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>
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