Fix #171: a library that can't be locked opens with a warning the user sees

When catalog.lock can't be locked (a file system without locks, such as
some network shares), the library opens unprotected, as documented, but
the promised warning went only to the log. It is now the first of the
library's warnings: library.info lists it under settingsWarnings, the
app shows it once in its notices, and lightcraft-cli run / mcp print the
library's warnings on stderr (stdout stays results / protocol only). A
normally locked library shows none.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01912WaK6Rmew3wxZuPyX7E8

apps/lightcraft-cli/src/main.rs

@@ -102,6 +102,14 @@ static ALLOC: dhat::Alloc = dhat::Alloc;
 
 /// Why `--library DIR` can't be opened; for a library open in another program, how to work with
 /// that one instead (issue #99).
+/// Print the open library's warnings (an unlockable library, damaged settings files) on stderr:
+/// stdout carries command results / MCP protocol messages only.
+fn library_warnings(session: &mut Session, who: &str) {
+    for w in session.take_library_warnings() {
+        eprintln!("{who}: warning: {w}");
+    }
+}
+
 fn library_error(dir: &str, e: lightcraft_engine::EngineError) -> String {
     match e {
         lightcraft_engine::EngineError::LibraryInUse(why) => format!(
@@ -317,6 +325,7 @@ fn mcp(args: &[String]) -> Result<(), String> {
                     let mut h = Headless::default();
                     let r = h.session.open_library(dir, demo).map_err(|e| library_error(dir, e))?;
                     eprintln!("lightcraft-cli mcp: opened library {dir} ({r:?})");
+                    library_warnings(&mut h.session, "lightcraft-cli mcp");
                     h
                 }
                 None if demo => Headless::demo(),
@@ -553,6 +562,7 @@ fn run(args: &[String]) -> Result<(), String> {
                     Some(dir) => {
                         let mut h = Headless::default();
                         h.session.open_library(dir, demo).map_err(|e| library_error(dir, e))?;
+                        library_warnings(&mut h.session, "lightcraft-cli");
                         h
                     }
                     None if demo => Headless::demo(),