diff --git a/src/state/queries/join-links.ts b/src/state/queries/join-links.ts
index ca1db05558..e53edc0291 100644
--- a/src/state/queries/join-links.ts
+++ b/src/state/queries/join-links.ts
@@ -1,17 +1,19 @@
 import {useCallback} from 'react'
 import {
   type $Typed,
-  AtpAgent,
   ChatBskyGroupDefs,
   type ChatBskyGroupGetJoinLinkPreviews,
 } from '@atproto/api'
+import {type Client} from '@atproto/lex'
 import {type QueryClient, useQuery, useQueryClient} from '@tanstack/react-query'
 
-import {CHAT_SERVICE, DM_SERVICE_HEADERS} from '#/lib/constants'
+import {CHAT_SERVICE} from '#/lib/constants'
+import {createLexClient} from '#/lib/lexClient'
 import {logger} from '#/logger'
 import {STALE} from '#/state/queries/index'
 import {createQueryKey, type StructuredQueryKey} from '#/state/queries/util'
-import {useAgent} from '#/state/session'
+import {useChatClient} from '#/state/session'
+import {chat} from '#/lexicons'
 
 /**
  * The three preview shapes we currently support. Excludes the `{$type: string}`
@@ -154,23 +156,34 @@ export function invalidateJoinLinkPreviewsForConvo(
   })
 }
 
+let publicChatClient: Client | undefined
+
+/**
+ * The unauthenticated {@link Client} for the chat service, used to resolve join
+ * links before the viewer has a session.
+ *
+ * It talks to {@link CHAT_SERVICE} directly rather than proxying through a PDS,
+ * so no `atproto-proxy` header is involved. A single module-level instance,
+ * because there is no session to scope it to and reconstructing it per call
+ * would be waste.
+ */
+function getPublicChatClient(): Client {
+  return (publicChatClient ??= createLexClient({service: CHAT_SERVICE}))
+}
+
 async function fetchJoinLinkPreviews({
-  agent,
+  client,
   codes,
   hasSession,
 }: {
-  agent: AtpAgent
+  client: Client
   codes: string[]
   hasSession: boolean
 }) {
-  const previewAgent = new AtpAgent({service: CHAT_SERVICE})
-  const res = hasSession
-    ? await agent.chat.bsky.group.getJoinLinkPreviews(
-        {codes},
-        {headers: DM_SERVICE_HEADERS},
-      )
-    : await previewAgent.chat.bsky.group.getJoinLinkPreviews({codes})
-  return res.data
+  return await (hasSession ? client : getPublicChatClient()).call(
+    chat.bsky.group.getJoinLinkPreviews,
+    {codes},
+  )
 }
 
 export function useJoinLinkPreviewsQuery({
@@ -188,14 +201,14 @@ export function useJoinLinkPreviewsQuery({
    */
   initialData?: ChatBskyGroupGetJoinLinkPreviews.OutputSchema
 }) {
-  const agent = useAgent()
+  const client = useChatClient()
 
   return useQuery({
     queryKey: createJoinLinkPreviewQueryKey({codes: codes ?? [], hasSession}),
     queryFn: async () => {
       if (!codes) throw new Error('No invite code')
       try {
-        return await fetchJoinLinkPreviews({agent, codes, hasSession})
+        return await fetchJoinLinkPreviews({client, codes, hasSession})
       } catch (error) {
         logger.error('Failed to fetch join link preview', {safeMessage: error})
         throw error
@@ -208,13 +221,13 @@ export function useJoinLinkPreviewsQuery({
 }
 
 export function usePrefetchJoinLinkPreviews() {
-  const agent = useAgent()
+  const client = useChatClient()
   const queryClient = useQueryClient()
 
   return ({codes, hasSession}: {codes: string[]; hasSession: boolean}) => {
     return queryClient.prefetchQuery({
       queryKey: createJoinLinkPreviewQueryKey({codes, hasSession}),
-      queryFn: () => fetchJoinLinkPreviews({agent, codes, hasSession}),
+      queryFn: () => fetchJoinLinkPreviews({client, codes, hasSession}),
       staleTime: STALE.SECONDS.FIFTEEN,
     })
   }
@@ -226,7 +239,7 @@ export function usePrefetchJoinLinkPreviews() {
  * Returns undefined if the preview can't be resolved.
  */
 export function useGetJoinLinkPreview() {
-  const agent = useAgent()
+  const client = useChatClient()
   const queryClient = useQueryClient()
 
   return useCallback(
@@ -241,7 +254,7 @@ export function useGetJoinLinkPreview() {
         const data = await queryClient.fetchQuery({
           queryKey: createJoinLinkPreviewQueryKey({codes: [code], hasSession}),
           queryFn: () =>
-            fetchJoinLinkPreviews({agent, codes: [code], hasSession}),
+            fetchJoinLinkPreviews({client, codes: [code], hasSession}),
           staleTime: STALE.SECONDS.FIFTEEN,
         })
         const found = data.joinLinkPreviews[0]
@@ -251,6 +264,6 @@ export function useGetJoinLinkPreview() {
         return undefined
       }
     },
-    [agent, queryClient],
+    [client, queryClient],
   )
 }
diff --git a/src/state/queries/messages/create-join-link.ts b/src/state/queries/messages/create-join-link.ts
index fbac855466..57269b93e3 100644
--- a/src/state/queries/messages/create-join-link.ts
+++ b/src/state/queries/messages/create-join-link.ts
@@ -5,9 +5,9 @@ import {
 } from '@atproto/api'
 import {useMutation, useQueryClient} from '@tanstack/react-query'
 
-import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {logger} from '#/logger'
-import {useAgent} from '#/state/session'
+import {useChatClient} from '#/state/session'
+import {chat} from '#/lexicons'
 import {
   rollbackConvoOptimistic,
   updateConvoOptimistic,
@@ -24,7 +24,7 @@ export function useCreateJoinLink(
   },
 ) {
   const queryClient = useQueryClient()
-  const agent = useAgent()
+  const client = useChatClient()
 
   return useMutation({
     mutationFn: async ({
@@ -35,11 +35,11 @@ export function useCreateJoinLink(
       requireApproval: boolean
     }) => {
       if (!convoId) throw new Error('No convoId provided')
-      const {data} = await agent.chat.bsky.group.createJoinLink(
-        {convoId, joinRule, requireApproval},
-        {headers: DM_SERVICE_HEADERS, encoding: 'application/json'},
-      )
-      return data
+      return await client.call(chat.bsky.group.createJoinLink, {
+        convoId,
+        joinRule,
+        requireApproval,
+      })
     },
     onMutate: ({joinRule, requireApproval}) => {
       if (!convoId) return
diff --git a/src/state/queries/messages/disable-join-link.ts b/src/state/queries/messages/disable-join-link.ts
index c143feb6cc..b995dbcc6f 100644
--- a/src/state/queries/messages/disable-join-link.ts
+++ b/src/state/queries/messages/disable-join-link.ts
@@ -4,10 +4,10 @@ import {
 } from '@atproto/api'
 import {useMutation, useQueryClient} from '@tanstack/react-query'
 
-import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {logger} from '#/logger'
 import {invalidateJoinLinkPreviewsForCode} from '#/state/queries/join-links'
-import {useAgent} from '#/state/session'
+import {useChatClient} from '#/state/session'
+import {chat} from '#/lexicons'
 import {
   rollbackConvoOptimistic,
   updateConvoOptimistic,
@@ -24,16 +24,12 @@ export function useDisableJoinLink(
   },
 ) {
   const queryClient = useQueryClient()
-  const agent = useAgent()
+  const client = useChatClient()
 
   return useMutation({
     mutationFn: async () => {
       if (!convoId) throw new Error('No convoId provided')
-      const {data} = await agent.chat.bsky.group.disableJoinLink(
-        {convoId},
-        {headers: DM_SERVICE_HEADERS, encoding: 'application/json'},
-      )
-      return data
+      return await client.call(chat.bsky.group.disableJoinLink, {convoId})
     },
     onMutate: () => {
       if (!convoId) return
diff --git a/src/state/queries/messages/edit-join-link.ts b/src/state/queries/messages/edit-join-link.ts
index 7e34ce88d9..7870c1f7e3 100644
--- a/src/state/queries/messages/edit-join-link.ts
+++ b/src/state/queries/messages/edit-join-link.ts
@@ -5,9 +5,9 @@ import {
 } from '@atproto/api'
 import {useMutation, useQueryClient} from '@tanstack/react-query'
 
-import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {logger} from '#/logger'
-import {useAgent} from '#/state/session'
+import {useChatClient} from '#/state/session'
+import {chat} from '#/lexicons'
 import {
   rollbackConvoOptimistic,
   updateConvoOptimistic,
@@ -24,7 +24,7 @@ export function useEditJoinLink(
   },
 ) {
   const queryClient = useQueryClient()
-  const agent = useAgent()
+  const client = useChatClient()
 
   return useMutation({
     mutationFn: async ({
@@ -35,11 +35,11 @@ export function useEditJoinLink(
       requireApproval: boolean
     }) => {
       if (!convoId) throw new Error('No convoId provided')
-      const {data} = await agent.chat.bsky.group.editJoinLink(
-        {convoId, joinRule, requireApproval},
-        {headers: DM_SERVICE_HEADERS, encoding: 'application/json'},
-      )
-      return data
+      return await client.call(chat.bsky.group.editJoinLink, {
+        convoId,
+        joinRule,
+        requireApproval,
+      })
     },
     onMutate: ({joinRule, requireApproval}) => {
       if (!convoId) return
diff --git a/src/state/queries/messages/enable-join-link.ts b/src/state/queries/messages/enable-join-link.ts
index 4febc85441..ef3b168068 100644
--- a/src/state/queries/messages/enable-join-link.ts
+++ b/src/state/queries/messages/enable-join-link.ts
@@ -1,10 +1,10 @@
 import {ChatBskyConvoDefs, type ChatBskyGroupEnableJoinLink} from '@atproto/api'
 import {useMutation, useQueryClient} from '@tanstack/react-query'
 
-import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {logger} from '#/logger'
 import {invalidateJoinLinkPreviewsForCode} from '#/state/queries/join-links'
-import {useAgent} from '#/state/session'
+import {useChatClient} from '#/state/session'
+import {chat} from '#/lexicons'
 import {
   rollbackConvoOptimistic,
   updateConvoOptimistic,
@@ -21,16 +21,12 @@ export function useEnableJoinLink(
   },
 ) {
   const queryClient = useQueryClient()
-  const agent = useAgent()
+  const client = useChatClient()
 
   return useMutation({
     mutationFn: async () => {
       if (!convoId) throw new Error('No convoId provided')
-      const {data} = await agent.chat.bsky.group.enableJoinLink(
-        {convoId},
-        {headers: DM_SERVICE_HEADERS, encoding: 'application/json'},
-      )
-      return data
+      return await client.call(chat.bsky.group.enableJoinLink, {convoId})
     },
     onMutate: () => {
       if (!convoId) return
diff --git a/src/state/queries/messages/join-requests.ts b/src/state/queries/messages/join-requests.ts
index 179dfafaaf..d36ebd60ae 100644
--- a/src/state/queries/messages/join-requests.ts
+++ b/src/state/queries/messages/join-requests.ts
@@ -4,15 +4,16 @@ import {
   type ChatBskyGroupListJoinRequests,
   type ChatBskyGroupRejectJoinRequest,
 } from '@atproto/api'
+import {type DidString} from '@atproto/syntax'
 import {
   type InfiniteData,
   useMutation,
   useQueryClient,
 } from '@tanstack/react-query'
 
-import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {logger} from '#/logger'
-import {useAgent} from '#/state/session'
+import {useChatClient} from '#/state/session'
+import {chat} from '#/lexicons'
 import {listConvoMembersQueryKey} from './list-convo-members'
 import {createListJoinRequestsQueryKey} from './list-join-requests'
 
@@ -34,21 +35,28 @@ export function useJoinRequestMutation<A extends JoinRequestAction>(
   },
 ) {
   const queryClient = useQueryClient()
-  const agent = useAgent()
+  const client = useChatClient()
 
   return useMutation({
     mutationFn: async ({member}: {member: string}) => {
       if (!convoId) throw new Error('No convoId provided')
-      const {data} =
+      // callers pass an already-resolved actor did
+      const memberDid = member as DidString
+      const data =
         action === 'approve'
-          ? await agent.chat.bsky.group.approveJoinRequest(
-              {convoId, member},
-              {headers: DM_SERVICE_HEADERS, encoding: 'application/json'},
-            )
-          : await agent.chat.bsky.group.rejectJoinRequest(
-              {convoId, member},
-              {headers: DM_SERVICE_HEADERS, encoding: 'application/json'},
-            )
+          ? await client.call(chat.bsky.group.approveJoinRequest, {
+              convoId,
+              member: memberDid,
+            })
+          : await client.call(chat.bsky.group.rejectJoinRequest, {
+              convoId,
+              member: memberDid,
+            })
+      /*
+       * The two branches have different output schemas, so the union cannot be
+       * narrowed from the `action` value alone - the cast carries the generic's
+       * mapping through, exactly as the pre-migration code did.
+       */
       return data as JoinRequestOutput<A>
     },
     onMutate: ({member}) => {
diff --git a/src/state/queries/messages/list-join-requests.ts b/src/state/queries/messages/list-join-requests.ts
index 64a999c118..bbb82eeca5 100644
--- a/src/state/queries/messages/list-join-requests.ts
+++ b/src/state/queries/messages/list-join-requests.ts
@@ -2,10 +2,10 @@ import {useEffect} from 'react'
 import {ChatBskyConvoDefs} from '@atproto/api'
 import {useInfiniteQuery, useQueryClient} from '@tanstack/react-query'
 
-import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {useMessagesEventBus} from '#/state/messages/events'
 import {createQueryKey} from '#/state/queries/util'
-import {useAgent} from '#/state/session'
+import {useChatClient} from '#/state/session'
+import {chat} from '#/lexicons'
 import {STALE} from '..'
 
 export const JOIN_REQUESTS_THRESHOLD = 20
@@ -22,7 +22,7 @@ export function useListJoinRequestsQuery({
   convoId: string | undefined
   enabled?: boolean
 }) {
-  const agent = useAgent()
+  const client = useChatClient()
   const queryClient = useQueryClient()
   const messagesBus = useMessagesEventBus()
   const isEnabled = enabled !== false && !!convoId
@@ -54,11 +54,12 @@ export function useListJoinRequestsQuery({
     enabled: isEnabled,
     queryKey: createListJoinRequestsQueryKey({convoId: convoId ?? ''}),
     queryFn: async ({pageParam}) => {
-      const {data} = await agent.chat.bsky.group.listJoinRequests(
-        {convoId: convoId!, cursor: pageParam, limit: JOIN_REQUESTS_THRESHOLD},
-        {headers: DM_SERVICE_HEADERS},
-      )
-      return data
+      return await client.call(chat.bsky.group.listJoinRequests, {
+        // guarded by `isEnabled`
+        convoId: convoId!,
+        cursor: pageParam,
+        limit: JOIN_REQUESTS_THRESHOLD,
+      })
     },
     initialPageParam: undefined as string | undefined,
     getNextPageParam: page => page.cursor,
diff --git a/src/state/queries/messages/mark-join-request-read.ts b/src/state/queries/messages/mark-join-request-read.ts
index ae6d7e88a7..3dfd995af0 100644
--- a/src/state/queries/messages/mark-join-request-read.ts
+++ b/src/state/queries/messages/mark-join-request-read.ts
@@ -1,9 +1,9 @@
 import {ChatBskyConvoDefs} from '@atproto/api'
 import {useMutation, useQueryClient} from '@tanstack/react-query'
 
-import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {logger} from '#/logger'
-import {useAgent} from '#/state/session'
+import {useChatClient} from '#/state/session'
+import {chat} from '#/lexicons'
 import {RQKEY as CONVO_KEY} from './conversation'
 import {
   type ConvoListQueryData,
@@ -12,15 +12,12 @@ import {
 
 export function useMarkJoinRequestsRead(convoId: string | undefined) {
   const queryClient = useQueryClient()
-  const agent = useAgent()
+  const client = useChatClient()
 
   return useMutation({
     mutationFn: async () => {
       if (!convoId) throw new Error('No convoId provided')
-      await agent.chat.bsky.group.updateJoinRequestsRead(
-        {convoId},
-        {headers: DM_SERVICE_HEADERS, encoding: 'application/json'},
-      )
+      await client.call(chat.bsky.group.updateJoinRequestsRead, {convoId})
     },
     onMutate: () => {
       if (!convoId) return
diff --git a/src/state/queries/messages/request-join-group-chat.ts b/src/state/queries/messages/request-join-group-chat.ts
index f4d5650346..b0a1922007 100644
--- a/src/state/queries/messages/request-join-group-chat.ts
+++ b/src/state/queries/messages/request-join-group-chat.ts
@@ -1,9 +1,9 @@
 import {type ChatBskyGroupRequestJoin} from '@atproto/api'
 import {useMutation, useQueryClient} from '@tanstack/react-query'
 
-import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {logger} from '#/logger'
-import {useAgent, useSession} from '#/state/session'
+import {useChatClient, useSession} from '#/state/session'
+import {chat} from '#/lexicons'
 import {RQKEY_ROOT as REQUESTS_RQKEY_ROOT} from './list-conversation-requests'
 
 export function useRequestJoinGroupChat({
@@ -13,7 +13,7 @@ export function useRequestJoinGroupChat({
   onSuccess?: (data: ChatBskyGroupRequestJoin.OutputSchema) => void
   onError?: (error: Error) => void
 } = {}) {
-  const agent = useAgent()
+  const client = useChatClient()
   const queryClient = useQueryClient()
   const {hasSession} = useSession()
 
@@ -22,11 +22,7 @@ export function useRequestJoinGroupChat({
       if (!hasSession) throw new Error('Must be logged in to join')
       if (!code) throw new Error('No invite code')
 
-      const res = await agent.chat.bsky.group.requestJoin(
-        {code},
-        {headers: DM_SERVICE_HEADERS},
-      )
-      return res.data
+      return await client.call(chat.bsky.group.requestJoin, {code})
     },
     onSuccess: data => {
       void queryClient.invalidateQueries({queryKey: [REQUESTS_RQKEY_ROOT]})
diff --git a/src/state/queries/messages/withdraw-join-group-chat.ts b/src/state/queries/messages/withdraw-join-group-chat.ts
index 2ede8c941d..736128ee25 100644
--- a/src/state/queries/messages/withdraw-join-group-chat.ts
+++ b/src/state/queries/messages/withdraw-join-group-chat.ts
@@ -1,9 +1,9 @@
 import {type ChatBskyGroupWithdrawJoinRequest} from '@atproto/api'
 import {useMutation, useQueryClient} from '@tanstack/react-query'
 
-import {DM_SERVICE_HEADERS} from '#/lib/constants'
 import {logger} from '#/logger'
-import {useAgent, useSession} from '#/state/session'
+import {useChatClient, useSession} from '#/state/session'
+import {chat} from '#/lexicons'
 import {
   type ConvoRequestListQueryData,
   optimisticDeleteJoinRequest,
@@ -17,7 +17,7 @@ export function useWithdrawJoinGroupChatRequest({
   onSuccess?: (data: ChatBskyGroupWithdrawJoinRequest.OutputSchema) => void
   onError?: (error: Error) => void
 } = {}) {
-  const agent = useAgent()
+  const client = useChatClient()
   const queryClient = useQueryClient()
   const {hasSession} = useSession()
 
@@ -27,11 +27,7 @@ export function useWithdrawJoinGroupChatRequest({
         throw new Error('Must be logged in to withdraw a join request')
       if (!convoId) throw new Error('No convoId provided')
 
-      const res = await agent.chat.bsky.group.withdrawJoinRequest(
-        {convoId},
-        {headers: DM_SERVICE_HEADERS},
-      )
-      return res.data
+      return await client.call(chat.bsky.group.withdrawJoinRequest, {convoId})
     },
     onSuccess: (data, {convoId}) => {
       queryClient.setQueriesData<ConvoRequestListQueryData>(