ${{ steps.determine-tags.outputs.runners_sha_primary_tag }}
       runners_distroless_sha_manifest_tag: ${{ steps.determine-tags.outputs.runners_distroless_sha_primary_tag }}
+      n8n_date_manifest_tag: ${{ steps.determine-tags.outputs.n8n_date_primary_tag }}
+      runners_date_manifest_tag: ${{ steps.determine-tags.outputs.runners_date_primary_tag }}
+      runners_distroless_date_manifest_tag: ${{ steps.determine-tags.outputs.runners_distroless_date_primary_tag }}
     steps:
       - name: Checkout code
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
+          ref: ${{ inputs.ref }}
           fetch-depth: 0
 
       - name: Setup and Build
@@ -104,12 +127,21 @@ jobs:
 
       - name: Determine Docker tags for all images
         id: determine-tags
+        env:
+          DATE_TAG: ${{ inputs.date_tag }}
+          SHORT_SHA: ${{ needs.determine-build-context.outputs.short_sha }}
         run: |
+          # Build the optional --date flag in shell (not via a template expansion) so
+          # the caller-supplied input never expands directly into the command line.
+          DATE_ARGS=()
+          if [ -n "${DATE_TAG:-}" ]; then DATE_ARGS=(--date "$DATE_TAG"); fi
+
           node .github/scripts/docker/docker-tags.mjs \
             --all \
             --version "${{ needs.determine-build-context.outputs.n8n_version }}" \
             --platform "${{ matrix.docker_platform }}" \
-            --sha "${GITHUB_SHA::7}" \
+            --sha "$SHORT_SHA" \
+            "${DATE_ARGS[@]}" \
             ${{ needs.determine-build-context.outputs.push_to_docker == 'true' && '--include-docker' || '' }}
 
           echo "=== Generated Docker Tags ==="
@@ -204,6 +236,10 @@ jobs:
           dockerhub-password: ${{ secrets.DOCKER_PASSWORD }}
 
       - name: Create GHCR multi-arch manifests
+        env:
+          N8N_DATE_MANIFEST_TAG: ${{ needs.build-and-push-docker.outputs.n8n_date_manifest_tag }}
+          RUNNERS_DATE_MANIFEST_TAG: ${{ needs.build-and-push-docker.outputs.runners_date_manifest_tag }}
+          RUNNERS_DISTROLESS_DATE_MANIFEST_TAG: ${{ needs.build-and-push-docker.outputs.runners_distroless_date_manifest_tag }}
         run: |
           RELEASE_TYPE="${{ needs.determine-build-context.outputs.release_type }}"
 
@@ -242,10 +278,19 @@ jobs:
           create_manifest "runners (sha)" "${{ needs.build-and-push-docker.outputs.runners_sha_manifest_tag }}"
           create_manifest "runners-distroless (sha)" "${{ needs.build-and-push-docker.outputs.runners_distroless_sha_manifest_tag }}"
 
+          # Create date-tagged manifests. The *_DATE_MANIFEST_TAG vars are empty unless the
+          # date_tag input was set (e.g. nightly), and create_manifest skips empty tags —
+          # so these calls are no-ops on non-dated builds.
+          create_manifest "n8n (date)" "$N8N_DATE_MANIFEST_TAG"
+          create_manifest "runners (date)" "$RUNNERS_DATE_MANIFEST_TAG"
+          create_manifest "runners-distroless (date)" "$RUNNERS_DISTROLESS_DATE_MANIFEST_TAG"
+
       - name: Create Docker Hub manifests
         if: needs.determine-build-context.outputs.push_to_docker == 'true'
         env:
           DOCKER_USERNAME: ${{ secrets.DOCKER_USERNAME }}
+          DATE_TAG: ${{ inputs.date_tag }}
+          SHORT_SHA: ${{ needs.determine-build-context.outputs.short_sha }}
         run: |
           VERSION="${{ needs.determine-build-context.outputs.n8n_version }}"
           DOCKER_BASE="$DOCKER_USERNAME"
@@ -257,8 +302,6 @@ jobs:
             ["runners-distroless"]="${VERSION}-distroless"
           )
 
-          SHORT_SHA="${GITHUB_SHA::7}"
-
           for image in "${!images[@]}"; do
             TAG_SUFFIX="${images[$image]}"
             IMAGE_NAME="${image//-distroless/}"  # Remove -distroless from image name
@@ -282,6 +325,21 @@ jobs:
               --tag "${DOCKER_BASE}/${IMAGE_NAME}:${SHA_SUFFIX}" \
               "${DOCKER_BASE}/${IMAGE_NAME}:${SHA_SUFFIX}-amd64" \
               "${DOCKER_BASE}/${IMAGE_NAME}:${SHA_SUFFIX}-arm64"
+
+            # Create date-tagged manifest when a date suffix was provided (e.g. v3-nightly-20260625)
+            # Mirrors the SHA suffix placement: <version>-<date> and <version>-<date>-distroless
+            if [[ -n "$DATE_TAG" ]]; then
+              if [[ "$image" == *"-distroless"* ]]; then
+                DATE_SUFFIX="${VERSION}-${DATE_TAG}-distroless"
+              else
+                DATE_SUFFIX="${TAG_SUFFIX}-${DATE_TAG}"
+              fi
+              echo "Creating Docker Hub date manifest for $image: ${DATE_SUFFIX}"
+              docker buildx imagetools create \
+                --tag "${DOCKER_BASE}/${IMAGE_NAME}:${DATE_SUFFIX}" \
+                "${DOCKER_BASE}/${IMAGE_NAME}:${DATE_SUFFIX}-amd64" \
+                "${DOCKER_BASE}/${IMAGE_NAME}:${DATE_SUFFIX}-arm64"
+            fi
           done
 
       - name: Get manifest digests for attestation
diff --git a/.github/workflows/util-sync-master-to-3x.yml b/.github/workflows/util-sync-master-to-3x.yml
new file mode 100644
index 00000000000..f56490c2291
--- /dev/null
+++ b/.github/workflows/util-sync-master-to-3x.yml
@@ -0,0 +1,105 @@
+# Syncs the master branch into the long-lived 3.x branch daily.
+#
+# During the v3 development window, master carries normal feature work (behind
+# opt-in flags) and 3.x is "master + breaking-change commits". This workflow
+# fast-forwards 3.x when possible, falls back to a three-way merge when 3.x has
+# diverged, and — when a merge conflict occurs — opens a draft conflict PR and
+# posts to #alerts-v3-sync. No further syncs run until that PR is resolved and merged.
+#
+# See .github/DEVELOPING_V3.md for the full v3 development model.
+
+name: 'Util: Sync master to 3.x'
+
+on:
+  schedule:
+    - cron: '0 6 * * *'
+  workflow_dispatch:
+
+# Serialize syncs — never run two at once.
+concurrency:
+  group: sync-master-to-3x
+  cancel-in-progress: false
+
+# Least privilege by default; each job opts into exactly what it needs.
+permissions: {}
+
+jobs:
+  sync:
+    name: Sync master into 3.x
+    if: github.repository == 'n8n-io/n8n'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      pull-requests: write
+    outputs:
+      conflict_pr: ${{ steps.sync.outputs.conflict_pr }}
+      conflict_owners: ${{ steps.sync.outputs.conflict_owners }}
+    steps:
+      - name: Generate GitHub App Token
+        id: app-token
+        uses: actions/create-github-app-token@29824e69f54612133e76f7eaac726eef6c875baf # v2.2.1
+        with:
+          app-id: ${{ secrets.N8N_ASSISTANT_APP_ID }}
+          private-key: ${{ secrets.N8N_ASSISTANT_PRIVATE_KEY }}
+          # Scope the installation token to only what the sync needs.
+          permission-contents: write # push to 3.x / the conflict branch
+          permission-pull-requests: write # open the conflict PR
+          permission-issues: write # create the conflict label
+
+      - name: Checkout 3.x
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          ref: 3.x
+          fetch-depth: 0
+          persist-credentials: false # we push with an explicit token URL instead
+
+      - name: Sync master into 3.x
+        id: sync
+        env:
+          GH_TOKEN: ${{ steps.app-token.outputs.token }}
+        run: node .github/scripts/sync-master-to-3x.mjs
+
+  notify-conflict:
+    name: Notify Slack about conflict PR
+    needs: [sync]
+    if: ${{ needs.sync.outputs.conflict_pr != '' }}
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read # checkout the slack scripts
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          sparse-checkout: .github/scripts/slack
+          sparse-checkout-cone-mode: false
+          persist-credentials: false
+      - name: Notify Slack
+        env:
+          SLACK_TOKEN: ${{ secrets.QBOT_SLACK_TOKEN }}
+          PR_URL: ${{ needs.sync.outputs.conflict_pr }}
+          OWNERS_TEXT: ${{ needs.sync.outputs.conflict_owners }}
+        run: |
+          node .github/scripts/slack/notify.mjs \
+            --channel '#alerts-v3-sync' \
+            --text "<${PR_URL}|master→3.x sync hit a conflict — resolve this PR>. Daily syncs are paused until it is merged. ${OWNERS_TEXT}"
+
+  notify-on-failure:
+    name: Notify Slack on failure
+    needs: [sync]
+    if: ${{ always() && needs.sync.result == 'failure' }}
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read # checkout the slack scripts
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        with:
+          sparse-checkout: .github/scripts/slack
+          sparse-checkout-cone-mode: false
+          persist-credentials: false
+      - name: Notify Slack
+        env:
+          SLACK_TOKEN: ${{ secrets.QBOT_SLACK_TOKEN }}
+          RUN_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
+        run: |
+          node .github/scripts/slack/notify.mjs \
+            --channel '#alerts-v3-sync' \
+            --text "<${RUN_URL}|master→3.x sync workflow failed unexpectedly>"
diff --git a/AGENTS.md b/AGENTS.md
index ca458142d4c..0310108cb21 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -22,6 +22,9 @@ frontend, and extensible node-based workflow engine.
   suggested by Linear, **unless it is a security fix** (see Security Fix
   Hygiene below)
 - Use mermaid diagrams in MD files when you need to visualise something
+- **Developing v3 features:** land normal feature work on `master` behind an
+  opt-in flag; introduce breaking changes only on the `3.x` branch. See
+  [.github/DEVELOPING_V3.md](.github/DEVELOPING_V3.md).
 
 ## Agent Skills and Claude Code Plugin