skip relink when content hasn't changed

build.cm

@@ -193,9 +193,34 @@ Build.build_package = function(pkg, target = Build.detect_host_target(), exclude
 // ============================================================================
 // Dynamic library building
 // ============================================================================
+
+// Compute link key from all inputs that affect the dylib output
+function compute_link_key(objects, ldflags, target_ldflags, target, cc) {
+  // Sort objects for deterministic hash
+  var sorted_objects = objects.slice().sort()
+
+  // Build a string representing all link inputs
+  var parts = []
+  parts.push('target:' + target)
+  parts.push('cc:' + cc)
+  for (var i = 0; i < sorted_objects.length; i++) {
+    // Object paths are content-addressed, so the path itself is the hash
+    parts.push('obj:' + sorted_objects[i])
+  }
+  for (var i = 0; i < ldflags.length; i++) {
+    parts.push('ldflag:' + ldflags[i])
+  }
+  for (var i = 0; i < target_ldflags.length; i++) {
+    parts.push('target_ldflag:' + target_ldflags[i])
+  }
+
+  return content_hash(parts.join('\n'))
+}
+
 // Build a dynamic library for a package
 // Output goes to .cell/lib/<package_name>.<ext>
 // Dynamic libraries do NOT link against core; undefined symbols are resolved at dlopen time
+// Uses content-addressed store + symlink for caching
 Build.build_dynamic = function(pkg, target = Build.detect_host_target(), buildtype = 'release') {
   var objects = Build.build_package(pkg, target, true, buildtype) // exclude main.c
 
@@ -205,11 +230,13 @@ Build.build_dynamic = function(pkg, target = Build.detect_host_target(), buildty
   }
 
   var lib_dir = shop.get_lib_dir()
+  var store_dir = lib_dir + '/store'
   ensure_dir(lib_dir)
+  ensure_dir(store_dir)
 
   var lib_name = shop.lib_name_for_package(pkg)
   var dylib_ext = toolchains[target].system == 'windows' ? '.dll' : (toolchains[target].system == 'darwin' ? '.dylib' : '.so')
-  var lib_path = lib_dir + '/' + lib_name + dylib_ext
+  var stable_path = lib_dir + '/' + lib_name + dylib_ext
 
   // Get link flags (with sigil replacement)
   var ldflags = replace_sigils_array(pkg_tools.get_flags(pkg, 'LDFLAGS', target))
@@ -219,6 +246,37 @@ Build.build_dynamic = function(pkg, target = Build.detect_host_target(), buildty
   var local_dir = get_local_dir()
   var tc = toolchains[target]
 
+  // Resolve relative -L paths in ldflags for hash computation
+  var resolved_ldflags = []
+  for (var i = 0; i < ldflags.length; i++) {
+    var flag = ldflags[i]
+    if (flag.startsWith('-L') && !flag.startsWith('-L/')) {
+      flag = '-L"' + pkg_dir + '/' + flag.substring(2) + '"'
+    }
+    resolved_ldflags.push(flag)
+  }
+
+  // Compute link key
+  var link_key = compute_link_key(objects, resolved_ldflags, target_ldflags, target, cc)
+  var store_path = store_dir + '/' + lib_name + '-' + link_key + dylib_ext
+
+  // Check if already linked in store
+  if (fd.is_file(store_path)) {
+    // Ensure symlink points to the store file
+    if (fd.is_link(stable_path)) {
+      var current_target = fd.readlink(stable_path)
+      if (current_target == store_path) {
+        // Already up to date
+        return stable_path
+      }
+      fd.unlink(stable_path)
+    } else if (fd.is_file(stable_path)) {
+      fd.unlink(stable_path)
+    }
+    fd.symlink(store_path, stable_path)
+    return stable_path
+  }
+
   // Build link command
   var cmd_parts = [cc, '-shared', '-fPIC']
 
@@ -228,6 +286,8 @@ Build.build_dynamic = function(pkg, target = Build.detect_host_target(), buildty
     cmd_parts.push('-undefined', 'dynamic_lookup')
     // Dead-strip unused code
     cmd_parts.push('-Wl,-dead_strip')
+    // Set install_name to stable path so runtime finds it correctly
+    cmd_parts.push('-Wl,-install_name,' + stable_path)
     // rpath for .cell/local libraries
     cmd_parts.push('-Wl,-rpath,@loader_path/../local')
     cmd_parts.push('-Wl,-rpath,' + local_dir)
@@ -253,30 +313,34 @@ Build.build_dynamic = function(pkg, target = Build.detect_host_target(), buildty
 
   // Do NOT link against core library - symbols resolved at dlopen time
 
-  // Add LDFLAGS (resolve relative -L paths)
-  for (var i = 0; i < ldflags.length; i++) {
-    var flag = ldflags[i]
-    if (flag.startsWith('-L') && !flag.startsWith('-L/')) {
-      flag = '-L"' + pkg_dir + '/' + flag.substring(2) + '"'
-    }
-    cmd_parts.push(flag)
+  // Add LDFLAGS
+  for (var i = 0; i < resolved_ldflags.length; i++) {
+    cmd_parts.push(resolved_ldflags[i])
   }
 
   for (var i = 0; i < target_ldflags.length; i++) {
     cmd_parts.push(target_ldflags[i])
   }
 
-  cmd_parts.push('-o', '"' + lib_path + '"')
+  cmd_parts.push('-o', '"' + store_path + '"')
 
   var cmd_str = cmd_parts.join(' ')
 
-  log.console('Linking ' + lib_path)
+  log.console('Linking ' + lib_name + dylib_ext)
   var ret = os.system(cmd_str)
   if (ret != 0) {
     throw new Error('Linking failed: ' + pkg)
   }
 
-  return lib_path
+  // Update symlink to point to the new store file
+  if (fd.is_link(stable_path)) {
+    fd.unlink(stable_path)
+  } else if (fd.is_file(stable_path)) {
+    fd.unlink(stable_path)
+  }
+  fd.symlink(store_path, stable_path)
+
+  return stable_path
 }
 
 // ============================================================================