feat: code block rendering, syntax highlighting, and compose fixes

.gitignore

@@ -29,6 +29,7 @@ Thumbs.db
 playwright-report/
 test-results/
 blob-report/
+.playwright-mcp/
 
 # Node modules (pnpm workspace hoists to root)
 node_modules/

crates/sprout-acp/src/base_prompt.md

@@ -23,6 +23,7 @@ Run `sprout --help` or `sprout <group> --help` for full usage.
 ## Communication Patterns
 
 - Address agents and humans with plain `@name` — do NOT bold or italicize mention text (formatting prevents alert delivery).
+- Message content supports GitHub-flavored Markdown. Use fenced code blocks with a language tag (` ```python `, ` ```typescript `, etc.) for syntax-highlighted rendering on desktop and mobile. Omitting the language tag renders monochrome.
 - Use `sprout messages thread` when responding in-thread; post new messages for new topics.
 - No push notifications — poll with `sprout messages get --channel <UUID> --since <ts>`. When `since` is set without `before`, results are oldest-first (chronological).
 

crates/sprout-mcp/src/server.rs

@@ -170,7 +170,8 @@ async fn resolve_content_mentions(
 pub struct SendMessageParams {
     /// UUID of the channel to post to.
     pub channel_id: String,
-    /// Message body text.
+    /// Message body text. Supports GitHub-flavored Markdown including fenced code
+    /// blocks with syntax highlighting.
     pub content: String,
     /// Nostr event kind. Defaults to KIND_STREAM_MESSAGE (NIP-29 group chat message).
     #[serde(default = "default_kind")]
@@ -890,7 +891,9 @@ impl SproutMcpServer {
     /// Send a message to a Sprout channel.
     #[tool(
         name = "send_message",
-        description = "Send a message to a Sprout channel. Include `parent_event_id` to reply in a thread. \
+        description = "Send a message to a Sprout channel. Content supports GitHub-flavored Markdown — \
+use fenced code blocks with a language tag for syntax-highlighted rendering. \
+Include `parent_event_id` to reply in a thread. \
 Set `broadcast_to_channel` to also surface the reply in the main channel timeline. \
 For forum channels, set `kind` to 45001 (post) or 45003 (comment with `parent_event_id`). \
 Default kind is 9 (stream message)."

desktop/src-tauri/src/managed_agents/nest_skill.md

@@ -74,6 +74,15 @@ Write commands are unaffected. `--format json` (default) returns full fields.
 
 Other kind values are rejected. Use `messages vote --event <id> --direction up|down` to vote on forum posts.
 
+## Message Formatting
+
+Message content is rendered as GitHub-flavored Markdown on both desktop and mobile. Key formatting:
+
+- **Fenced code blocks**: triple-backtick with a language tag for syntax highlighting (190+ languages supported). Omitting the language tag renders a styled monochrome block.
+- **Inline code**: single backticks for inline monospace.
+- **Mentions**: plain `@name` — do NOT bold or italicize (formatting prevents alert delivery).
+- **Links, images, tables, blockquotes, headings**: standard GFM.
+
 ## Mem Patch Workflow
 
 For safe concurrent writes, use hash-based conflict detection:

desktop/src/features/messages/lib/codeBlockExtensions.ts

@@ -23,7 +23,20 @@ export function handleCodeFenceEnter(ed: Editor): boolean | undefined {
     "",
   );
 
-  if (FENCE_AT_START.test(textBefore)) return false;
+  const startMatch = textBefore.match(FENCE_AT_START);
+  if (startMatch) {
+    const { tr, schema } = ed.state;
+    const attrs = startMatch[1] ? { language: startMatch[1] } : {};
+    tr.delete($cursor.start(), $cursor.pos);
+    tr.setBlockType(
+      tr.mapping.map($cursor.start()),
+      tr.mapping.map($cursor.start()),
+      schema.nodes.codeBlock,
+      attrs,
+    );
+    ed.view.dispatch(tr);
+    return true;
+  }
 
   const m = textBefore.match(FENCE_AFTER_BREAK);
   if (!m) return undefined;

desktop/src/shared/styles/globals.css

@@ -173,6 +173,43 @@
   }
 }
 
+/* ── Code block line numbers & diff ────────────────────────────────── */
+.code-block-lines {
+  counter-reset: code-line;
+}
+
+.code-block-lines [data-line] {
+  display: block;
+  counter-increment: code-line;
+}
+
+.code-block-lines [data-line]::before {
+  content: counter(code-line);
+  display: inline-block;
+  width: 2.5ch;
+  margin-right: 1.5ch;
+  text-align: right;
+  color: hsl(var(--muted-foreground) / 0.4);
+  user-select: none;
+  pointer-events: none;
+}
+
+.code-line-diff-add {
+  background-color: hsl(120 40% 50% / 0.15);
+}
+
+.code-line-diff-remove {
+  background-color: hsl(0 60% 50% / 0.15);
+}
+
+.dark .code-line-diff-add {
+  background-color: hsl(120 40% 50% / 0.12);
+}
+
+.dark .code-line-diff-remove {
+  background-color: hsl(0 60% 50% / 0.12);
+}
+
 @layer base {
   :root {
     /* Catppuccin Latte (mauve accent) */