ACP champagne (#35609)

cherry pick changes from #35510 onto latest main

Release Notes:

- N/A

---------

Co-authored-by: Nathan Sobo <nathan@zed.dev>
Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Lukas Wirth <lukas@zed.dev>

crates/agent2/src/templates.rs

@@ -0,0 +1,57 @@
+use std::sync::Arc;
+
+use anyhow::Result;
+use handlebars::Handlebars;
+use rust_embed::RustEmbed;
+use serde::Serialize;
+
+#[derive(RustEmbed)]
+#[folder = "src/templates"]
+#[include = "*.hbs"]
+struct Assets;
+
+pub struct Templates(Handlebars<'static>);
+
+impl Templates {
+    pub fn new() -> Arc<Self> {
+        let mut handlebars = Handlebars::new();
+        handlebars.register_embed_templates::<Assets>().unwrap();
+        Arc::new(Self(handlebars))
+    }
+}
+
+pub trait Template: Sized {
+    const TEMPLATE_NAME: &'static str;
+
+    fn render(&self, templates: &Templates) -> Result<String>
+    where
+        Self: Serialize + Sized,
+    {
+        Ok(templates.0.render(Self::TEMPLATE_NAME, self)?)
+    }
+}
+
+#[derive(Serialize)]
+pub struct BaseTemplate {
+    pub os: String,
+    pub shell: String,
+    pub worktrees: Vec<WorktreeData>,
+}
+
+impl Template for BaseTemplate {
+    const TEMPLATE_NAME: &'static str = "base.hbs";
+}
+
+#[derive(Serialize)]
+pub struct WorktreeData {
+    pub root_name: String,
+}
+
+#[derive(Serialize)]
+pub struct GlobTemplate {
+    pub project_roots: String,
+}
+
+impl Template for GlobTemplate {
+    const TEMPLATE_NAME: &'static str = "glob.hbs";
+}