feat: add web search, file edit, MCP management, file refs, and /stop to CLI/TUI

1. Web search tools (multi-provider): web_search, web_search_news, web_search_providers
   - Brave, Tavily, SearXNG (env-var activated), DuckDuckGo (always available)
   - Auto mode tries providers in priority order

2. File edit tool (fs_edit_file): targeted text replacement with validation
   - Unique oldText matching, overlap detection, atomic application
   - Sandboxed with size limits

3. MCP management commands: /mcp status, /mcp servers, /mcp reconnect <name>
   - Shows connection status, tool counts, errors for all MCP servers
   - Reconnect disconnected servers from the TUI

4. File reference in chat: @path/to/file inline expansion + /attach command
   - Auto-detects @file patterns and inlines contents as fenced code blocks
   - 256KB per file limit, max 10 files per message
   - Language-aware syntax highlighting hints

5. /stop command: abort streaming via Pi SDK abort()
   - New AbortPayload type in @mosaic/types
   - Gateway abort handler calls piSession.abort()
   - TUI emits abort event on /stop

packages/cli/src/tui/app.tsx

@@ -15,6 +15,7 @@ import { useConversations } from './hooks/use-conversations.js';
 import { useSearch } from './hooks/use-search.js';
 import { executeHelp, executeStatus, executeHistory, commandRegistry } from './commands/index.js';
 import { fetchConversationMessages } from './gateway-api.js';
+import { expandFileRefs, hasFileRefs, handleAttachCommand } from './file-ref.js';
 
 export interface TuiAppProps {
   gatewayUrl: string;
@@ -85,6 +86,36 @@ export function TuiApp({
   // combo is handled by the top-level useInput handler (e.g. Ctrl+T → 't').
   const ctrlJustFired = useRef(false);
 
+  // Wrap sendMessage to expand @file references before sending
+  const sendMessageWithFileRefs = useCallback(
+    (content: string) => {
+      if (!hasFileRefs(content)) {
+        socket.sendMessage(content);
+        return;
+      }
+      void expandFileRefs(content)
+        .then(({ expandedMessage, filesAttached, errors }) => {
+          for (const err of errors) {
+            socket.addSystemMessage(err);
+          }
+          if (filesAttached.length > 0) {
+            socket.addSystemMessage(
+              `📎 Attached ${filesAttached.length} file(s): ${filesAttached.join(', ')}`,
+            );
+          }
+          socket.sendMessage(expandedMessage);
+        })
+        .catch((err: unknown) => {
+          socket.addSystemMessage(
+            `File expansion failed: ${err instanceof Error ? err.message : String(err)}`,
+          );
+          // Send original message without expansion
+          socket.sendMessage(content);
+        });
+    },
+    [socket],
+  );
+
   const handleLocalCommand = useCallback(
     (parsed: ParsedCommand) => {
       switch (parsed.command) {
@@ -123,9 +154,36 @@ export function TuiApp({
               socket.addSystemMessage('Failed to create new conversation.');
             });
           break;
+        case 'attach': {
+          if (!parsed.args) {
+            socket.addSystemMessage('Usage: /attach <file-path>');
+            break;
+          }
+          void handleAttachCommand(parsed.args)
+            .then(({ content, error }) => {
+              if (error) {
+                socket.addSystemMessage(`Attach error: ${error}`);
+              } else if (content) {
+                // Send the file content as a user message
+                socket.sendMessage(content);
+              }
+            })
+            .catch((err: unknown) => {
+              socket.addSystemMessage(
+                `Attach failed: ${err instanceof Error ? err.message : String(err)}`,
+              );
+            });
+          break;
+        }
         case 'stop':
-          // Currently no stop mechanism exposed — show feedback
-          socket.addSystemMessage('Stop is not available for the current session.');
+          if (socket.isStreaming && socket.socketRef.current?.connected && socket.conversationId) {
+            socket.socketRef.current.emit('abort', {
+              conversationId: socket.conversationId,
+            });
+            socket.addSystemMessage('Abort signal sent.');
+          } else {
+            socket.addSystemMessage('No active stream to stop.');
+          }
           break;
         case 'cost': {
           const u = socket.tokenUsage;
@@ -348,7 +406,7 @@ export function TuiApp({
           }
           setTuiInput(val);
         }}
-        onSubmit={socket.sendMessage}
+        onSubmit={sendMessageWithFileRefs}
         onSystemMessage={socket.addSystemMessage}
         onLocalCommand={handleLocalCommand}
         onGatewayCommand={handleGatewayCommand}

packages/cli/src/tui/commands/registry.ts

@@ -56,6 +56,22 @@ const LOCAL_COMMANDS: CommandDef[] = [
     available: true,
     scope: 'core',
   },
+  {
+    name: 'attach',
+    description: 'Attach a file to the next message (@file syntax also works inline)',
+    aliases: [],
+    args: [
+      {
+        name: 'path',
+        type: 'string' as const,
+        optional: false,
+        description: 'File path to attach',
+      },
+    ],
+    execution: 'local',
+    available: true,
+    scope: 'core',
+  },
   {
     name: 'new',
     description: 'Start a new conversation',

packages/cli/src/tui/file-ref.ts

@@ -0,0 +1,202 @@
+/**
+ * File reference expansion for TUI chat input.
+ *
+ * Detects @path/to/file patterns in user messages, reads the file contents,
+ * and inlines them as fenced code blocks in the message.
+ *
+ * Supports:
+ *   - @relative/path.ts
+ *   - @./relative/path.ts
+ *   - @/absolute/path.ts
+ *   - @~/home-relative/path.ts
+ *
+ * Also provides an /attach <path> command handler.
+ */
+
+import { readFile, stat } from 'node:fs/promises';
+import { resolve, extname, basename } from 'node:path';
+import { homedir } from 'node:os';
+
+const MAX_FILE_SIZE = 256 * 1024; // 256 KB
+const MAX_FILES_PER_MESSAGE = 10;
+
+/**
+ * Regex to detect @file references in user input.
+ * Matches @<path> where path starts with /, ./, ~/, or a word char,
+ * and continues until whitespace or end of string.
+ * Excludes @mentions that look like usernames (no dots/slashes).
+ */
+const FILE_REF_PATTERN = /(?:^|\s)@((?:\.{0,2}\/|~\/|[a-zA-Z0-9_])[^\s]+)/g;
+
+interface FileRefResult {
+  /** The expanded message text with file contents inlined */
+  expandedMessage: string;
+  /** Files that were successfully read */
+  filesAttached: string[];
+  /** Errors encountered while reading files */
+  errors: string[];
+}
+
+function resolveFilePath(ref: string): string {
+  if (ref.startsWith('~/')) {
+    return resolve(homedir(), ref.slice(2));
+  }
+  return resolve(process.cwd(), ref);
+}
+
+function getLanguageHint(filePath: string): string {
+  const ext = extname(filePath).toLowerCase();
+  const map: Record<string, string> = {
+    '.ts': 'typescript',
+    '.tsx': 'typescript',
+    '.js': 'javascript',
+    '.jsx': 'javascript',
+    '.py': 'python',
+    '.rb': 'ruby',
+    '.rs': 'rust',
+    '.go': 'go',
+    '.java': 'java',
+    '.c': 'c',
+    '.cpp': 'cpp',
+    '.h': 'c',
+    '.hpp': 'cpp',
+    '.cs': 'csharp',
+    '.sh': 'bash',
+    '.bash': 'bash',
+    '.zsh': 'zsh',
+    '.fish': 'fish',
+    '.json': 'json',
+    '.yaml': 'yaml',
+    '.yml': 'yaml',
+    '.toml': 'toml',
+    '.xml': 'xml',
+    '.html': 'html',
+    '.css': 'css',
+    '.scss': 'scss',
+    '.md': 'markdown',
+    '.sql': 'sql',
+    '.graphql': 'graphql',
+    '.dockerfile': 'dockerfile',
+    '.tf': 'terraform',
+    '.vue': 'vue',
+    '.svelte': 'svelte',
+  };
+  return map[ext] ?? '';
+}
+
+/**
+ * Check if the input contains any @file references.
+ */
+export function hasFileRefs(input: string): boolean {
+  FILE_REF_PATTERN.lastIndex = 0;
+  return FILE_REF_PATTERN.test(input);
+}
+
+/**
+ * Expand @file references in a message by reading file contents
+ * and appending them as fenced code blocks.
+ */
+export async function expandFileRefs(input: string): Promise<FileRefResult> {
+  const refs: string[] = [];
+  FILE_REF_PATTERN.lastIndex = 0;
+  let match;
+  while ((match = FILE_REF_PATTERN.exec(input)) !== null) {
+    const ref = match[1]!;
+    if (!refs.includes(ref)) {
+      refs.push(ref);
+    }
+  }
+
+  if (refs.length === 0) {
+    return { expandedMessage: input, filesAttached: [], errors: [] };
+  }
+
+  if (refs.length > MAX_FILES_PER_MESSAGE) {
+    return {
+      expandedMessage: input,
+      filesAttached: [],
+      errors: [`Too many file references (${refs.length}). Maximum is ${MAX_FILES_PER_MESSAGE}.`],
+    };
+  }
+
+  const filesAttached: string[] = [];
+  const errors: string[] = [];
+  const attachments: string[] = [];
+
+  for (const ref of refs) {
+    const filePath = resolveFilePath(ref);
+    try {
+      const info = await stat(filePath);
+      if (!info.isFile()) {
+        errors.push(`@${ref}: not a file`);
+        continue;
+      }
+      if (info.size > MAX_FILE_SIZE) {
+        errors.push(
+          `@${ref}: file too large (${(info.size / 1024).toFixed(0)} KB, limit ${MAX_FILE_SIZE / 1024} KB)`,
+        );
+        continue;
+      }
+      const content = await readFile(filePath, 'utf8');
+      const lang = getLanguageHint(filePath);
+      const name = basename(filePath);
+      attachments.push(`\n📎 ${ref} (${name}):\n\`\`\`${lang}\n${content}\n\`\`\``);
+      filesAttached.push(ref);
+    } catch (err) {
+      const msg = err instanceof Error ? err.message : String(err);
+      // Only report meaningful errors — ENOENT is common for false @mention matches
+      if (msg.includes('ENOENT')) {
+        // Check if this looks like a file path (has extension or slash)
+        if (ref.includes('/') || ref.includes('.')) {
+          errors.push(`@${ref}: file not found`);
+        }
+        // Otherwise silently skip — likely an @mention, not a file ref
+      } else {
+        errors.push(`@${ref}: ${msg}`);
+      }
+    }
+  }
+
+  if (attachments.length === 0) {
+    return { expandedMessage: input, filesAttached, errors };
+  }
+
+  const expandedMessage = input + '\n' + attachments.join('\n');
+  return { expandedMessage, filesAttached, errors };
+}
+
+/**
+ * Handle the /attach <path> command.
+ * Reads a file and returns the content formatted for inclusion in the chat.
+ */
+export async function handleAttachCommand(
+  args: string,
+): Promise<{ content: string; error?: string }> {
+  const filePath = args.trim();
+  if (!filePath) {
+    return { content: '', error: 'Usage: /attach <file-path>' };
+  }
+
+  const resolved = resolveFilePath(filePath);
+  try {
+    const info = await stat(resolved);
+    if (!info.isFile()) {
+      return { content: '', error: `Not a file: ${filePath}` };
+    }
+    if (info.size > MAX_FILE_SIZE) {
+      return {
+        content: '',
+        error: `File too large (${(info.size / 1024).toFixed(0)} KB, limit ${MAX_FILE_SIZE / 1024} KB)`,
+      };
+    }
+    const content = await readFile(resolved, 'utf8');
+    const lang = getLanguageHint(resolved);
+    const name = basename(resolved);
+    return {
+      content: `📎 Attached file: ${name} (${filePath})\n\`\`\`${lang}\n${content}\n\`\`\``,
+    };
+  } catch (err) {
+    const msg = err instanceof Error ? err.message : String(err);
+    return { content: '', error: `Failed to read file: ${msg}` };
+  }
+}