A pure-failable `main` (`-> !` / `-> !Named`) that lets an error reach the
function boundary now exits 1 and prints `error: unhandled error reached
main: error.<tag>` + the return trace to stderr, instead of returning the
raw tag id truncated as the exit code with no diagnostic. Success exits 0;
a `catch`-absorbed error exits 0 (buffer cleared).
Codegen wrapper so JIT and AOT behave identically (no host-side special-
casing):
- emit_llvm.zig: the `.ret` arm detects a failable main and routes to
new `emitFailableMainRet` — `icmp ne tag, 0` → success block `ret i32 0`
/ error block GEPs the tag name out of the always-linked tag-name table,
calls `sx_trace_report_unhandled`, `ret i32 1`. main's bare-u32 returns
(success `ret(0)` + each raise's `ret(tag)`) all funnel through it.
- sx_trace.c: new `sx_trace_report_unhandled(tag, name, name_len)` prints
the header + surviving frames to stderr (placeholder frame format mirrors
trace.sx until DWARF/E3.0). Lives next to the buffer it reads.
- lower.zig validateMainSignature: the pure-failable arm sets
needs_trace_runtime so the AOT path auto-links sx_trace.c even when the
body emits no other push/clear.
Value-carrying `-> (T, !)` main stays gate-rejected (multi-slot wrapper is
a separate slice). examples/244-failable-main.sx.
Add the trace buffer that raise/try push to and catch/or/destructure clear,
following the JNI-TLS precedent exactly (a thread_local IR global doesn't work
under the ORC JIT, which doesn't init TLS for AddObjectFile'd objects).
- library/vendors/sx_trace_runtime/sx_trace.c: a `_Thread_local` fixed-cap ring
(32 frames) of opaque u64s + C API (push / clear / len / truncated /
frame_at). Overflow keeps the newest CAP frames and latches `truncated`
(Zig-style); frame_at returns oldest-to-newest. The frame is opaque — the
E3.3 formatter dispatches on context (PC at runtime, packed (func_id, offset)
at comptime).
- build.zig: link the .c into the compiler so the JIT resolves sx_trace_* via
dlsym (and so the unit test links against it).
- src/runtime_trace.test.zig: exercises push / overflow-survives-newest / clear
/ len / truncated / ordering against the linked C — grounds the buffer logic
without shipping throwaway sx builtins.
- lower.zig getTraceFids(): lazily declares the sx_trace_push/clear externs +
sets needs_trace_runtime. Declared now; the raise/try push sites and the
absorbing clear sites get wired at E3.2.
- core.zig: auto-injects the .c as a #source for AOT when needs_trace_runtime,
mirroring the JNI env runtime.
Gates: zig build, zig build test (incl. the new buffer tests), bash
tests/run_examples.sh (277 passed; no codegen change this step — lone failure
is the user's uncommitted 213-canonical-map pack WIP).
