feat: add a runtime Towerfile field and a bun runtime

.github/workflows/test-rust.yml

@@ -35,6 +35,13 @@ jobs:
         with:
           save-if: ${{ github.ref_name == 'main' }}
 
+      # The bun runtime tests run bun from PATH. They're unix-only, like the runtime's bun support.
+      - name: Set up bun
+        if: runner.os == 'Linux'
+        uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: 1.4.4
+
       - name: Compile tests
         run: >
           cargo test --all-features --no-run

crates/tower-cmd/src/error.rs

@@ -63,6 +63,15 @@ pub enum Error {
     #[snafu(display("No [project] section found in pyproject.toml"))]
     MissingProjectSection,
 
+    #[snafu(display("package.json not found at {}", path))]
+    PackageJsonNotFound { path: String },
+
+    #[snafu(display("Failed to parse package.json: {}", source))]
+    InvalidPackageJson { source: serde_json::Error },
+
+    #[snafu(display("No pyproject.toml or package.json found in {}", dir))]
+    ProjectFileNotFound { dir: String },
+
     // File I/O errors
     #[snafu(display("File I/O error: {}", source))]
     IoError { source: std::io::Error },

crates/tower-cmd/src/mcp.rs

@@ -83,6 +83,9 @@ struct UpdateTowerfileRequest {
     /// Compute size for each run: one of basic.xsmall, basic.small,
     /// basic.medium, basic.large. Omit to let Tower apply its default.
     run_size: Option<String>,
+    /// What starts the script: python, bash or bun. Omit to follow the
+    /// script's extension (.sh runs with bash, anything else with Python).
+    runtime: Option<String>,
 }
 
 #[derive(Debug, Deserialize, JsonSchema)]
@@ -1023,7 +1026,7 @@ impl TowerService {
     }
 
     #[tool(
-        description = "Update Towerfile config (app name, script, description, source, run_size). Use this instead of editing TOML. Optional: working_directory."
+        description = "Update Towerfile config (app name, script, description, source, run_size, runtime). Use this instead of editing TOML. Optional: working_directory."
     )]
     async fn tower_file_update(
         &self,
@@ -1045,6 +1048,9 @@ impl TowerService {
             if let Some(run_size) = request.run_size {
                 tf.app.run_size = Some(run_size);
             }
+            if let Some(runtime) = request.runtime {
+                tf.app.runtime = Some(runtime);
+            }
             Ok("Towerfile updated".into())
         })
     }
@@ -1139,21 +1145,18 @@ impl TowerService {
     }
 
     #[tool(
-        description = "Generate Towerfile from pyproject.toml (first step). Don't add build systems to pyproject.toml. Optional: working_directory."
+        description = "Generate Towerfile from pyproject.toml, or from package.json for a bun app (first step). Don't add build systems to pyproject.toml. Optional: working_directory."
     )]
     async fn tower_file_generate(
         &self,
         Parameters(request): Parameters<GenerateTowerfileRequest>,
     ) -> Result<CallToolResult, McpError> {
         let working_dir = Self::resolve_working_directory(&request.common);
-        let pyproject_path = working_dir.join("pyproject.toml");
-        let content = match TowerfileGenerator::from_pyproject(
-            Some(pyproject_path.to_str().unwrap()),
-            request.script_path.as_deref(),
-        ) {
-            Ok(content) => content,
-            Err(e) => return Self::error_result("Failed to generate Towerfile", e),
-        };
+        let content =
+            match TowerfileGenerator::from_dir(&working_dir, request.script_path.as_deref()) {
+                Ok(content) => content,
+                Err(e) => return Self::error_result("Failed to generate Towerfile", e),
+            };
 
         let towerfile_path = working_dir.join("Towerfile");
         match std::fs::write(&towerfile_path, &content) {
@@ -1191,6 +1194,11 @@ All tools accept optional working_directory parameter to specify which project t
    DO NOT add [build-system], [tool.hatchling], [tool.setuptools] or similar
    Skip this step if project with pyproject.toml already exists
 
+   JAVASCRIPT OR TYPESCRIPT PROJECT (if creating new):
+   Use 'bun init -y' in project directory to create package.json and index.ts
+   Skip this step if project with package.json already exists
+   tower_file_generate then writes a Towerfile with runtime = "bun"
+
 1. TOWERFILE (required for all Tower operations):
    tower_file_generate → tower_file_update → tower_file_add/edit/remove_parameter → tower_file_validate
    CRITICAL: Always use tower_file_update or tower_file_add/edit/remove_parameter to modify
@@ -1218,8 +1226,8 @@ All tools accept optional working_directory parameter to specify which project t
    tower_secrets_create, tower_secrets_list - store credentials, API keys, database passwords
 
 TYPICAL WORKFLOW:
-1. Check if pyproject.toml exists (or create with uv init)
-2. tower_file_generate - creates Towerfile from pyproject.toml
+1. Check if pyproject.toml or package.json exists (or create with uv init / bun init -y)
+2. tower_file_generate - creates Towerfile from pyproject.toml or package.json
 3. tower_run_local - test locally (can access tower secrets)
 4. tower_apps_create - create app in Tower cloud
 5. tower_deploy - deploy code to Tower
@@ -1331,7 +1339,7 @@ Rules:
 - MCP tools are the authoritative Tower interface (not wrappers)
 - Use tower_file_update/add/edit/remove_parameter to modify Towerfiles (never edit TOML directly)
 - DO NOT add hatchling/setuptools to pyproject.toml - Tower handles deployment
-- Tower apps need: pyproject.toml (deps only), Python code, Towerfile
+- Tower apps need: pyproject.toml (deps only), Python code, Towerfile; or, for bun apps, package.json, JavaScript or TypeScript code, Towerfile
 - Pass run parameters as a JSON object {\"key\": \"value\"}, not as CLI flags
 - There is no --param or --params flag
 

crates/tower-cmd/src/skill.rs

@@ -182,6 +182,8 @@ uv init
 
 Creates `pyproject.toml`, `main.py`, `README.md`. Keep `pyproject.toml` minimal — `[project]` metadata and dependencies only. No `[build-system]`, `[tool.hatchling]`, or similar. Skip if a `pyproject.toml` already exists.
 
+For a JavaScript or TypeScript app, run `bun init -y` instead, which creates `package.json` and `index.ts`. Skip it if a `package.json` already exists. Without a `pyproject.toml`, `tower_file_generate` reads `package.json` and sets `runtime = "bun"`.
+
 ### 1. Towerfile
 
 ```
@@ -192,6 +194,8 @@ Always use `tower_file_update` or `tower_file_add/edit/remove_parameter` to modi
 
 To give an app more compute, set `run_size` via `tower_file_update`: one of `basic.xsmall`, `basic.small`, `basic.medium` (the default), `basic.large`. It is versioned with the code, and self-hosted runners ignore it.
 
+To run JavaScript or TypeScript, set `runtime` to `bun` via `tower_file_update` and point `script` at a `.ts`, `.tsx`, `.js`, `.jsx`, `.mjs` or `.cjs` file. Dependencies come from `package.json` (and `bun.lock`). Without `runtime`, `.sh` scripts run with bash and everything else with Python.
+
 ### 2. Local development (preferred)
 
 ```