feat: Chat leads the left nav, agent work beside chats, and a Combined Inbox + Task List flag (#15100)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work
> - The left nav is the main way people move between tasks, the inbox,
and Agent Chat
> - The nav has separate Inbox and Tasks rows that show overlapping
work, and Chat is one row among many
> - The side panel beside a chat shows the conversation's own artifacts,
not the work the agent did
> - People want Chat to be easy to find, and they want one place for
their task views
> - This pull request moves Chat to the top of Work, shows the agent's
tasks and artifacts beside each chat, and adds an experimental flag that
folds Inbox into Tasks
> - The benefit is a shorter nav and a chat view that shows what the
agent is working on. Both changes stay off until an operator enables
them

## Linked Issues or Issue Description

Refs #14706 (the secondary Agent Chat navigation this change builds on)
Refs #14848 (reopen the last visited agent chat)

**Subsystem affected**
UI navigation (left nav, mobile tab bar), Agent Chat side panel, task
list and inbox, and the company artifacts API.

**Problem or motivation**
Inbox and Tasks are two nav rows for overlapping work. Chat sits in the
top group with no clear home. The chat rail lists only agents you
already talked to, so you cannot see your other teammates there. The
side panel beside a chat shows only the conversation's own artifacts. It
does not show the tasks and files the agent made.

**Proposed solution**
With Agent Chat on, Chat leads the Work section and the rail lists every
eligible agent. The chat side panel opens on the agent's tasks as cards,
and the agent's artifacts are available from +. A new experimental flag,
Combined Inbox + Task List, makes Inbox a set of views inside Tasks.

**Alternatives considered**
Rebuilding the inbox inside the task list. Instead, `/issues` hosts the
existing Inbox component for inbox views and the existing task list for
status views, so all inbox behaviour stays the same.

**Roadmap alignment**
Agent Chat (ROADMAP.md, "Agent Chat (including CEO Chat)"). All changes
are behind experimental flags that are off by default.

## What Changed

- **Agent Chat nav (streamlined shell):** Chat is the first row of Work,
not a top-group row. Workspaces leaves the nav while Agent Chat is on.
The mobile tab bar is Home · Chat · + · Tasks · Agents. The legacy shell
keeps master's top-group Chat row.
- **Chat rail:** `AgentConversationsSidebar` lists every eligible agent.
The open chat is first, then conversations by recent activity, then the
rest of the roster alphabetically. Terminated agents and agents you left
are omitted unless you have history with them. The picker still marks
only real conversations as "Open chat".
- **Chat side panel:** a new default Tasks tab shows one card per task
the agent created, was assigned, commented on, or acted on, newest
first. It has the task list's filter popover and a sort control. **+ →
Artifacts** shows the agent's artifacts as cards. Cards open in a new
tab. Agent Chat off keeps the old Artifacts tab.
- **Artifacts API:** `GET /api/companies/:companyId/artifacts` accepts
`agentId`. The filter applies to documents, work products, and
attachments by the agent each result is attributed to. The shared
validator and the UI client carry the new parameter, and the OpenAPI
entry picks it up from the shared schema.
- **Combined Inbox + Task List flag (`enableCombinedInboxTasks`, off by
default):** new card in Settings > Experimental. The Inbox row goes away
and its badge moves to Tasks. A Views menu on `/issues` covers Mine,
Unread, Blocked, Recent, Everything, All, Active, Backlog, and Done.
Bare `/issues` opens the last-used view (default Mine). Links that carry
`assignee`, `workspace`, `participantAgentId`, or `q` open All so the
filter is kept. `/inbox/*` and
`/issues/{all,active,backlog,done,recent}` redirect to the matching
view. `/inbox/requests` stays its own page.
- **Task detail breadcrumb:** the view key now decides the source, so
quick-archive still works after a reload from an inbox view.
- **Docs:** `doc/PRODUCT.md` and `doc/SPEC.md` describe the chat rail,
the chat side panel, and the new flag.

## Verification

- `cd ui && npx vitest run --no-file-parallelism src/components/chat
src/components/task-side-panel/TaskSidePanel.test.tsx
src/components/AgentConversationsSidebar.test.tsx
src/components/Sidebar.test.tsx
src/components/SidebarCompanyMenu.test.tsx
src/components/Layout.test.tsx src/pages/AgentChats.test.tsx
src/pages/InstanceExperimentalSettings.test.tsx
src/lib/task-views.test.ts src/lib/issueDetailBreadcrumb.test.ts
src/pages/Inbox.test.tsx src/pages/Issues.test.tsx src/App.test.tsx
src/App.activity-routing.test.tsx
src/components/MobileBottomNav.test.tsx
src/components/CommandPalette.test.tsx`: 20 files, 356 tests pass.
- `cd server && npx vitest run
src/__tests__/company-artifacts-service.test.ts`: 13/13 pass, including
the new agent-filter test across all three artifact sources.
- The new rail test fails against the unmodified rail.
- `pnpm check:token-gates`: all gates clean.
- Manual: enable Agent Chat in Settings > Experimental. Open Chat. The
rail lists all agents. Open a chat. The side panel shows the agent's
tasks. Use **+ → Artifacts** to see the agent's artifacts. Then enable
Combined Inbox + Task List. The Inbox row goes away, and Tasks shows a
Views menu.
- Snapshot baselines are intentionally not updated. See
`doc/design/DECISION-SHEET.md`, "Per-change snapshot verification
demoted to dormant (Jul 13 2026)".

## Risks

- With both flags off, the app behaves like master. The only exception
is the API: it accepts a new optional query parameter.
- With Agent Chat on, the rail can list many agents in a large company.
It uses the agent list the app already loads, and search filters it.
- The Tasks panel reads at most 200 recently updated tasks per agent and
says so when it reaches the limit. The Artifacts panel reads at most 500
of the agent's artifacts.
- Combined Inbox + Task List changes what bare `/issues` opens for
people who enable it. Deep links with a task filter still open All.

## Model Used

- Claude (Anthropic), model ID `claude-opus-5-5`, through Claude Code
with tool use (shell, file edit, test runs). Extended thinking was
enabled.

## 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
- [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
- [ ] All Paperclip CI gates are green
- [ ] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: scotttong <squadbot000@gmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

doc/PRODUCT.md

@@ -209,10 +209,26 @@ telemetry. See [Announcements](ANNOUNCEMENTS.md).
 
 ### Agent chat discovery
 
-With Agent Chat enabled, the Chats sidebar always includes the company's
-earliest-created agent, plus personal starred agents and up to four other recent
-conversations. First use has the same compact rows as returning use. The compose
-icon shares a column with stars and appears on hover or keyboard focus (always on
-touch). It opens a company-wide name/role search, independent of sidebar membership.
+With Agent Chat enabled, Chat is the first row of the Work section and opens a
+secondary sidebar beside the primary nav. It lists every agent you can chat
+with: the open conversation first, then your other conversations by recent
+activity, then the rest of the roster alphabetically. Terminated agents and
+agents you have left are omitted unless you have history with them. Search
+filters by name, title, or role; **+** starts or reopens a conversation.
 Selecting an agent opens their persistent conversation; it does not reset history
 or create a task until the existing first-write flow requires one.
+
+Beside a conversation, the side panel opens on the agent's tasks: one card per
+task the agent created, was assigned, commented on, or acted on, newest first,
+with the task list's filters and a sort control. The agent's artifacts are a
+second card stack available from the panel's **+** menu. Both open in a new tab
+so the conversation stays open.
+
+### Combined Inbox + Task List
+
+An opt-in experimental setting (`enableCombinedInboxTasks`, off by default)
+folds Inbox into Tasks. The Inbox nav row goes away and its unread badge moves
+to Tasks. A Views menu on the task list covers the inbox views (Mine, Unread,
+Blocked, Recent, Everything) and the task-status views (All, Active, Backlog,
+Done). Bare `/issues` opens the last-used view, defaulting to Mine; links that
+carry a task filter open All. Old `/inbox` links redirect to the matching view.

doc/SPEC.md

@@ -299,7 +299,7 @@ should name the rejected action and the specific restriction.
 
 There is no separate messaging or chat system. Tasks are the communication channel. This keeps all context attached to the work it relates to and creates a natural audit trail.
 
-Experimental Agent Chat presents one persistent task per person and agent as a simplified conversation. Chat has a searchable secondary sidebar with agent avatars; adding an agent starts or reopens their single conversation. It retains the task composer, transcript, tools, attachments, documents, and existing Subtasks panel, with ordinary company visibility. New execution tasks are ordinary project tasks, not children of the conversation. Idle conversations wait for a message without entering execution-task work queues. Agents clarify goals here and create assigned tasks for substantial execution. `/new` resets provider context at an ordered session boundary within the same task while preserving visible history. `enableAgentChat` is disabled by default; the V1 lifecycle and rollout contract is specified in `SPEC-implementation.md`.
+Experimental Agent Chat presents one persistent task per person and agent as a simplified conversation. Chat has a searchable secondary sidebar with agent avatars that lists every eligible agent, conversations first; adding an agent starts or reopens their single conversation. It retains the task composer, transcript, tools, attachments, documents, and existing Subtasks panel, with ordinary company visibility. New execution tasks are ordinary project tasks, not children of the conversation. Idle conversations wait for a message without entering execution-task work queues. Agents clarify goals here and create assigned tasks for substantial execution. `/new` resets provider context at an ordered session boundary within the same task while preserving visible history. `enableAgentChat` is disabled by default; the V1 lifecycle and rollout contract is specified in `SPEC-implementation.md`.
 
 ### Question recipients