P5.4: migrate all callers to on_build; delete set_post_link_callback

on_build is now the sole post-build callback mechanism. Migrated the 9 callers
(0602/0603/1611/1614/1615/1616 + the platform bundle_main) from
opts.set_post_link_callback(cb) to on_build(cb), giving each callback the
(opt: BuildOptions) param. Deleted set_post_link_callback from build.sx,
compiler_lib (bound_fns + handleSetPostLinkCallback), and the VM arm.

Reworked the P5 smoke tests for the new semantics: an on_build override REPLACES
the build (must emit+link or delegate), unlike the old post-link callback which
ran after the auto-link. 1662 (queries) + 1664 (override+List-grow) now delegate
to default_pipeline for the real build; deleted 1661/1663 (the primitives are now
exercised by every AOT build). bundle_main invoked with pass_options=true.

Benign 37-.ir churn (build.sx shrank). 703/0 both gates.

examples/0602-comptime-interp-cast-ptr-cmp.sx

@@ -18,7 +18,7 @@ bug :: (cmd: [:0]u8) -> ?R {
     R.{ x = 1 }
 }
 
-post_link :: () -> bool {
+post_link :: (opt: BuildOptions) -> bool abi(.compiler) {
     if r := bug("echo hi") { puts("ok"); } else { puts("null"); }
     true
 }
@@ -28,7 +28,7 @@ post_link :: () -> bool {
 // `set_post_link_callback()` compiler-API calls are permitted.
 configure :: () abi(.compiler) {
     opts := build_options();
-    opts.set_post_link_callback(post_link);
+    on_build(post_link);
 }
 #run configure();
 

examples/0603-comptime-interp-variadic-any.sx

@@ -10,7 +10,7 @@
 
 puts :: (s: [:0]u8) -> i32 extern libc;
 
-cb :: () -> bool {
+cb :: (opt: BuildOptions) -> bool abi(.compiler) {
     a := format("{}", "x");
     puts("1-arg ok");
     b := format("{} {}", "x", "y");
@@ -25,7 +25,7 @@ cb :: () -> bool {
 // `set_post_link_callback()` compiler-API calls are permitted.
 configure :: () abi(.compiler) {
     opts := build_options();
-    opts.set_post_link_callback(cb);
+    on_build(cb);
 }
 #run configure();
 

examples/1611-platform-post-link-callback.sx

@@ -10,14 +10,14 @@
 
 puts :: (s: [:0]u8) -> i32 extern libc;
 
-post_link :: () -> bool {
+post_link :: (opt: BuildOptions) -> bool abi(.compiler) {
     puts("[post-link] callback fired");
     true
 }
 
 configure :: () abi(.compiler) {
     opts := build_options();
-    opts.set_post_link_callback(post_link);
+    on_build(post_link);
 }
 #run configure();
 

examples/1614-platform-macos-bundle.sx

@@ -11,7 +11,7 @@ configure :: () abi(.compiler) {
     opts := build_options();
     opts.set_bundle_path("HelloApp.app");
     opts.set_bundle_id("co.example.hello");
-    opts.set_post_link_callback(bundle_main);
+    on_build(bundle_main);
 }
 #run configure();
 

examples/1615-platform-ios-sim-bundle.sx

@@ -13,7 +13,7 @@ configure :: () abi(.compiler) {
     opts := build_options();
     opts.set_bundle_path("IosSimApp.app");
     opts.set_bundle_id("co.example.iossim");
-    opts.set_post_link_callback(bundle_main);
+    on_build(bundle_main);
 }
 #run configure();
 

examples/1616-platform-ios-device-bundle.sx

@@ -32,7 +32,7 @@ configure :: () abi(.compiler) {
     opts.set_bundle_id("co.swipelab.sxprobe");
     opts.set_codesign_identity("Apple Development: Alexandru Agrapine (DC8VVHJ9W4)");
     opts.set_provisioning_profile("/Users/agra/Downloads/SwipeS32DevProfile.mobileprovision");
-    opts.set_post_link_callback(bundle_main);
+    on_build(bundle_main);
 }
 #run configure();
 

examples/1661-platform-post-link-vm-list.sx

@@ -1,33 +0,0 @@
-#import "modules/std.sx";
-#import "modules/build.sx";
-
-// P5.1 smoke test — the post-link build driver runs on the comptime VM,
-// not the legacy interpreter.
-//
-// The callback allocates and GROWS a `List` (three appends). Comptime List
-// growth works only on the VM; the legacy interp fails it (issue 0141:
-// `struct_get: base has no fields`). So this build SUCCEEDS only because
-// `core.invokeByFuncId` routes the post-link callback through the VM.
-//
-// AOT note: the corpus snapshots an AOT example's *executed binary* streams,
-// and the build step's own stdout is discarded — so the callback's success is
-// observed via the build EXIT CODE. On the VM the callback returns true, the
-// build links cleanly (exit 0), and the binary runs → "runtime main". If the
-// driver regressed to the legacy interp the callback would bail, the build
-// would exit non-zero, and this snapshot would fail.
-
-post_link :: () -> bool abi(.compiler) {
-    names := List(string).{};
-    names.append("alpha");
-    names.append("beta");
-    names.append("gamma");
-    return names.len == 3;
-}
-
-configure :: () abi(.compiler) {
-    opts := build_options();
-    opts.set_post_link_callback(post_link);
-}
-#run configure();
-
-main :: () { print("runtime main\n"); }

examples/1662-platform-build-pipeline-queries.sx

@@ -2,16 +2,12 @@
 #import "modules/build.sx";
 #import "modules/compiler.sx";
 
-// P5.2 smoke test — the build-pipeline query primitives (`c_object_paths` /
-// `link_libraries` / `emit_object`) run on the comptime VM: the list queries
-// return a `List(string)` the VM builds in flat memory; `emit_object` returns
-// the compiler-emitted object path. Registered as a post-link callback (which
-// runs on the VM — core.invokeByFuncId), so the build state is live there.
-//
-// The `#import c` source compiles to one `.o`, so `c_object_paths()` must return
-// a one-element list whose single string is the (non-empty) object path. AOT
-// snapshots the executed binary, so success is observed via the build exit code:
-// the callback returns true only if the VM-built list is well-formed.
+// P5.4 — the build-pipeline query primitives on the comptime VM. A custom
+// `on_build` override inspects the build metadata (`c_object_paths` returns the
+// VM-built `List(string)` of C companion objects), then DELEGATES to the stdlib
+// `default_pipeline` for the real emit + link. The `#import c` source compiles to
+// one object, so `c_object_paths()` must be a one-element list of a non-empty
+// path. AOT runs the produced binary → "runtime main: 42".
 
 #import c {
     #source "1662-platform-build-pipeline-queries.c";
@@ -19,25 +15,18 @@
 
 c_marker :: () -> i64 extern;
 
-check :: () -> bool abi(.compiler) {
+build :: (opt: BuildOptions) -> bool abi(.compiler) {
     objs := c_object_paths();
-    libs := link_libraries();
-    obj := emit_object();              // the compiler-emitted sx object path
-    if obj.len == 0 { return false; }
     if objs.len != 1 { return false; }
     if objs.items[0].len == 0 { return false; }
-    // `link_libraries` must be a well-formed (possibly empty) list — touch each
-    // entry so a malformed fat pointer would fault rather than pass silently.
+    // link_libraries must be a well-formed (possibly empty) list — touch each.
+    libs := link_libraries();
     sum : i64 = 0;
     i : i64 = 0;
     while i < libs.len { sum += libs.items[i].len; i += 1; }
-    return sum >= 0;
+    if sum < 0 { return false; }
+    return default_pipeline(opt);   // the real emit + link
 }
-
-configure :: () abi(.compiler) {
-    opts := build_options();
-    opts.set_post_link_callback(check);
-}
-#run configure();
+#run on_build(build);
 
 main :: () { print("runtime main: {}\n", c_marker()); }

examples/1663-platform-build-pipeline-link.sx

@@ -1,31 +0,0 @@
-#import "modules/std.sx";
-#import "modules/build.sx";
-#import "modules/compiler.sx";
-
-// P5.2b smoke test — the `link` build-pipeline ACTION runs on the comptime VM,
-// dispatching through the host-installed linker hook (the VM can't link itself).
-// The post-link callback (which runs on the VM — core.invokeByFuncId) re-links
-// the build's own objects into a temp output via the sx `link` primitive. A link
-// failure bails → the build fails; success → the callback returns true and the
-// build's binary runs ("runtime main"). AOT snapshots the binary, so the link's
-// success is observed via the build exit code.
-
-relink :: () -> bool abi(.compiler) {
-    objs := List(string).{};
-    cobjs := c_object_paths();
-    i : i64 = 0;
-    while i < cobjs.len { objs.append(cobjs.items[i]); i += 1; }
-    objs.append(emit_object());
-    fws := List(string).{};
-    flags := List(string).{};
-    link(objs, ".sx-tmp/1663-link-out", link_libraries(), fws, flags, "");
-    return true;
-}
-
-configure :: () abi(.compiler) {
-    opts := build_options();
-    opts.set_post_link_callback(relink);
-}
-#run configure();
-
-main :: () { print("runtime main\n"); }

examples/1664-platform-on-build-callback.sx

@@ -1,17 +1,20 @@
 #import "modules/std.sx";
 #import "modules/build.sx";
-#import "modules/compiler.sx";
 
-// P5.3 smoke test — `on_build(build)` registers the build callback (the Phase 5
-// form), and the compiler invokes it post-codegen WITH the BuildOptions handle
-// as an arg (`build :: (opt: BuildOptions) -> bool`). This exercises the VM
-// entry that passes an explicit arg after the implicit context (runEntryArgs).
-// The callback uses the build-pipeline primitives (no opt accessors yet) and
-// returns true; AOT observes success via the build exit code.
+// P5.4 — the `on_build` override. A user `#run on_build(build);` replaces the
+// stdlib `default_pipeline` as the build driver; the compiler invokes it after
+// codegen with the `BuildOptions` handle. This build GROWS a `List` on the build
+// VM (comptime List growth works only on the VM — issue 0141; the legacy interp
+// fails it) then DELEGATES to `default_pipeline` for the real emit + link, so a
+// working binary is still produced → "runtime main".
 
 build :: (opt: BuildOptions) -> bool abi(.compiler) {
-    obj := emit_object();
-    return obj.len > 0;
+    names := List(string).{};
+    names.append("alpha");
+    names.append("beta");
+    names.append("gamma");
+    if names.len != 3 { return false; }
+    return default_pipeline(opt);
 }
 #run on_build(build);
 

examples/expected/1202-ffi-cc-c-large-aggregate.ir

@@ -689,9 +689,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1309-ffi-objc-class-method-lowering.ir

@@ -1191,9 +1191,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1314-ffi-objc-class-dealloc-roundtrip.ir

@@ -1207,9 +1207,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1329-ffi-objc-call-03-selector-sharing.ir

@@ -1183,9 +1183,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1347-ffi-objc-dsl-07-mangling-table.ir

@@ -1209,9 +1209,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1402-ffi-jni-call-03-methodid-sharing.ir

@@ -1185,9 +1185,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1403-ffi-jni-call-04-jint-return.ir

@@ -1183,9 +1183,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1404-ffi-jni-call-05-jlong-return.ir

@@ -1183,9 +1183,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1405-ffi-jni-call-06-jdouble-return.ir

@@ -1183,9 +1183,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1406-ffi-jni-call-07-jboolean-return.ir

@@ -1183,9 +1183,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1407-ffi-jni-call-08-jobject-return.ir

@@ -1183,9 +1183,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1408-ffi-jni-call-09-static.ir

@@ -1183,9 +1183,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1418-ffi-jni-class-08-call.ir

@@ -1183,9 +1183,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1421-ffi-jni-env-02-lexical-direct.ir

@@ -1183,9 +1183,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1425-ffi-jni-main-03-ctor.ir

@@ -696,9 +696,6 @@ declare ptr @BuildOptions.jni_main_java_source_at(i64, i64) #0
 ; Function Attrs: nounwind
 declare i64 @build_options() #0
 
-; Function Attrs: nounwind
-declare void @set_post_link_callback(i64, ptr) #0
-
 ; Function Attrs: nounwind
 declare void @on_build(ptr) #0
 

examples/expected/1661-platform-post-link-vm-list.build

@@ -1 +0,0 @@
-{ "aot": true }

examples/expected/1661-platform-post-link-vm-list.exit

@@ -1 +0,0 @@
-0

examples/expected/1661-platform-post-link-vm-list.stderr

@@ -1 +0,0 @@
-

examples/expected/1661-platform-post-link-vm-list.stdout

@@ -1 +0,0 @@
-runtime main

examples/expected/1663-platform-build-pipeline-link.build

@@ -1 +0,0 @@
-{ "aot": true }

examples/expected/1663-platform-build-pipeline-link.exit

@@ -1 +0,0 @@
-0

examples/expected/1663-platform-build-pipeline-link.stderr

@@ -1 +0,0 @@
-

examples/expected/1663-platform-build-pipeline-link.stdout

@@ -1 +0,0 @@
-runtime main