feat(chat): simplify Slack onboarding and account linking (#13638)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work.
> - Chat connections let people start and continue that work from Slack.
> - Setup mixed app creation, credentials, URL verification, account
linking, and testing on the same screens.
> - People also needed a safe way to link their own Slack identity after
the first operator finished setup.
> - This pull request gives each step a clear place and keeps membership
approval separate from identity linking.
> - It also makes connection details easier to use and fixes misleading
callback health behind HTTPS proxies.

## Linked Issues or Issue Description

**Subsystem affected**
Cross-cutting: chat routes and services, shared contracts, and the Apps
board UI.

**Problem or motivation**
Slack onboarding made users find settings without enough guidance. A
second user needed operator help to link their account. Activity stopped
at 100 records, and TLS termination could mark working callbacks as
stale.

**Proposed solution**
Use six setup steps with editable app names, a generated manifest,
credential guidance, URL verification, account linking, and an optional
message test. Send each Slack user a private, expiring confirmation
link. Require company membership or an approved access request before
linking. Add cursor pagination and tolerate the internal HTTP hop in
callback diagnostics.

**Roadmap alignment**
This improves the existing connected-app surface and supports CEO Chat
without changing the task-and-comments model. The maintainer requested
and reviewed the flow during a live Slack test drive.

**Additional context**
Related work: #7, #3349, #13000, and #13620. Those cover broader chat
capabilities, older webhook paths, or plugins. This PR improves the
existing native connector's setup and account-linking flow. HTTPS
documentation was published separately in
paperclipai/paperclip-docs#128.

## What Changed

- Split Slack onboarding into six clickable sidebar steps. Keep
secondary and primary actions on one row.
- Generate the Slack creation link and read-only manifest from editable
app, bot, and command names. Add credential prefix validation and direct
instructions.
- Add live account-link status and an optional mention-based message
test.
- Add private, single-use Slack account invitations and membership
access requests. Retain cloud authentication/bootstrap checks and
enforce the chat rollout flag in all identity APIs. Default new Slack
connections to linked users only.
- Put Settings, Access, Conversations, and Activity in the sidebar.
Simplify conversation rows and remove active header badges.
- Add 25-item activity pages, stable timestamp/ID cursors, and replay
safety across pages. Preserve the legacy array API for clients without
pagination parameters.
- Fix false callback warnings when HTTPS terminates at a proxy. Keep
host, port, and path drift detection.
- Document the setup flow, pagination, callback diagnostics, and shared
wizard footer rule.

## Verification

- Passed: `pnpm -r typecheck`, `pnpm build`, and `pnpm
check:token-gates`.
- Passed: focused Slack callback and pagination integration tests; UI
clipboard, wizard, pagination, and activity tests; OpenAPI route tests.
The final access-gate fix also passes 27 focused tests covering cloud
authentication/bootstrap, nonmember invitations, token validity, and the
server-enforced rollout flag.
- Passed: all 1,002 chat integration tests, 6,356 UI tests, and all 11
provider browser scenarios (including mobile light/dark navigation).
After rebase, the identity route, sidebar, and 25 clipboard tests pass.
- The full local `pnpm test:run` was attempted. The first run found 14
Slack fixtures that needed explicit guest access; those are fixed and
the complete chat suite passes. Unrelated embedded PostgreSQL
startup/resource failures and timeouts prevented a clean full local run.
All CI checks pass on `2d858b036`, including the full chat, server,
workspace, build, typecheck, and browser suites.
- Live test drive: Slack app creation, credential setup, URL
verification, private account confirmation, mention messages, and thread
replies. Verified the callback warning clears for the existing proxied
connection.
- Review: create a Slack connection, follow the six steps, link a second
user's account, and browse older activity with Next and Previous.

## Risks

- Identity invitations carry a temporary capability. Tokens are hashed,
expire after 15 minutes, work once, and require explicit confirmation by
a company member. Access requests do not grant membership.
- New Slack connections reject unlinked people by default. Existing
connection settings remain intact.
- Activity is a live ledger. Updated action rows can move forward in
time. Older pages do not poll.
- Proxy tolerance affects health display only. Slack signature checks
and proxy authentication settings remain unchanged.
- No database migration or package-lock changes.

## Model Used

OpenAI Codex, based on GPT-6, with reasoning, repository tools, code
execution, and browser verification. The runtime does not expose an
exact model build ID or context-window size.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass (targeted suites; full
local-run limitations documented above)
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

ui/src/api/chatEndpoints.ts

@@ -1,5 +1,7 @@
 import { api } from "./client";
 import type {
+  SlackAppConfiguration,
+  UpdateChatEndpointInput,
   PhotonProjectInspection,
   PhotonChannelConfiguration,
   ChatPublicationBatchStatus,
@@ -41,6 +43,8 @@ export interface ChatEndpointResource {
 export interface ChatIdentityLink {
   id: string;
   principalId: string;
+  /** Latest discovery-only connect command received by this endpoint. */
+  lastConnectAt?: string | null;
   externalLabel: string;
   externalDetail?: string | null;
   paperclipUserId?: string | null;
@@ -73,6 +77,8 @@ export interface ExternalChannelBindingSummary {
 }
 
 export interface ChatIdentityLinkPreview {
+  selfService?: boolean;
+  canConfirm?: boolean;
   endpointId: string;
   companyId: string;
   companyName: string;
@@ -114,11 +120,14 @@ export interface ChatEndpoint {
   activity?: ChatActivityItem[];
   setup?: {
     step: string;
+    testStartedAt?: string | null;
+    testSkipped?: boolean;
     authorizationUrl?: string | null;
     providerUrl?: string | null;
     webhookUrl?: string | null;
     messagingEndpoint?: string | null;
     command?: string | null;
+    slackApp?: SlackAppConfiguration;
     webhookVerifiedAt?: string | null;
     webhookSecretConfigured?: boolean;
     callbackSurfaces?: {
@@ -180,12 +189,7 @@ export const chatEndpointsApi = {
   ) => api.post<ChatEndpoint>(`/companies/${companyId}/chat-endpoints`, input),
   update: (
     endpointId: string,
-    input: Partial<
-      Pick<
-        ChatEndpoint,
-        "allowDirectMessages" | "allowGroupChats" | "allowUnlinkedPeople"
-      >
-    >,
+    input: UpdateChatEndpointInput,
   ) => api.patch<ChatEndpoint>(`/chat-endpoints/${endpointId}`, input),
   setup: (
     endpointId: string,
@@ -204,6 +208,9 @@ export const chatEndpointsApi = {
     ),
   test: (endpointId: string) =>
     api.post<ChatEndpoint>(`/chat-endpoints/${endpointId}/test`, {}),
+  finishSlackSetup: (endpointId: string) => api.post<ChatEndpoint>(`/chat-endpoints/${endpointId}/finish`, {}),
+  setupTestStatus: (endpointId: string) => api.get<{ messageReceivedAt: string | null }>(`/chat-endpoints/${endpointId}/test-status`),
+  requestIdentityAccess: (token: string) => api.post<{ status: "member" | "pending_approval" }>("/chat-identity-links/request-access", { token }),
   listResources: async (endpointId: string) =>
     rows(
       await api.get<ListResponse<ChatEndpointResource>>(
@@ -252,6 +259,10 @@ export const chatEndpointsApi = {
         `/chat-endpoints/${endpointId}/activity`,
       ),
     ),
+  listActivityPage: (endpointId: string, cursor?: string) =>
+    api.get<{ items: ChatActivityItem[]; nextCursor: string | null }>(
+      `/chat-endpoints/${endpointId}/activity?limit=25${cursor ? `&cursor=${encodeURIComponent(cursor)}` : ""}`,
+    ),
   getIssueBinding: (issueId: string) =>
     api.get<ExternalChannelBindingSummary | null>(
       `/issues/${issueId}/chat-binding`,