v0.13.0

Added

• The interpreter now supports spawn, cross-process messaging, timers, and I/O in scripts and koja run --backend=interpreter — process programs that previously required --backend=llvm now run identically on both backends.
• A process stuck in long-running CPU-bound work — an infinite loop, tail recursion, or deep non-tail recursion alike — no longer freezes the others. The runtime now periodically interrupts such work so every process gets a fair turn, and higher-priority processes get a larger share.
• Per-process scheduling priority via Process.priority() returning Priority.Low, Priority.Normal, or Priority.High (default Normal); the scheduler serves higher priorities first but periodically forces the lowest non-empty tier so lower priorities aren't starved.
• Graceful shutdown on SIGTERM: the runtime stops accepting new spawns and gives the program a grace period (default 30s, configurable with the KOJA_GRACE_MS environment variable) to wind itself down. A process that handles the Shutdown lifecycle signal can exit cleanly; anything still running when the grace period elapses is stopped so the program always terminates.
• Compiled (--backend=llvm) programs now print a source backtrace on panic — ** (panic) <message> followed by file:line: name() frames for the user's call chain, including across spawned processes. Function-granular DWARF, so each frame resolves to its function's declaration line.

Changed

• Message passing and process spawning are dramatically faster (roughly 10× and 25× in micro-benchmarks). When one process sends to, replies to, or spawns another, the runtime now keeps the pair on the same CPU core instead of handing the work off across threads, eliminating a context switch and wakeup per message. Programs that run many processes at once also make better use of every core: each worker thread keeps its own run queue and pulls work from busier threads when it would otherwise sit idle. This is a performance change only — no difference in behavior — and applies to the compiled (--backend=llvm) backend.
• Cooperative preemption is now much cheaper: the fairness check is a near-free inline operation that only calls into the scheduler once a process has used up its turn, instead of a function call on every check. Tight loops run measurably faster as a result (~2× on a 200M-iteration micro-benchmark).
• Scheduler timers and deadlines are now backed by a single hashed timing wheel (plus an overflow heap for far-future entries) instead of two binary heaps, making timer arming amortized O(1).

Fixed

• --release now actually engages LLVM -O3 optimization; previously the flag only affected linking and emitted unoptimized (-O0) code.
• A process blocked in a synchronous syscall (e.g. socket accept) now wakes when a lifecycle signal (SIGTERM → Shutdown) arrives, instead of staying stuck until the I/O happens to complete.