Fix #832: --automation-read-root and --automation-write-root confine the MCP server's files

vectorcraft-cli mcp and vectorcraft --control take the flags PhotoCraft
takes. While roots are in force, every path a command reads (open, place,
relink, SVG image links, library and profile loads, plug-ins, preset
imports, font searches) must lie inside the read root and every path it
writes (save, export, package, Export for Screens and for Web, print to
file, captures, library saves) inside the write root. Paths are made
absolute, links are followed (a missing file's nearest folder's), and the
result is compared by whole components, ignoring case on Windows; `..`
below a missing folder, dangling links and device names are refused. A
root left out grants none of its access; without the flags nothing
changes.

The checks live in one place, vectorcraft_engine::file_access, consulted
by the engine's file helpers and the app's file services. The headless
server confines its whole process; the app confines control requests,
the frames carrying input they inject and the background saves they
start, leaving the person at the keyboard and the app's own folders
alone. The screenshot tool now has the backend write its file.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/vectorcraft-cli/src/main.rs

@@ -1,7 +1,7 @@
 //! `vectorcraft-cli`: VectorCraft from the command line.
 //!
 //! ```text
-//! vectorcraft-cli mcp [--connect 127.0.0.1:7979 | --headless]
+//! vectorcraft-cli mcp [--connect 127.0.0.1:7979 | --headless] [--automation-read-root DIR] [--automation-write-root DIR]
 //! vectorcraft-cli run [--in FILE] [--cmd id [--params '{json}']]... [--export out.svg]... [--scale 2]
 //! vectorcraft-cli commands
 //! vectorcraft-cli convert IN OUT [--scale 2] [--artboard 0 | --range 1-3,5] [--outline-text] [--replace-lossy]
@@ -14,6 +14,7 @@
 #![deny(unsafe_code)]
 
 use std::io::Write;
+use std::path::Path;
 use std::process::ExitCode;
 
 /// `println!` / `print!` that end the program quietly when stdout is closed
@@ -50,6 +51,7 @@ mod prefs_dir;
 mod system_fonts;
 
 use serde_json::{Value, json};
+use vectorcraft_engine::file_access::{self, AutomationRoots};
 use vectorcraft_mcp::{Backend, DEFAULT_ADDR, Headless, Remote, Server};
 
 /// stdout went away. A reader that stopped early (a closed pipe) ends the program quietly, as
@@ -66,9 +68,13 @@ const USAGE: &str = "\
 vectorcraft-cli — VectorCraft automation
 
 USAGE:
-  vectorcraft-cli mcp [--connect ADDR | --headless]
+  vectorcraft-cli mcp [--connect ADDR | --headless] [--automation-read-root DIR] [--automation-write-root DIR]
       Run the MCP server on stdio. Default: connect to a running app at 127.0.0.1:7979
       (vectorcraft --control 7979), falling back to a headless in-process session.
+      --automation-read-root / --automation-write-root confine the files the agent's commands read
+      (open, place, relink, library loads…) and write (save, export, package, library saves…) to
+      DIR, links followed; a root left out grants none of its access. They imply --headless: a
+      running app enforces its own (vectorcraft --control PORT --automation-read-root DIR …).
 
   vectorcraft-cli run [--in FILE] [--cmd ID [--params JSON]]... [--export FILE]... [--scale N]
       Headless batch: open FILE (any readable format) or start a new document, run commands in
@@ -145,18 +151,42 @@ fn main() -> ExitCode {
 fn mcp(args: &[String]) -> Result<(), String> {
     let mut connect: Option<String> = None;
     let mut headless = false;
+    let (mut read_root, mut write_root): (Option<String>, Option<String>) = (None, None);
     let mut it = args.iter();
     while let Some(a) = it.next() {
-        match a.as_str() {
+        // The roots also come as `--flag=DIR`, as the other Craft apps take them.
+        let (flag, inline) = match a.split_once('=') {
+            Some((f, v)) if f.starts_with("--automation-") => (f, Some(v.to_string())),
+            _ => (a.as_str(), None),
+        };
+        match flag {
             "--connect" => connect = Some(it.next().cloned().ok_or("--connect needs an address")?),
             "--headless" => headless = true,
+            "--automation-read-root" | "--automation-write-root" => {
+                let dir = inline.or_else(|| it.next().cloned()).ok_or_else(|| format!("{flag} needs a folder"))?;
+                let slot = if flag == "--automation-read-root" { &mut read_root } else { &mut write_root };
+                if slot.replace(dir).is_some() {
+                    return Err(format!("{flag} is given twice: it takes one folder"));
+                }
+            }
             other => return Err(format!("unknown mcp option `{other}`")),
         }
     }
     if headless && connect.is_some() {
         return Err("use either --connect or --headless".into());
     }
-    let backend: Box<dyn Backend> = if headless {
+    let roots = AutomationRoots::new(read_root.as_deref().map(Path::new), write_root.as_deref().map(Path::new))?;
+    if roots.is_some() && connect.is_some() {
+        return Err("--automation-read-root and --automation-write-root confine the headless server; a running app enforces its own roots:                     start it with `vectorcraft --control <port> --automation-read-root <dir> --automation-write-root <dir>`"
+            .into());
+    }
+    let backend: Box<dyn Backend> = if let Some(roots) = roots {
+        // Every thread of this process, not only the server's: nothing reaches past the roots.
+        file_access::confine_process(roots.clone());
+        let show = |root: Option<&Path>| root.map_or_else(|| "none".to_string(), |r| r.display().to_string());
+        eprintln!("vectorcraft-cli: files confined: read root {}, write root {}", show(roots.read_root()), show(roots.write_root()));
+        Box::new(Headless::with_document().with_automation_roots(Some(roots)))
+    } else if headless {
         Box::new(Headless::with_document())
     } else if let Some(addr) = connect {
         // Explicit address: fail loudly if the app isn't there.

apps/vectorcraft-cli/tests/cli.rs

@@ -83,6 +83,58 @@ fn mcp_headless_over_stdio() {
     assert_eq!(replies[3]["result"]["content"][0]["type"], "image");
 }
 
+/// `mcp --automation-read-root` / `--automation-write-root` (#832): the flags are checked before the
+/// server starts, and the process then reads and writes only inside its roots.
+#[test]
+fn mcp_automation_roots() {
+    let base = tmp("roots");
+    for d in ["in", "out", "outside"] {
+        std::fs::create_dir_all(base.join(d)).unwrap();
+    }
+    let svg = r#"<svg xmlns="http://www.w3.org/2000/svg" width="40" height="30"><rect width="20" height="10"/></svg>"#;
+    std::fs::write(base.join("in/a.svg"), svg).unwrap();
+    std::fs::write(base.join("outside/b.svg"), svg).unwrap();
+    let dir = |d: &str| base.join(d).to_string_lossy().into_owned();
+    let fails = |args: &[&str], why: &str| {
+        let out = Command::new(BIN).args(args).stdin(Stdio::null()).output().unwrap();
+        let err = String::from_utf8_lossy(&out.stderr);
+        assert!(!out.status.success() && err.contains(why), "{args:?}: {err}");
+    };
+    fails(&["mcp", "--automation-read-root", &dir("missing")], "cannot open the automation read root");
+    fails(&["mcp", "--automation-read-root", &dir("in"), "--automation-read-root", &dir("out")], "given twice");
+    fails(&["mcp", "--automation-write-root"], "needs a folder");
+    fails(&["mcp", "--connect", "127.0.0.1:1", &format!("--automation-write-root={}", dir("out"))], "a running app enforces its own roots");
+
+    let mut child = Command::new(BIN)
+        .args(["mcp", "--automation-read-root", &dir("in"), &format!("--automation-write-root={}", dir("out"))])
+        .stdin(Stdio::piped())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::null())
+        .spawn()
+        .unwrap();
+    let call = |id: u64, name: &str, args: Value| json!({"jsonrpc":"2.0","id":id,"method":"tools/call","params":{"name":name,"arguments":args}});
+    let file = |d: &str, f: &str| base.join(d).join(f).to_string_lossy().into_owned();
+    {
+        let mut stdin = child.stdin.take().unwrap();
+        for m in [
+            call(1, "open_file", json!({"path": file("in", "a.svg")})),
+            call(2, "open_file", json!({"path": file("outside", "b.svg")})),
+            call(3, "export", json!({"path": file("out", "a.png")})),
+            call(4, "export", json!({"path": file("in", "a.png")})),
+            call(5, "save_file", json!({"path": file("outside", "a.vectorcraft")})),
+        ] {
+            writeln!(stdin, "{m}").unwrap();
+        }
+    }
+    let out = child.wait_with_output().unwrap();
+    assert!(out.status.success());
+    let replies: Vec<Value> = String::from_utf8(out.stdout).unwrap().lines().map(|l| serde_json::from_str(l).unwrap()).collect();
+    let errors: Vec<bool> = replies.iter().map(|r| r["result"]["isError"] == true).collect();
+    assert_eq!(errors, [false, true, false, true, true], "{replies:?}");
+    assert!(replies[1]["result"]["content"][0]["text"].as_str().unwrap().contains("outside the read root"));
+    assert!(base.join("out/a.png").is_file() && !base.join("in/a.png").exists() && !base.join("outside/a.vectorcraft").exists());
+}
+
 /// End-to-end protocol sweep over stdio against the compiled binary. The in-process
 /// tests drive `Server::handle_line` directly, so the binary's own wiring (argument
 /// parsing, logger install, stdout pollution, notification order) is untested: this