Add hashtag link detection. Closes #134.

frontend/src/App.tsx

@@ -31,6 +31,12 @@ interface ChannelUnreadMarker {
   lastReadAt: number | null;
 }
 
+interface NewMessagePrefillRequest {
+  tab: 'hashtag';
+  hashtagName: string;
+  nonce: number;
+}
+
 interface UnreadBoundaryBackfillParams {
   activeConversation: Conversation | null;
   unreadMarker: ChannelUnreadMarker | null;
@@ -77,6 +83,8 @@ export function App() {
   const messageInputRef = useRef<MessageInputHandle>(null);
   const [rawPackets, setRawPackets] = useState<RawPacket[]>([]);
   const [channelUnreadMarker, setChannelUnreadMarker] = useState<ChannelUnreadMarker | null>(null);
+  const [newMessagePrefillRequest, setNewMessagePrefillRequest] =
+    useState<NewMessagePrefillRequest | null>(null);
   const [visibilityVersion, setVisibilityVersion] = useState(0);
   const lastUnreadBackfillAttemptRef = useRef<string | null>(null);
   const {
@@ -103,8 +111,8 @@ export function App() {
     setDistanceUnit,
     handleCloseSettingsView,
     handleToggleSettingsView,
-    handleOpenNewMessage,
+    handleOpenNewMessage: openNewMessageModal,
-    handleCloseNewMessage,
+    handleCloseNewMessage: closeNewMessageModal,
     handleToggleCracker,
   } = useAppShell();
 
@@ -413,6 +421,34 @@ export function App() {
     [fetchUndecryptedCount, setChannels]
   );
 
+  const handleOpenNewMessage = useCallback(() => {
+    setNewMessagePrefillRequest(null);
+    openNewMessageModal();
+  }, [openNewMessageModal]);
+
+  const handleCloseNewMessage = useCallback(() => {
+    setNewMessagePrefillRequest(null);
+    closeNewMessageModal();
+  }, [closeNewMessageModal]);
+
+  const handleChannelReferenceClick = useCallback(
+    (channelName: string) => {
+      const existingChannel = channels.find((channel) => channel.name === channelName);
+      if (existingChannel) {
+        handleNavigateToChannel(existingChannel.key);
+        return;
+      }
+
+      setNewMessagePrefillRequest((previous) => ({
+        tab: 'hashtag',
+        hashtagName: channelName.slice(1),
+        nonce: (previous?.nonce ?? 0) + 1,
+      }));
+      openNewMessageModal();
+    },
+    [channels, handleNavigateToChannel, openNewMessageModal]
+  );
+
   const statusProps = {
     health,
     config,
@@ -468,6 +504,7 @@ export function App() {
     onOpenContactInfo: handleOpenContactInfo,
     onOpenChannelInfo: handleOpenChannelInfo,
     onSenderClick: handleSenderClick,
+    onChannelReferenceClick: handleChannelReferenceClick,
     onLoadOlder: fetchOlderMessages,
     onResendChannelMessage: handleResendChannelMessage,
     onTargetReached: () => setTargetMessageId(null),
@@ -526,6 +563,7 @@ export function App() {
   };
   const newMessageModalProps = {
     undecryptedCount,
+    prefillRequest: newMessagePrefillRequest,
     onCreateContact: handleCreateContact,
     onCreateChannel: handleCreateChannel,
     onCreateHashtagChannel: handleCreateHashtagChannel,

frontend/src/components/ConversationPane.tsx

@@ -65,6 +65,7 @@ interface ConversationPaneProps {
   onOpenContactInfo: (publicKey: string, fromChannel?: boolean) => void;
   onOpenChannelInfo: (channelKey: string) => void;
   onSenderClick: (sender: string) => void;
+  onChannelReferenceClick?: (channelName: string) => void;
   onLoadOlder: () => Promise<void>;
   onResendChannelMessage: (messageId: number, newTimestamp?: boolean) => Promise<void>;
   onTargetReached: () => void;
@@ -131,6 +132,7 @@ export function ConversationPane({
   onOpenContactInfo,
   onOpenChannelInfo,
   onSenderClick,
+  onChannelReferenceClick,
   onLoadOlder,
   onResendChannelMessage,
   onTargetReached,
@@ -284,6 +286,7 @@ export function ConversationPane({
             activeConversation.type === 'channel' ? onDismissUnreadMarker : undefined
           }
           onSenderClick={activeConversation.type === 'channel' ? onSenderClick : undefined}
+          onChannelReferenceClick={onChannelReferenceClick}
           onLoadOlder={onLoadOlder}
           onResendChannelMessage={
             activeConversation.type === 'channel' ? onResendChannelMessage : undefined

frontend/src/components/MessageList.tsx

@@ -11,7 +11,11 @@ import {
 import type { Channel, Contact, Message, MessagePath, RadioConfig, RawPacket } from '../types';
 import { CONTACT_TYPE_REPEATER, CONTACT_TYPE_ROOM } from '../types';
 import { api } from '../api';
-import { formatTime, parseSenderFromText } from '../utils/messageParser';
+import {
+  findLinkedChannelReferences,
+  formatTime,
+  parseSenderFromText,
+} from '../utils/messageParser';
 import { formatHopCounts, type SenderInfo } from '../utils/pathUtils';
 import { getDirectContactRoute } from '../utils/pathUtils';
 import { ContactAvatar } from './ContactAvatar';
@@ -33,6 +37,7 @@ interface MessageListProps {
   onSenderClick?: (sender: string) => void;
   onLoadOlder?: () => void;
   onResendChannelMessage?: (messageId: number, newTimestamp?: boolean) => void;
+  onChannelReferenceClick?: (channelName: string) => void;
   radioName?: string;
   config?: RadioConfig | null;
   onOpenContactInfo?: (publicKey: string, fromChannel?: boolean) => void;
@@ -48,8 +53,64 @@ interface MessageListProps {
 const URL_PATTERN =
   /https?:\/\/(www\.)?[-a-zA-Z0-9@:%._+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_+.~#?&//=]*)/g;
 
-// Helper to convert URLs in a plain text string into clickable links
+function renderChannelReferences(
-function linkifyText(text: string, keyPrefix: string): ReactNode[] {
+  text: string,
+  keyPrefix: string,
+  onChannelReferenceClick?: (channelName: string) => void
+): ReactNode[] {
+  const references = findLinkedChannelReferences(text);
+  if (references.length === 0) {
+    return [text];
+  }
+
+  const parts: ReactNode[] = [];
+  let lastIndex = 0;
+
+  references.forEach((reference, index) => {
+    if (reference.start > lastIndex) {
+      parts.push(text.slice(lastIndex, reference.start));
+    }
+
+    const className =
+      'rounded px-0.5 font-medium text-primary underline underline-offset-2 transition-colors';
+    if (onChannelReferenceClick) {
+      parts.push(
+        <button
+          key={`${keyPrefix}-channel-${index}`}
+          type="button"
+          className={cn(
+            className,
+            'inline border-0 bg-transparent p-0 align-baseline hover:text-primary/80 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring'
+          )}
+          onClick={() => onChannelReferenceClick(reference.label)}
+        >
+          {reference.label}
+        </button>
+      );
+    } else {
+      parts.push(
+        <span key={`${keyPrefix}-channel-${index}`} className={className}>
+          {reference.label}
+        </span>
+      );
+    }
+
+    lastIndex = reference.end;
+  });
+
+  if (lastIndex < text.length) {
+    parts.push(text.slice(lastIndex));
+  }
+
+  return parts;
+}
+
+// Helper to convert URLs and channel references in a plain text string into rich content
+function linkifyText(
+  text: string,
+  keyPrefix: string,
+  onChannelReferenceClick?: (channelName: string) => void
+): ReactNode[] {
   const parts: ReactNode[] = [];
   let lastIndex = 0;
   let match: RegExpExecArray | null;
@@ -58,7 +119,13 @@ function linkifyText(text: string, keyPrefix: string): ReactNode[] {
   URL_PATTERN.lastIndex = 0;
   while ((match = URL_PATTERN.exec(text)) !== null) {
     if (match.index > lastIndex) {
-      parts.push(text.slice(lastIndex, match.index));
+      parts.push(
+        ...renderChannelReferences(
+          text.slice(lastIndex, match.index),
+          `${keyPrefix}-text-${keyIndex}`,
+          onChannelReferenceClick
+        )
+      );
     }
     parts.push(
       <a
@@ -74,15 +141,27 @@ function linkifyText(text: string, keyPrefix: string): ReactNode[] {
     lastIndex = match.index + match[0].length;
   }
 
-  if (lastIndex === 0) return [text];
+  if (lastIndex === 0) {
+    return renderChannelReferences(text, keyPrefix, onChannelReferenceClick);
+  }
   if (lastIndex < text.length) {
-    parts.push(text.slice(lastIndex));
+    parts.push(
+      ...renderChannelReferences(
+        text.slice(lastIndex),
+        `${keyPrefix}-tail`,
+        onChannelReferenceClick
+      )
+    );
   }
   return parts;
 }
 
 // Helper to render text with highlighted @[Name] mentions and clickable URLs
-function renderTextWithMentions(text: string, radioName?: string): ReactNode {
+function renderTextWithMentions(
+  text: string,
+  radioName?: string,
+  onChannelReferenceClick?: (channelName: string) => void
+): ReactNode {
   const mentionPattern = /@\[([^\]]+)\]/g;
   const parts: ReactNode[] = [];
   let lastIndex = 0;
@@ -92,7 +171,13 @@ function renderTextWithMentions(text: string, radioName?: string): ReactNode {
   while ((match = mentionPattern.exec(text)) !== null) {
     // Add text before the match (with linkification)
     if (match.index > lastIndex) {
-      parts.push(...linkifyText(text.slice(lastIndex, match.index), `pre-${keyIndex}`));
+      parts.push(
+        ...linkifyText(
+          text.slice(lastIndex, match.index),
+          `pre-${keyIndex}`,
+          onChannelReferenceClick
+        )
+      );
     }
 
     const mentionedName = match[1];
@@ -115,7 +200,7 @@ function renderTextWithMentions(text: string, radioName?: string): ReactNode {
 
   // Add remaining text after last match (with linkification)
   if (lastIndex < text.length) {
-    parts.push(...linkifyText(text.slice(lastIndex), `post-${keyIndex}`));
+    parts.push(...linkifyText(text.slice(lastIndex), `post-${keyIndex}`, onChannelReferenceClick));
   }
 
   return parts.length > 0 ? parts : text;
@@ -188,6 +273,7 @@ export function MessageList({
   onSenderClick,
   onLoadOlder,
   onResendChannelMessage,
+  onChannelReferenceClick,
   radioName,
   config,
   onOpenContactInfo,
@@ -911,7 +997,7 @@ export function MessageList({
                   <div className="break-words whitespace-pre-wrap">
                     {content.split('\n').map((line, i, arr) => (
                       <span key={i}>
-                        {renderTextWithMentions(line, radioName)}
+                        {renderTextWithMentions(line, radioName, onChannelReferenceClick)}
                         {i < arr.length - 1 && <br />}
                       </span>
                     ))}

frontend/src/components/NewMessageModal.tsx

@@ -1,4 +1,4 @@
-import { useState, useRef } from 'react';
+import { useEffect, useRef, useState } from 'react';
 import { Dice5 } from 'lucide-react';
 import {
   Dialog,
@@ -20,6 +20,11 @@ type Tab = 'new-contact' | 'new-channel' | 'hashtag';
 interface NewMessageModalProps {
   open: boolean;
   undecryptedCount: number;
+  prefillRequest?: {
+    tab: 'hashtag';
+    hashtagName: string;
+    nonce: number;
+  } | null;
   onClose: () => void;
   onCreateContact: (name: string, publicKey: string, tryHistorical: boolean) => Promise<void>;
   onCreateChannel: (name: string, key: string, tryHistorical: boolean) => Promise<void>;
@@ -29,6 +34,7 @@ interface NewMessageModalProps {
 export function NewMessageModal({
   open,
   undecryptedCount,
+  prefillRequest = null,
   onClose,
   onCreateContact,
   onCreateChannel,
@@ -53,6 +59,24 @@ export function NewMessageModal({
     setError('');
   };
 
+  useEffect(() => {
+    if (!open || !prefillRequest) {
+      return;
+    }
+
+    setTab(prefillRequest.tab);
+    setName(prefillRequest.hashtagName);
+    setContactKey('');
+    setChannelKey('');
+    setTryHistorical(false);
+    setPermitCapitals(false);
+    setError('');
+    setLoading(false);
+    requestAnimationFrame(() => {
+      hashtagInputRef.current?.focus();
+    });
+  }, [open, prefillRequest]);
+
   const handleCreate = async () => {
     setError('');
     setLoading(true);

frontend/src/test/messageList.test.tsx

@@ -140,6 +140,59 @@ describe('MessageList channel sender rendering', () => {
     expect(screen.getByRole('button', { name: 'View info for Alice' })).toBeInTheDocument();
   });
 
+  it('renders valid channel references as clickable links and ignores invalid ones', async () => {
+    const user = userEvent.setup();
+    const onChannelReferenceClick = vi.fn();
+
+    render(
+      <MessageList
+        messages={[
+          createMessage({
+            text: 'Alice: Join #mesh-room now skip #bad--room and visit https://example.com/#also-skip',
+          }),
+        ]}
+        contacts={[]}
+        loading={false}
+        onChannelReferenceClick={onChannelReferenceClick}
+      />
+    );
+
+    const linkedChannel = screen.getByRole('button', { name: '#mesh-room' });
+    expect(linkedChannel).toBeInTheDocument();
+    expect(screen.queryByRole('button', { name: '#bad--room' })).not.toBeInTheDocument();
+    expect(
+      screen.getByRole('link', { name: 'https://example.com/#also-skip' })
+    ).toBeInTheDocument();
+
+    await user.click(linkedChannel);
+
+    expect(onChannelReferenceClick).toHaveBeenCalledWith('#mesh-room');
+  });
+
+  it('links valid channel references in direct messages too', async () => {
+    const user = userEvent.setup();
+    const onChannelReferenceClick = vi.fn();
+
+    render(
+      <MessageList
+        messages={[
+          createMessage({
+            type: 'PRIV',
+            text: 'check #ops-room',
+            conversation_key: 'ab'.repeat(32),
+          }),
+        ]}
+        contacts={[]}
+        loading={false}
+        onChannelReferenceClick={onChannelReferenceClick}
+      />
+    );
+
+    await user.click(screen.getByRole('button', { name: '#ops-room' }));
+
+    expect(onChannelReferenceClick).toHaveBeenCalledWith('#ops-room');
+  });
+
   it('renders and dismisses an unread marker at the first unread message boundary', async () => {
     const user = userEvent.setup();
     const messages = [

frontend/src/test/messageParser.test.ts

@@ -6,7 +6,12 @@
  */
 
 import { describe, it, expect } from 'vitest';
-import { parseSenderFromText, formatTime } from '../utils/messageParser';
+import {
+  findLinkedChannelReferences,
+  formatTime,
+  isValidLinkedChannelName,
+  parseSenderFromText,
+} from '../utils/messageParser';
 
 describe('parseSenderFromText', () => {
   it('extracts sender and content from "sender: message" format', () => {
@@ -95,3 +100,31 @@ describe('formatTime', () => {
     expect(result).toMatch(/\d{1,2}:\d{2}/); // time portion
   });
 });
+
+describe('linked channel references', () => {
+  it('accepts lowercase alphanumeric names with single dashes', () => {
+    expect(isValidLinkedChannelName('ops')).toBe(true);
+    expect(isValidLinkedChannelName('ops-1')).toBe(true);
+    expect(isValidLinkedChannelName('1-2-3')).toBe(true);
+  });
+
+  it('rejects uppercase, leading or trailing dashes, and repeated dashes', () => {
+    expect(isValidLinkedChannelName('Ops')).toBe(false);
+    expect(isValidLinkedChannelName('-ops')).toBe(false);
+    expect(isValidLinkedChannelName('ops-')).toBe(false);
+    expect(isValidLinkedChannelName('ops--room')).toBe(false);
+  });
+
+  it('finds standalone linked channel references in message text', () => {
+    expect(findLinkedChannelReferences('Join #mesh-room then say hi in #ops2')).toEqual([
+      { label: '#mesh-room', start: 5, end: 15 },
+      { label: '#ops2', start: 31, end: 36 },
+    ]);
+  });
+
+  it('ignores invalid or embedded channel-like text', () => {
+    expect(
+      findLinkedChannelReferences('skip #Bad #bad--name abc#ops #ops- #opsRoom #ops_room #good-room,')
+    ).toEqual([]);
+  });
+});

frontend/src/test/newMessageModal.test.tsx

@@ -32,7 +32,10 @@ describe('NewMessageModal form reset', () => {
     vi.clearAllMocks();
   });
 
-  function renderModal(open = true) {
+  function renderModal(
+    open = true,
+    overrides: Partial<Parameters<typeof NewMessageModal>[0]> = {}
+  ) {
     return render(
       <NewMessageModal
         open={open}
@@ -41,6 +44,7 @@ describe('NewMessageModal form reset', () => {
         onCreateContact={onCreateContact}
         onCreateChannel={onCreateChannel}
         onCreateHashtagChannel={onCreateHashtagChannel}
+        {...overrides}
       />
     );
   }
@@ -50,6 +54,26 @@ describe('NewMessageModal form reset', () => {
   }
 
   describe('hashtag tab', () => {
+    it('prefills the hashtag tab from a linked channel request', async () => {
+      renderModal(true, {
+        prefillRequest: {
+          tab: 'hashtag',
+          hashtagName: 'mesh-room',
+          nonce: 1,
+        },
+      });
+
+      await waitFor(() => {
+        expect(screen.getByRole('tab', { name: 'Hashtag Channel' })).toHaveAttribute(
+          'data-state',
+          'active'
+        );
+      });
+      expect((screen.getByPlaceholderText('channel-name') as HTMLInputElement).value).toBe(
+        'mesh-room'
+      );
+    });
+
     it('clears name after successful Create', async () => {
       const user = userEvent.setup();
       const { unmount } = renderModal();

frontend/src/utils/messageParser.ts

@@ -2,6 +2,9 @@
  * Parse sender from channel message text.
  * Channel messages have format "sender: message".
  */
+const HASHTAG_CHANNEL_NAME_PATTERN = /^[a-z0-9]+(?:-[a-z0-9]+)*$/;
+const HASHTAG_CHANNEL_REFERENCE_PATTERN = /(^|\s)(#[a-z0-9]+(?:-[a-z0-9]+)*)(?=$|\s)/g;
+
 export function parseSenderFromText(text: string): { sender: string | null; content: string } {
   const colonIndex = text.indexOf(': ');
   if (colonIndex > 0 && colonIndex < 50) {
@@ -17,6 +20,35 @@ export function parseSenderFromText(text: string): { sender: string | null; cont
   return { sender: null, content: text };
 }
 
+export interface HashtagChannelReference {
+  label: string;
+  start: number;
+  end: number;
+}
+
+export function isValidLinkedChannelName(name: string): boolean {
+  return HASHTAG_CHANNEL_NAME_PATTERN.test(name);
+}
+
+export function findLinkedChannelReferences(text: string): HashtagChannelReference[] {
+  const references: HashtagChannelReference[] = [];
+  let match: RegExpExecArray | null;
+
+  HASHTAG_CHANNEL_REFERENCE_PATTERN.lastIndex = 0;
+  while ((match = HASHTAG_CHANNEL_REFERENCE_PATTERN.exec(text)) !== null) {
+    const prefix = match[1];
+    const label = match[2];
+    const start = match.index + prefix.length;
+    references.push({
+      label,
+      start,
+      end: start + label.length,
+    });
+  }
+
+  return references;
+}
+
 /**
  * Format a Unix timestamp to a time string.
  * Shows date for messages not from today.