Use private host transport in containerized CI

.github/workflows/candidate.yml

@@ -298,6 +298,13 @@ jobs:
           actual_client_sha="$(git -C ruby-client rev-parse HEAD)"
           test "$actual_client_sha" = "$EXPECTED_CLIENT_SHA"
           echo "value=$actual_client_sha" >> "$GITHUB_OUTPUT"
+      - name: Resolve the private Docker host transport
+        run: |
+          probe_host="$(ip -4 route show default | awk '/^default / {print $3; exit}')"
+          ruby -ripaddr -e \
+            'address = IPAddr.new(ARGV.fetch(0)); exit(address.ipv4? && address.private? ? 0 : 1)' \
+            "$probe_host"
+          echo "OPENCODE_PROBE_HOST=$probe_host" >> "$GITHUB_ENV"
       - name: Exercise the complete manifest matrix without artifact claims
         env:
           BUNDLE_GEMFILE: ${{ github.workspace }}/ruby-client/Gemfile

scripts/run_image_contract.sh

@@ -6,6 +6,7 @@ image="${OPENCODE_IMAGE:-}"
 gem_path="${OPENCODE_RUBY_PATH:-}"
 expected_gem_commit="${OPENCODE_RUBY_COMMIT:-}"
 evidence_path="${OPENCODE_COMPAT_EVIDENCE_PATH:-}"
+probe_host="${OPENCODE_PROBE_HOST:-127.0.0.1}"
 container_name="opencode-compat-${RANDOM}-$$"
 llm_container_name="opencode-compat-llm-${RANDOM}-$$"
 network_name="opencode-compat-net-${RANDOM}-$$"
@@ -97,6 +98,18 @@ if [[ ! "$image" =~ ^[^[:space:]@]+@sha256:[0-9a-f]{64}$ ]]; then
     exit 2
   fi
 fi
+if ! ruby -ripaddr -e '
+  begin
+    address = IPAddr.new(ARGV.fetch(0))
+    valid = address.ipv4? && (address.loopback? || address.private?)
+  rescue IPAddr::InvalidAddressError
+    valid = false
+  end
+  exit(valid ? 0 : 1)
+' "$probe_host"; then
+  echo "OPENCODE_PROBE_HOST must be a loopback or private IPv4 address" >&2
+  exit 2
+fi
 
 if [[ ! "$expected_gem_commit" =~ ^[0-9a-f]{40}$ ]]; then
   echo "OPENCODE_RUBY_COMMIT must be a full lowercase 40-character Git commit" >&2
@@ -171,7 +184,7 @@ config_json="$(jq -cn --arg url "http://compat-llm:8080/v1" '{
 docker run --detach \
   --name "$container_name" \
   --network "$network_name" \
-  --publish 127.0.0.1::4096 \
+  --publish "${probe_host}::4096" \
   --env "OPENCODE_CONFIG_CONTENT=$config_json" \
   --env OPENCODE_DISABLE_AUTOUPDATE=1 \
   --env OPENCODE_DISABLE_AUTOCOMPACT=1 \
@@ -183,7 +196,7 @@ docker run --detach \
 opencode_container_started=1
 
 host_port="$(docker port "$container_name" 4096/tcp | sed -E 's/.*:([0-9]+)$/\1/' | head -1)"
-base_url="http://127.0.0.1:${host_port}"
+base_url="http://${probe_host}:${host_port}"
 
 ready=0
 for _ in $(seq 1 120); do

test/image_contract_evidence_test.rb

@@ -108,6 +108,23 @@ class ImageContractEvidenceTest < Minitest::Test
     assert_failed_without_docker(evidence_path)
   end
 
+  def test_rejects_malformed_ipv6_and_public_probe_hosts_before_docker
+    checkout, commit = git_checkout
+
+    ["not-an-address", "::1", "8.8.8.8"].each_with_index do |probe_host, index|
+      evidence_path = File.join(@tmp, "probe-host-#{index}.json")
+      environment = base_environment(checkout, commit, evidence_path).merge(
+        "OPENCODE_PROBE_HOST" => probe_host
+      )
+
+      _output, error, status = run_contract(environment)
+
+      assert_equal 2, status.exitstatus
+      assert_match(/loopback or private IPv4 address/, error)
+      assert_failed_without_docker(evidence_path)
+    end
+  end
+
   private
 
   def base_environment(checkout, commit, evidence_path)

test/repository_test.rb

@@ -287,6 +287,9 @@ class RepositoryTest < Minitest::Test
     assert_includes workflow, "exact-image-contract-gitea:"
     assert_includes workflow, "if: github.server_url != 'https://github.com'"
     assert_includes workflow, "run: scripts/run_image_matrix_contract.sh"
+    assert_includes workflow, "ip -4 route show default"
+    assert_includes workflow, "address.ipv4? && address.private?"
+    assert_includes workflow, 'echo "OPENCODE_PROBE_HOST=$probe_host" >> "$GITHUB_ENV"'
     assert_operator workflow.scan('BUNDLE_GEMFILE: ${{ github.workspace }}/ruby-client/Gemfile').length, :>=, 2
     assert_operator workflow.scan("generated JSON is transient and is not review evidence").length, :>=, 3
 
@@ -327,6 +330,9 @@ class RepositoryTest < Minitest::Test
     assert_includes runner, "exact_live_contract.rb"
     assert_includes runner, 'docker cp "$repo_root/scripts/fake_llm.py"'
     refute_includes runner, '--volume "$repo_root/scripts:/compat:ro"'
+    assert_includes runner, '--publish "${probe_host}::4096"'
+    assert_includes runner, 'base_url="http://${probe_host}:${host_port}"'
+    refute_includes runner, "--publish 0.0.0.0"
     assert_includes runner, "OPENCODE_COMPAT_EVIDENCE_PATH"
     assert_includes runner, "OPENCODE_EXPECTED_VERSION"
     refute_match(/request_count.*-lt\s+1/, runner)