fix elb: cp instead of mv for .elh files, preserves headers for downstream modules

elb.el

@@ -1,4 +1,4 @@
-// elb.el — El Build Coordinator
+// elb.el - El Build Coordinator
 //
 // The build system for El programs. Written in El. Builds El.
 //
@@ -16,11 +16,11 @@
 //   3. For each file: if .el is newer than .elh/.c, compile with elc --emit-header
 //   4. Link all .c files + el_runtime.c into the final binary
 //
-// Each module compiles independently — no 128K-line blobs.
+// Each module compiles independently - no 128K-line blobs.
 // Downstream compilations read .elh headers (function signatures only),
 // not source. Incremental: only recompile what changed.
 
-// ── Flags ─────────────────────────────────────────────────────────────────────
+// -- Flags ---------------------------------------------------------------------
 
 fn flag_bool(argv: [String], name: String) -> Bool {
     let n: Int = native_list_len(argv)
@@ -47,7 +47,7 @@ fn flag_val(argv: [String], name: String, default_val: String) -> String {
     return default_val
 }
 
-// ── Manifest parsing ──────────────────────────────────────────────────────────
+// -- Manifest parsing ----------------------------------------------------------
 //
 // Read the entry file from manifest.el:
 //   build { entry "soul.el" }
@@ -100,7 +100,7 @@ fn parse_manifest_name(src: String) -> String {
     return "out"
 }
 
-// ── Path helpers ───────────────────────────────────────────────────────────────
+// -- Path helpers ---------------------------------------------------------------
 
 fn dirname_of(path: String) -> String {
     let n: Int = str_len(path)
@@ -148,14 +148,14 @@ fn file_is_newer(a: String, b: String) -> Bool {
     let cmd: String = "test -f " + b + " && test " + a + " -nt " + b + " && echo yes || echo no"
     let result: String = str_trim(exec_capture(cmd))
     if str_eq(result, "yes") { return true }
-    // b doesn't exist — check with test -f
+    // b doesn't exist - check with test -f
     let exist_cmd: String = "test -f " + b + " && echo exists || echo missing"
     let exist: String = str_trim(exec_capture(exist_cmd))
     if str_eq(exist, "missing") { return true }
     return false
 }
 
-// ── Import graph walker ────────────────────────────────────────────────────────
+// -- Import graph walker --------------------------------------------------------
 //
 // Walk import statements in each .el file to build the dependency graph.
 // Returns a list of absolute paths in topological order (deps before dependents).
@@ -219,7 +219,7 @@ fn walk_imports(src_path: String, visited: [String], order: [String]) -> Map<Str
     return { "visited": visited, "order": order }
 }
 
-// ── Build ──────────────────────────────────────────────────────────────────────
+// -- Build ----------------------------------------------------------------------
 
 fn compile_module(src_path: String, out_dir: String, elc_bin: String, dry_run: Bool, verbose: Bool) -> Bool {
     let bname: String = basename_noext(src_path)
@@ -246,13 +246,23 @@ fn compile_module(src_path: String, out_dir: String, elc_bin: String, dry_run: B
         println("elb: compile failed: " + src_path)
         return false
     }
+
+    // Move the generated .elh (written next to the source by elc) into
+    // out_dir so that #include "module.elh" lines in the generated .c
+    // files resolve correctly when cc is invoked with -I <out_dir>.
+    let src_elh: String = path_with_ext(src_path, ".elh")
+    let mv_cmd: String = "cp " + src_elh + " " + elh_out + " 2>/dev/null || true"
+    exec_command(mv_cmd)
+
     return true
 }
 
-fn link_binary(c_files: [String], out_bin: String, runtime_path: String, dry_run: Bool) -> Bool {
+fn link_binary(c_files: [String], out_bin: String, runtime_path: String, out_dir: String, dry_run: Bool) -> Bool {
     let n: Int = native_list_len(c_files)
     let parts: [String] = native_list_empty()
-    let parts = native_list_append(parts, "cc -O2 -I " + dirname_of(runtime_path))
+    // Include both the runtime dir (for el_runtime.h) and the output dir
+    // (for module.elh cross-module forward declarations).
+    let parts = native_list_append(parts, "cc -O2 -I " + dirname_of(runtime_path) + " -I " + out_dir)
     let i = 0
     while i < n {
         let f: String = native_list_get(c_files, i)
@@ -273,7 +283,7 @@ fn link_binary(c_files: [String], out_bin: String, runtime_path: String, dry_run
     return true
 }
 
-// ── Main ───────────────────────────────────────────────────────────────────────
+// -- Main -----------------------------------------------------------------------
 
 fn main() -> Void {
     let argv: [String] = args()
@@ -311,7 +321,7 @@ fn main() -> Void {
         }
     }
     if str_eq(runtime_path, "") {
-        println("elb: cannot locate el_runtime.c — use --runtime=PATH")
+        println("elb: cannot locate el_runtime.c - use --runtime=PATH")
         exit(1)
     }
 
@@ -359,11 +369,11 @@ fn main() -> Void {
 
     // Link
     let out_bin: String = out_dir + "/" + pkg_name
-    let linked: Bool = link_binary(c_files, out_bin, runtime_path, dry_run)
+    let linked: Bool = link_binary(c_files, out_bin, runtime_path, out_dir, dry_run)
     if !linked {
         println("elb: link failed")
         exit(1)
     }
 
-    println("elb: done → " + out_bin)
+    println("elb: done -> " + out_bin)
 }