Add hooks, @file mentions, session search/fork/export, follow-scroll

- Hooks ([[hooks]]): pre_tool, post_tool, user_prompt, stop; sandboxed, exit 2 blocks
- @file mentions with autocomplete; mentioned files/folders are attached to the prompt
- Session full-text search in the sidebar, fork into a copy, export as Markdown/JSON
- Chat follows the newest message until the user scrolls up; jump-to-latest button
- SVG activity spark and thinking icon instead of Unicode/emoji glyphs
- File search ranks name matches first and returns relative paths

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/src/mentions.rs

@@ -0,0 +1,83 @@
+//! `@path` mentions in user prompts: the mentioned files (or folder listings)
+//! are attached to the prompt, read with the regular read/list tools.
+
+use crate::app::App;
+use crate::tools::{Tool, ToolCtx};
+use crate::types::Part;
+use serde_json::json;
+use std::path::PathBuf;
+use std::sync::Arc;
+use tokio_util::sync::CancellationToken;
+
+const MAX_MENTIONS: usize = 10;
+const MAX_CHARS: usize = 60_000;
+
+/// `@token`s at the start of the text or after whitespace (not e-mail addresses).
+pub fn find(text: &str) -> Vec<String> {
+    let re = regex::Regex::new(r"(?:^|\s)@([\w./~+\-]+)").unwrap();
+    let mut out: Vec<String> = Vec::new();
+    for c in re.captures_iter(text) {
+        let token = c[1].trim_end_matches(['.', ',', ';', ':', '!', '?', ')']).to_string();
+        if !token.is_empty() && !out.contains(&token) {
+            out.push(token);
+        }
+    }
+    out
+}
+
+/// Parts to append to a user prompt for its mentions.
+pub async fn expand(app: &Arc<App>, session_id: &str, text: &str) -> Vec<Part> {
+    let tokens = find(text);
+    if tokens.is_empty() {
+        return vec![];
+    }
+    let Ok(session) = app.session(session_id) else { return vec![] };
+    let cwd = PathBuf::from(&session.cwd);
+    let ctx = ToolCtx {
+        app: app.clone(),
+        session_id: session_id.to_string(),
+        call_id: String::new(),
+        cwd: cwd.clone(),
+        cancel: CancellationToken::new(),
+        agent: session.agent.clone(),
+        roots: app.user_roots(session.owner_id.as_deref()),
+        sandbox: crate::sandbox::spec_for(app, session.owner_id.as_deref()),
+        clean_room: session.clean_room(app.config().craft.clean_room),
+    };
+    let mut parts = Vec::new();
+    for token in tokens.into_iter().take(MAX_MENTIONS) {
+        let Ok(path) = ctx.resolve_read(&token) else { continue };
+        if !path.exists() {
+            continue;
+        }
+        let res = if path.is_dir() {
+            crate::tools::fs::List.run(json!({"path": token}), &ctx).await
+        } else {
+            crate::tools::fs::Read.run(json!({"path": token}), &ctx).await
+        };
+        let Ok(out) = res else { continue };
+        let mut content = out.content;
+        if content.len() > MAX_CHARS {
+            let mut end = MAX_CHARS;
+            while !content.is_char_boundary(end) {
+                end -= 1;
+            }
+            content.truncate(end);
+            content.push_str("\n[… truncated – read the rest with the read tool]");
+        }
+        let kind = if path.is_dir() { "folder" } else { "file" };
+        parts.push(Part::Text { text: format!("<mentioned-{kind} path=\"{token}\">\n{content}\n</mentioned-{kind}>") });
+        parts.extend(out.images.into_iter().map(|image| Part::Image { image }));
+    }
+    parts
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn finds_mentions() {
+        assert_eq!(super::find("look at @src/main.rs, and @README.md."), vec!["src/main.rs", "README.md"]);
+        assert!(super::find("mail me at a@b.de").is_empty());
+        assert_eq!(super::find("@docs/ please"), vec!["docs/"]);
+    }
+}