removing the need for panic and _start snippets in user space binaries

library/runtime/runtime.zig

@@ -4,12 +4,11 @@
 //! shim. It is compiled into each binary (inheriting its `.large` code model and
 //! freestanding target), so all user programs share one implementation.
 //!
-//! A user binary needs three lines:
-//!   const runtime = @import("runtime");
-//!   pub const panic = runtime.panic;
-//!   comptime { _ = &runtime.start._start; }   // pull the entry shim in
-//! and a `pub fn main() void` or `pub fn main(init: runtime.process.Init) void`
-//! (arguments arrive via `init`).
+//! A user binary only defines a `pub fn main() void` or
+//! `pub fn main(init: runtime.process.Init) void` (arguments arrive via `init`).
+//! The panic handler and the `_start` entry pull live in the shared compilation
+//! root, library/runtime/root.zig, which build.zig wires around every program —
+//! nothing to declare per source file.
 
 pub const system = @import("system.zig");
 /// Monotonic time, delays, and deadlines over the kernel clock/sleep/timer syscalls
@@ -65,7 +64,7 @@ pub const scanout_protocol = @import("scanout-protocol");
 /// `std.os.danos` are staged. See docs/zig-self-hosting.md.
 pub const fs = @import("fs.zig");
 
-/// Re-exported so a user binary can `pub const panic = runtime.panic;`.
+/// Re-exported so the root shim (root.zig) can install it as the panic handler.
 pub const panic = start.panic;
 
 /// Process entry types: the `Init` handed to `main`, and its `Arguments`.