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Issue #99: Library: exclusive lock so two processes can't open one library

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Two processes on one library each kept their own catalog and seq counter;
the last snapshot silently dropped the other's edits.

- lightcraft_catalog:🔒 LibraryLock holds an exclusive OS lock
  (std File::try_lock: flock / LockFileEx) on <library>/catalog.lock for
  the session; who holds it goes to catalog.lock.owner (separate file: a
  Windows lock also blocks reads). Released on drop and by the OS when the
  process dies, so leftover files from a crash never lock anyone out. File
  systems without lock support open unprotected with a warning.
- Session::open_library takes the lock before reading anything and fails
  with EngineError::LibraryInUse ("this library is already open in
  LightCraft 0.x (process N on host)"); reopening the session's own
  library hands its lock over.
- lightcraft-cli (mcp/run/snapshot --library) adds how to drive the
  running app instead (--control + mcp --connect).
- Tests: in-process, leftover files, a killed child process, two engine
  sessions, CLI e2e (mcp --library holds it, run --library is refused).
  Existing tests that reopened a library while it was open now drop the
  first session.
- docs: parity row LRC-LIB-CATALOG-LOCK, mcp.md, web.md (no guard across
  browser tabs yet), whats-new.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Brandon Thomas
2026-10-05 17:48:34 -04:00
co-authored by Claude Opus 5.5
parent 572b55a44a
commit ee4b78f646
14 changed files with 388 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files
apps/lightcraft-cli/src/main.rs
+14 -3
View File
@@ -91,6 +91,17 @@ USAGE:
#[global_allocator]
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).
fn library_error(dir: &str, e: lightcraft_engine::EngineError) -> String {
match e {
lightcraft_engine::EngineError::LibraryInUse(why) => format!(
"{dir}: {why}\nTo work with the library while the app has it open, start the app with `--control PORT` and use `lightcraft-cli mcp --connect 127.0.0.1:PORT`."
),
e => format!("{dir}: {e}"),
}
}
fn main() -> ExitCode {
// `--features dhat-heap`: count allocations; the profile is written when `_heap` drops
// (LIGHTCRAFT_DHAT_FILE, default dhat-heap.json).
@@ -182,7 +193,7 @@ fn mcp(args: &[String]) -> Result<(), String> {
let mut h = match &library {
Some(dir) => {
let mut h = Headless::default();
let r = h.session.open_library(dir, demo).map_err(|e| e.to_string())?;
let r = h.session.open_library(dir, demo).map_err(|e| library_error(dir, e))?;
eprintln!("lightcraft-cli mcp: opened library {dir} ({r:?})");
h
}
@@ -419,7 +430,7 @@ fn run(args: &[String]) -> Result<(), String> {
let mut h = match &library {
Some(dir) => {
let mut h = Headless::default();
h.session.open_library(dir, demo).map_err(|e| e.to_string())?;
h.session.open_library(dir, demo).map_err(|e| library_error(dir, e))?;
h
}
None if demo => Headless::demo(),
@@ -580,7 +591,7 @@ fn snapshot(args: &[String]) -> Result<(), String> {
let mut session = match &library {
Some(dir) => {
let mut s = Session::new().with_fs();
s.open_library(dir, false).map_err(|e| format!("{dir}: {e}"))?;
s.open_library(dir, false).map_err(|e| library_error(dir, e))?;
s
}
None if files.is_empty() => Session::with_demo().with_fs(),