MCP MVP

ARCHITECTURE.md

@@ -8,7 +8,7 @@ StartOS is an open-source Linux distribution for running personal servers. It ma
 - Frontend: Angular 21 + TypeScript + Taiga UI 5
 - Container runtime: Node.js/TypeScript with LXC
 - Database/State: Patch-DB (git submodule) - storage layer with reactive frontend sync
-- API: JSON-RPC via rpc-toolkit (see `core/rpc-toolkit.md`)
+- API: JSON-RPC via rpc-toolkit (see `core/rpc-toolkit.md`), MCP for LLM agents (see `core/mcp/ARCHITECTURE.md`)
 - Auth: Password + session cookie, public/private key signatures, local authcookie (see `core/src/middleware/auth/`)
 
 ## Project Structure
@@ -28,7 +28,7 @@ StartOS is an open-source Linux distribution for running personal servers. It ma
 
 ## Components
 
-- **`core/`** — Rust backend daemon. Produces a single binary `startbox` that is symlinked as `startd` (main daemon), `start-cli` (CLI), `start-container` (runs inside LXC containers), `registrybox` (package registry), and `tunnelbox` (VPN/tunnel). Handles all backend logic: RPC API, service lifecycle, networking (DNS, ACME, WiFi, Tor, WireGuard), backups, and database state management. See [core/ARCHITECTURE.md](core/ARCHITECTURE.md).
+- **`core/`** — Rust backend daemon. Produces a single binary `startbox` that is symlinked as `startd` (main daemon), `start-cli` (CLI), `start-container` (runs inside LXC containers), `registrybox` (package registry), and `tunnelbox` (VPN/tunnel). Handles all backend logic: RPC API, MCP server for LLM agents, service lifecycle, networking (DNS, ACME, WiFi, Tor, WireGuard), backups, and database state management. See [core/ARCHITECTURE.md](core/ARCHITECTURE.md).
 
 - **`web/`** — Angular 21 + TypeScript workspace using Taiga UI 5. Contains three applications (admin UI, setup wizard, VPN management) and two shared libraries (common components/services, marketplace). Communicates with the backend exclusively via JSON-RPC. See [web/ARCHITECTURE.md](web/ARCHITECTURE.md).
 
@@ -54,7 +54,7 @@ Rust (core/)
 Key make targets along this chain:
 
 | Step | Command                                 | What it does                      |
-|---|---|---|
+| ---- | --------------------------------------- | --------------------------------- |
 | 1    | `cargo check -p start-os`               | Verify Rust compiles              |
 | 2    | `make ts-bindings`                      | Export ts-rs types → rsync to SDK |
 | 3    | `cd sdk && make baseDist dist`          | Build SDK packages                |
@@ -90,6 +90,17 @@ StartOS uses Patch-DB for reactive state synchronization:
 
 This means the UI is always eventually consistent with the backend — after any mutating API call, the frontend waits for the corresponding PatchDB diff before resolving, so the UI reflects the result immediately.
 
+## MCP Server (LLM Agent Interface)
+
+StartOS includes an [MCP](https://modelcontextprotocol.io/) (Model Context Protocol) server at `/mcp`, enabling LLM agents to discover and invoke the same operations available through the UI and CLI. The MCP server runs inside the StartOS server process alongside the RPC API.
+
+- **Tools**: Every RPC method is exposed as an MCP tool with LLM-optimized descriptions and JSON Schema inputs. Agents call `tools/list` to discover what's available and `tools/call` to invoke operations.
+- **Resources**: System state is exposed via MCP resources backed by Patch-DB. Agents subscribe to `startos:///public` and receive debounced revision diffs over SSE, maintaining a local state cache without polling.
+- **Auth**: Same session cookie auth as the UI — no separate credentials.
+- **Transport**: MCP Streamable HTTP — POST for requests, GET for SSE notification stream, DELETE for session teardown.
+
+See [core/ARCHITECTURE.md](core/ARCHITECTURE.md#mcp-server) for implementation details.
+
 ## Further Reading
 
 - [core/ARCHITECTURE.md](core/ARCHITECTURE.md) — Rust backend architecture

core/ARCHITECTURE.md

@@ -23,6 +23,7 @@ The crate produces a single binary `startbox` that is symlinked under different
 - `src/context/` — Context types (RpcContext, CliContext, InitContext, DiagnosticContext)
 - `src/service/` — Service lifecycle management with actor pattern (`service_actor.rs`)
 - `src/db/model/` — Patch-DB models (`public.rs` synced to frontend, `private.rs` backend-only)
+- `src/mcp/` — MCP server for LLM agents (see [MCP Server](#mcp-server) below)
 - `src/net/` — Networking (DNS, ACME, WiFi, Tor via Arti, WireGuard)
 - `src/s9pk/` — S9PK package format (merkle archive)
 - `src/registry/` — Package registry management
@@ -38,16 +39,19 @@ See [rpc-toolkit.md](rpc-toolkit.md) for full handler patterns and configuration
 Patch-DB provides diff-based state synchronization. Changes to `db/model/public.rs` automatically sync to the frontend.
 
 **Key patterns:**
+
 - `db.peek().await` — Get a read-only snapshot of the database state
 - `db.mutate(|db| { ... }).await` — Apply mutations atomically, returns `MutateResult`
 - `#[derive(HasModel)]` — Derive macro for types stored in the database, generates typed accessors
 
 **Generated accessor types** (from `HasModel` derive):
+
 - `as_field()` — Immutable reference: `&Model<T>`
 - `as_field_mut()` — Mutable reference: `&mut Model<T>`
 - `into_field()` — Owned value: `Model<T>`
 
 **`Model<T>` APIs** (from `db/prelude.rs`):
+
 - `.de()` — Deserialize to `T`
 - `.ser(&value)` — Serialize from `T`
 - `.mutate(|v| ...)` — Deserialize, mutate, reserialize
@@ -63,6 +67,12 @@ See [i18n-patterns.md](i18n-patterns.md) for internationalization key convention
 
 See [core-rust-patterns.md](core-rust-patterns.md) for common utilities (Invoke trait, Guard pattern, mount guards, Apply trait, etc.).
 
+## MCP Server
+
+The MCP (Model Context Protocol) server at `src/mcp/` exposes the StartOS RPC API to LLM agents via the Streamable HTTP transport at `/mcp`. Tools wrap the existing RPC handlers; resources expose Patch-DB state with debounced SSE subscriptions; auth reuses the UI session cookie.
+
+See [src/mcp/ARCHITECTURE.md](src/mcp/ARCHITECTURE.md) for transport details, session lifecycle, tool dispatch, resource subscriptions, CORS, and body size limits.
+
 ## Related Documentation
 
 - [rpc-toolkit.md](rpc-toolkit.md) — JSON-RPC handler patterns

core/src/db/mod.rs

@@ -163,13 +163,13 @@ pub struct SubscribeRes {
     pub guid: Guid,
 }
 
-struct DbSubscriber {
+pub(crate) struct DbSubscriber {
-    rev: u64,
+    pub(crate) rev: u64,
-    sub: UnboundedReceiver<Revision>,
+    pub(crate) sub: UnboundedReceiver<Revision>,
-    sync_db: watch::Receiver<u64>,
+    pub(crate) sync_db: watch::Receiver<u64>,
 }
 impl DbSubscriber {
-    async fn recv(&mut self) -> Option<Revision> {
+    pub(crate) async fn recv(&mut self) -> Option<Revision> {
         loop {
             tokio::select! {
                 rev = self.sub.recv() => {

core/src/lib.rs

@@ -63,6 +63,7 @@ pub mod init;
 pub mod install;
 pub mod logs;
 pub mod lxc;
+pub mod mcp;
 pub mod middleware;
 pub mod net;
 pub mod notifications;

core/src/mcp/ARCHITECTURE.md

@@ -0,0 +1,96 @@
+# MCP Server Architecture
+
+The Model Context Protocol server embedded in StartOS (`core/src/mcp/`).
+
+## Transport: Streamable HTTP (MCP 2025-03-26)
+
+The server implements the **Streamable HTTP** transport from the MCP spec, not the older stdio or SSE-only transports. A single route (`/mcp`) handles all three HTTP methods:
+
+| Method      | Purpose                                                                          |
+| ----------- | -------------------------------------------------------------------------------- |
+| **POST**    | JSON-RPC 2.0 requests from client (initialize, tools/call, resources/read, etc.) |
+| **GET**     | Opens an SSE stream for server→client notifications (resource change events)     |
+| **DELETE**  | Explicitly ends a session                                                        |
+| **OPTIONS** | CORS preflight                                                                   |
+
+A discovery endpoint at `/.well-known/mcp` returns `{"mcp_endpoint":"/mcp"}`.
+
+## Authentication
+
+Every HTTP method (POST, GET, DELETE) validates the caller's session cookie via `ValidSessionToken::from_header` before processing. This reuses the same auth infrastructure as the main StartOS web UI — MCP clients must present a valid session cookie obtained through the normal login flow. Unauthenticated requests get a 401.
+
+## Session Lifecycle
+
+1. **Create**: Client sends `initialize` via POST. Server generates a UUID session ID, creates an `McpSession` with a bounded mpsc channel (256 messages), and returns the ID in the `Mcp-Session-Id` response header.
+
+2. **Connect SSE**: Client opens a GET with the session ID header. The server takes the receiver half of the notification channel (`take_notification_rx`) and streams it as SSE events. Only one GET connection per session is allowed (the rx is moved, not cloned).
+
+3. **Use**: Client sends tool calls, resource reads, subscriptions via POST. All POST requests must include a valid session ID header — the server validates it against the session map before processing.
+
+4. **Teardown**: Three paths:
+   - Client sends DELETE -> session is removed, subscription tasks are aborted.
+   - SSE stream disconnects -> `CleanupStream`'s `PinnedDrop` impl removes the session.
+   - Session is never connected -> background sweep task (every 30s) removes sessions older than 60s that never had a GET stream attached.
+
+## Module Structure
+
+```
+core/src/mcp/
+├── mod.rs        — HTTP handlers, routing, MCP method dispatch, shell execution, CORS
+├── protocol.rs   — JSON-RPC 2.0 types, MCP request/response structs, error codes
+├── session.rs    — Session map, create/remove/sweep, resource subscriptions with debounce
+└── tools.rs      — Tool registry (67 tools), HashMap<String, ToolEntry> mapping names → RPC methods + schemas
+```
+
+## Tool Dispatch
+
+`tool_registry()` returns a `HashMap<String, ToolEntry>`, each mapping:
+
+- An MCP tool name (e.g. `"package.start"`)
+- A JSON Schema for input validation (sent to clients via `tools/list`)
+- A backing RPC method name (usually identical to the tool name)
+- Flags: `sync_db` (whether to flush DB sequence after success), `needs_session` (whether to inject `__Auth_session`)
+
+When `tools/call` arrives:
+
+1. Look up the tool by name via HashMap O(1) lookup.
+2. Convert arguments from `serde_json::Value` to `imbl_value::Value`.
+3. **Special-case**: If `rpc_method` is `"__shell__"` or `"__package_shell__"`, dispatch to `handle_shell_exec` / `handle_package_shell_exec` directly (no RPC handler). Both set `kill_on_drop(true)` to ensure timed-out processes are terminated.
+4. Otherwise, optionally inject `__Auth_session` into params, then call `server.handle_command(rpc_method, params)`.
+5. On success: if `sync_db` is true, flush the DB sequence. Return the result pretty-printed as a text content block.
+6. On error: return the error as a text content block with `is_error: true`, using `McpResponse::ok` (MCP spec: tool errors are results, not JSON-RPC errors).
+
+## Shell Execution
+
+Two shell tools bypass the RPC layer entirely:
+
+- **`system.shell`** (`__shell__`): Runs `/bin/bash -c <command>` on the host with `kill_on_drop(true)`. 30s default timeout, 300s max.
+- **`package.shell`** (`__package_shell__`): Resolves the target package's subcontainer via `Service::resolve_subcontainer`, then runs `/bin/sh -c <command>` inside it via `lxc-attach` (also `kill_on_drop(true)`). Same timeout behavior.
+
+## Resource Subscriptions
+
+Four resources are exposed:
+
+- `startos:///public` — full public DB tree
+- `startos:///public/serverInfo` — server metadata
+- `startos:///public/packageData` — installed packages
+- `startos:///mcp/system-prompt` — curated AI assistant context (text/plain)
+
+Resource URIs are validated to only allow `/public/**` subtrees and the special `/mcp/system-prompt` path. Attempts to access non-public paths (e.g. `startos:///private/...`) are rejected.
+
+`resources/read` parses the URI into a `JsonPointer`, calls `ctx.db.dump(&pointer)`, and returns the JSON. The system prompt resource is handled as a special case, returning server info and version.
+
+`resources/subscribe` creates a `DbSubscriber` that watches the patch-db for changes at the given pointer. Changes are **debounced** (500ms window): the subscriber collects multiple revisions and merges their `DiffPatch`es before sending a single `notifications/resources/updated` notification over the SSE channel. The subscription task runs as a spawned tokio task; its `JoinHandle` is stored in the session so it can be aborted on unsubscribe or session teardown. Re-subscribing to the same URI aborts the prior subscription first.
+
+## CORS
+
+- Preflight (OPTIONS): reflects the request's `Origin`, `Access-Control-Request-Method`, and `Access-Control-Request-Headers` back. Sets `Allow-Credentials: true` and caches for 24h.
+- Normal responses (`apply_cors`): reflects the request's `Origin` header when present, falls back to `*` when absent. Exposes the `Mcp-Session-Id` header. This matches the behavior of the rpc-toolkit `Cors` middleware used by the main UI.
+- CORS headers are applied to all response types: POST JSON-RPC, GET SSE, DELETE, and error responses.
+
+## Body Size Limits
+
+POST request bodies are limited to 1 MiB:
+
+1. `Content-Length` header is checked **before** reading the body (rejects oversized requests immediately).
+2. After reading, the actual body size is re-checked as defense-in-depth for chunked transfers that lack `Content-Length`.

core/src/mcp/protocol.rs

@@ -0,0 +1,211 @@
+use serde::{Deserialize, Serialize};
+use serde_json::Value as JsonValue;
+
+// JSON-RPC 2.0 error codes
+pub const PARSE_ERROR: i32 = -32700;
+pub const INVALID_REQUEST: i32 = -32600;
+pub const METHOD_NOT_FOUND: i32 = -32601;
+pub const INVALID_PARAMS: i32 = -32602;
+pub const INTERNAL_ERROR: i32 = -32603;
+
+pub const PROTOCOL_VERSION: &str = "2025-03-26";
+
+// === JSON-RPC 2.0 envelope ===
+
+#[derive(Deserialize)]
+pub struct McpRequest {
+    pub jsonrpc: String,
+    pub id: Option<JsonValue>,
+    pub method: String,
+    #[serde(default)]
+    pub params: Option<JsonValue>,
+}
+
+#[derive(Serialize)]
+pub struct McpResponse {
+    pub jsonrpc: &'static str,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub id: Option<JsonValue>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub result: Option<JsonValue>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub error: Option<McpError>,
+}
+
+impl McpResponse {
+    pub fn ok(id: Option<JsonValue>, result: JsonValue) -> Self {
+        Self {
+            jsonrpc: "2.0",
+            id,
+            result: Some(result),
+            error: None,
+        }
+    }
+
+    pub fn error(id: Option<JsonValue>, code: i32, message: String, data: Option<JsonValue>) -> Self {
+        Self {
+            jsonrpc: "2.0",
+            id,
+            result: None,
+            error: Some(McpError {
+                code,
+                message,
+                data,
+            }),
+        }
+    }
+}
+
+#[derive(Serialize)]
+pub struct McpError {
+    pub code: i32,
+    pub message: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub data: Option<JsonValue>,
+}
+
+// === initialize ===
+
+#[derive(Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct InitializeParams {
+    pub protocol_version: String,
+    #[serde(default)]
+    pub capabilities: JsonValue,
+    #[serde(default)]
+    pub client_info: Option<ClientInfo>,
+}
+
+#[derive(Deserialize)]
+pub struct ClientInfo {
+    pub name: String,
+    #[serde(default)]
+    pub version: Option<String>,
+}
+
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct InitializeResult {
+    pub protocol_version: &'static str,
+    pub capabilities: ServerCapabilities,
+    pub server_info: ServerInfo,
+}
+
+#[derive(Serialize)]
+pub struct ServerCapabilities {
+    pub tools: ToolsCapability,
+    pub resources: ResourcesCapability,
+}
+
+#[derive(Serialize)]
+pub struct ToolsCapability {}
+
+#[derive(Serialize)]
+pub struct ResourcesCapability {
+    pub subscribe: bool,
+}
+
+#[derive(Serialize)]
+pub struct ServerInfo {
+    pub name: &'static str,
+    pub version: String,
+}
+
+// === tools/list ===
+
+#[derive(Serialize, Clone)]
+#[serde(rename_all = "camelCase")]
+pub struct ToolDefinition {
+    pub name: String,
+    pub description: String,
+    pub input_schema: JsonValue,
+}
+
+#[derive(Serialize)]
+pub struct ToolsListResult {
+    pub tools: Vec<ToolDefinition>,
+}
+
+// === tools/call ===
+
+#[derive(Deserialize)]
+pub struct ToolsCallParams {
+    pub name: String,
+    #[serde(default)]
+    pub arguments: JsonValue,
+}
+
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ToolsCallResult {
+    pub content: Vec<ContentBlock>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub is_error: Option<bool>,
+}
+
+#[derive(Serialize)]
+#[serde(tag = "type")]
+pub enum ContentBlock {
+    #[serde(rename = "text")]
+    Text { text: String },
+}
+
+// === resources/list ===
+
+#[derive(Serialize, Clone)]
+#[serde(rename_all = "camelCase")]
+pub struct ResourceDefinition {
+    pub uri: String,
+    pub name: String,
+    pub description: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub mime_type: Option<String>,
+}
+
+#[derive(Serialize)]
+pub struct ResourcesListResult {
+    pub resources: Vec<ResourceDefinition>,
+}
+
+// === resources/read ===
+
+#[derive(Deserialize)]
+pub struct ResourcesReadParams {
+    pub uri: String,
+}
+
+#[derive(Serialize)]
+pub struct ResourcesReadResult {
+    pub contents: Vec<ResourceContent>,
+}
+
+#[derive(Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ResourceContent {
+    pub uri: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub mime_type: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub text: Option<String>,
+}
+
+// === resources/subscribe + unsubscribe ===
+
+#[derive(Deserialize)]
+pub struct ResourcesSubscribeParams {
+    pub uri: String,
+}
+
+#[derive(Deserialize)]
+pub struct ResourcesUnsubscribeParams {
+    pub uri: String,
+}
+
+// === Server→client notification ===
+
+#[derive(Serialize)]
+pub struct McpNotification {
+    pub jsonrpc: &'static str,
+    pub method: &'static str,
+    pub params: serde_json::Value,
+}

core/src/mcp/session.rs

@@ -0,0 +1,232 @@
+use std::collections::HashMap;
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+use patch_db::json_ptr::JsonPointer;
+use patch_db::DiffPatch;
+use serde_json::Value as JsonValue;
+use tokio::sync::mpsc;
+use tokio::task::JoinHandle;
+use uuid::Uuid;
+
+use crate::context::RpcContext;
+use crate::db::DbSubscriber;
+use crate::prelude::*;
+use crate::util::sync::SyncMutex;
+
+use super::protocol::McpNotification;
+
+pub(crate) type SessionMap = Arc<SyncMutex<HashMap<String, McpSession>>>;
+
+/// Maximum time a session can exist without a GET stream before being cleaned up.
+const SESSION_STALE_TIMEOUT: Duration = Duration::from_secs(60);
+
+/// Maximum buffered notifications before backpressure kicks in.
+const NOTIFICATION_CHANNEL_BOUND: usize = 256;
+
+pub(crate) struct McpSession {
+    pub notification_tx: mpsc::Sender<JsonValue>,
+    pub notification_rx: Option<mpsc::Receiver<JsonValue>>,
+    pub subscriptions: HashMap<String, JoinHandle<()>>,
+    pub created_at: Instant,
+}
+
+pub(crate) fn create_session(sessions: &SessionMap) -> String {
+    let id = Uuid::new_v4().to_string();
+    let (tx, rx) = mpsc::channel(NOTIFICATION_CHANNEL_BOUND);
+    sessions.mutate(|map| {
+        map.insert(
+            id.clone(),
+            McpSession {
+                notification_tx: tx,
+                notification_rx: Some(rx),
+                subscriptions: HashMap::new(),
+                created_at: Instant::now(),
+            },
+        );
+    });
+    id
+}
+
+/// Sweep stale sessions. Call this from any frequent code path (POST handler, create_session).
+pub(crate) fn sweep_stale_sessions_if_needed(sessions: &SessionMap) {
+    sessions.mutate(|map| sweep_stale_sessions(map));
+}
+
+/// Remove sessions that were created but never connected a GET stream within the timeout.
+fn sweep_stale_sessions(map: &mut HashMap<String, McpSession>) {
+    let stale: Vec<String> = map
+        .iter()
+        .filter(|(_, session)| {
+            // Session is stale if rx is still present (no GET connected) and it's old
+            session.notification_rx.is_some()
+                && session.created_at.elapsed() > SESSION_STALE_TIMEOUT
+        })
+        .map(|(id, _)| id.clone())
+        .collect();
+    for id in stale {
+        tracing::info!(
+            target: "mcp_audit",
+            session_id = %id,
+            "Sweeping stale MCP session (no GET stream connected)"
+        );
+        if let Some(session) = map.remove(&id) {
+            for (_, handle) in session.subscriptions {
+                handle.abort();
+            }
+        }
+    }
+}
+
+pub(crate) fn remove_session(sessions: &SessionMap, id: &str) {
+    sessions.mutate(|map| {
+        if let Some(session) = map.remove(id) {
+            for (_, handle) in session.subscriptions {
+                handle.abort();
+            }
+        }
+    });
+}
+
+/// Take the notification receiver from a session (for use by the SSE stream).
+/// Returns None if the session doesn't exist or the rx was already taken.
+pub(crate) fn take_notification_rx(
+    sessions: &SessionMap,
+    id: &str,
+) -> Option<mpsc::Receiver<JsonValue>> {
+    sessions.mutate(|map| map.get_mut(id)?.notification_rx.take())
+}
+
+/// Check whether the given session ID exists in the session map.
+pub(crate) fn session_exists(sessions: &SessionMap, id: &str) -> bool {
+    sessions.peek(|map| map.contains_key(id))
+}
+
+/// Parse a `startos:///...` URI into a JsonPointer.
+fn parse_resource_uri(uri: &str) -> Result<JsonPointer, Error> {
+    let path = uri.strip_prefix("startos://").ok_or_else(|| {
+        Error::new(
+            eyre!("Invalid resource URI: must start with startos://"),
+            ErrorKind::InvalidRequest,
+        )
+    })?;
+    path.parse::<JsonPointer>()
+        .with_kind(ErrorKind::InvalidRequest)
+}
+
+pub(crate) async fn subscribe_resource(
+    ctx: &RpcContext,
+    sessions: &SessionMap,
+    session_id: &str,
+    uri: &str,
+) -> Result<(), Error> {
+    let pointer = parse_resource_uri(uri)?;
+
+    let (dump, sub) = ctx.db.dump_and_sub(pointer).await;
+    let mut db_sub = DbSubscriber {
+        rev: dump.id,
+        sub,
+        sync_db: ctx.sync_db.subscribe(),
+    };
+
+    let tx = sessions
+        .peek(|map| map.get(session_id).map(|s| s.notification_tx.clone()))
+        .ok_or_else(|| Error::new(eyre!("Session not found"), ErrorKind::InvalidRequest))?;
+
+    let uri_owned = uri.to_string();
+
+    let handle = tokio::spawn(async move {
+        loop {
+            // Wait for first revision
+            let first = match db_sub.recv().await {
+                Some(rev) => rev,
+                None => break,
+            };
+
+            // Debounce: collect more revisions for up to 500ms
+            let mut merged_id = first.id;
+            let mut merged_patch = first.patch;
+
+            let debounce = tokio::time::sleep(Duration::from_millis(500));
+            tokio::pin!(debounce);
+
+            loop {
+                tokio::select! {
+                    _ = &mut debounce => break,
+                    rev = db_sub.recv() => {
+                        match rev {
+                            Some(rev) => {
+                                merged_id = rev.id;
+                                merged_patch.append(rev.patch);
+                            }
+                            None => {
+                                // Subscriber closed — send what we have and exit
+                                let _ = send_notification(&tx, &uri_owned, merged_id, &merged_patch);
+                                return;
+                            }
+                        }
+                    }
+                }
+            }
+
+            if send_notification(&tx, &uri_owned, merged_id, &merged_patch).is_err() {
+                break; // SSE stream closed or channel full
+            }
+        }
+    });
+
+    // Store the task handle, aborting any prior subscription for the same URI
+    sessions.mutate(|map| {
+        if let Some(session) = map.get_mut(session_id) {
+            if let Some(old_handle) = session.subscriptions.remove(uri) {
+                tracing::info!(
+                    target: "mcp_audit",
+                    uri = %uri,
+                    session_id = %session_id,
+                    "Aborting prior subscription for re-subscribed URI"
+                );
+                old_handle.abort();
+            }
+            session.subscriptions.insert(uri.to_string(), handle);
+        }
+    });
+
+    Ok(())
+}
+
+fn send_notification(
+    tx: &mpsc::Sender<JsonValue>,
+    uri: &str,
+    id: u64,
+    patch: &DiffPatch,
+) -> Result<(), ()> {
+    let notification = McpNotification {
+        jsonrpc: "2.0",
+        method: "notifications/resources/updated",
+        params: serde_json::json!({
+            "uri": uri,
+            "revision": {
+                "id": id,
+                "patch": patch,
+            }
+        }),
+    };
+    tx.try_send(serde_json::to_value(&notification).unwrap_or_default())
+        .map_err(|e| {
+            tracing::warn!(
+                target: "mcp_audit",
+                uri = %uri,
+                "Notification channel full or closed, dropping notification: {e}"
+            );
+        })
+}
+
+pub(crate) fn unsubscribe_resource(sessions: &SessionMap, session_id: &str, uri: &str) {
+    sessions.mutate(|map| {
+        if let Some(session) = map.get_mut(session_id) {
+            if let Some(handle) = session.subscriptions.remove(uri) {
+                handle.abort();
+            }
+        }
+    });
+}

core/src/net/static_server.rs

@@ -100,6 +100,17 @@ impl UiContext for RpcContext {
                 })
             })
             .nest("/s9pk", s9pk_router(self.clone()))
+            .route("/mcp", crate::mcp::mcp_router(self.clone()))
+            .route(
+                "/.well-known/mcp",
+                get(|| async {
+                    Response::builder()
+                        .status(StatusCode::OK)
+                        .header(CONTENT_TYPE, "application/json")
+                        .body(Body::from(r#"{"mcp_endpoint":"/mcp"}"#))
+                        .unwrap()
+                }),
+            )
             .route(
                 "/static/local-root-ca.crt",
                 get(move || {

core/src/service/mod.rs

@@ -94,7 +94,17 @@ pub async fn get_data_version(id: &PackageId) -> Result<Option<String>, Error> {
     maybe_read_file_to_string(&path).await
 }
 
-struct RootCommand(pub String);
+pub(crate) struct RootCommand(pub String);
+
+/// Resolved subcontainer info, ready for command construction.
+pub(crate) struct ResolvedSubcontainer {
+    pub container_id: ContainerId,
+    pub subcontainer_id: Guid,
+    pub image_id: ImageId,
+    pub user: InternedString,
+    pub workdir: Option<String>,
+    pub root_command: RootCommand,
+}
 
 #[derive(Clone, Debug, Serialize, Deserialize, Default, TS)]
 pub struct MiB(pub u64);
@@ -706,6 +716,158 @@ impl Service {
             .clone();
         Ok(container_id)
     }
+
+    /// Resolve a subcontainer by optional filters (guid, name, or imageId).
+    /// If no filter is provided and there is exactly one subcontainer, it is returned.
+    /// Errors if no match found or multiple matches found (with the list in error info).
+    pub(crate) async fn resolve_subcontainer(
+        &self,
+        subcontainer: Option<InternedString>,
+        name: Option<InternedString>,
+        image_id: Option<ImageId>,
+        user: Option<InternedString>,
+    ) -> Result<ResolvedSubcontainer, Error> {
+        let id = &self.seed.id;
+        let container = &self.seed.persistent_container;
+        let root_dir = container
+            .lxc_container
+            .get()
+            .map(|x| x.rootfs_dir().to_owned())
+            .or_not_found(format!("container for {id}"))?;
+
+        let subcontainer_upper = subcontainer.as_ref().map(|x| AsRef::<str>::as_ref(x).to_uppercase());
+        let name_upper = name.as_ref().map(|x| AsRef::<str>::as_ref(x).to_uppercase());
+        let image_id_upper = image_id.as_ref().map(|x| AsRef::<Path>::as_ref(x).to_string_lossy().to_uppercase());
+
+        let subcontainers = container.subcontainers.lock().await;
+        let matches: Vec<_> = subcontainers
+            .iter()
+            .filter(|(x, wrapper)| {
+                if let Some(sc) = subcontainer_upper.as_ref() {
+                    AsRef::<str>::as_ref(x).contains(sc.as_str())
+                } else if let Some(n) = name_upper.as_ref() {
+                    AsRef::<str>::as_ref(&wrapper.name)
+                        .to_uppercase()
+                        .contains(n.as_str())
+                } else if let Some(img) = image_id_upper.as_ref() {
+                    let Some(wrapper_image_id) = AsRef::<Path>::as_ref(&wrapper.image_id).to_str()
+                    else {
+                        return false;
+                    };
+                    wrapper_image_id.to_uppercase().contains(img.as_str())
+                } else {
+                    true
+                }
+            })
+            .collect();
+
+        let Some((subcontainer_id, matched_image_id)) = matches
+            .first()
+            .map::<(Guid, ImageId), _>(|&x| (x.0.clone(), x.1.image_id.clone()))
+        else {
+            drop(subcontainers);
+            let info = container
+                .subcontainers
+                .lock()
+                .await
+                .iter()
+                .map(|(g, s)| SubcontainerInfo {
+                    id: g.clone(),
+                    name: s.name.clone(),
+                    image_id: s.image_id.clone(),
+                })
+                .collect::<Vec<_>>();
+            return Err(Error::new(
+                eyre!("{}", t!("service.mod.no-matching-subcontainers", id = id)),
+                ErrorKind::NotFound,
+            )
+            .with_info(to_value(&info)?));
+        };
+
+        if matches.len() > 1 {
+            let info = matches
+                .into_iter()
+                .map(|(g, s)| SubcontainerInfo {
+                    id: g.clone(),
+                    name: s.name.clone(),
+                    image_id: s.image_id.clone(),
+                })
+                .collect::<Vec<_>>();
+            return Err(Error::new(
+                eyre!("{}", t!("service.mod.multiple-subcontainers-found", id = id,)),
+                ErrorKind::InvalidRequest,
+            )
+            .with_info(to_value(&info)?));
+        }
+
+        let passwd = root_dir
+            .join("media/startos/subcontainers")
+            .join(subcontainer_id.as_ref())
+            .join("etc")
+            .join("passwd");
+
+        let image_meta = serde_json::from_str::<Value>(
+            &tokio::fs::read_to_string(
+                root_dir
+                    .join("media/startos/images/")
+                    .join(&matched_image_id)
+                    .with_extension("json"),
+            )
+            .await?,
+        )
+        .with_kind(ErrorKind::Deserialization)?;
+
+        let resolved_user = user
+            .or_else(|| image_meta["user"].as_str().map(InternedString::intern))
+            .unwrap_or_else(|| InternedString::intern("root"));
+
+        let root_command = get_passwd_command(passwd, &*resolved_user).await;
+        let workdir = image_meta["workdir"].as_str().map(|s| s.to_owned());
+
+        Ok(ResolvedSubcontainer {
+            container_id: self.container_id()?,
+            subcontainer_id,
+            image_id: matched_image_id,
+            user: resolved_user,
+            workdir,
+            root_command,
+        })
+    }
+
+    /// Build a `Command` for executing inside a resolved subcontainer (non-interactive).
+    pub(crate) fn build_subcontainer_command(
+        resolved: &ResolvedSubcontainer,
+        command: &[&str],
+    ) -> Command {
+        let root_path =
+            Path::new("/media/startos/subcontainers").join(resolved.subcontainer_id.as_ref());
+        let mut cmd = Command::new("lxc-attach");
+        cmd.kill_on_drop(true);
+        cmd.arg(&*resolved.container_id)
+            .arg("--")
+            .arg("start-container")
+            .arg("subcontainer")
+            .arg("exec")
+            .arg("--env-file")
+            .arg(
+                Path::new("/media/startos/images")
+                    .join(&resolved.image_id)
+                    .with_extension("env"),
+            )
+            .arg("--user")
+            .arg(&*resolved.user);
+        if let Some(ref workdir) = resolved.workdir {
+            cmd.arg("--workdir").arg(workdir);
+        }
+        cmd.arg(&root_path).arg("--");
+        if command.is_empty() {
+            cmd.arg(&resolved.root_command.0);
+        } else {
+            cmd.args(command);
+        }
+        cmd
+    }
+
     #[instrument(skip_all)]
     pub async fn stats(&self) -> Result<ServiceStats, Error> {
         let container = &self.seed.persistent_container;
@@ -799,124 +961,26 @@ pub async fn attach(
         user,
     }: AttachParams,
 ) -> Result<Guid, Error> {
-    let (container_id, subcontainer_id, image_id, user, workdir, root_command) = {
+    let resolved = {
-        let id = &id;
+        let service = ctx.services.get(&id).await;
-
+        let service_ref = service.as_ref().or_not_found(&id)?;
-        let service = ctx.services.get(id).await;
+        service_ref
-
+            .resolve_subcontainer(
-        let service_ref = service.as_ref().or_not_found(id)?;
+                subcontainer.map(|g| InternedString::intern(g.as_ref())),
-
+                name,
-        let container = &service_ref.seed.persistent_container;
+                image_id,
-        let root_dir = container
+                user,
-            .lxc_container
+            )
-            .get()
+            .await?
-            .map(|x| x.rootfs_dir().to_owned())
-            .or_not_found(format!("container for {id}"))?;
-
-        let subcontainer = subcontainer.map(|x| AsRef::<str>::as_ref(&x).to_uppercase());
-        let name = name.map(|x| AsRef::<str>::as_ref(&x).to_uppercase());
-        let image_id = image_id.map(|x| AsRef::<Path>::as_ref(&x).to_string_lossy().to_uppercase());
-
-        let subcontainers = container.subcontainers.lock().await;
-        let subcontainer_ids: Vec<_> = subcontainers
-            .iter()
-            .filter(|(x, wrapper)| {
-                if let Some(subcontainer) = subcontainer.as_ref() {
-                    AsRef::<str>::as_ref(x).contains(AsRef::<str>::as_ref(subcontainer))
-                } else if let Some(name) = name.as_ref() {
-                    AsRef::<str>::as_ref(&wrapper.name)
-                        .to_uppercase()
-                        .contains(AsRef::<str>::as_ref(name))
-                } else if let Some(image_id) = image_id.as_ref() {
-                    let Some(wrapper_image_id) = AsRef::<Path>::as_ref(&wrapper.image_id).to_str()
-                    else {
-                        return false;
     };
-                    wrapper_image_id
+    let ResolvedSubcontainer {
-                        .to_uppercase()
+        container_id,
-                        .contains(AsRef::<str>::as_ref(&image_id))
-                } else {
-                    true
-                }
-            })
-            .collect();
-        let Some((subcontainer_id, image_id)) = subcontainer_ids
-            .first()
-            .map::<(Guid, ImageId), _>(|&x| (x.0.clone(), x.1.image_id.clone()))
-        else {
-            drop(subcontainers);
-            let subcontainers = container
-                .subcontainers
-                .lock()
-                .await
-                .iter()
-                .map(|(g, s)| SubcontainerInfo {
-                    id: g.clone(),
-                    name: s.name.clone(),
-                    image_id: s.image_id.clone(),
-                })
-                .collect::<Vec<_>>();
-            return Err(Error::new(
-                eyre!("{}", t!("service.mod.no-matching-subcontainers", id = id)),
-                ErrorKind::NotFound,
-            )
-            .with_info(to_value(&subcontainers)?));
-        };
-
-        let passwd = root_dir
-            .join("media/startos/subcontainers")
-            .join(subcontainer_id.as_ref())
-            .join("etc")
-            .join("passwd");
-
-        let image_meta = serde_json::from_str::<Value>(
-            &tokio::fs::read_to_string(
-                root_dir
-                    .join("media/startos/images/")
-                    .join(&image_id)
-                    .with_extension("json"),
-            )
-            .await?,
-        )
-        .with_kind(ErrorKind::Deserialization)?;
-
-        let user = user
-            .clone()
-            .or_else(|| image_meta["user"].as_str().map(InternedString::intern))
-            .unwrap_or_else(|| InternedString::intern("root"));
-
-        let root_command = get_passwd_command(passwd, &*user).await;
-
-        let workdir = image_meta["workdir"].as_str().map(|s| s.to_owned());
-
-        if subcontainer_ids.len() > 1 {
-            let subcontainers = subcontainer_ids
-                .into_iter()
-                .map(|(g, s)| SubcontainerInfo {
-                    id: g.clone(),
-                    name: s.name.clone(),
-                    image_id: s.image_id.clone(),
-                })
-                .collect::<Vec<_>>();
-            return Err(Error::new(
-                eyre!(
-                    "{}",
-                    t!("service.mod.multiple-subcontainers-found", id = id,)
-                ),
-                ErrorKind::InvalidRequest,
-            )
-            .with_info(to_value(&subcontainers)?));
-        }
-
-        (
-            service_ref.container_id()?,
         subcontainer_id,
         image_id,
-            user.into(),
+        user,
         workdir,
         root_command,
-        )
+    } = resolved;
-    };
 
     let guid = Guid::new();
     async fn handler(