Return-trace frames now resolve to real `func at file:line:col`
in-process — no DWARF, no symbolizer.
- New niladic, span-stamped `.trace_frame` IR op (mirrors is_comptime):
carries no operands; each backend derives the frame from context.
lower.zig's placeholderTraceFrame emits it; the existing
sx_trace_push call consumes it.
- emit_llvm: resolve the op's span + current function to
{file(basename), line, col, func}, build an interned Frame global
({string,i32,i32,string}, strings cached by content), push its
address (ptrtoint).
- interp: pack (func_id << 32 | span.start) for the comptime resolver
(slice 3b); never a pointer.
- sx_trace.c report_unhandled derefs SxFrame; trace.sx gains the Frame
struct, frame_at -> *Frame, and field-reading to_string. Layout
mirrored in 3 places with cross-ref comments.
Verified JIT + AOT. Snapshots 243/244/247 regenerated (placeholder ->
func at file:line:col). Gates: zig build, zig build test,
run_examples.sh -> 290 passed.
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.
