githubnext
diff --git a/‎AGENTS.md‎
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diff --git a/‎docs/runtimes.md‎
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diff --git a/‎src/compile/common.rs‎
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diff --git a/‎src/compile/extensions/mod.rs‎
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@@ -99,8 +99,14 @@ Every compiled pipeline runs as three sequential jobs:
 │   │   └── upload_workitem_attachment.rs
 │   ├── runtimes/         # Runtime environment implementations (one dir per runtime)
 │   │   ├── mod.rs        # Module entry point
-│   │   └── lean/         # Lean 4 theorem prover runtime
-│   │       ├── mod.rs    # Config types, install helpers
+│   │   ├── lean/         # Lean 4 theorem prover runtime
+│   │   │   ├── mod.rs    # Config types, install helpers
+│   │   │   └── extension.rs # CompilerExtension impl
+│   │   ├── python/       # Python runtime
+│   │   │   ├── mod.rs    # Config types, install/auth helpers
+│   │   │   └── extension.rs # CompilerExtension impl
+│   │   └── node/         # Node.js runtime
+│   │       ├── mod.rs    # Config types, install/auth helpers
 │   │       └── extension.rs # CompilerExtension impl
 │   ├── data/
 │   │   ├── base.yml          # Base pipeline template for standalone
@@ -156,8 +162,8 @@ index to jump to the right page.
   in the pipeline UI, including the auto-injected `clearMemory` parameter.
 - [`docs/tools.md`](docs/tools.md) — `tools:` configuration (bash allow-list,
   `edit`, `cache-memory`, `azure-devops` MCP).
-- [`docs/runtimes.md`](docs/runtimes.md) — `runtimes:` configuration (currently
-  Lean 4).
+- [`docs/runtimes.md`](docs/runtimes.md) — `runtimes:` configuration (Lean 4,
+  Python, Node.js).
 - [`docs/targets.md`](docs/targets.md) — target platforms: `standalone` and
   `1es`.
 - [`docs/safe-outputs.md`](docs/safe-outputs.md) — full reference for every
 
@@ -33,3 +33,87 @@ When enabled, the compiler:
 - Emits a compile-time warning if `tools.bash` is empty (Lean requires bash access)
 
 **Note:** In the 1ES target, the bash command allow-list is updated but elan installation must be done manually via `steps:` front matter. The 1ES target handles network isolation separately.
+
+### Python (`python:`)
+
+Python runtime. Auto-installs Python via `UsePythonVersion@0`, emits `PipAuthenticate@1` for internal feed access, adds Python ecosystem domains to the AWF network allowlist, extends the bash command allow-list, and optionally injects feed URL env vars for pip and uv.
+
+```yaml
+# Simple enablement (installs default Python 3.x)
+runtimes:
+  python: true
+
+# With options (pin version, configure feed)
+runtimes:
+  python:
+    version: "3.12"
+    feed-url: "https://pkgs.dev.azure.com/myorg/_packaging/myfeed/pypi/simple/"
+```
+
+**Fields:**
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `version` | string | Python version to install (e.g., `"3.12"`, `"3.11"`). Passed to `UsePythonVersion@0` `versionSpec`. Defaults to latest 3.x. |
+| `feed-url` | string | Internal PyPI feed URL. Injects `PIP_INDEX_URL` and `UV_DEFAULT_INDEX` env vars into the agent environment. |
+| `config` | string | Path to a pip/uv config file. Accepted with a warning — the file will not be available inside the AWF agent environment until proxy-auth support lands. |
+
+When enabled, the compiler:
+- Injects `UsePythonVersion@0` into `{{ prepare_steps }}` (runs before AWF)
+- If `feed-url` is set, also injects `PipAuthenticate@1` to authenticate the ADO build service identity for internal feeds
+- Auto-adds `python`, `python3`, `pip`, `pip3`, `uv` to the bash command allow-list
+- Adds Python ecosystem domains to the network allowlist (pypi.org, pythonhosted.org, etc.)
+- If `feed-url` is set, injects `PIP_INDEX_URL` and `UV_DEFAULT_INDEX` env vars into the agent environment
+- Appends a prompt supplement informing the agent about Python availability
+- No AWF mounts or PATH prepends needed — `UsePythonVersion@0` installs to `/opt/hostedtoolcache` (auto-mounted by AWF) and publishes PATH entries that AWF merges via `$GITHUB_PATH`
+
+**Note:** `PipAuthenticate@1` is currently emitted with an empty `artifactFeeds` input, which configures credentials for all feeds accessible to the build service identity. If your internal feed requires scoped authentication to a specific Azure Artifacts feed, this may need future refinement.
+
+### Node.js (`node:`)
+
+Node.js runtime. Auto-installs Node.js via `NodeTool@0`, emits `npmAuthenticate@0` for internal feed access, adds Node ecosystem domains to the AWF network allowlist, extends the bash command allow-list, and optionally injects feed URL env vars for npm.
+
+```yaml
+# Simple enablement (installs default Node LTS)
+runtimes:
+  node: true
+
+# With options (pin version, configure feed)
+runtimes:
+  node:
+    version: "22.x"
+    feed-url: "https://pkgs.dev.azure.com/ORG/PROJECT/_packaging/FEED/npm/registry/"
+```
+
+**Fields:**
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `version` | string | Node.js version to install (e.g., `"22.x"`, `"20.x"`). Passed to `NodeTool@0` `versionSpec`. Defaults to `"22.x"`. |
+| `feed-url` | string | Internal npm registry URL. Injects `NPM_CONFIG_REGISTRY` env var into the agent environment. |
+| `config` | string | Path to an .npmrc config file. Accepted with a warning — the file will not be available inside the AWF agent environment until proxy-auth support lands. |
+
+When enabled, the compiler:
+- Injects `NodeTool@0` into `{{ prepare_steps }}` (runs before AWF)
+- If `feed-url` or `config` is set, also injects `npmAuthenticate@0` (and an ensure-`.npmrc` step) to authenticate the ADO build service identity for internal feeds
+- Auto-adds `node`, `npm`, `npx` to the bash command allow-list
+- Adds Node ecosystem domains to the network allowlist (npmjs.org, nodejs.org, etc.)
+- If `feed-url` is set, injects `NPM_CONFIG_REGISTRY` env var into the agent environment
+- Appends a prompt supplement informing the agent about Node.js availability
+- No AWF mounts or PATH prepends needed — `NodeTool@0` installs to `/opt/hostedtoolcache` (auto-mounted by AWF) and publishes PATH entries that AWF merges via `$GITHUB_PATH`
+- Note: AWF overlays `~/.npmrc` with `/dev/null` for credential security — the `NPM_CONFIG_REGISTRY` env var approach avoids conflicting with this overlay
+
+### Combining Runtimes
+
+Multiple runtimes can be enabled simultaneously:
+
+```yaml
+runtimes:
+  python:
+    version: "3.12"
+  node:
+    version: "22.x"
+  lean: true
+```
+
+All runtime extensions are sorted into `ExtensionPhase::Runtime` and execute before tool extensions (`ExtensionPhase::Tool`), ensuring language toolchains are available before any tools that depend on them.
@@ -1912,6 +1912,71 @@ pub fn collect_awf_path_prepends(extensions: &[super::extensions::Extension]) ->
         .collect()
 }
 
+/// Collects `agent_env_vars()` from all extensions, validates keys against
+/// `BLOCKED_ENV_KEYS`, deduplicates (bails on collision), and formats them
+/// as YAML `KEY: "value"` lines for injection into the `{{ engine_env }}` block.
+///
+/// Returns an empty string if no extensions declare env vars.
+pub fn collect_agent_env_vars(extensions: &[super::extensions::Extension]) -> anyhow::Result<String> {
+    use crate::engine::BLOCKED_ENV_KEYS;
+    use crate::validate;
+    use std::collections::HashSet;
+
+    let mut lines = Vec::new();
+    let mut seen_keys = HashSet::new();
+
+    for ext in extensions {
+        for (key, value) in ext.agent_env_vars() {
+            // Deduplicate: bail on collision
+            if !seen_keys.insert(key.clone()) {
+                anyhow::bail!(
+                    "Extension '{}' declares agent env var '{}' which was already declared \
+                     by a previous extension. Each env var key must be unique.",
+                    ext.name(),
+                    key,
+                );
+            }
+
+            // Validate key is not blocked
+            if BLOCKED_ENV_KEYS.iter().any(|blocked| key.eq_ignore_ascii_case(blocked)) {
+                anyhow::bail!(
+                    "Extension '{}' declares agent env var '{}' which conflicts with a \
+                     compiler-controlled environment variable.",
+                    ext.name(),
+                    key,
+                );
+            }
+
+            // Validate key format
+            if !validate::is_valid_env_var_name(&key) {
+                anyhow::bail!(
+                    "Extension '{}' declares agent env var '{}' with invalid key format. \
+                     Keys must contain only ASCII alphanumerics and underscores.",
+                    ext.name(),
+                    key,
+                );
+            }
+
+            // Validate value for injection (defence in depth — covers ADO expressions,
+            // pipeline commands, template markers, and newlines)
+            validate::reject_pipeline_injection(&value, &format!("agent env var '{key}'"))?;
+
+            if value.contains('"') || value.contains('\'') {
+                anyhow::bail!(
+                    "Extension '{}' agent env var '{}' value contains a quote character \
+                     which would produce malformed YAML or bash syntax.",
+                    ext.name(),
+                    key,
+                );
+            }
+
+            lines.push(format!("{key}: \"{value}\""));
+        }
+    }
+
+    Ok(lines.join("\n"))
+}
+
 // ==================== Shared compile flow ====================
 
 /// Target-specific overrides for the shared compile flow.
@@ -2104,6 +2169,12 @@ pub async fn compile_shared(
     if !awf_path_env.is_empty() {
         engine_env = format!("{engine_env}\n{awf_path_env}");
     }
+
+    // Append extension-declared agent env vars (e.g., PIP_INDEX_URL, NPM_CONFIG_REGISTRY)
+    let agent_env = collect_agent_env_vars(extensions)?;
+    if !agent_env.is_empty() {
+        engine_env = format!("{engine_env}\n{agent_env}");
+    }
     let engine_log_dir = ctx.engine.log_dir();
     let acquire_write_token = generate_acquire_ado_token(
         front_matter
@@ -2505,6 +2576,8 @@ mod tests {
         });
         fm.runtimes = Some(crate::compile::types::RuntimesConfig {
             lean: Some(crate::runtimes::lean::LeanRuntimeConfig::Enabled(true)),
+            python: None,
+            node: None,
         });
         let params = CompileContext::for_test(&fm).engine.args(&fm, &crate::compile::extensions::collect_extensions(&fm)).unwrap();
         assert!(params.contains("shell(lean)"), "lean command should be allowed");
@@ -2525,6 +2598,8 @@ mod tests {
         });
         fm.runtimes = Some(crate::compile::types::RuntimesConfig {
             lean: Some(crate::runtimes::lean::LeanRuntimeConfig::Enabled(true)),
+            python: None,
+            node: None,
         });
         let params = CompileContext::for_test(&fm).engine.args(&fm, &crate::compile::extensions::collect_extensions(&fm)).unwrap();
         assert!(params.contains("--allow-all-tools"), "wildcard should use --allow-all-tools");
 
@@ -324,6 +324,17 @@ pub trait CompilerExtension {
     fn awf_path_prepends(&self) -> Vec<String> {
         vec![]
     }
+
+    /// Environment variables to inject into the agent execution environment.
+    ///
+    /// Returns `(key, value)` pairs that are emitted as `KEY: "value"` in
+    /// the `{{ engine_env }}` YAML block. Used by runtimes to configure
+    /// package managers via env vars (e.g., `PIP_INDEX_URL`, `NPM_CONFIG_REGISTRY`).
+    ///
+    /// Keys are validated against `BLOCKED_ENV_KEYS` at collection time.
+    fn agent_env_vars(&self) -> Vec<(String, String)> {
+        vec![]
+    }
 }
 
 /// Mount access mode for an AWF bind mount.
@@ -534,6 +545,9 @@ macro_rules! extension_enum {
             fn awf_path_prepends(&self) -> Vec<String> {
                 match self { $( $Enum::$Variant(e) => e.awf_path_prepends(), )+ }
             }
+            fn agent_env_vars(&self) -> Vec<(String, String)> {
+                match self { $( $Enum::$Variant(e) => e.agent_env_vars(), )+ }
+            }
         }
     };
 }
@@ -547,6 +561,8 @@ pub use crate::tools::azure_devops::AzureDevOpsExtension;
 pub use crate::tools::cache_memory::CacheMemoryExtension;
 pub use github::GitHubExtension;
 pub use crate::runtimes::lean::LeanExtension;
+pub use crate::runtimes::node::NodeExtension;
+pub use crate::runtimes::python::PythonExtension;
 pub use safe_outputs::SafeOutputsExtension;
 pub use trigger_filters::TriggerFiltersExtension;
 
@@ -559,6 +575,8 @@ extension_enum! {
         GitHub(GitHubExtension),
         SafeOutputs(SafeOutputsExtension),
         Lean(LeanExtension),
+        Python(PythonExtension),
+        Node(NodeExtension),
         AzureDevOps(AzureDevOpsExtension),
         CacheMemory(CacheMemoryExtension),
         TriggerFilters(TriggerFiltersExtension),
@@ -593,6 +611,16 @@ pub fn collect_extensions(front_matter: &FrontMatter) -> Vec<Extension> {
             extensions.push(Extension::Lean(LeanExtension::new(lean.clone())));
         }
     }
+    if let Some(python) = front_matter.runtimes.as_ref().and_then(|r| r.python.as_ref()) {
+        if python.is_enabled() {
+            extensions.push(Extension::Python(PythonExtension::new(python.clone())));
+        }
+    }
+    if let Some(node) = front_matter.runtimes.as_ref().and_then(|r| r.node.as_ref()) {
+        if node.is_enabled() {
+            extensions.push(Extension::Node(NodeExtension::new(node.clone())));
+        }
+    }
 
     // ── First-party tools (ExtensionPhase::Tool) ──
     if let Some(tools) = front_matter.tools.as_ref() {