fix build regression

build.cm

@@ -127,7 +127,8 @@ var SALT_MACH = 'mach'        // mach bytecode blob
 var SALT_MCODE = 'mcode'      // mcode IR (JSON)
 var SALT_DEPS = 'deps'        // cached cc -MM dependency list
 var SALT_FAIL = 'fail'        // cached compilation failure
-var SALT_BMFST = 'bmfst'      // stat-based build manifest
+var SALT_BMFST = 'bmfst'      // stat-based build manifest (object level)
+var SALT_BMFST_DL = 'bmfst_dl'  // stat-based build manifest (dylib level)
 
 function cache_path(content, salt) {
   return get_build_dir() + '/' + content_hash(content + '\n' + salt)
@@ -185,6 +186,54 @@ function bmfst_save(cmd_str, src_path, deps, obj_path) {
   fd.slurpwrite(mf_path, stone(blob(json.encode(mf))))
 }
 
+// Dylib-level stat manifest — keyed on compile cmd + link info + src path.
+// All key inputs are available without reading any files.
+
+function bmfst_dl_key(setup, link_info) {
+  var parts = [setup.cmd_str, setup.src_path]
+  push(parts, 'target:' + text(link_info.target))
+  push(parts, 'cc:' + text(link_info.cc))
+  arrfor(link_info.extra_objects, function(obj) {
+    if (obj != null) push(parts, 'extra:' + text(obj))
+  })
+  arrfor(link_info.ldflags, function(flag) {
+    push(parts, 'ldflag:' + text(flag))
+  })
+  arrfor(link_info.target_ldflags, function(flag) {
+    push(parts, 'target_ldflag:' + text(flag))
+  })
+  return text(parts, '\n')
+}
+
+function bmfst_dl_probe(setup, link_info) {
+  var mf_path = cache_path(bmfst_dl_key(setup, link_info), SALT_BMFST_DL)
+  if (!fd.is_file(mf_path)) return null
+  var mf = json.decode(text(fd.slurp(mf_path)))
+  if (!mf || !mf.d || !mf.dylib) return null
+  if (!fd.is_file(mf.dylib)) return null
+  var ok = true
+  arrfor(mf.d, function(entry) {
+    if (!ok) return
+    var st = memo_stat(entry.p)
+    if (!st || st.m != entry.m || st.s != entry.s)
+      ok = false
+  })
+  if (!ok) return null
+  return mf.dylib
+}
+
+function bmfst_dl_save(setup, link_info, deps, dylib_path) {
+  var entries = []
+  arrfor(deps, function(dep_path) {
+    var st = memo_stat(dep_path)
+    if (st)
+      push(entries, {p: dep_path, m: st.m, s: st.s})
+  })
+  var mf = {dylib: dylib_path, d: entries}
+  var mf_path = cache_path(bmfst_dl_key(setup, link_info), SALT_BMFST_DL)
+  fd.slurpwrite(mf_path, stone(blob(json.encode(mf))))
+}
+
 // ============================================================================
 // Dependency scanning helpers
 // ============================================================================
@@ -525,6 +574,17 @@ Build.build_module_dylib = function(pkg, file, target, opts) {
 
   var link_info = {extra_objects: _extra, ldflags: resolved_ldflags, target_ldflags: target_ldflags, target: _target, cc: cc}
 
+  // Stat-based dylib manifest — zero file reads on warm cache
+  var mf_dylib = null
+  if (!_opts.force) {
+    mf_dylib = bmfst_dl_probe(setup, link_info)
+    if (mf_dylib) {
+      if (_opts.verbose) log.build('[verbose] manifest hit: ' + file)
+      log.shop('manifest hit ' + file)
+      return mf_dylib
+    }
+  }
+
   // Probe source key — check dylib cache before compiling
   var probe = probe_source_key(setup, file)
   var dylib_path = null
@@ -547,6 +607,7 @@ Build.build_module_dylib = function(pkg, file, target, opts) {
     dylib_path = cache_path(dylib_content, SALT_DYLIB)
     if (!_opts.force && fd.is_file(dylib_path)) {
       log.shop('cache hit ' + file)
+      bmfst_dl_save(setup, link_info, probe.deps, dylib_path)
       return dylib_path
     }
 
@@ -568,7 +629,10 @@ Build.build_module_dylib = function(pkg, file, target, opts) {
       if (post_probe && post_probe.full_content) {
         dylib_content = compute_dylib_content(post_probe.full_content, link_info)
         dylib_path = cache_path(dylib_content, SALT_DYLIB)
-        if (fd.is_file(dylib_path)) return dylib_path
+        if (fd.is_file(dylib_path)) {
+          bmfst_dl_save(setup, link_info, post_probe.deps, dylib_path)
+          return dylib_path
+        }
       }
     }
   }
@@ -631,6 +695,13 @@ Build.build_module_dylib = function(pkg, file, target, opts) {
     return null
   }
 
+  // Save dylib manifest for future stat-based probes
+  var mf_deps = null
+  if (fallback_probe && fallback_probe.deps) mf_deps = fallback_probe.deps
+  if (post_probe && post_probe.deps) mf_deps = post_probe.deps
+  if (probe && probe.deps) mf_deps = probe.deps
+  if (mf_deps) bmfst_dl_save(setup, link_info, mf_deps, dylib_path)
+
   return dylib_path
 }
 
@@ -1093,6 +1164,7 @@ Build.SALT_MCODE = SALT_MCODE
 Build.SALT_DEPS = SALT_DEPS
 Build.SALT_FAIL = SALT_FAIL
 Build.SALT_BMFST = SALT_BMFST
+Build.SALT_BMFST_DL = SALT_BMFST_DL
 Build.cache_path = cache_path
 Build.manifest_path = manifest_path
 Build.native_sanitize_flags = native_sanitize_flags