diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6c1de0eb..f67c3533 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -25,6 +25,9 @@ jobs:
       - name: Validate cmux scheme test configuration
         run: ./tests/test_ci_scheme_testaction_debug.sh
 
+      - name: Validate GhosttyKit checksum verification
+        run: ./tests/test_ci_ghosttykit_checksum_verification.sh
+
   web-typecheck:
     runs-on: ubuntu-latest
     defaults:
@@ -70,31 +73,8 @@ jobs:
           xcrun --sdk macosx --show-sdk-path
 
       - name: Download pre-built GhosttyKit.xcframework
-        env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          set -euo pipefail
-          GHOSTTY_SHA=$(git -C ghostty rev-parse HEAD)
-          TAG="xcframework-$GHOSTTY_SHA"
-          URL="https://github.com/manaflow-ai/ghostty/releases/download/$TAG/GhosttyKit.xcframework.tar.gz"
-          echo "Downloading xcframework for ghostty $GHOSTTY_SHA"
-          MAX_RETRIES=30
-          RETRY_DELAY=20
-          for i in $(seq 1 $MAX_RETRIES); do
-            if curl -fSL -o GhosttyKit.xcframework.tar.gz "$URL"; then
-              echo "Download succeeded on attempt $i"
-              break
-            fi
-            if [ "$i" -eq "$MAX_RETRIES" ]; then
-              echo "Failed to download xcframework after $MAX_RETRIES attempts" >&2
-              exit 1
-            fi
-            echo "Attempt $i/$MAX_RETRIES failed, retrying in ${RETRY_DELAY}s..."
-            sleep $RETRY_DELAY
-          done
-          tar xzf GhosttyKit.xcframework.tar.gz
-          rm GhosttyKit.xcframework.tar.gz
-          test -d GhosttyKit.xcframework
+          ./scripts/download-prebuilt-ghosttykit.sh
 
       - name: Clean DerivedData
         run: |
@@ -203,31 +183,8 @@ jobs:
           xcodebuild -version
 
       - name: Download pre-built GhosttyKit.xcframework
-        env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          set -euo pipefail
-          GHOSTTY_SHA=$(git -C ghostty rev-parse HEAD)
-          TAG="xcframework-$GHOSTTY_SHA"
-          URL="https://github.com/manaflow-ai/ghostty/releases/download/$TAG/GhosttyKit.xcframework.tar.gz"
-          echo "Downloading xcframework for ghostty $GHOSTTY_SHA"
-          MAX_RETRIES=30
-          RETRY_DELAY=20
-          for i in $(seq 1 $MAX_RETRIES); do
-            if curl -fSL -o GhosttyKit.xcframework.tar.gz "$URL"; then
-              echo "Download succeeded on attempt $i"
-              break
-            fi
-            if [ "$i" -eq "$MAX_RETRIES" ]; then
-              echo "Failed to download xcframework after $MAX_RETRIES attempts" >&2
-              exit 1
-            fi
-            echo "Attempt $i/$MAX_RETRIES failed, retrying in ${RETRY_DELAY}s..."
-            sleep $RETRY_DELAY
-          done
-          tar xzf GhosttyKit.xcframework.tar.gz
-          rm GhosttyKit.xcframework.tar.gz
-          test -d GhosttyKit.xcframework
+          ./scripts/download-prebuilt-ghosttykit.sh
 
       - name: Clean DerivedData
         run: rm -rf ~/Library/Developer/Xcode/DerivedData/GhosttyTabs-*
diff --git a/.github/workflows/nightly.yml b/.github/workflows/nightly.yml
index 3b9a0866..18caadc3 100644
--- a/.github/workflows/nightly.yml
+++ b/.github/workflows/nightly.yml
@@ -116,31 +116,8 @@ jobs:
           npm install --global "create-dmg@${CREATE_DMG_VERSION}"
 
       - name: Download pre-built GhosttyKit.xcframework
-        env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          set -euo pipefail
-          GHOSTTY_SHA=$(git -C ghostty rev-parse HEAD)
-          TAG="xcframework-$GHOSTTY_SHA"
-          URL="https://github.com/manaflow-ai/ghostty/releases/download/$TAG/GhosttyKit.xcframework.tar.gz"
-          echo "Downloading xcframework for ghostty $GHOSTTY_SHA"
-          MAX_RETRIES=30
-          RETRY_DELAY=20
-          for i in $(seq 1 $MAX_RETRIES); do
-            if curl -fSL -o GhosttyKit.xcframework.tar.gz "$URL"; then
-              echo "Download succeeded on attempt $i"
-              break
-            fi
-            if [ "$i" -eq "$MAX_RETRIES" ]; then
-              echo "Failed to download xcframework after $MAX_RETRIES attempts" >&2
-              exit 1
-            fi
-            echo "Attempt $i/$MAX_RETRIES failed, retrying in ${RETRY_DELAY}s..."
-            sleep $RETRY_DELAY
-          done
-          tar xzf GhosttyKit.xcframework.tar.gz
-          rm GhosttyKit.xcframework.tar.gz
-          test -d GhosttyKit.xcframework
+          ./scripts/download-prebuilt-ghosttykit.sh
 
       - name: Cache Swift packages
         uses: actions/cache@5a3ec84eff668545956fd18022155c47e93e2684 # v4
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 200f003a..ec935c63 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -103,31 +103,8 @@ jobs:
 
       - name: Download pre-built GhosttyKit.xcframework
         if: steps.guard_release_assets.outputs.skip_all != 'true'
-        env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          set -euo pipefail
-          GHOSTTY_SHA=$(git -C ghostty rev-parse HEAD)
-          TAG="xcframework-$GHOSTTY_SHA"
-          URL="https://github.com/manaflow-ai/ghostty/releases/download/$TAG/GhosttyKit.xcframework.tar.gz"
-          echo "Downloading xcframework for ghostty $GHOSTTY_SHA"
-          MAX_RETRIES=30
-          RETRY_DELAY=20
-          for i in $(seq 1 $MAX_RETRIES); do
-            if curl -fSL -o GhosttyKit.xcframework.tar.gz "$URL"; then
-              echo "Download succeeded on attempt $i"
-              break
-            fi
-            if [ "$i" -eq "$MAX_RETRIES" ]; then
-              echo "Failed to download xcframework after $MAX_RETRIES attempts" >&2
-              exit 1
-            fi
-            echo "Attempt $i/$MAX_RETRIES failed, retrying in ${RETRY_DELAY}s..."
-            sleep $RETRY_DELAY
-          done
-          tar xzf GhosttyKit.xcframework.tar.gz
-          rm GhosttyKit.xcframework.tar.gz
-          test -d GhosttyKit.xcframework
+          ./scripts/download-prebuilt-ghosttykit.sh
 
       - name: Cache Swift packages
         if: steps.guard_release_assets.outputs.skip_all != 'true'
diff --git a/scripts/download-prebuilt-ghosttykit.sh b/scripts/download-prebuilt-ghosttykit.sh
new file mode 100755
index 00000000..cc3c520b
--- /dev/null
+++ b/scripts/download-prebuilt-ghosttykit.sh
@@ -0,0 +1,71 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+
+if [ -n "${GHOSTTY_SHA:-}" ]; then
+  GHOSTTY_SHA="$GHOSTTY_SHA"
+else
+  if [ ! -d "$REPO_ROOT/ghostty" ] || ! git -C "$REPO_ROOT/ghostty" rev-parse --is-inside-work-tree >/dev/null 2>&1; then
+    echo "Missing ghostty submodule. Run ./scripts/setup.sh or git submodule update --init --recursive first." >&2
+    exit 1
+  fi
+  GHOSTTY_SHA="$(git -C "$REPO_ROOT/ghostty" rev-parse HEAD)"
+fi
+
+TAG="xcframework-$GHOSTTY_SHA"
+ARCHIVE_NAME="${GHOSTTYKIT_ARCHIVE_NAME:-GhosttyKit.xcframework.tar.gz}"
+OUTPUT_DIR="${GHOSTTYKIT_OUTPUT_DIR:-GhosttyKit.xcframework}"
+CHECKSUMS_FILE="${GHOSTTYKIT_CHECKSUMS_FILE:-$SCRIPT_DIR/ghosttykit-checksums.txt}"
+DOWNLOAD_URL="${GHOSTTYKIT_URL:-https://github.com/manaflow-ai/ghostty/releases/download/$TAG/$ARCHIVE_NAME}"
+DOWNLOAD_RETRIES="${GHOSTTYKIT_DOWNLOAD_RETRIES:-30}"
+DOWNLOAD_RETRY_DELAY="${GHOSTTYKIT_DOWNLOAD_RETRY_DELAY:-20}"
+
+if [ ! -f "$CHECKSUMS_FILE" ]; then
+  echo "Missing checksum file: $CHECKSUMS_FILE" >&2
+  exit 1
+fi
+
+EXPECTED_SHA256="$(
+  awk -v sha="$GHOSTTY_SHA" '
+    $1 == sha {
+      print $2
+      found = 1
+      exit
+    }
+    END {
+      if (!found) {
+        exit 1
+      }
+    }
+  ' "$CHECKSUMS_FILE" || true
+)"
+
+if [ -z "$EXPECTED_SHA256" ]; then
+  echo "Missing pinned GhosttyKit checksum for ghostty $GHOSTTY_SHA in $CHECKSUMS_FILE" >&2
+  exit 1
+fi
+
+echo "Downloading $ARCHIVE_NAME for ghostty $GHOSTTY_SHA"
+curl --fail --show-error --location \
+  --retry "$DOWNLOAD_RETRIES" \
+  --retry-delay "$DOWNLOAD_RETRY_DELAY" \
+  --retry-all-errors \
+  -o "$ARCHIVE_NAME" \
+  "$DOWNLOAD_URL"
+
+ACTUAL_SHA256="$(shasum -a 256 "$ARCHIVE_NAME" | awk '{print $1}')"
+if [ "$ACTUAL_SHA256" != "$EXPECTED_SHA256" ]; then
+  echo "$ARCHIVE_NAME checksum mismatch" >&2
+  echo "Expected: $EXPECTED_SHA256" >&2
+  echo "Actual:   $ACTUAL_SHA256" >&2
+  exit 1
+fi
+
+rm -rf "$OUTPUT_DIR"
+tar xzf "$ARCHIVE_NAME"
+rm "$ARCHIVE_NAME"
+test -d "$OUTPUT_DIR"
+
+echo "Verified and extracted $OUTPUT_DIR"
diff --git a/scripts/ghosttykit-checksums.txt b/scripts/ghosttykit-checksums.txt
new file mode 100644
index 00000000..29794d12
--- /dev/null
+++ b/scripts/ghosttykit-checksums.txt
@@ -0,0 +1,4 @@
+# Pinned GhosttyKit.xcframework.tar.gz checksums keyed by ghostty submodule SHA.
+# Update this file in a reviewed PR whenever the ghostty submodule SHA changes.
+# Format: <ghostty_sha> <sha256>
+7dd589824d4c9bda8265355718800cccaf7189a0 3915af4256850a0a7bee671c3ba0a47cbfee5dbfc6d71caf952acefdf2ee4207
diff --git a/tests/test_ci_ghosttykit_checksum_verification.sh b/tests/test_ci_ghosttykit_checksum_verification.sh
new file mode 100755
index 00000000..1eba6ecf
--- /dev/null
+++ b/tests/test_ci_ghosttykit_checksum_verification.sh
@@ -0,0 +1,138 @@
+#!/usr/bin/env bash
+# Regression test for the pinned GhosttyKit artifact verification helper.
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "$0")/.." && pwd)"
+SCRIPT="$ROOT_DIR/scripts/download-prebuilt-ghosttykit.sh"
+TMP_DIR="$(mktemp -d)"
+trap 'rm -rf "$TMP_DIR"' EXIT
+
+WORKFLOWS=(
+  "$ROOT_DIR/.github/workflows/ci.yml"
+  "$ROOT_DIR/.github/workflows/nightly.yml"
+  "$ROOT_DIR/.github/workflows/release.yml"
+)
+
+FIXTURE_SHA="7dd589824d4c9bda8265355718800cccaf7189a0"
+FIXTURE_DIR="$TMP_DIR/fixture"
+SUCCESS_DIR="$TMP_DIR/success"
+MISMATCH_DIR="$TMP_DIR/mismatch"
+MISSING_ENTRY_DIR="$TMP_DIR/missing-entry"
+BIN_DIR="$TMP_DIR/bin"
+CHECKSUMS_FILE="$TMP_DIR/ghosttykit-checksums.txt"
+SUCCESS_LOG="$TMP_DIR/curl-success.log"
+MISMATCH_LOG="$TMP_DIR/curl-mismatch.log"
+MISMATCH_OUTPUT="$TMP_DIR/mismatch.out"
+MISSING_ENTRY_OUTPUT="$TMP_DIR/missing-entry.out"
+
+mkdir -p "$FIXTURE_DIR/GhosttyKit.xcframework" "$SUCCESS_DIR" "$MISMATCH_DIR" "$MISSING_ENTRY_DIR" "$BIN_DIR"
+printf 'fixture\n' > "$FIXTURE_DIR/GhosttyKit.xcframework/marker.txt"
+(cd "$FIXTURE_DIR" && tar czf "$TMP_DIR/GhosttyKit.xcframework.tar.gz" GhosttyKit.xcframework)
+ACTUAL_SHA256="$(shasum -a 256 "$TMP_DIR/GhosttyKit.xcframework.tar.gz" | awk '{print $1}')"
+printf '%s %s\n' "$FIXTURE_SHA" "$ACTUAL_SHA256" > "$CHECKSUMS_FILE"
+
+for workflow in "${WORKFLOWS[@]}"; do
+  if ! grep -Fq './scripts/download-prebuilt-ghosttykit.sh' "$workflow"; then
+    echo "FAIL: $workflow must call download-prebuilt-ghosttykit.sh"
+    exit 1
+  fi
+done
+
+cat > "$BIN_DIR/curl" <<'EOF'
+#!/usr/bin/env bash
+set -euo pipefail
+
+LOG_FILE="${TEST_CURL_LOG:?}"
+FIXTURE_ARCHIVE="${TEST_FIXTURE_ARCHIVE:?}"
+OUTPUT=""
+
+while [ "$#" -gt 0 ]; do
+  case "$1" in
+    -o)
+      OUTPUT="$2"
+      shift 2
+      ;;
+    *)
+      printf '%s\n' "$1" >> "$LOG_FILE"
+      shift
+      ;;
+  esac
+done
+
+if [ -z "$OUTPUT" ]; then
+  echo "curl stub missing -o output path" >&2
+  exit 1
+fi
+
+cp "$FIXTURE_ARCHIVE" "$OUTPUT"
+EOF
+chmod +x "$BIN_DIR/curl"
+
+(
+  cd "$SUCCESS_DIR"
+  PATH="$BIN_DIR:$PATH" \
+  TEST_CURL_LOG="$SUCCESS_LOG" \
+  TEST_FIXTURE_ARCHIVE="$TMP_DIR/GhosttyKit.xcframework.tar.gz" \
+  GHOSTTY_SHA="$FIXTURE_SHA" \
+  GHOSTTYKIT_CHECKSUMS_FILE="$CHECKSUMS_FILE" \
+  "$SCRIPT"
+)
+
+if [ ! -f "$SUCCESS_DIR/GhosttyKit.xcframework/marker.txt" ]; then
+  echo "FAIL: verification helper did not extract GhosttyKit.xcframework"
+  exit 1
+fi
+
+if [ -f "$SUCCESS_DIR/GhosttyKit.xcframework.tar.gz" ]; then
+  echo "FAIL: verification helper did not clean up the downloaded archive"
+  exit 1
+fi
+
+for expected_arg in --retry --retry-delay --retry-all-errors; do
+  if ! grep -Fxq -- "$expected_arg" "$SUCCESS_LOG"; then
+    echo "FAIL: curl invocation missing $expected_arg"
+    exit 1
+  fi
+done
+
+printf '%s %s\n' "$FIXTURE_SHA" "0000000000000000000000000000000000000000000000000000000000000000" > "$CHECKSUMS_FILE"
+
+if (
+  cd "$MISMATCH_DIR"
+  PATH="$BIN_DIR:$PATH" \
+  TEST_CURL_LOG="$MISMATCH_LOG" \
+  TEST_FIXTURE_ARCHIVE="$TMP_DIR/GhosttyKit.xcframework.tar.gz" \
+  GHOSTTY_SHA="$FIXTURE_SHA" \
+  GHOSTTYKIT_CHECKSUMS_FILE="$CHECKSUMS_FILE" \
+  "$SCRIPT"
+) >"$MISMATCH_OUTPUT" 2>&1; then
+  echo "FAIL: verification helper succeeded with an invalid pinned checksum"
+  exit 1
+fi
+
+if ! grep -Fq "GhosttyKit.xcframework.tar.gz checksum mismatch" "$MISMATCH_OUTPUT"; then
+  echo "FAIL: verification helper did not report checksum mismatch"
+  exit 1
+fi
+
+printf '%s %s\n' "0000000000000000000000000000000000000000" "$ACTUAL_SHA256" > "$CHECKSUMS_FILE"
+
+if (
+  cd "$MISSING_ENTRY_DIR"
+  PATH="$BIN_DIR:$PATH" \
+  TEST_CURL_LOG="$MISMATCH_LOG" \
+  TEST_FIXTURE_ARCHIVE="$TMP_DIR/GhosttyKit.xcframework.tar.gz" \
+  GHOSTTY_SHA="$FIXTURE_SHA" \
+  GHOSTTYKIT_CHECKSUMS_FILE="$CHECKSUMS_FILE" \
+  "$SCRIPT"
+) >"$MISSING_ENTRY_OUTPUT" 2>&1; then
+  echo "FAIL: verification helper succeeded without a pinned checksum entry"
+  exit 1
+fi
+
+if ! grep -Fq "Missing pinned GhosttyKit checksum for ghostty $FIXTURE_SHA" "$MISSING_ENTRY_OUTPUT"; then
+  echo "FAIL: verification helper did not report a missing pinned checksum entry"
+  exit 1
+fi
+
+echo "PASS: GhosttyKit verification helper enforces pinned checksums"