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+---
+phase: 22
+slug: agent-streaming
+status: draft
+shadcn_initialized: true
+preset: new-york / neutral / cssVariables
+created: 2026-04-01
+revised: 2026-04-01
+---
+
+# Phase 22 — UI Design Contract
+
+> Visual and interaction contract for frontend phases. Generated by gsd-ui-researcher, verified by gsd-ui-checker.
+
+---
+
+## Design System
+
+| Property | Value |
+|----------|-------|
+| Tool | shadcn (new-york style) — carried forward from Phase 21 |
+| Preset | new-york, baseColor: neutral, cssVariables: true |
+| Component library | Radix UI (via shadcn) |
+| Icon library | lucide-react (^0.574.0) |
+| Font | System UI stack (inherited from existing CSS — no custom font declared) |
+
+Source: `ui/components.json`, `ui/src/index.css` (unchanged from Phase 21)
+
+**shadcn components already installed (usable without install):**
+`Avatar`, `Badge`, `Button`, `Card`, `Checkbox`, `Command`, `Dialog`, `DropdownMenu`, `Input`, `Popover`, `ScrollArea`, `Select`, `Separator`, `Sheet`, `Skeleton`, `Tabs`, `Textarea`, `Tooltip`
+
+**New shadcn components for this phase (install before use):**
+None required — `Select` and `DropdownMenu` cover the AgentSelector. `Avatar` covers the agent badge avatar slot.
+
+**New npm packages for this phase (not shadcn registry):**
+- `virtua` ^0.49.0 — virtualized list for ChatMessageList (PERF-03). Install: `pnpm --filter @paperclipai/ui add virtua`
+- Server: `openai` or `ai` SDK — LLM streaming. See RESEARCH.md for provider resolution. Not a UI registry concern.
+
+---
+
+## Focal Point
+
+The primary focal point of Phase 22 is the **streaming message in progress** — specifically the assistant message bubble that receives incoming tokens. While tokens arrive, the bubble is the only animated element on screen. The Stop button (rendered inside `ChatInput` in place of Send) is the secondary focal point during streaming.
+
+---
+
+## Spacing Scale
+
+Carried forward from Phase 21 without change. Source: 21-UI-SPEC.md.
+
+| Token | Value | Usage |
+|-------|-------|-------|
+| xs | 4px | Icon gaps (`gap-1`), inline icon + label spacing |
+| sm | 8px | Compact padding inside list items, badge padding, button icon padding |
+| sm+ | 12px | Conversation list item vertical padding (`py-3`) — named exception, follows `EntityRow` pattern |
+| md | 16px | Default element padding (`p-4`), chat panel header padding |
+| lg | 24px | Section padding on desktop (`p-6`) |
+| xl | 32px | Gap between major UI zones |
+| 2xl | 48px | Empty-state vertical padding (`py-12`) |
+| 3xl | 64px | Page-level section breaks (not applicable in panel context) |
+
+**Phase 22 additions:**
+
+| Token | Value | Usage |
+|-------|-------|-------|
+| agent-badge-gap | 8px (sm) | Gap between agent avatar and agent name in `ChatAgentBadge` |
+| agent-avatar | 20px | Width and height of the agent avatar circle in `ChatAgentBadge` |
+| streaming-dot | 8px (sm) | Width and height of the pulsing streaming cursor dot |
+
+Exceptions (unchanged from Phase 21):
+- `sm+` (12px): conversation list item vertical padding only.
+- Touch targets: `min-height: 44px` on coarse-pointer devices (global `index.css` rule).
+- Chat input bottom padding: `pb-[calc(env(safe-area-inset-bottom)+16px)]` on mobile.
+
+---
+
+## Typography
+
+Carried forward from Phase 21 without change. Source: 21-UI-SPEC.md.
+
+Two weights only: regular (400) and semibold (600).
+
+| Role | Size | Weight | Line Height | Tailwind Class |
+|------|------|--------|-------------|----------------|
+| Body | 14px | 400 (regular) | 1.5 | `text-sm` |
+| Label | 13px | 400 (regular) | 1.4 | `text-[13px]` |
+| Heading | 16px | 600 (semibold) | 1.25 | `text-base font-semibold` |
+| Meta / Timestamp | 12px | 400 (regular) | 1.4 | `text-xs text-muted-foreground` |
+
+**Phase 22 typography additions:**
+- Agent name in `ChatAgentBadge`: Label (13px / regular / `text-muted-foreground`). Not semibold — the name is contextual metadata, not a heading.
+- Slash command suggestion label in the command popover: Body (14px / regular).
+- Agent selector trigger label: Label (13px / regular), truncated with `truncate`.
+- Stop button label (text inside ChatInput during streaming): Body (14px / regular), no special weight. The Square icon carries the visual signal.
+
+Rules (unchanged):
+- Agent message content inside `ChatMarkdownMessage` uses `prose prose-sm` — do not override.
+- The chat input `Textarea` uses Body (14px / regular).
+- Timestamps use Meta (12px / regular / muted-foreground), visible on hover only.
+
+---
+
+## Color
+
+All colors reference CSS custom properties already declared for all three themes in `ui/src/index.css`. Never hard-code hex values. Source: 21-UI-SPEC.md + RESEARCH.md Pattern 6.
+
+| Role | CSS Variable | 60/30/10 | Usage |
+|------|-------------|----------|-------|
+| Dominant surface | `--background` | 60% | Chat panel background, message list background |
+| Secondary surface | `--card` / `--sidebar` | 30% | Conversation list sidebar, code block container |
+| Accent | `--primary` | 10% | Send button, active conversation border-left, filled pin icon |
+| Muted | `--muted` | — | Input background, empty state icon container, streaming cursor background |
+| Muted foreground | `--muted-foreground` | — | Placeholder text, timestamps, agent name in badge, secondary labels |
+| Destructive | `--destructive` | — | Delete conversation action only (carried from Phase 21) |
+| Border | `--border` | — | Dividers, chat panel border, input border |
+
+Accent (`--primary`) reserved for exactly these elements (Phase 22 carries Phase 21 list, no additions):
+1. The "Send message" primary action button background
+2. The active conversation in the sidebar (left-border indicator)
+3. Filled pin icon on pinned conversations
+
+**Phase 22 agent colors — CSS custom properties (THEME-03):**
+
+Agent role colors use `--chart-1` through `--chart-5` CSS custom properties already declared for all three themes in `ui/src/index.css`. These are the ONLY variables permitted for agent identity coloring. Implementation via `bg-[hsl(var(--chart-N))]` Tailwind utility.
+
+| Agent Role | CSS Variable | Tailwind Class |
+|------------|-------------|----------------|
+| `ceo` | `--chart-1` | `bg-[hsl(var(--chart-1))]` |
+| `pm` | `--chart-2` | `bg-[hsl(var(--chart-2))]` |
+| `engineer` | `--chart-3` | `bg-[hsl(var(--chart-3))]` |
+| `general` / `generalist` | `--chart-4` | `bg-[hsl(var(--chart-4))]` |
+| `brainstormer` | `--chart-5` | `bg-[hsl(var(--chart-5))]` |
+| Unknown / fallback | `--muted` | `bg-muted` |
+
+Text on all agent color backgrounds: `text-white` (sufficient contrast on all three themes per chart variable definitions). Do not use `text-foreground` — the chart variables are saturated colors and require white text.
+
+**Stop button color:** The Stop button uses `variant="destructive"` from shadcn Button — it uses `--destructive` background with destructive-foreground text. This signals urgency (cancel an ongoing action) without being confused with a data-destructive action.
+
+---
+
+## Component Inventory
+
+### Modified from Phase 21
+
+#### ChatInput (modified)
+- Existing behavior fully preserved (auto-resize, Enter/Shift+Enter, Escape)
+- **Addition: Stop button during streaming**
+  - When `streaming === true`: Send button is replaced by a Stop button
+  - Stop button: `variant="destructive"`, icon-only (`Square` from lucide, 16px), `aria-label="Stop generation"`
+  - Stop button is NEVER disabled — it must always be clickable during streaming
+  - Layout: same position as Send button (flex row right of Textarea). Dimensions identical to Send button so the layout does not shift when toggling.
+- **Addition: Slash command popover**
+  - Trigger: when input value starts with `/` and matches a known prefix
+  - Popover appears above the input (`<Popover>` with `side="top" align="start"`)
+  - Contents: list of matching commands using `<Command>` component (already installed)
+  - Command item format: `/{command}` label (14px / regular) + destination agent name (13px / muted-foreground)
+  - Dismiss: Escape, backspace past `/`, or clicking away
+  - Max 5 items displayed; no scrolling inside the popover
+  - Commands list (hardcoded):
+
+| Command | Label | Agent Destination |
+|---------|-------|-------------------|
+| `/brainstorm` | Brainstorm an idea | Brainstormer |
+| `/ask-pm` | Ask the PM | PM |
+| `/ask-engineer` | Ask the Engineer | Engineer |
+| `/task` | Create a task | Engineer |
+| `/search` | Search conversations | Generalist |
+
+- **Addition: @mention popover**
+  - Trigger: when input value starts with `@` and has at least 1 character following
+  - Same `<Popover>` + `<Command>` pattern as slash commands
+  - Contents: filtered list of agent names from `useAgents()` cache
+  - Item format: `AgentBadge` (20px avatar) + agent name (14px / regular)
+  - Dismiss: same as slash command popover
+- **No change to aria-label, placeholder, or keyboard shortcuts**
+
+#### ChatMessageList (modified)
+- **Replace flat div with `<VList>` from `virtua` (PERF-03)**
+  - Drop `<ScrollArea>` wrapper — `virtua` manages scroll internally
+  - `<VList style={{ flex: 1 }} ref={listRef}>` wraps all message items
+  - Auto-scroll to bottom logic: `isAtBottom` state derived from VList `onScroll` callback — only auto-scroll when `isAtBottom === true`
+  - Threshold: `isAtBottom = scrollOffset + clientHeight >= scrollSize - 80` (80px tolerance)
+- **Addition: streaming optimistic message**
+  - When `streaming === true`: append a synthetic `ChatMessageItem` at bottom with:
+    - `role: "assistant"`
+    - `content: partialContent` (from `useStreamMessage` hook)
+    - `isStreaming: true` prop
+  - Streaming indicator: a pulsing dot (`w-2 h-2 rounded-full bg-muted animate-pulse`) appended after the last rendered markdown token
+  - The streaming item has no timestamp (omit timestamp row entirely while `isStreaming`)
+  - The streaming item has no action buttons (edit/retry are not shown on in-progress messages)
+- **Addition: message action buttons (edit/retry) on existing assistant messages**
+  - Visible on hover only (`opacity-0 group-hover:opacity-100 transition-opacity duration-150`)
+  - Position: below the message bubble, right-aligned (`flex justify-end gap-1 mt-1`)
+  - Retry button: `variant="ghost" size="icon-sm"`, icon `RotateCcw` (14px), `aria-label="Retry response"`
+  - Edit button: on user messages only — `variant="ghost" size="icon-sm"`, icon `Pencil` (14px), `aria-label="Edit message"`
+  - While streaming is in progress (`streaming === true`): hide all action buttons on all messages (prevent conflicting actions)
+- **Addition: `ChatAgentBadge` above each assistant message bubble**
+  - See new component spec below
+
+#### ChatPanel (modified)
+- **Addition: `AgentSelector` in the panel header**
+  - Position: right side of the header bar (flex row, `ml-auto` before close button)
+  - See new component spec below
+- Header height remains 48px — AgentSelector must fit within this height
+- No other structural changes
+
+### New Components for Phase 22
+
+#### ChatAgentBadge
+- Rendered above each assistant message bubble in `ChatMessageList`
+- Layout: `flex items-center gap-2 mb-1` (8px gap — `sm` token; 4px margin-bottom)
+- Avatar: 20px circle (`w-5 h-5 rounded-full flex items-center justify-center`), background color from `agentRoleColorClass(agent.role)` (see Color section)
+  - If agent has an `icon` value: render `AgentIcon` at 12px size inside the circle
+  - If no icon: render the first letter of `agent.name` at `text-[10px] font-semibold text-white`
+- Agent name: Label (13px / regular / `text-muted-foreground`), truncated at 120px max-width
+- Source: `agent.name` and `agent.role` resolved client-side from `useAgents(companyId)` cache keyed by `agentId` on the message
+- Fallback when agent not found in cache: show `Bot` icon (lucide, 12px) + "Agent" as name, `bg-muted` background — never throw or show nothing
+
+#### AgentSelector
+- Location: ChatPanel header, right side before the close button
+- Component: `<Select>` (shadcn) with a custom trigger styled to match the 48px header height
+- Trigger: compact, `h-8 px-2 py-1`, shows current agent avatar (16px, same color circle pattern as ChatAgentBadge) + agent name Label (13px / regular)
+- Dropdown items: each agent as a `<SelectItem>`, showing `ChatAgentBadge`-style avatar (16px) + agent name (14px / regular) in a flex row
+- Current agent persisted to `conversation.agentId` via `PATCH /api/conversations/:id` — this is the per-conversation default agent
+- Empty state: if no agents available, show a single disabled item "No agents configured"
+- Loading state: `<Skeleton className="h-8 w-28" />` while agents are fetching
+- Tooltip on the selector trigger: "Active agent for this conversation" (shown on hover via `<Tooltip>`)
+
+---
+
+## Interaction Contract
+
+### Streaming lifecycle (CHAT-01, CHAT-12)
+
+| State | ChatInput | ChatMessageList |
+|-------|-----------|-----------------|
+| Idle | Send button enabled; textarea enabled | No streaming indicator |
+| Sending user message | Send button disabled, `Loader2` spin icon, textarea disabled | User message appears immediately (optimistic insert) |
+| Streaming in progress | **Stop button** (`variant="destructive"`, Square icon); textarea disabled | Streaming assistant message at bottom with pulsing dot; action buttons hidden on all messages |
+| Stop clicked | Stop button transitions briefly to `Loader2` for 200ms, then reverts to Send | Streaming message remains in list with last received content (partial); pulsing dot removed; action buttons re-appear |
+| Stream complete | Reverts to Send button; textarea re-enabled and focused | Streaming indicator removed; persisted message replaces optimistic; `RotateCcw` + other action buttons appear on hover |
+| Stream error | Reverts to Send button; textarea re-enabled; error toast fires | Streaming message removed from list |
+
+### Message editing inline (CHAT-10)
+
+- Trigger: click `Pencil` icon on hover over any user message
+- The user message bubble text is replaced with a `<Textarea>` pre-filled with the original content
+- Min height: 40px; max height: 120px; `variant: none` (no extra border — let the bubble container provide the boundary)
+- Confirm: Enter (without Shift), or a "Regenerate" button (`variant="default"`, 14px label "Regenerate") that appears below the edit area
+- Cancel: Escape — restores original content, hides textarea
+- On submit: POST the edited content to `PUT /api/messages/:id`; this re-triggers the stream from that point; messages after the edited message are NOT removed from the UI in Phase 22 (branching is Phase 24 scope)
+- While editing: all other action buttons in the list are hidden
+
+### Response regeneration (CHAT-11)
+
+- Trigger: click `RotateCcw` on hover over any existing assistant message
+- Confirmation: none — immediate action
+- Behavior: re-invokes the stream route for that message position; a new streaming message appears below the existing one; the existing assistant message is retained in the list until the new stream completes, at which point the existing message is replaced with the new one in-place
+- While regenerating: Stop button active in ChatInput; all other action buttons hidden
+
+### Agent selector interaction (CHAT-08)
+
+- Trigger: open `AgentSelector` dropdown in ChatPanel header
+- Selection: clicking an agent item immediately calls `PATCH /api/conversations/:id` with `{ agentId }` and updates local state optimistically
+- Error: if PATCH fails, revert to previous agent selection and show a toast: "Couldn't update agent. Try again."
+- The selected agent takes effect on the next message sent — it does NOT retroactively re-label past messages
+
+### Slash command and @mention routing (INPUT-05, INPUT-06)
+
+- Slash command: when ChatInput contains `/ask-engineer Hello`, the command prefix is parsed before send; the message body "Hello" is sent with `targetRole: "engineer"` as a per-message agent override; the conversation's `agentId` is NOT changed
+- @mention: same per-message override behavior; `@engineer Hello` extracts `targetName: "engineer"` and resolves to the matching agent by name (case-insensitive)
+- If a command is recognized but the target agent does not exist in `useAgents()` cache: show inline toast "No engineer agent found. Message sent to active agent." and fall back to `conversation.agentId`
+- If the `/` prefix does not match any known command: send as plain text (no routing, no error)
+- Popover keyboard navigation: arrow keys move selection, Enter selects, Tab accepts, Escape dismisses
+
+### Auto-scroll behavior during streaming (PERF-03)
+
+- When `isAtBottom === true` at the time a new token arrives: call `listRef.current?.scrollToIndex(allMessages.length - 1, { smooth: false })` to keep bottom in view
+- When user has scrolled up (isAtBottom === false): do NOT scroll; show a "Jump to bottom" button: `<Button variant="outline" size="sm">` with a `ChevronDown` icon (16px), positioned `absolute bottom-20 right-4 z-10` relative to the message list container. Clicking it scrolls to bottom and sets `isAtBottom = true`
+- "Jump to bottom" button disappears immediately when `isAtBottom === true`
+
+---
+
+## Copywriting Contract
+
+Source: Claude's discretion (discuss phase skipped). Follows Phase 21 tone: direct, lowercase preference, no corporate language.
+
+| Element | Copy |
+|---------|------|
+| Stop button tooltip | "Stop generation" |
+| Retry button tooltip | "Retry response" |
+| Edit button tooltip (on user message) | "Edit message" |
+| Edit confirm button | "Regenerate" |
+| Edit cancel instruction | Press Escape to cancel |
+| Streaming indicator aria-label | "Response streaming" |
+| Agent selector tooltip | "Active agent for this conversation" |
+| Agent selector empty | "No agents configured" |
+| Jump to bottom button aria-label | "Jump to bottom" |
+| Slash command popover heading | (none — no heading; list items self-describe) |
+| @mention popover heading | (none — no heading; agent names self-describe) |
+| Error: stream failed | "Response failed. Try again." |
+| Error: edit failed | "Couldn't update message. Try again." |
+| Error: agent update failed | "Couldn't update agent. Try again." |
+| Error: target agent not found | "No {role} agent found. Message sent to active agent." |
+| Error: retry failed | "Retry failed. Try again." |
+| Toast on stop (if partial message not saved) | (no toast — stopping is expected; silent is correct) |
+
+No new destructive actions in Phase 22. The Stop generation action is a cancellation, not a destructive action — no confirmation required.
+
+---
+
+## Accessibility Contract
+
+Carried forward from Phase 21. Phase 22 additions:
+
+- `ChatAgentBadge` avatar: `aria-hidden="true"` (decorative — the agent name provides the text label)
+- Agent name in `ChatAgentBadge`: `aria-label="Agent: {agent.name}"` on the containing span
+- `AgentSelector` trigger: `aria-label="Active agent: {currentAgent.name}"` (dynamically updated)
+- Stop button: `aria-label="Stop generation"`, never `aria-disabled` — always interactive during streaming
+- Streaming message container: `aria-live="off"` — do NOT use `aria-live="polite"` on the partial content container; the completed persisted message in the `role="log"` container is sufficient for screen reader announcement. Streaming token-by-token announcement would be noisy.
+- Edit textarea: `aria-label="Edit message"`, `aria-multiline="true"`
+- "Jump to bottom" button: `aria-label="Jump to bottom"`, `aria-hidden="true"` when not visible
+- Slash command popover: `role="listbox"`, each item `role="option"`, `aria-selected` on highlighted item
+- @mention popover: same `role="listbox"` pattern
+
+---
+
+## Animation Contract
+
+All animations use Tailwind utilities or existing CSS transitions. No new animation libraries.
+
+Carried from Phase 21:
+
+| Element | Animation | Duration | Easing |
+|---------|-----------|----------|--------|
+| Chat panel open/close | `transition-[width]` | 100ms | `ease-out` |
+| Conversation list item hover | `transition-colors` | 150ms | Tailwind default |
+
+Phase 22 additions:
+
+| Element | Animation | Duration | Easing |
+|---------|-----------|----------|--------|
+| Streaming cursor dot | `animate-pulse` (Tailwind) | continuous | built-in |
+| Message action buttons (edit/retry/stop) | `transition-opacity` | 150ms | `ease-out` |
+| Send → Stop button swap | `transition-opacity` | 100ms | `ease-out` (cross-fade; layout does NOT shift) |
+| "Jump to bottom" button appear/disappear | `transition-opacity` | 150ms | `ease-out` |
+| AgentSelector dropdown open | Radix `<Select>` built-in animation | 150ms | Radix default |
+| Slash/mention popover open | `transition-opacity duration-100` | 100ms | `ease-out` |
+
+No enter/exit animations for new streaming tokens — tokens append directly with no animation. This keeps PERF-02 (100ms latency) achievable without layout thrashing.
+
+---
+
+## Registry Safety
+
+| Registry | Blocks Used | Safety Gate |
+|----------|-------------|-------------|
+| shadcn official | All components from Phase 21 + `Command`, `Popover`, `Select` (already installed) | not required |
+| Third-party registries | none | not applicable |
+
+`virtua` is installed via npm (not shadcn registry). npm packages are not subject to the shadcn registry safety gate.
+
+No third-party shadcn registry blocks are declared for this phase.
+
+---
+
+## Checker Sign-Off
+
+- [ ] Dimension 1 Copywriting: PASS
+- [ ] Dimension 2 Visuals: PASS
+- [ ] Dimension 3 Color: PASS
+- [ ] Dimension 4 Typography: PASS
+- [ ] Dimension 5 Spacing: PASS
+- [ ] Dimension 6 Registry Safety: PASS
+
+**Approval:** pending