diff --git a/.github/workflows/_build.yml b/.github/workflows/_build.yml
index 47b5b17b5..b69f3ff9b 100644
--- a/.github/workflows/_build.yml
+++ b/.github/workflows/_build.yml
@@ -31,7 +31,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-latest
+          - os: ubuntu-22.04
             goos: linux
             goarch: amd64
             cc: gcc
diff --git a/.github/workflows/_smoke.yml b/.github/workflows/_smoke.yml
index 1dd85e1be..23aae942b 100644
--- a/.github/workflows/_smoke.yml
+++ b/.github/workflows/_smoke.yml
@@ -31,7 +31,7 @@ jobs:
           BROAD: ${{ inputs.broad_platforms }}
         run: |
           CORE_UNIX='[
-            {"os":"ubuntu-latest","goos":"linux","goarch":"amd64"},
+            {"os":"ubuntu-22.04","goos":"linux","goarch":"amd64"},
             {"os":"ubuntu-24.04-arm","goos":"linux","goarch":"arm64"},
             {"os":"macos-14","goos":"darwin","goarch":"arm64"},
             {"os":"macos-15-intel","goos":"darwin","goarch":"amd64"}
@@ -41,12 +41,9 @@ jobs:
           # Broad legs are REQUIRED gates (no optional / continue-on-error):
           # every smoke leg must pass. No `optional` flags anywhere.
           #
-          # NOTE: the *dynamic* linux binary links glibc 2.38+ and cannot run on
-          # older distros by design — older-glibc coverage is the -portable (static)
-          # binary's job, exercised green by the smoke-linux-portable broad legs
-          # (ubuntu-22.04 / 22.04-arm). So the dynamic broad legs stay on
-          # forward-compatible OSes only (macOS); running the dynamic binary on
-          # ubuntu-22.04 would fail Phase 1 (glibc too old), not a real regression.
+          # The standard linux-amd64 artifact is built against Ubuntu 22.04 and
+          # is smoke-tested on that glibc baseline. The static portable binaries
+          # retain their separate older-glibc coverage below.
           BROAD_UNIX='[
             {"os":"macos-15","goos":"darwin","goarch":"arm64"}
           ]'
diff --git a/tests/test_venue_parity_contract.sh b/tests/test_venue_parity_contract.sh
index c847106b2..54c7ef5ec 100755
--- a/tests/test_venue_parity_contract.sh
+++ b/tests/test_venue_parity_contract.sh
@@ -40,6 +40,7 @@ python3 - "$ROOT" <<'PYEOF'
 from __future__ import annotations
 
 import pathlib
+import json
 import re
 import sys
 
@@ -261,6 +262,67 @@ for name, pattern, why in REQUIRED:
     if path.exists() and not re.search(pattern, path.read_text()):
         failures.append(f"{name}: missing required `{pattern}` — {why}")
 
+# The standard x86_64 release binary must be built and exercised on the
+# Ubuntu 22.04 glibc baseline; the static portable artifact has its own lane.
+build_lines = [
+    line for line in (workflows / "_build.yml").read_text().splitlines()
+    if not line.lstrip().startswith("#")
+]
+build_text = "\n".join(build_lines)
+build_job = re.search(
+    r"(?ms)^  build-unix:\s*\n(.*?)(?=^  build-windows:)", build_text)
+build_matrix = re.search(
+    r"(?ms)^      matrix:\s*\n(.*?)(?=^    runs-on:)",
+    build_job.group(1) if build_job else "")
+build_targets = re.findall(
+    r"(?m)^          - os:\s*(\S+)\s*\n"
+    r"            goos:\s*(\S+)\s*\n"
+    r"            goarch:\s*(\S+)\s*$",
+    build_matrix.group(1) if build_matrix else "")
+linux_amd64_builds = [
+    runner for runner, goos, goarch in build_targets
+    if goos == "linux" and goarch == "amd64"
+]
+if (not build_job or not build_matrix or linux_amd64_builds != ["ubuntu-22.04"]
+        or not re.search(
+            r"(?m)^    runs-on:\s*\$\{\{\s*matrix\.os\s*\}\}\s*$",
+            build_job.group(1))):
+    failures.append(
+        "_build.yml: standard linux-amd64 release binary must build on "
+        "ubuntu-22.04")
+
+smoke_text = "\n".join(
+    line for line in (workflows / "_smoke.yml").read_text().splitlines()
+    if not line.lstrip().startswith("#")
+)
+core_unix = re.search(
+    r"(?ms)^\s*CORE_UNIX='(\[.*?^\s*\])'\s*$", smoke_text)
+try:
+    core_unix_targets = json.loads(core_unix.group(1)) if core_unix else []
+except json.JSONDecodeError:
+    core_unix_targets = []
+if not any(target == {
+        "os": "ubuntu-22.04", "goos": "linux", "goarch": "amd64"
+} for target in core_unix_targets):
+    failures.append(
+        "_smoke.yml: standard linux-amd64 release artifact must smoke on "
+        "ubuntu-22.04")
+
+smoke_unix_job = re.search(
+    r"(?ms)^  smoke-unix:\s*\n(.*?)(?=^  smoke-windows:)", smoke_text)
+if (not re.search(
+        r'UNIX=\$\(jq[^\n]*--argjson a "\$CORE_UNIX"', smoke_text)
+        or not smoke_unix_job
+        or not re.search(
+            r"(?m)^    runs-on:\s*\$\{\{\s*matrix\.os\s*\}\}\s*$",
+            smoke_unix_job.group(1))
+        or not re.search(
+            r"(?m)^      matrix:\s*\$\{\{\s*fromJSON\(needs\.setup-matrix\.outputs\.unix\)\s*\}\}\s*$",
+            smoke_unix_job.group(1))):
+    failures.append(
+        "_smoke.yml: standard linux-amd64 smoke must consume CORE_UNIX "
+        "through the smoke-unix matrix")
+
 # Defender posture: hosted Windows runners have real-time protection
 # POLICY-LOCKED OFF (verified 2026-07-27: WinDefend starts, Set-MpPreference
 # accepts, RTP stays off), so runner jobs must NOT gate on enabling it; the