127 panic branch synthesized

// Test 210_127: panic branch synthesis — unhandled `| ?!oom` is ignorable
// (no compile error) but UNSAFE to ignore: the synthesized handler body is
// @panic(...), so the program crashes LOUDLY if the branch ever fires.
//
// This is the runtime half of the doctrine: "assert, don't fall back / let
// it fail loudly." The failure is visible in the type (| ?!), recovery is
// opt-in (handle `| oom _ |> _` to mute), and ignoring it is loud (panic).
//
// What this test pins (COMPILE_ONLY — must compile):
//   - The flow omits a handler for `oom` (a panic branch).
//   - It MUST compile (panic branches are ignorable — no exhaustiveness
//     error, unlike a missing required `|` branch).
//   - The emitted switch MUST include an `.oom` arm whose body is
//     @panic(...) — not an empty no-op (that's `| ?`), and not absent.
//
// Contrast 210_016 (optional branches ignored): there the unhandled
// optional branches synthesize empty no-op bodies. Here the unhandled
// panic branch synthesizes a @panic body. Same mechanism, loud body.

~pub event alloc { n: usize }
| success []u8
| ?!oom usize

~proc alloc|zig {
    return .{ .success = &.{} };
}

~alloc(n: 4)
| success _ |> _
// NO `| oom _ |> _` handler — unhandled panic branch.
// Must compile; emits .oom => @panic("...") arm.