Fix generic DM create failure on chat permission 403s (#14128)

## Summary
- Handle `createChat` permission failures (`403`) by opening the
inbox-unavailable modal instead of showing a generic "Failed to create
chat" toast.
- Refresh blockers, blockees, and chat permissions before opening the
modal so the correct call-to-action (follow/unblock/learn more) is
shown.
- Keep existing generic error toast + sentry reporting behavior for
non-`403` failures.

## Files Changed
- `packages/common/src/store/pages/chat/sagas.ts`
- Added `inboxUnavailableModalActions` usage in `doCreateChat` catch
path.
  - Added conditional `403` handling for single-recipient DM creates.

## Validation
- Could not run lint in this environment because `eslint` is not
installed in the workspace runtime (`sh: eslint: not found`).
- Verified patch via `git diff` and scoped logic review.

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Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Ray Jacobson <raymondjacobson@users.noreply.github.com>

Author: 3 people

packages/common/src/store/pages/chat/sagas.ts

@@ -30,6 +30,7 @@ import { Feature } from '~/models/ErrorReporting'
 import { ID } from '~/models/Identifiers'
 import { Status } from '~/models/Status'
 import * as toastActions from '~/store/ui/toast/slice'
+import { inboxUnavailableModalActions } from '~/store/ui/modals'
 import dayjs from '~/utils/dayjs'
 
 import {
@@ -93,6 +94,7 @@ const {
 const { getChatsSummary, getChat, getUnfurlMetadata, getNonOptimisticChat } =
   chatSelectors
 const { toast } = toastActions
+const { open: openInboxUnavailableModal } = inboxUnavailableModalActions
 
 const CHAT_PAGE_SIZE = 30
 const MESSAGES_PAGE_SIZE = 50
@@ -433,14 +435,29 @@ function* doCreateChat(action: ReturnType<typeof createChat>) {
       yield* call(track, make({ eventName: Name.CREATE_CHAT_SUCCESS }))
     }
   } catch (e) {
-    yield* put(
-      toast({
-        type: 'error',
-        content: 'Something went wrong. Failed to create chat.'
-      })
-    )
+    const isForbiddenError = isResponseError(e) && e.response?.status === 403
+    if (isForbiddenError && userIds.length === 1) {
+      // Refresh chat permissions and block state so InboxUnavailable can show
+      // the right next action for the target user.
+      yield* put(fetchBlockees())
+      yield* put(fetchBlockers())
+      yield* put(fetchPermissions({ userIds }))
+      yield* put(
+        openInboxUnavailableModal({
+          userId: userIds[0],
+          presetMessage
+        })
+      )
+    } else {
+      yield* put(
+        toast({
+          type: 'error',
+          content: 'Something went wrong. Failed to create chat.'
+        })
+      )
+    }
     const reportToSentry = yield* getContext('reportToSentry')
-    if (!isResponseError(e) || e.response?.status !== 403) {
+    if (!isForbiddenError) {
       reportToSentry({
         name: 'Chats',
         error: e as Error,