diff --git a/.github/workflows/backfill-attestations.yml b/.github/workflows/backfill-attestations.yml
new file mode 100644
index 00000000..0f637948
--- /dev/null
+++ b/.github/workflows/backfill-attestations.yml
@@ -0,0 +1,59 @@
+name: Backfill Release Signatures
+
+on:
+  workflow_dispatch:
+
+permissions: {}
+
+jobs:
+  sign:
+    name: Sign existing release artifacts
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    permissions:
+      contents: write
+      id-token: write
+    steps:
+      - name: Install cosign
+        uses: sigstore/cosign-installer@398d4b0eeef1380460a10c8013a76f728fb906ac # v3
+
+      - name: Sign release artifacts
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          WORKDIR=$(mktemp -d)
+          REPO="${{ github.repository }}"
+          signed=0
+          skipped=0
+
+          for tag in $(gh release list --repo "$REPO" --limit 30 --json tagName --jq '.[].tagName'); do
+            echo "=== $tag ==="
+            existing=$(gh release view "$tag" --repo "$REPO" --json assets --jq '.assets[].name')
+
+            for asset in $(echo "$existing" | grep -E '\.(tar\.gz|zip)$'); do
+              bundle="${asset}.sigstore.json"
+
+              # Skip if already signed
+              if echo "$existing" | grep -qF "$bundle"; then
+                echo "  $asset — already signed, skipping"
+                skipped=$((skipped + 1))
+                continue
+              fi
+
+              echo "  Signing $asset..."
+              gh release download "$tag" --repo "$REPO" --pattern "$asset" --dir "$WORKDIR" --clobber
+
+              cosign sign-blob --yes \
+                --bundle "$WORKDIR/$bundle" \
+                "$WORKDIR/$asset"
+
+              gh release upload "$tag" --repo "$REPO" "$WORKDIR/$bundle" --clobber
+
+              rm -f "$WORKDIR/$asset" "$WORKDIR/$bundle"
+              signed=$((signed + 1))
+            done
+          done
+
+          rm -rf "$WORKDIR"
+          echo ""
+          echo "Done: $signed artifacts signed, $skipped already signed"
diff --git a/.github/workflows/release-binaries.yml b/.github/workflows/release-binaries.yml
index 41b84ddd..82e5d5ee 100644
--- a/.github/workflows/release-binaries.yml
+++ b/.github/workflows/release-binaries.yml
@@ -20,6 +20,8 @@ jobs:
     timeout-minutes: 15
     permissions:
       contents: write
+      id-token: write
+      attestations: write
     strategy:
       fail-fast: false
       matrix:
@@ -78,13 +80,32 @@ jobs:
           Remove-Item "archgate.exe"
           (Get-FileHash "${{ matrix.artifact }}.zip" -Algorithm SHA256).Hash.ToLower() + "  ${{ matrix.artifact }}.zip" | Out-File -Encoding ascii "${{ matrix.artifact }}.zip.sha256"
 
+      - name: Attest build provenance (Unix)
+        if: runner.os != 'Windows'
+        id: attest-unix
+        uses: actions/attest-build-provenance@a2bbfa25375fe432b6a289bc6b6cd05ecd0c4c32 # v4
+        with:
+          subject-path: ${{ matrix.artifact }}.tar.gz
+
+      - name: Attest build provenance (Windows)
+        if: runner.os == 'Windows'
+        id: attest-win
+        uses: actions/attest-build-provenance@a2bbfa25375fe432b6a289bc6b6cd05ecd0c4c32 # v4
+        with:
+          subject-path: ${{ matrix.artifact }}.zip
+
       - name: Upload release asset (Unix)
         if: runner.os != 'Windows'
         env:
           GH_TOKEN: ${{ github.token }}
         run: |
           TAG="${{ github.event.release.tag_name || inputs.tag }}"
-          gh release upload "$TAG" "${{ matrix.artifact }}.tar.gz" "${{ matrix.artifact }}.tar.gz.sha256" --clobber
+          cp "${{ steps.attest-unix.outputs.bundle-path }}" "${{ matrix.artifact }}.tar.gz.sigstore.json"
+          gh release upload "$TAG" \
+            "${{ matrix.artifact }}.tar.gz" \
+            "${{ matrix.artifact }}.tar.gz.sha256" \
+            "${{ matrix.artifact }}.tar.gz.sigstore.json" \
+            --clobber
 
       - name: Upload release asset (Windows)
         if: runner.os == 'Windows'
@@ -93,4 +114,5 @@ jobs:
           GH_TOKEN: ${{ github.token }}
         run: |
           $tag = "${{ github.event.release.tag_name || inputs.tag }}"
-          gh release upload $tag "${{ matrix.artifact }}.zip" "${{ matrix.artifact }}.zip.sha256" --clobber
+          Copy-Item "${{ steps.attest-win.outputs.bundle-path }}" "${{ matrix.artifact }}.zip.sigstore.json"
+          gh release upload $tag "${{ matrix.artifact }}.zip" "${{ matrix.artifact }}.zip.sha256" "${{ matrix.artifact }}.zip.sigstore.json" --clobber
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 7165062f..8fdca477 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -52,7 +52,7 @@ jobs:
         run: bun install --frozen-lockfile
       - name: Context check
         id: check
-        uses: TrigenSoftware/simple-release-action@v1
+        uses: TrigenSoftware/simple-release-action@a796225481a62b5b46b37d4481ef7fb114a6d399 # v1
         with:
           workflow: check
           github-token: ${{ steps.generate_token.outputs.token }}
@@ -85,7 +85,7 @@ jobs:
       - name: Install dependencies
         run: bun install --frozen-lockfile
       - name: Create or update pull request
-        uses: TrigenSoftware/simple-release-action@v1
+        uses: TrigenSoftware/simple-release-action@a796225481a62b5b46b37d4481ef7fb114a6d399 # v1
         with:
           workflow: pull-request
           github-token: ${{ github.token }}
@@ -151,7 +151,7 @@ jobs:
       - name: Ensure main is up-to-date before release
         run: git pull --rebase origin main
       - name: Release
-        uses: TrigenSoftware/simple-release-action@v1
+        uses: TrigenSoftware/simple-release-action@a796225481a62b5b46b37d4481ef7fb114a6d399 # v1
         with:
           workflow: release
           github-token: ${{ steps.generate_token.outputs.token }}
diff --git a/tests/formats/adr-fuzz.test.ts b/tests/formats/adr-fuzz.test.ts
new file mode 100644
index 00000000..26a2d5b0
Binary files /dev/null and b/tests/formats/adr-fuzz.test.ts differ
diff --git a/tests/formats/project-config-fuzz.test.ts b/tests/formats/project-config-fuzz.test.ts
new file mode 100644
index 00000000..ba04339d
--- /dev/null
+++ b/tests/formats/project-config-fuzz.test.ts
@@ -0,0 +1,224 @@
+import { describe, expect, test } from "bun:test";
+
+import {
+  DomainNameSchema,
+  DomainPrefixSchema,
+  ProjectConfigSchema,
+} from "../../src/formats/project-config";
+
+// ---------------------------------------------------------------------------
+// Generators — hand-rolled to avoid adding a devDependency (ARCH-006)
+// ---------------------------------------------------------------------------
+
+const ASCII = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
+const SPECIAL = "!@#$%^&*()_+-=[]{}|;':\",./<>?\\\n\r\t ";
+
+function randomInt(max: number): number {
+  return Math.floor(Math.random() * max);
+}
+
+function randomString(maxLen: number, charset = ASCII + SPECIAL): string {
+  const len = randomInt(maxLen);
+  return Array.from(
+    { length: len },
+    () => charset[randomInt(charset.length)]
+  ).join("");
+}
+
+// ---------------------------------------------------------------------------
+// DomainNameSchema fuzz
+// ---------------------------------------------------------------------------
+
+const ITERATIONS = 500;
+
+describe("DomainNameSchema fuzz", () => {
+  test(`validates ${ITERATIONS} random strings without crashing`, () => {
+    for (let i = 0; i < ITERATIONS; i++) {
+      const input = randomString(50);
+      const result = DomainNameSchema.safeParse(input);
+      expect(result).toHaveProperty("success");
+    }
+  });
+
+  test("boundary cases for length constraints (min 2, max 32)", () => {
+    const cases = [
+      "", // too short
+      "a", // 1 char — too short
+      "ab", // 2 chars — minimum
+      "a".repeat(32), // 32 chars — maximum
+      "a".repeat(33), // 33 chars — over limit
+      "a".repeat(1000),
+    ];
+    for (const c of cases) {
+      const result = DomainNameSchema.safeParse(c);
+      expect(result).toHaveProperty("success");
+    }
+  });
+
+  test("regex boundary cases for kebab-case", () => {
+    const cases = [
+      "backend", // valid
+      "ml-ops", // valid
+      "a1", // valid — letter then digit
+      "1abc", // invalid — starts with digit
+      "-abc", // invalid — starts with hyphen
+      "abc-", // valid — ends with hyphen (regex allows it)
+      "ABC", // invalid — uppercase
+      "aB", // invalid — mixed case
+      "ab cd", // invalid — space
+      "ab_cd", // invalid — underscore
+      "ab.cd", // invalid — dot
+      "ab--cd", // valid — double hyphen
+      "a-b-c-d-e-f", // valid — many hyphens
+      "ñ", // invalid — non-ASCII
+      "a\n", // invalid — newline
+    ];
+    for (const c of cases) {
+      const result = DomainNameSchema.safeParse(c);
+      expect(result).toHaveProperty("success");
+    }
+  });
+
+  test("handles non-string types", () => {
+    const cases = [
+      null,
+      undefined,
+      0,
+      false,
+      true,
+      [],
+      {},
+      NaN,
+      Infinity,
+      Symbol("test"),
+      () => {},
+    ];
+    for (const c of cases) {
+      const result = DomainNameSchema.safeParse(c);
+      expect(result).toHaveProperty("success");
+      expect(result.success).toBe(false);
+    }
+  });
+});
+
+// ---------------------------------------------------------------------------
+// DomainPrefixSchema fuzz
+// ---------------------------------------------------------------------------
+
+describe("DomainPrefixSchema fuzz", () => {
+  test(`validates ${ITERATIONS} random strings without crashing`, () => {
+    for (let i = 0; i < ITERATIONS; i++) {
+      const input = randomString(20);
+      const result = DomainPrefixSchema.safeParse(input);
+      expect(result).toHaveProperty("success");
+    }
+  });
+
+  test("boundary cases for length constraints (min 2, max 10)", () => {
+    const cases = [
+      "",
+      "A", // 1 char — too short
+      "AB", // 2 chars — minimum
+      "A".repeat(10), // 10 chars — maximum
+      "A".repeat(11), // 11 chars — over limit
+      "A".repeat(1000),
+    ];
+    for (const c of cases) {
+      const result = DomainPrefixSchema.safeParse(c);
+      expect(result).toHaveProperty("success");
+    }
+  });
+
+  test("regex boundary cases for uppercase pattern", () => {
+    const cases = [
+      "GEN", // valid
+      "MLOPS", // valid
+      "ML_OPS", // valid — underscore allowed
+      "A1", // valid — letter then digit
+      "1ABC", // invalid — starts with digit
+      "_ABC", // invalid — starts with underscore
+      "abc", // invalid — lowercase
+      "Ab", // invalid — mixed case
+      "AB CD", // invalid — space
+      "AB-CD", // invalid — hyphen
+    ];
+    for (const c of cases) {
+      const result = DomainPrefixSchema.safeParse(c);
+      expect(result).toHaveProperty("success");
+    }
+  });
+});
+
+// ---------------------------------------------------------------------------
+// ProjectConfigSchema fuzz
+// ---------------------------------------------------------------------------
+
+describe("ProjectConfigSchema fuzz", () => {
+  test(`validates ${ITERATIONS} random config objects without crashing`, () => {
+    for (let i = 0; i < ITERATIONS; i++) {
+      const domainCount = randomInt(10);
+      const domains: Record<string, unknown> = {};
+
+      for (let j = 0; j < domainCount; j++) {
+        const key =
+          Math.random() > 0.5
+            ? randomString(15, "abcdefghijklmnopqrstuvwxyz0123456789-")
+            : randomString(15);
+        const value =
+          Math.random() > 0.5
+            ? randomString(8, "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_")
+            : randomString(8);
+        domains[key] = value;
+      }
+
+      const config: Record<string, unknown> = { domains };
+
+      // Randomly add extra top-level keys
+      if (Math.random() > 0.7) {
+        config[randomString(10)] = randomString(20);
+      }
+
+      const result = ProjectConfigSchema.safeParse(config);
+      expect(result).toHaveProperty("success");
+    }
+  });
+
+  test("handles extreme domain counts", () => {
+    // Many domains
+    const domains: Record<string, string> = {};
+    for (let i = 0; i < 100; i++) {
+      domains[`domain${String.fromCodePoint(97 + (i % 26))}${i}`] = `D${i}`;
+    }
+    const result = ProjectConfigSchema.safeParse({ domains });
+    expect(result).toHaveProperty("success");
+  });
+
+  test("handles wrong shapes for domains field", () => {
+    const cases = [
+      { domains: null },
+      { domains: "not-an-object" },
+      { domains: 42 },
+      { domains: [] },
+      { domains: true },
+      { domains: { valid: 123 } }, // value is number, not string
+      { domains: { valid: null } }, // value is null
+      { domains: { valid: undefined } }, // value is undefined
+      { domains: { "": "" } }, // empty keys/values
+    ];
+    for (const c of cases) {
+      const result = ProjectConfigSchema.safeParse(c);
+      expect(result).toHaveProperty("success");
+    }
+  });
+
+  test("defaults correctly for missing or empty input", () => {
+    const cases = [undefined, {}, { domains: {} }];
+    for (const c of cases) {
+      const result = ProjectConfigSchema.safeParse(c);
+      expect(result.success).toBe(true);
+      if (result.success) {
+        expect(result.data.domains).toEqual({});
+      }
+    }
+  });
+});