diff --git a/mac/Package.swift b/mac/Package.swift
index 51898da4..9c6ba17a 100644
--- a/mac/Package.swift
+++ b/mac/Package.swift
@@ -4,7 +4,11 @@ import PackageDescription
 let package = Package(
     name: "CodeBurnMenubar",
     platforms: [
-        .macOS(.v15)
+        // macOS 14 (Sonoma) is the floor: matches Info.plist LSMinimumSystemVersion,
+        // the CLI install guard (MIN_MACOS_MAJOR=14), and mac/README. The earlier .v15
+        // bump for NSAttributedString(attachment:) was a misdiagnosis — that initializer
+        // is AppKit since macOS 10.0, so the binary's minos must not exclude Sonoma users.
+        .macOS(.v14)
     ],
     products: [
         .executable(name: "CodeBurnMenubar", targets: ["CodeBurnMenubar"])
diff --git a/mac/README.md b/mac/README.md
index b12b836d..ce614ab7 100644
--- a/mac/README.md
+++ b/mac/README.md
@@ -30,6 +30,30 @@ swift build -c release
 .build/release/CodeBurnMenubar                # launch
 ```
 
+#### On macOS 14 (Sonoma) without Xcode 16
+
+`swift build` above assumes the macOS 15 SDK, whose SwiftUI marks the `View`
+protocol `@MainActor`. The Sonoma SDK (shipped with Command Line Tools) lacks
+that annotation, so a plain build fails with ~80 `main actor-isolated ... from a
+nonisolated context` errors.
+
+(The `-10825` launch failure itself is fixed by `Package.swift`'s `.macOS(.v14)`
+deployment target: ld64 drops the macOS-15-only `libswift_errno.dylib`
+dependency for any build with that target, regardless of which SDK built it —
+including the CI-distributed release. This local-build path exists only for
+the narrower case of building on a Sonoma machine with nothing but the
+Command Line Tools, where the SDK's un-annotated `View` protocol needs the
+`@MainActor` patch below.)
+
+Use the helper, which builds against the local macOS 14 SDK with a standalone
+[swift.org](https://www.swift.org/install/macos/) Swift 6.x toolchain and
+adds explicit `@MainActor` to the views in a scratch copy (repo sources stay
+clean), producing a `minos = 14.0` bundle installed to `~/Applications`:
+
+```bash
+mac/Scripts/build-local.sh         # then: codeburn menubar
+```
+
 ## Build & run (dev against a local CLI checkout)
 
 ```bash
@@ -52,7 +76,10 @@ Release installs record a persistent absolute CLI path in `~/Library/Application
 
 ```
 mac/
-├── Package.swift                     SwiftPM manifest
+├── Package.swift                     SwiftPM manifest (deployment target: macOS 14)
+├── Scripts/
+│   ├── package-app.sh                CI: universal signed .app + zip + checksum
+│   └── build-local.sh                Local macOS 14 build (Sonoma SDK + @MainActor patch)
 ├── Sources/CodeBurnMenubar/
 │   ├── CodeBurnApp.swift             @main + MenuBarExtra scene
 │   ├── AppStore.swift                @Observable store + enums
diff --git a/mac/Scripts/build-local.sh b/mac/Scripts/build-local.sh
new file mode 100755
index 00000000..7498c902
--- /dev/null
+++ b/mac/Scripts/build-local.sh
@@ -0,0 +1,150 @@
+#!/usr/bin/env bash
+# ============================================================================
+# build-local.sh — Build CodeBurnMenubar.app on a macOS 14 (Sonoma) machine.
+# ============================================================================
+# Why this exists
+# ---------------
+# Package.swift's `.macOS(.v14)` deployment target already fixes the -10825
+# launch failure for every build, including the CI-distributed release: ld64
+# drops the macOS-15-only libswift_errno.dylib dependency based on the
+# deployment target, not the SDK used to build. This script is not about that.
+#
+# It exists for the narrower case of building on a Sonoma machine that only
+# has the Command Line Tools (macOS 14 SDK). That SDK's SwiftUI does NOT carry
+# the @MainActor annotations the macOS 15 SDK added to the `View` protocol, so
+# a plain `swift build` there fails with ~80 `main actor-isolated ... from a
+# nonisolated context` errors. This script copies the sources to a scratch
+# dir, gives every `View`/`App` conformance an explicit `@MainActor` there
+# (repo sources stay untouched), and builds a universal bundle with a
+# swift.org Swift 6.2 toolchain against the local macOS 14 SDK.
+#
+# Prerequisites
+#   - Command Line Tools (provides the macOS 14 SDK + sips/iconutil/codesign)
+#   - A swift.org Swift 6.x toolchain in ~/Library/Developer/Toolchains/
+#       download: https://www.swift.org/install/macos/  (Swift 6.2 recommended)
+#
+# Usage: mac/Scripts/build-local.sh [<version>]   (defaults to "dev")
+# ----------------------------------------------------------------------------
+set -euo pipefail
+
+VERSION="${1:-dev}"
+BUNDLE_ID="org.agentseal.codeburn-menubar"
+EXE="CodeBurnMenubar"
+MIN_MACOS="14.0"
+
+ROOT=$(cd "$(dirname "$0")/../.." && pwd)
+MAC_DIR="${ROOT}/mac"
+ICON_SOURCE="${ROOT}/assets/menubar-logo.png"
+SCRATCH="$(mktemp -d /tmp/codeburn-local-build.XXXXXX)"
+APPS="${HOME}/Applications"
+BUNDLE="${APPS}/${EXE}.app"
+
+trap 'rm -rf "${SCRATCH}"' EXIT
+
+# --- locate a Swift 6.x toolchain -------------------------------------------
+TC=""
+for cand in "${HOME}/Library/Developer/Toolchains/swift-6.2-RELEASE.xctoolchain" \
+            "${HOME}/Library/Developer/Toolchains/swift-latest.xctoolchain" \
+            /Library/Developer/Toolchains/swift-latest.xctoolchain; do
+  [[ -x "${cand}/usr/bin/swift" ]] && { TC="${cand}"; break; }
+done
+if [[ -z "${TC}" ]]; then
+  echo "✗ No swift.org Swift 6.x toolchain found in ~/Library/Developer/Toolchains/." >&2
+  echo "  Install one from https://www.swift.org/install/macos/ (Swift 6.2)." >&2
+  exit 1
+fi
+SWIFT="${TC}/usr/bin/swift"
+export SDKROOT="$(xcrun --sdk macosx --show-sdk-path)"
+SDK_VERSION="$(xcrun --sdk macosx --show-sdk-version)"
+case "${SDK_VERSION}" in
+  14.*) ;;
+  *)
+    echo "✗ Active SDK is macOS ${SDK_VERSION}, not 14.x — xcode-select is likely" >&2
+    echo "  pointed at a newer Xcode instead of the Command Line Tools. Run:" >&2
+    echo "    sudo xcode-select -s /Library/Developer/CommandLineTools" >&2
+    exit 1
+    ;;
+esac
+echo "▸ Toolchain : $("${SWIFT}" --version | head -1)"
+echo "▸ SDK       : ${SDKROOT} (${SDK_VERSION})"
+
+# --- copy sources and add explicit @MainActor to SwiftUI views --------------
+echo "▸ Staging sources in ${SCRATCH}..."
+# Tests/ is copied only so the manifest's testTarget path resolves; `swift build`
+# (product only) never compiles it, so it needs no @MainActor patching.
+cp -R "${MAC_DIR}/Sources" "${MAC_DIR}/Tests" "${MAC_DIR}/Package.swift" "${SCRATCH}/"
+find "${SCRATCH}/Sources" -name "*.swift" -print0 | while IFS= read -r -d '' f; do
+  # Slurp mode ([^{]* spans newlines) so this also catches multi-line generic
+  # struct headers and `extension X: View` conformances, not just the
+  # single-line `struct X: View {` shape the current sources happen to use.
+  perl -0777 -i -pe '
+    s/^((?:private |public |fileprivate |internal )?(?:struct|extension)\s+\w+(?:<[^{]*?>)?\s*:[^{]*\bView\b[^{]*\{)/\@MainActor\n$1/gm;
+    s/^(struct\s+\w+\s*:[^{]*\bApp\b[^{]*\{)/\@MainActor\n$1/gm;
+    s/\@MainActor\n\@MainActor\n/\@MainActor\n/g;
+  ' "$f"
+done
+
+# --- build each arch separately, then lipo into one universal binary --------
+# `swift build --arch arm64 --arch x86_64` together shells out to xcbuild,
+# which the Command Line Tools doesn't ship — each arch alone stays on the
+# plain SwiftPM build path, so build twice and merge with lipo instead.
+BINS=()
+for arch in arm64 x86_64; do
+  echo "▸ Building ${arch} release..."
+  ( cd "${SCRATCH}" && "${SWIFT}" build -c release --arch "${arch}" )
+  bin="$(cd "${SCRATCH}" && "${SWIFT}" build -c release --arch "${arch}" --show-bin-path)/${EXE}"
+  [[ -x "${bin}" ]] || { echo "✗ ${arch} build produced no binary" >&2; exit 1; }
+  BINS+=("${bin}")
+done
+BIN="${SCRATCH}/${EXE}-universal"
+lipo -create -output "${BIN}" "${BINS[@]}"
+
+# --- assemble the .app bundle ------------------------------------------------
+echo "▸ Assembling ${BUNDLE}..."
+pkill -x "${EXE}" 2>/dev/null || true; sleep 1
+rm -rf "${BUNDLE}"
+mkdir -p "${BUNDLE}/Contents/MacOS" "${BUNDLE}/Contents/Resources"
+cp "${BIN}" "${BUNDLE}/Contents/MacOS/${EXE}"
+cp "${ICON_SOURCE}" "${BUNDLE}/Contents/Resources/menubar-logo.png"
+
+ICONSET="${SCRATCH}/AppIcon.iconset"; mkdir -p "${ICONSET}"
+for spec in "16:16x16" "32:16x16@2x" "32:32x32" "64:32x32@2x" "128:128x128" \
+            "256:128x128@2x" "256:256x256" "512:256x256@2x" "512:512x512"; do
+  sips -z "${spec%%:*}" "${spec%%:*}" "${ICON_SOURCE}" --out "${ICONSET}/icon_${spec##*:}.png" >/dev/null
+done
+cp "${ICON_SOURCE}" "${ICONSET}/icon_512x512@2x.png"
+iconutil -c icns "${ICONSET}" -o "${BUNDLE}/Contents/Resources/AppIcon.icns"
+
+cat > "${BUNDLE}/Contents/Info.plist" <<PLIST
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+    <key>CFBundleDevelopmentRegion</key><string>en</string>
+    <key>CFBundleDisplayName</key><string>CodeBurn Menubar</string>
+    <key>CFBundleExecutable</key><string>${EXE}</string>
+    <key>CFBundleIconFile</key><string>AppIcon</string>
+    <key>CFBundleIdentifier</key><string>${BUNDLE_ID}</string>
+    <key>CFBundleInfoDictionaryVersion</key><string>6.0</string>
+    <key>CFBundleName</key><string>${EXE}</string>
+    <key>CFBundlePackageType</key><string>APPL</string>
+    <key>CFBundleShortVersionString</key><string>${VERSION}</string>
+    <key>CFBundleVersion</key><string>${VERSION}</string>
+    <key>LSMinimumSystemVersion</key><string>${MIN_MACOS}</string>
+    <key>LSUIElement</key><true/>
+    <key>NSHighResolutionCapable</key><true/>
+    <key>NSHumanReadableCopyright</key><string>© AgentSeal</string>
+</dict>
+</plist>
+PLIST
+printf 'APPL????' > "${BUNDLE}/Contents/PkgInfo"
+
+echo "▸ Ad-hoc signing..."
+codesign --force --sign - --timestamp=none --deep "${BUNDLE}"
+codesign --verify --deep --strict "${BUNDLE}"
+
+echo ""
+echo "✓ Installed ${BUNDLE}"
+lipo -info "${BUNDLE}/Contents/MacOS/${EXE}" | sed 's/^/  /'
+vtool -show-build "${BUNDLE}/Contents/MacOS/${EXE}" 2>/dev/null | grep -iE "minos|sdk" | sed 's/^/  /'
+echo "  Launch with: codeburn menubar   (or: open '${BUNDLE}')"
diff --git a/mac/Scripts/package-app.sh b/mac/Scripts/package-app.sh
index 3041eda0..bc019f8f 100755
--- a/mac/Scripts/package-app.sh
+++ b/mac/Scripts/package-app.sh
@@ -120,6 +120,20 @@ else
 fi
 codesign --verify --deep --strict "${BUNDLE}"
 
+echo "▸ Verifying deployment target and libswift_errno absence..."
+BUILT_EXE="${BUNDLE}/Contents/MacOS/${EXECUTABLE_NAME}"
+BAD_MINOS=$(vtool -show-build "${BUILT_EXE}" 2>/dev/null | awk '/minos/{print $2}' | grep -v '^14\.0$' || true)
+if [[ -n "${BAD_MINOS}" ]]; then
+  echo "✗ Expected minos 14.0 for every arch slice, found: ${BAD_MINOS}" >&2
+  echo "  Did Package.swift's platforms: [.macOS(...)] regress past .v14?" >&2
+  exit 1
+fi
+if otool -L "${BUILT_EXE}" | grep -q libswift_errno; then
+  echo "✗ ${BUILT_EXE} links libswift_errno.dylib (macOS 15+ only) — would fail on Sonoma with -10825." >&2
+  exit 1
+fi
+echo "  minos 14.0 confirmed, no libswift_errno dependency."
+
 ZIP_NAME="CodeBurnMenubar-${ASSET_VERSION}.zip"
 ZIP_PATH="${DIST_DIR}/${ZIP_NAME}"
 echo "▸ Packaging ${ZIP_NAME}..."