MCP server: modelcraft-cli mcp (headless or bridged), read/write roots, end-to-end analysis over MCP (#48)

* io: read and write roots that confine an automation client's file access

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* engine: every file a command reads or writes is checked against the session's roots

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* engine: headless pictures of a session (model, geometry, deformed shape and contours)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* mcp: MCP server over stdio with headless and connected backends, roots and caps

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* cli: modelcraft-cli mcp [--connect ADDR | --headless] with automation read and write roots

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* mcp: end-to-end analysis of a corpus part over MCP (open, tet mesh, define, solve, probe, render)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* docs: MCP server (docs/mcp.md), Claude Code setup, roots; architecture, README, roadmap, attribution

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

---------

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/mod.rs

@@ -16,7 +16,9 @@ use modelcraft_model::MAX_LABEL;
 use serde::Deserialize;
 use serde_json::{Value, json};
 
-use crate::{CommandSpec, EngineError, Result};
+use modelcraft_io::roots::Access;
+
+use crate::{CommandSpec, EngineError, Result, Session};
 
 pub static ALL: &[CommandSpec] = &[
     model::INFO,
@@ -158,14 +160,22 @@ pub(crate) fn labels(p: &Value, key: &str, max_len: usize) -> Result<Vec<u32>> {
         .ok_or_else(|| EngineError::Params(format!("`{key}` must be labels in 1..={MAX_LABEL}")))
 }
 
-/// A required path parameter.
-pub(crate) fn path_param<'a>(p: &'a Value, key: &str) -> Result<&'a str> {
+/// A required path parameter, as given.
+fn path_param<'a>(p: &'a Value, key: &str) -> Result<&'a str> {
     p.get(key)
         .and_then(Value::as_str)
         .filter(|s| !s.trim().is_empty() && s.len() <= modelcraft_io::MAX_PATH_LEN && !s.contains('\0'))
         .ok_or_else(|| EngineError::Params(format!("`{key}` must be a file path")))
 }
 
+/// A required path parameter naming a file (or folder) the command reads or writes: the path
+/// to use, checked against the session's [`Session::file_access`] (as given while unconfined;
+/// resolved, links followed, when confined). Every command that touches a file named by a
+/// parameter takes its path from here.
+pub(crate) fn file_param(s: &Session, p: &Value, key: &str, access: Access) -> Result<String> {
+    s.checked_path(path_param(p, key)?, access)
+}
+
 /// An optional number parameter.
 pub(crate) fn optional_number(p: &Value, key: &str, default: f64) -> Result<f64> {
     match p.get(key) {