feat: moderation locking (#5070)

* feat: base locking impl

* feat: lock logic in place in rev endpoint + fetch rev

* feat: frontend impl and finalize

* feat: auto skip if using the moderation queue page

* fix: qa issues

* fix: async state + locking fix

* fix: lint

* fix: fmt

* fix: qa issue

* fix: qa + redirect bug

* fix: lint

* feat: delete all locks endpoint for admins

* fix: dedupe

* fix: fmt

* fix: project redirect move to middleware

* fix: lint

apps/frontend/nuxt.config.ts

@@ -311,7 +311,7 @@ export default defineNuxtConfig({
 	compatibilityDate: '2025-01-01',
 	telemetry: false,
 	experimental: {
-		asyncContext: true,
+		asyncContext: isProduction(),
 	},
 })
 

apps/frontend/src/components/ui/moderation/ModerationQueueCard.vue

@@ -127,11 +127,9 @@ import dayjs from 'dayjs'
 import { computed } from 'vue'
 
 import type { ModerationProject } from '~/helpers/moderation'
-import { useModerationStore } from '~/store/moderation.ts'
 
 const { addNotification } = injectNotificationManager()
 const formatRelativeTime = useRelativeTime()
-const moderationStore = useModerationStore()
 
 const baseId = useId()
 
@@ -139,6 +137,10 @@ const props = defineProps<{
 	queueEntry: ModerationProject
 }>()
 
+const emit = defineEmits<{
+	startFromProject: [projectId: string]
+}>()
+
 function getDaysQueued(date: Date): number {
 	const now = new Date()
 	const diff = now.getTime() - date.getTime()
@@ -201,16 +203,6 @@ const quickActions: OverflowMenuOption[] = [
 ]
 
 function openProjectForReview() {
-	moderationStore.setSingleProject(props.queueEntry.project.id)
-	navigateTo({
-		name: 'type-id',
-		params: {
-			type: 'project',
-			id: props.queueEntry.project.slug || props.queueEntry.project.id,
-		},
-		state: {
-			showChecklist: true,
-		},
-	})
+	emit('startFromProject', props.queueEntry.project.id)
 }
 </script>

apps/frontend/src/middleware/project-canonicalize.global.ts

@@ -0,0 +1,56 @@
+import { getProjectTypeForUrlShorthand } from '~/helpers/projects.js'
+import { useServerModrinthClient } from '~/server/utils/api-client'
+
+// All valid project type URL segments
+const PROJECT_TYPES = ['project', 'mod', 'plugin', 'datapack', 'shader', 'resourcepack', 'modpack']
+
+export default defineNuxtRouteMiddleware(async (to) => {
+	// Only handle project routes
+	if (!to.params.id || !PROJECT_TYPES.includes(to.params.type as string)) {
+		return
+	}
+
+	const authToken = useCookie('auth-token')
+	const client = useServerModrinthClient({ authToken: authToken.value || undefined })
+	const tags = useGeneratedState()
+
+	try {
+		const project = await client.labrinth.projects_v2.get(to.params.id as string)
+
+		if (!project) {
+			return
+		}
+
+		// Determine the correct URL type
+		const correctType = getProjectTypeForUrlShorthand(
+			project.project_type,
+			project.loaders,
+			tags.value,
+		)
+
+		// Preserve the rest of the path (subpages like /versions, /settings, etc.)
+		const pathParts = to.path.split('/')
+		pathParts.splice(0, 3) // Remove '', type, and id
+		const remainder = pathParts.filter((x) => x).join('/')
+
+		// Build the canonical path
+		const canonicalPath = `/${correctType}/${project.slug}${remainder ? `/${remainder}` : ''}`
+
+		// Only redirect if the path actually changed
+		if (to.path !== canonicalPath) {
+			return navigateTo(
+				{
+					path: canonicalPath,
+					query: to.query,
+					hash: to.hash,
+				},
+				{
+					redirectCode: 301,
+					replace: true,
+				},
+			)
+		}
+	} catch {
+		// Let the page handle 404s and other errors
+	}
+})

apps/frontend/src/pages/[type]/[id].vue

@@ -1019,8 +1019,12 @@ import { userCollectProject, userFollowProject } from '~/composables/user.js'
 import { useModerationStore } from '~/store/moderation.ts'
 import { reportProject } from '~/utils/report-helpers.ts'
 
+definePageMeta({
+	key: (route) => route.fullPath,
+})
+
 const data = useNuxtApp()
-const route = useNativeRoute()
+const route = useRoute()
 const config = useRuntimeConfig()
 const moderationStore = useModerationStore()
 const notifications = injectNotificationManager()
@@ -1539,8 +1543,6 @@ try {
 		),
 	])
 
-	await updateProjectRoute()
-
 	versions = shallowRef(toRaw(versions))
 	versionsV3 = shallowRef(toRaw(versionsV3))
 	versions.value = (versions.value ?? []).map((v) => ({
@@ -1621,22 +1623,6 @@ if (!project.value) {
 	})
 }
 
-if (
-	project.value.project_type !== route.params.type ||
-	(route.params.id !== project.value.slug && !flags.value.disablePrettyProjectUrlRedirects)
-) {
-	let path = route.fullPath.split('/')
-	path.splice(0, 3)
-	path = path.filter((x) => x)
-
-	await navigateTo(
-		`/${project.value.project_type}/${project.value.slug}${
-			path.length > 0 ? `/${path.join('/')}` : ''
-		}`,
-		{ redirectCode: 301, replace: true },
-	)
-}
-
 // Members should be an array of all members, without the accepted ones, and with the user with the Owner role at the start
 // The rest of the members should be sorted by role, then by name
 const members = computed(() => {

apps/frontend/src/pages/moderation/index.vue

@@ -89,6 +89,7 @@
 				:queue-entry="item"
 				:owner="item.owner"
 				:org="item.org"
+				@start-from-project="startFromProject"
 			/>
 		</div>
 
@@ -112,6 +113,7 @@ import {
 	Combobox,
 	type ComboboxOption,
 	defineMessages,
+	injectNotificationManager,
 	Pagination,
 	useVIntl,
 } from '@modrinth/ui'
@@ -123,6 +125,7 @@ import { enrichProjectBatch, type ModerationProject } from '~/helpers/moderation
 import { useModerationStore } from '~/store/moderation.ts'
 
 const { formatMessage } = useVIntl()
+const { addNotification } = injectNotificationManager()
 const moderationStore = useModerationStore()
 const route = useRoute()
 const router = useRouter()
@@ -342,13 +345,105 @@ function goToPage(page: number) {
 	currentPage.value = page
 }
 
-function moderateAllInFilter() {
-	moderationStore.setQueue(filteredProjects.value.map((queueItem) => queueItem.project.id))
+async function findFirstUnlockedProject(): Promise<ModerationProject | null> {
+	let skippedCount = 0
+
+	while (moderationStore.hasItems) {
+		const currentId = moderationStore.getCurrentProjectId()
+		if (!currentId) return null
+
+		const project = filteredProjects.value.find((p) => p.project.id === currentId)
+		if (!project) {
+			moderationStore.completeCurrentProject(currentId, 'skipped')
+			continue
+		}
+
+		try {
+			const lockStatus = await moderationStore.checkLock(currentId)
+
+			if (!lockStatus.locked || lockStatus.expired) {
+				if (skippedCount > 0) {
+					addNotification({
+						title: 'Skipped locked projects',
+						text: `Skipped ${skippedCount} project(s) being moderated by others.`,
+						type: 'info',
+					})
+				}
+				return project
+			}
+
+			// Project is locked, skip it
+			moderationStore.completeCurrentProject(currentId, 'skipped')
+			skippedCount++
+		} catch {
+			return project
+		}
+	}
+
+	return null
+}
+
+async function moderateAllInFilter() {
+	// Start from the current page - get projects from current page onwards
+	const startIndex = (currentPage.value - 1) * itemsPerPage
+	const projectsFromCurrentPage = filteredProjects.value.slice(startIndex)
+	const projectIds = projectsFromCurrentPage.map((queueItem) => queueItem.project.id)
+	moderationStore.setQueue(projectIds)
+
+	// Find first unlocked project
+	const targetProject = await findFirstUnlockedProject()
+
+	if (!targetProject) {
+		addNotification({
+			title: 'All projects locked',
+			text: 'All projects in queue are currently being moderated by others.',
+			type: 'warning',
+		})
+		return
+	}
+
 	navigateTo({
 		name: 'type-id',
 		params: {
 			type: 'project',
-			id: moderationStore.getCurrentProjectId(),
+			id: targetProject.project.slug,
+		},
+		state: {
+			showChecklist: true,
+		},
+	})
+}
+
+async function startFromProject(projectId: string) {
+	// Find the index of the clicked project in the filtered list
+	const projectIndex = filteredProjects.value.findIndex((p) => p.project.id === projectId)
+	if (projectIndex === -1) {
+		// Project not found in filtered list, just moderate it alone
+		moderationStore.setSingleProject(projectId)
+	} else {
+		// Start queue from this project onwards
+		const projectsFromHere = filteredProjects.value.slice(projectIndex)
+		const projectIds = projectsFromHere.map((queueItem) => queueItem.project.id)
+		moderationStore.setQueue(projectIds)
+	}
+
+	// Find first unlocked project
+	const targetProject = await findFirstUnlockedProject()
+
+	if (!targetProject) {
+		addNotification({
+			title: 'All projects locked',
+			text: 'All projects in queue are currently being moderated by others.',
+			type: 'warning',
+		})
+		return
+	}
+
+	navigateTo({
+		name: 'type-id',
+		params: {
+			type: 'project',
+			id: targetProject.project.slug,
 		},
 		state: {
 			showChecklist: true,

apps/frontend/src/server/routes/api/tags/game-versions.ts

@@ -6,7 +6,7 @@ const CACHE_MAX_AGE = 60 * 10 // 10 minutes
 
 export default defineCachedEventHandler(
 	async (event) => {
-		const client = useServerModrinthClient(event)
+		const client = useServerModrinthClient({ event })
 
 		const response = await client.request<Labrinth.Tags.v2.GameVersion[]>('/tag/game_version', {
 			api: 'labrinth',

apps/frontend/src/server/utils/api-client.ts

@@ -1,4 +1,4 @@
-import { type NuxtClientConfig, NuxtModrinthClient } from '@modrinth/api-client'
+import { AuthFeature, type NuxtClientConfig, NuxtModrinthClient } from '@modrinth/api-client'
 import type { H3Event } from 'h3'
 
 async function getRateLimitKeyFromSecretsStore(): Promise<string | undefined> {
@@ -11,14 +11,30 @@ async function getRateLimitKeyFromSecretsStore(): Promise<string | undefined> {
 	}
 }
 
-export function useServerModrinthClient(event: H3Event): NuxtModrinthClient {
-	const config = useRuntimeConfig(event)
+export interface ServerModrinthClientOptions {
+	event?: H3Event
+	authToken?: string
+}
+
+export function useServerModrinthClient(options?: ServerModrinthClientOptions): NuxtModrinthClient {
+	const config = useRuntimeConfig(options?.event)
 	const apiBaseUrl = (config.apiBaseUrl || config.public.apiBaseUrl).replace('/v2/', '/')
 
+	const features = []
+
+	if (options?.authToken) {
+		features.push(
+			new AuthFeature({
+				token: options.authToken,
+				tokenPrefix: '',
+			}),
+		)
+	}
+
 	const clientConfig: NuxtClientConfig = {
 		labrinthBaseUrl: apiBaseUrl,
 		rateLimitKey: config.rateLimitKey || getRateLimitKeyFromSecretsStore,
-		features: [],
+		features,
 	}
 
 	return new NuxtModrinthClient(clientConfig)

apps/frontend/src/store/moderation.ts

@@ -9,6 +9,26 @@ export interface ModerationQueue {
 	lastUpdated: Date
 }
 
+export interface LockedByUser {
+	id: string
+	username: string
+	avatar_url?: string
+}
+
+export interface LockStatusResponse {
+	locked: boolean
+	locked_by?: LockedByUser
+	locked_at?: string
+	expired?: boolean
+}
+
+export interface LockAcquireResponse {
+	success: boolean
+	locked_by?: LockedByUser
+	locked_at?: string
+	expired?: boolean
+}
+
 const EMPTY_QUEUE: Partial<ModerationQueue> = {
 	items: [],
 
@@ -28,6 +48,8 @@ pinia.use(piniaPluginPersistedstate)
 export const useModerationStore = defineStore('moderation', {
 	state: () => ({
 		currentQueue: createEmptyQueue(),
+		currentLock: null as { projectId: string; lockedAt: Date } | null,
+		isQueueMode: false,
 	}),
 
 	getters: {
@@ -41,6 +63,7 @@ export const useModerationStore = defineStore('moderation', {
 
 	actions: {
 		setQueue(projectIDs: string[]) {
+			this.isQueueMode = true
 			this.currentQueue = {
 				items: [...projectIDs],
 				total: projectIDs.length,
@@ -51,6 +74,7 @@ export const useModerationStore = defineStore('moderation', {
 		},
 
 		setSingleProject(projectId: string) {
+			this.isQueueMode = false
 			this.currentQueue = {
 				items: [projectId],
 				total: 1,
@@ -78,8 +102,71 @@ export const useModerationStore = defineStore('moderation', {
 		},
 
 		resetQueue() {
+			this.isQueueMode = false
 			this.currentQueue = createEmptyQueue()
 		},
+
+		async acquireLock(projectId: string): Promise<LockAcquireResponse> {
+			try {
+				const response = (await useBaseFetch(`moderation/lock/${projectId}`, {
+					method: 'POST',
+					internal: true,
+				})) as LockAcquireResponse
+
+				if (response.success) {
+					this.currentLock = { projectId, lockedAt: new Date() }
+				}
+
+				return response
+			} catch (error) {
+				console.error('Failed to acquire moderation lock:', error)
+				// Return a failed response so the UI can handle it gracefully
+				return { success: false }
+			}
+		},
+
+		async releaseLock(projectId: string): Promise<boolean> {
+			try {
+				const response = (await useBaseFetch(`moderation/lock/${projectId}`, {
+					method: 'DELETE',
+					internal: true,
+				})) as { success: boolean }
+
+				if (this.currentLock?.projectId === projectId) {
+					this.currentLock = null
+				}
+
+				return response.success
+			} catch {
+				return false
+			}
+		},
+
+		async checkLock(projectId: string): Promise<LockStatusResponse> {
+			try {
+				const response = (await useBaseFetch(`moderation/lock/${projectId}`, {
+					method: 'GET',
+					internal: true,
+				})) as LockStatusResponse
+				return response
+			} catch (error) {
+				console.error('Failed to check moderation lock:', error)
+				// Return unlocked status on error so moderation can proceed
+				return { locked: false }
+			}
+		},
+
+		async refreshLock(): Promise<boolean> {
+			if (!this.currentLock) return false
+
+			try {
+				const response = await this.acquireLock(this.currentLock.projectId)
+				return response.success
+			} catch (error) {
+				console.error('Failed to refresh moderation lock:', error)
+				return false
+			}
+		},
 	},
 
 	persist: {

apps/labrinth/.sqlx/query-15ce2cf3154ba3358461b375504ca2de7f5b8b742c0196e71ab2139174fcc12f.json

@@ -0,0 +1,46 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n\t\t\tSELECT\n\t\t\t\tml.project_id,\n\t\t\t\tml.moderator_id,\n\t\t\t\tu.username as moderator_username,\n\t\t\t\tu.avatar_url as moderator_avatar_url,\n\t\t\t\tml.locked_at\n\t\t\tFROM moderation_locks ml\n\t\t\tINNER JOIN users u ON u.id = ml.moderator_id\n\t\t\tWHERE ml.project_id = $1\n\t\t\t",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "project_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 1,
+        "name": "moderator_id",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 2,
+        "name": "moderator_username",
+        "type_info": "Varchar"
+      },
+      {
+        "ordinal": 3,
+        "name": "moderator_avatar_url",
+        "type_info": "Varchar"
+      },
+      {
+        "ordinal": 4,
+        "name": "locked_at",
+        "type_info": "Timestamptz"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Int8"
+      ]
+    },
+    "nullable": [
+      false,
+      false,
+      false,
+      true,
+      false
+    ]
+  },
+  "hash": "15ce2cf3154ba3358461b375504ca2de7f5b8b742c0196e71ab2139174fcc12f"
+}

apps/labrinth/.sqlx/query-420453c85418f57da3f89396b0625b98efbb2f38fb2d113c2f894481f41dc24c.json

@@ -0,0 +1,14 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "UPDATE moderation_locks SET locked_at = NOW() WHERE project_id = $1",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Int8"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "420453c85418f57da3f89396b0625b98efbb2f38fb2d113c2f894481f41dc24c"
+}

apps/labrinth/.sqlx/query-47df2d46f068e3158387ac8928238fecfa2d81d93bc72602d14be0c61c1195e5.json

@@ -0,0 +1,15 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "DELETE FROM moderation_locks WHERE project_id = $1 AND moderator_id = $2",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Int8",
+        "Int8"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "47df2d46f068e3158387ac8928238fecfa2d81d93bc72602d14be0c61c1195e5"
+}

apps/labrinth/.sqlx/query-60ee89bff8241dd00a1aa33d072cb8b78a9b5d935097391247b0c14fa25f1118.json

@@ -0,0 +1,12 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "DELETE FROM moderation_locks",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": []
+    },
+    "nullable": []
+  },
+  "hash": "60ee89bff8241dd00a1aa33d072cb8b78a9b5d935097391247b0c14fa25f1118"
+}

apps/labrinth/.sqlx/query-72c050caf23ce0e7d9f2dbe2eca92147c88570ba9757a8204861187f0da7dbb1.json

@@ -0,0 +1,15 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "UPDATE moderation_locks SET moderator_id = $1, locked_at = NOW() WHERE project_id = $2",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Int8",
+        "Int8"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "72c050caf23ce0e7d9f2dbe2eca92147c88570ba9757a8204861187f0da7dbb1"
+}

apps/labrinth/.sqlx/query-834f4aca2ff23ccd041cd1028145561f625e7edfadb21f89a41d0c16cd25763a.json

@@ -0,0 +1,15 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "INSERT INTO moderation_locks (project_id, moderator_id, locked_at)\n\t\t\tVALUES ($1, $2, NOW())\n\t\t\tON CONFLICT (project_id) DO UPDATE\n\t\t\tSET moderator_id = EXCLUDED.moderator_id, locked_at = EXCLUDED.locked_at",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "Int8",
+        "Int8"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "834f4aca2ff23ccd041cd1028145561f625e7edfadb21f89a41d0c16cd25763a"
+}

apps/labrinth/.sqlx/query-e5a83a4d578f76e6e3298054960368931e5f711c6ce4e4af6b0ad523600da425.json

@@ -0,0 +1,12 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "DELETE FROM moderation_locks WHERE locked_at < NOW() - INTERVAL '15 minutes'",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": []
+    },
+    "nullable": []
+  },
+  "hash": "e5a83a4d578f76e6e3298054960368931e5f711c6ce4e4af6b0ad523600da425"
+}

apps/labrinth/migrations/20260106225635_moderation_locks.sql

@@ -0,0 +1,8 @@
+CREATE TABLE moderation_locks (
+	project_id BIGINT PRIMARY KEY REFERENCES mods(id) ON DELETE CASCADE,
+	moderator_id BIGINT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+	locked_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP NOT NULL
+);
+
+CREATE INDEX idx_moderation_locks_moderator ON moderation_locks(moderator_id);
+CREATE INDEX idx_moderation_locks_locked_at ON moderation_locks(locked_at);

apps/labrinth/src/database/models/mod.rs

@@ -11,6 +11,7 @@ pub mod ids;
 pub mod image_item;
 pub mod legacy_loader_fields;
 pub mod loader_fields;
+pub mod moderation_lock_item;
 pub mod notification_item;
 pub mod notifications_deliveries_item;
 pub mod notifications_template_item;
@@ -53,6 +54,8 @@ pub use thread_item::{DBThread, DBThreadMessage};
 pub use user_item::DBUser;
 pub use version_item::DBVersion;
 
+pub use moderation_lock_item::{DBModerationLock, ModerationLockWithUser};
+
 #[derive(Error, Debug)]
 pub enum DatabaseError {
     #[error("Error while interacting with the database: {0}")]

apps/labrinth/src/database/models/moderation_lock_item.rs

@@ -0,0 +1,163 @@
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use sqlx::PgPool;
+
+use crate::database::models::{DBProjectId, DBUserId};
+
+const LOCK_EXPIRY_MINUTES: i64 = 15;
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct DBModerationLock {
+    pub project_id: DBProjectId,
+    pub moderator_id: DBUserId,
+    pub locked_at: DateTime<Utc>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ModerationLockWithUser {
+    pub project_id: DBProjectId,
+    pub moderator_id: DBUserId,
+    pub moderator_username: String,
+    pub moderator_avatar_url: Option<String>,
+    pub locked_at: DateTime<Utc>,
+    pub expired: bool,
+}
+
+impl DBModerationLock {
+    /// Check if a lock is expired (older than 15 minutes)
+    pub fn is_expired(&self) -> bool {
+        Utc::now()
+            .signed_duration_since(self.locked_at)
+            .num_minutes()
+            >= LOCK_EXPIRY_MINUTES
+    }
+
+    /// Try to acquire or refresh a lock for a project.
+    /// Returns Ok(Ok(())) if lock acquired/refreshed, Ok(Err(lock)) if blocked by another moderator.
+    pub async fn acquire(
+        project_id: DBProjectId,
+        moderator_id: DBUserId,
+        pool: &PgPool,
+    ) -> Result<Result<(), ModerationLockWithUser>, sqlx::Error> {
+        // First check if there's an existing lock
+        let existing = Self::get_with_user(project_id, pool).await?;
+
+        if let Some(lock) = existing {
+            // Same moderator - refresh the lock
+            if lock.moderator_id == moderator_id {
+                sqlx::query!(
+					"UPDATE moderation_locks SET locked_at = NOW() WHERE project_id = $1",
+					project_id as DBProjectId
+				)
+				.execute(pool)
+				.await?;
+                return Ok(Ok(()));
+            }
+
+            // Different moderator but lock expired - take over
+            if lock.expired {
+                sqlx::query!(
+					"UPDATE moderation_locks SET moderator_id = $1, locked_at = NOW() WHERE project_id = $2",
+					moderator_id as DBUserId,
+					project_id as DBProjectId
+				)
+				.execute(pool)
+				.await?;
+                return Ok(Ok(()));
+            }
+
+            // Different moderator, not expired - blocked
+            return Ok(Err(lock));
+        }
+
+        // No existing lock - create new one
+        sqlx::query!(
+            "INSERT INTO moderation_locks (project_id, moderator_id, locked_at)
+			VALUES ($1, $2, NOW())
+			ON CONFLICT (project_id) DO UPDATE
+			SET moderator_id = EXCLUDED.moderator_id, locked_at = EXCLUDED.locked_at",
+            project_id as DBProjectId,
+            moderator_id as DBUserId
+        )
+        .execute(pool)
+        .await?;
+
+        Ok(Ok(()))
+    }
+
+    /// Get lock status for a project, including moderator username
+    pub async fn get_with_user(
+        project_id: DBProjectId,
+        pool: &PgPool,
+    ) -> Result<Option<ModerationLockWithUser>, sqlx::Error> {
+        let row = sqlx::query!(
+            r#"
+			SELECT
+				ml.project_id,
+				ml.moderator_id,
+				u.username as moderator_username,
+				u.avatar_url as moderator_avatar_url,
+				ml.locked_at
+			FROM moderation_locks ml
+			INNER JOIN users u ON u.id = ml.moderator_id
+			WHERE ml.project_id = $1
+			"#,
+            project_id as DBProjectId
+        )
+        .fetch_optional(pool)
+        .await?;
+
+        Ok(row.map(|r| {
+            let locked_at: DateTime<Utc> = r.locked_at;
+            let expired =
+                Utc::now().signed_duration_since(locked_at).num_minutes()
+                    >= LOCK_EXPIRY_MINUTES;
+
+            ModerationLockWithUser {
+                project_id: DBProjectId(r.project_id),
+                moderator_id: DBUserId(r.moderator_id),
+                moderator_username: r.moderator_username,
+                moderator_avatar_url: r.moderator_avatar_url,
+                locked_at,
+                expired,
+            }
+        }))
+    }
+
+    /// Release a lock (only if held by the specified moderator)
+    pub async fn release(
+        project_id: DBProjectId,
+        moderator_id: DBUserId,
+        pool: &PgPool,
+    ) -> Result<bool, sqlx::Error> {
+        let result = sqlx::query!(
+			"DELETE FROM moderation_locks WHERE project_id = $1 AND moderator_id = $2",
+			project_id as DBProjectId,
+			moderator_id as DBUserId
+		)
+		.execute(pool)
+		.await?;
+
+        Ok(result.rows_affected() > 0)
+    }
+
+    /// Clean up expired locks (can be called periodically)
+    pub async fn cleanup_expired(pool: &PgPool) -> Result<u64, sqlx::Error> {
+        let result = sqlx::query!(
+			"DELETE FROM moderation_locks WHERE locked_at < NOW() - INTERVAL '15 minutes'"
+		)
+		.execute(pool)
+		.await?;
+
+        Ok(result.rows_affected())
+    }
+
+    /// Delete all moderation locks (admin only)
+    pub async fn delete_all(pool: &PgPool) -> Result<u64, sqlx::Error> {
+        let result = sqlx::query!("DELETE FROM moderation_locks")
+            .execute(pool)
+            .await?;
+
+        Ok(result.rows_affected())
+    }
+}

apps/labrinth/src/routes/internal/moderation/mod.rs

@@ -1,5 +1,7 @@
 use super::ApiError;
+use crate::auth::get_user_from_headers;
 use crate::database;
+use crate::database::models::DBModerationLock;
 use crate::database::redis::RedisPool;
 use crate::models::ids::OrganizationId;
 use crate::models::projects::{Project, ProjectStatus};
@@ -7,8 +9,9 @@ use crate::queue::moderation::{ApprovalType, IdentifiedFile, MissingMetadata};
 use crate::queue::session::AuthQueue;
 use crate::util::error::Context;
 use crate::{auth::check_is_moderator_from_headers, models::pats::Scopes};
-use actix_web::{HttpRequest, get, post, web};
+use actix_web::{HttpRequest, delete, get, post, web};
 use ariadne::ids::{UserId, random_base62};
+use chrono::{DateTime, Utc};
 use ownership::get_projects_ownership;
 use serde::{Deserialize, Serialize};
 use sqlx::PgPool;
@@ -21,6 +24,10 @@ pub fn config(cfg: &mut utoipa_actix_web::service_config::ServiceConfig) {
     cfg.service(get_projects)
         .service(get_project_meta)
         .service(set_project_meta)
+        .service(acquire_lock)
+        .service(get_lock_status)
+        .service(release_lock)
+        .service(delete_all_locks)
         .service(
             utoipa_actix_web::scope("/tech-review")
                 .configure(tech_review::config),
@@ -76,6 +83,59 @@ pub enum Ownership {
     },
 }
 
+/// Response for lock status check
+#[derive(Debug, Serialize, Deserialize, utoipa::ToSchema)]
+pub struct LockStatusResponse {
+    /// Whether the project is currently locked
+    pub locked: bool,
+    /// Information about who holds the lock (if locked)
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub locked_by: Option<LockedByUser>,
+    /// When the lock was acquired
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub locked_at: Option<DateTime<Utc>>,
+    /// Whether the lock has expired (>15 minutes old)
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub expired: Option<bool>,
+}
+
+/// Information about the moderator holding the lock
+#[derive(Debug, Serialize, Deserialize, utoipa::ToSchema)]
+pub struct LockedByUser {
+    /// User ID (base62 encoded)
+    pub id: String,
+    /// Username
+    pub username: String,
+    /// Avatar URL
+    pub avatar_url: Option<String>,
+}
+
+/// Response for successful lock acquisition
+#[derive(Debug, Serialize, Deserialize, utoipa::ToSchema)]
+pub struct LockAcquireResponse {
+    /// Whether lock was successfully acquired
+    pub success: bool,
+    /// If blocked, info about who holds the lock
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub locked_by: Option<LockedByUser>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub locked_at: Option<DateTime<Utc>>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub expired: Option<bool>,
+}
+
+/// Response for lock release
+#[derive(Debug, Serialize, Deserialize, utoipa::ToSchema)]
+pub struct LockReleaseResponse {
+    pub success: bool,
+}
+
+/// Response for deleting all locks
+#[derive(Debug, Serialize, Deserialize, utoipa::ToSchema)]
+pub struct DeleteAllLocksResponse {
+    pub deleted_count: u64,
+}
+
 /// Fetch all projects which are in the moderation queue.
 #[utoipa::path(
     responses((status = OK, body = inline(Vec<FetchedProject>)))
@@ -422,3 +482,185 @@ async fn set_project_meta(
 
     Ok(())
 }
+
+/// Acquire or refresh a moderation lock on a project.
+/// Returns success if acquired, or info about who holds the lock if blocked.
+#[utoipa::path(
+    responses(
+        (status = OK, body = LockAcquireResponse),
+        (status = NOT_FOUND, description = "Project not found")
+    )
+)]
+#[post("/lock/{project_id}")]
+async fn acquire_lock(
+    req: HttpRequest,
+    pool: web::Data<PgPool>,
+    redis: web::Data<RedisPool>,
+    session_queue: web::Data<AuthQueue>,
+    path: web::Path<(String,)>,
+) -> Result<web::Json<LockAcquireResponse>, ApiError> {
+    let user = check_is_moderator_from_headers(
+        &req,
+        &**pool,
+        &redis,
+        &session_queue,
+        Scopes::PROJECT_WRITE,
+    )
+    .await?;
+
+    let project_id_str = path.into_inner().0;
+    let project =
+        database::models::DBProject::get(&project_id_str, &**pool, &redis)
+            .await?
+            .ok_or(ApiError::NotFound)?;
+
+    let db_project_id = project.inner.id;
+    let db_user_id = database::models::DBUserId::from(user.id);
+
+    match DBModerationLock::acquire(db_project_id, db_user_id, &pool).await? {
+        Ok(()) => Ok(web::Json(LockAcquireResponse {
+            success: true,
+            locked_by: None,
+            locked_at: None,
+            expired: None,
+        })),
+        Err(lock) => Ok(web::Json(LockAcquireResponse {
+            success: false,
+            locked_by: Some(LockedByUser {
+                id: UserId::from(lock.moderator_id).to_string(),
+                username: lock.moderator_username,
+                avatar_url: lock.moderator_avatar_url,
+            }),
+            locked_at: Some(lock.locked_at),
+            expired: Some(lock.expired),
+        })),
+    }
+}
+
+/// Check the lock status for a project
+#[utoipa::path(
+    responses(
+        (status = OK, body = LockStatusResponse),
+        (status = NOT_FOUND, description = "Project not found")
+    )
+)]
+#[get("/lock/{project_id}")]
+async fn get_lock_status(
+    req: HttpRequest,
+    pool: web::Data<PgPool>,
+    redis: web::Data<RedisPool>,
+    session_queue: web::Data<AuthQueue>,
+    path: web::Path<(String,)>,
+) -> Result<web::Json<LockStatusResponse>, ApiError> {
+    check_is_moderator_from_headers(
+        &req,
+        &**pool,
+        &redis,
+        &session_queue,
+        Scopes::PROJECT_READ,
+    )
+    .await?;
+
+    let project_id_str = path.into_inner().0;
+    let project =
+        database::models::DBProject::get(&project_id_str, &**pool, &redis)
+            .await?
+            .ok_or(ApiError::NotFound)?;
+
+    let db_project_id = project.inner.id;
+
+    match DBModerationLock::get_with_user(db_project_id, &pool).await? {
+        Some(lock) => Ok(web::Json(LockStatusResponse {
+            locked: true,
+            locked_by: Some(LockedByUser {
+                id: UserId::from(lock.moderator_id).to_string(),
+                username: lock.moderator_username,
+                avatar_url: lock.moderator_avatar_url,
+            }),
+            locked_at: Some(lock.locked_at),
+            expired: Some(lock.expired),
+        })),
+        None => Ok(web::Json(LockStatusResponse {
+            locked: false,
+            locked_by: None,
+            locked_at: None,
+            expired: None,
+        })),
+    }
+}
+
+/// Release a moderation lock on a project
+#[utoipa::path(
+    responses(
+        (status = OK, body = LockReleaseResponse),
+        (status = NOT_FOUND, description = "Project not found")
+    )
+)]
+#[delete("/lock/{project_id}")]
+async fn release_lock(
+    req: HttpRequest,
+    pool: web::Data<PgPool>,
+    redis: web::Data<RedisPool>,
+    session_queue: web::Data<AuthQueue>,
+    path: web::Path<(String,)>,
+) -> Result<web::Json<LockReleaseResponse>, ApiError> {
+    let user = check_is_moderator_from_headers(
+        &req,
+        &**pool,
+        &redis,
+        &session_queue,
+        Scopes::PROJECT_WRITE,
+    )
+    .await?;
+
+    let project_id_str = path.into_inner().0;
+    let project =
+        database::models::DBProject::get(&project_id_str, &**pool, &redis)
+            .await?
+            .ok_or(ApiError::NotFound)?;
+
+    let db_project_id = project.inner.id;
+    let db_user_id = database::models::DBUserId::from(user.id);
+
+    let released =
+        DBModerationLock::release(db_project_id, db_user_id, &pool).await?;
+
+    let _ = DBModerationLock::cleanup_expired(&pool).await;
+
+    Ok(web::Json(LockReleaseResponse { success: released }))
+}
+
+/// Delete all moderation locks (admin only)
+#[utoipa::path(
+    responses(
+        (status = OK, body = DeleteAllLocksResponse),
+        (status = UNAUTHORIZED, description = "Not an admin")
+    )
+)]
+#[delete("/locks")]
+async fn delete_all_locks(
+    req: HttpRequest,
+    pool: web::Data<PgPool>,
+    redis: web::Data<RedisPool>,
+    session_queue: web::Data<AuthQueue>,
+) -> Result<web::Json<DeleteAllLocksResponse>, ApiError> {
+    let user = get_user_from_headers(
+        &req,
+        &**pool,
+        &redis,
+        &session_queue,
+        Scopes::PROJECT_WRITE,
+    )
+    .await?
+    .1;
+
+    if !user.role.is_admin() {
+        return Err(ApiError::CustomAuthentication(
+            "You must be an admin to delete all locks".to_string(),
+        ));
+    }
+
+    let deleted_count = DBModerationLock::delete_all(&pool).await?;
+
+    Ok(web::Json(DeleteAllLocksResponse { deleted_count }))
+}

apps/labrinth/src/routes/v3/projects.rs

@@ -6,7 +6,9 @@ use crate::auth::{filter_visible_projects, get_user_from_headers};
 use crate::database::models::notification_item::NotificationBuilder;
 use crate::database::models::project_item::{DBGalleryItem, DBModCategory};
 use crate::database::models::thread_item::ThreadMessageBuilder;
-use crate::database::models::{DBTeamMember, ids as db_ids, image_item};
+use crate::database::models::{
+    DBModerationLock, DBTeamMember, ids as db_ids, image_item,
+};
 use crate::database::redis::RedisPool;
 use crate::database::{self, models as db_models};
 use crate::file_hosting::{FileHost, FileHostPublicity};
@@ -368,6 +370,23 @@ pub async fn project_edit(
             ));
         }
 
+        // If a moderator is completing a review (changing from Processing to another status),
+        // check if another moderator holds an active lock on this project
+        if user.role.is_mod()
+            && project_item.inner.status == ProjectStatus::Processing
+            && status != &ProjectStatus::Processing
+            && let Some(lock) =
+                DBModerationLock::get_with_user(project_item.inner.id, &pool)
+                    .await?
+            && lock.moderator_id != db_ids::DBUserId::from(user.id)
+            && !lock.expired
+        {
+            return Err(ApiError::CustomAuthentication(format!(
+                "This project is currently being moderated by @{}. Please wait for them to finish or for the lock to expire.",
+                lock.moderator_username
+            )));
+        }
+
         if status == &ProjectStatus::Processing {
             if project_item.versions.is_empty() {
                 return Err(ApiError::InvalidInput(String::from(