feat(v3): agent preview terminal — read-only xterm.js tracking agent activity

v2/src/lib/components/Terminal/AgentPreviewPane.svelte

@@ -0,0 +1,197 @@
+<script lang="ts">
+  import { onMount, onDestroy } from 'svelte';
+  import { Terminal } from '@xterm/xterm';
+  import { CanvasAddon } from '@xterm/addon-canvas';
+  import { FitAddon } from '@xterm/addon-fit';
+  import { getXtermTheme, onThemeChange } from '../../stores/theme.svelte';
+  import { getAgentSession } from '../../stores/agents.svelte';
+  import type {
+    ToolCallContent,
+    ToolResultContent,
+    InitContent,
+    CostContent,
+    ErrorContent,
+    TextContent,
+    AgentMessage,
+  } from '../../adapters/sdk-messages';
+  import '@xterm/xterm/css/xterm.css';
+
+  interface Props {
+    sessionId: string;
+  }
+
+  let { sessionId }: Props = $props();
+
+  let terminalEl: HTMLDivElement;
+  let term: Terminal;
+  let fitAddon: FitAddon;
+  let resizeObserver: ResizeObserver | null = null;
+  let unsubTheme: (() => void) | null = null;
+
+  /** Track how many messages we've already rendered */
+  let renderedCount = 0;
+
+  let session = $derived(getAgentSession(sessionId));
+
+  // Watch for new messages and render them
+  $effect(() => {
+    if (!session || !term) return;
+    const msgs = session.messages;
+    if (msgs.length <= renderedCount) return;
+
+    const newMsgs = msgs.slice(renderedCount);
+    for (const msg of newMsgs) {
+      renderMessage(msg);
+    }
+    renderedCount = msgs.length;
+  });
+
+  // Reset when sessionId changes
+  $effect(() => {
+    // Access sessionId to track it
+    void sessionId;
+    renderedCount = 0;
+    if (term) {
+      term.clear();
+      term.write('\x1b[90m● Watching agent activity...\x1b[0m\r\n');
+    }
+  });
+
+  function renderMessage(msg: AgentMessage) {
+    switch (msg.type) {
+      case 'init': {
+        const c = msg.content as InitContent;
+        term.write(`\x1b[32m● Session started\x1b[0m \x1b[90m(${c.model})\x1b[0m\r\n`);
+        break;
+      }
+      case 'tool_call': {
+        const tc = msg.content as ToolCallContent;
+        if (tc.name === 'Bash') {
+          const cmd = (tc.input as { command?: string })?.command ?? '';
+          term.write(`\r\n\x1b[36m❯ ${escapeForTerminal(cmd)}\x1b[0m\r\n`);
+        } else if (tc.name === 'Read' || tc.name === 'Write' || tc.name === 'Edit') {
+          const input = tc.input as { file_path?: string };
+          const path = input?.file_path ?? '';
+          term.write(`\x1b[33m[${tc.name}]\x1b[0m \x1b[90m${escapeForTerminal(path)}\x1b[0m\r\n`);
+        } else if (tc.name === 'Grep' || tc.name === 'Glob') {
+          const input = tc.input as { pattern?: string };
+          const pattern = input?.pattern ?? '';
+          term.write(`\x1b[33m[${tc.name}]\x1b[0m \x1b[90m${escapeForTerminal(pattern)}\x1b[0m\r\n`);
+        } else {
+          term.write(`\x1b[33m[${tc.name}]\x1b[0m\r\n`);
+        }
+        break;
+      }
+      case 'tool_result': {
+        const tr = msg.content as ToolResultContent;
+        const output = typeof tr.output === 'string'
+          ? tr.output
+          : JSON.stringify(tr.output, null, 2);
+        if (output) {
+          // Truncate long outputs (show first 80 lines)
+          const lines = output.split('\n');
+          const truncated = lines.length > 80;
+          const display = truncated ? lines.slice(0, 80).join('\n') : output;
+          term.write(escapeForTerminal(display));
+          if (!display.endsWith('\n')) term.write('\r\n');
+          if (truncated) {
+            term.write(`\x1b[90m... (${lines.length - 80} more lines)\x1b[0m\r\n`);
+          }
+        }
+        break;
+      }
+      case 'text': {
+        const tc = msg.content as TextContent;
+        // Show brief text indicator (first line only)
+        const firstLine = tc.text.split('\n')[0].slice(0, 120);
+        term.write(`\x1b[37m${escapeForTerminal(firstLine)}\x1b[0m\r\n`);
+        break;
+      }
+      case 'error': {
+        const ec = msg.content as ErrorContent;
+        term.write(`\x1b[31m✗ ${escapeForTerminal(ec.message)}\x1b[0m\r\n`);
+        break;
+      }
+      case 'cost': {
+        const cc = msg.content as CostContent;
+        const cost = cc.totalCostUsd.toFixed(4);
+        const dur = (cc.durationMs / 1000).toFixed(1);
+        term.write(`\r\n\x1b[90m● Session complete ($${cost}, ${dur}s, ${cc.numTurns} turns)\x1b[0m\r\n`);
+        break;
+      }
+      // Skip thinking, status, unknown
+    }
+  }
+
+  /** Escape text for xterm — convert \n to \r\n */
+  function escapeForTerminal(text: string): string {
+    return text.replace(/\r?\n/g, '\r\n');
+  }
+
+  onMount(() => {
+    term = new Terminal({
+      theme: getXtermTheme(),
+      fontFamily: "'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace",
+      fontSize: 13,
+      lineHeight: 1.2,
+      cursorBlink: false,
+      cursorStyle: 'underline',
+      scrollback: 10000,
+      allowProposedApi: true,
+      disableStdin: true,
+    });
+
+    fitAddon = new FitAddon();
+    term.loadAddon(fitAddon);
+    term.loadAddon(new CanvasAddon());
+    term.open(terminalEl);
+    fitAddon.fit();
+
+    term.write('\x1b[90m● Watching agent activity...\x1b[0m\r\n');
+
+    // If session already has messages, render them
+    const s = getAgentSession(sessionId);
+    if (s && s.messages.length > 0) {
+      for (const msg of s.messages) {
+        renderMessage(msg);
+      }
+      renderedCount = s.messages.length;
+    }
+
+    // Resize handling with debounce
+    let resizeTimer: ReturnType<typeof setTimeout>;
+    resizeObserver = new ResizeObserver(() => {
+      clearTimeout(resizeTimer);
+      resizeTimer = setTimeout(() => {
+        fitAddon.fit();
+      }, 100);
+    });
+    resizeObserver.observe(terminalEl);
+
+    // Hot-swap theme
+    unsubTheme = onThemeChange(() => {
+      term.options.theme = getXtermTheme();
+    });
+  });
+
+  onDestroy(() => {
+    resizeObserver?.disconnect();
+    unsubTheme?.();
+    term?.dispose();
+  });
+</script>
+
+<div class="agent-preview-container" bind:this={terminalEl}></div>
+
+<style>
+  .agent-preview-container {
+    width: 100%;
+    height: 100%;
+    overflow: hidden;
+  }
+
+  .agent-preview-container :global(.xterm) {
+    height: 100%;
+    padding: 4px;
+  }
+</style>

v2/src/lib/components/Workspace/ProjectBox.svelte

@@ -74,7 +74,7 @@
   </div>
 
   <div class="project-terminal-area">
-    <TerminalTabs {project} />
+    <TerminalTabs {project} agentSessionId={mainSessionId} />
   </div>
 </div>
 

v2/src/lib/components/Workspace/TerminalTabs.svelte

@@ -7,12 +7,14 @@
     type TerminalTab,
   } from '../../stores/workspace.svelte';
   import TerminalPane from '../Terminal/TerminalPane.svelte';
+  import AgentPreviewPane from '../Terminal/AgentPreviewPane.svelte';
 
   interface Props {
     project: ProjectConfig;
+    agentSessionId?: string | null;
   }
 
-  let { project }: Props = $props();
+  let { project, agentSessionId }: Props = $props();
 
   let tabs = $derived(getTerminalTabs(project.id));
   let activeTabId = $state<string | null>(null);
@@ -38,6 +40,26 @@
     activeTabId = id;
   }
 
+  function addAgentPreviewTab() {
+    if (!agentSessionId) return;
+    // Don't create duplicate — check if one already exists for this session
+    const existing = tabs.find(
+      t => t.type === 'agent-preview' && t.agentSessionId === agentSessionId,
+    );
+    if (existing) {
+      activeTabId = existing.id;
+      return;
+    }
+    const id = crypto.randomUUID();
+    addTerminalTab(project.id, {
+      id,
+      title: 'Agent Preview',
+      type: 'agent-preview',
+      agentSessionId,
+    });
+    activeTabId = id;
+  }
+
   function closeTab(tabId: string) {
     removeTerminalTab(project.id, tabId);
   }
@@ -66,19 +88,30 @@
         >×</button>
       </div>
     {/each}
-    <button class="tab-add" onclick={addShellTab} title="New shell (Ctrl+N)">+</button>
+    <button class="tab-add" onclick={addShellTab} title="New shell">+</button>
+    {#if agentSessionId}
+      <button
+        class="tab-add tab-agent-preview"
+        onclick={addAgentPreviewTab}
+        title="Watch agent activity"
+      >👁</button>
+    {/if}
   </div>
 
   <div class="tab-content">
     {#each tabs as tab (tab.id)}
       <div class="tab-pane" class:visible={activeTabId === tab.id}>
         {#if activeTabId === tab.id}
+          {#if tab.type === 'agent-preview' && tab.agentSessionId}
+            <AgentPreviewPane sessionId={tab.agentSessionId} />
+          {:else}
             <TerminalPane
               cwd={project.cwd}
               shell={tab.type === 'ssh' ? '/usr/bin/ssh' : undefined}
               onExit={() => handleTabExit(tab.id)}
             />
           {/if}
+        {/if}
       </div>
     {/each}
 
@@ -171,6 +204,10 @@
     background: var(--ctp-surface0);
   }
 
+  .tab-agent-preview {
+    font-size: 0.7rem;
+  }
+
   .tab-content {
     flex: 1;
     position: relative;

v2/src/lib/stores/workspace.svelte.ts

@@ -7,9 +7,11 @@ export type WorkspaceTab = 'sessions' | 'docs' | 'context' | 'settings';
 export interface TerminalTab {
   id: string;
   title: string;
-  type: 'shell' | 'ssh' | 'agent-terminal';
+  type: 'shell' | 'ssh' | 'agent-terminal' | 'agent-preview';
   /** SSH session ID if type === 'ssh' */
   sshSessionId?: string;
+  /** Agent session ID if type === 'agent-preview' */
+  agentSessionId?: string;
 }
 
 // --- Core state ---