diff --git a/.github/workflows/security-scan.yml b/.github/workflows/security-scan.yml
index c3b8fa5db..a23b04caf 100644
--- a/.github/workflows/security-scan.yml
+++ b/.github/workflows/security-scan.yml
@@ -16,10 +16,12 @@
 # pull_request workflows upload to refs/pull/N/merge, so no single ref ever holds
 # all tools. Bundling at the workflow/check level is ref-independent.
 #
-# NOTE on dependency-review: dependency graph can be unavailable on some repos.
-# Treat that as "not enforceable here" instead of making the required workflow
-# unsatisfiable; keep medium-or-higher dependency findings hard-failing where the
-# API is supported.
+# NOTE on dependency-review: unavailable evidence is not a clean result. Only
+# an exact base/head comparison returning HTTP 200 may reach the pinned hard
+# gate. Malformed revisions or repository names fail closed before the
+# network call. Every other probe outcome fails closed without printing the
+# response body. Diagnostics include allowlisted repository visibility. See
+# docs/doctoring/dependency-review-fail-closed.md.
 #
 # NOTE on trivy-fs: it scans the whole repo, so a pre-existing FIXABLE
 # MEDIUM/HIGH/CRITICAL finding blocks every PR in that repo until it is fixed.
@@ -257,9 +259,11 @@ jobs:
       contents: read
       pull-requests: read
     steps:
-      - name: Checkout
+      - name: Checkout exact head
         uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
+          repository: ${{ github.event.pull_request.head.repo.full_name }}
+          ref: ${{ github.event.pull_request.head.sha }}
           persist-credentials: false
       - name: Check dependency review support
         id: dependency_review_support
@@ -268,36 +272,51 @@ jobs:
           BASE_SHA: ${{ github.event.pull_request.base.sha }}
           HEAD_SHA: ${{ github.event.pull_request.head.sha }}
           REPOSITORY: ${{ github.repository }}
+          REPOSITORY_VISIBILITY: ${{ github.event.repository.visibility }}
         run: |
           set -euo pipefail
 
           api_url="${GITHUB_API_URL:-https://api.github.com}"
-          response_file="$(mktemp)"
+          case "${REPOSITORY_VISIBILITY}" in
+            public|private|internal) visibility="${REPOSITORY_VISIBILITY}" ;;
+            *) visibility="unknown" ;;
+          esac
+          revision_pattern='^[0-9a-fA-F]{40}$|^[0-9a-fA-F]{64}$'
+          repository_pattern='^[A-Za-z0-9_.-]+/[A-Za-z0-9_.-]+$'
+          if ! [[ "${BASE_SHA}" =~ $revision_pattern ]] || ! [[ "${HEAD_SHA}" =~ $revision_pattern ]]; then
+            echo "::error::Dependency review evidence unavailable for ${REPOSITORY} (visibility ${visibility}) at exact base ${BASE_SHA} and head ${HEAD_SHA}: HTTP unavailable; curl exit uncalled. Malformed revision. Supply the pull request's exact 40- or 64-character hex base and head SHAs, then rerun. Failing closed."
+            exit 1
+          fi
+          if ! [[ "${REPOSITORY}" =~ $repository_pattern ]]; then
+            echo "::error::Dependency review evidence unavailable for ${REPOSITORY} (visibility ${visibility}) at exact base ${BASE_SHA} and head ${HEAD_SHA}: HTTP unavailable; curl exit uncalled. Malformed repository. Use the canonical owner/name and rerun. Failing closed."
+            exit 1
+          fi
+          set +e
           status="$(
-            curl -fsS -o "$response_file" -w '%{http_code}' \
+            curl -sS --connect-timeout 10 --max-time 30 \
+              -o /dev/null \
+              -w '%{http_code}' \
               -H "Accept: application/vnd.github+json" \
               -H "Authorization: Bearer ${GH_TOKEN}" \
               -H "X-GitHub-Api-Version: 2022-11-28" \
-              "${api_url}/repos/${REPOSITORY}/dependency-graph/compare/${BASE_SHA}...${HEAD_SHA}" \
-              || true
+              "${api_url}/repos/${REPOSITORY}/dependency-graph/compare/${BASE_SHA}...${HEAD_SHA}"
           )"
+          curl_status=$?
+          set -e
 
-          if [ "$status" = "200" ]; then
-            echo "supported=true" >>"$GITHUB_OUTPUT"
-            exit 0
-          fi
+          case "$status" in
+            [0-9][0-9][0-9]) http_status="$status" ;;
+            "") http_status="unavailable" ;;
+            *) http_status="malformed" ;;
+          esac
 
-          if [ "$status" = "403" ] || [ "$status" = "404" ]; then
-            echo "::warning::Dependency review is unavailable for ${REPOSITORY}; skipping dependency-review hard gate."
-            echo "supported=false" >>"$GITHUB_OUTPUT"
-            exit 0
+          if [ "$curl_status" -ne 0 ] || [ "$http_status" != "200" ]; then
+            echo "::error::Dependency review evidence unavailable for ${REPOSITORY} (visibility ${visibility}) at exact base ${BASE_SHA} and head ${HEAD_SHA}: HTTP ${http_status}; curl exit ${curl_status}. Verify dependency-graph/security configuration and GitHub service behavior, then rerun. Failing closed."
+            exit 1
           fi
 
-          echo "::error::Dependency review support check failed with HTTP ${status}."
-          cat "$response_file"
-          exit 1
+          echo "supported=true" >>"$GITHUB_OUTPUT"
       - name: Dependency review
-        if: steps.dependency_review_support.outputs.supported == 'true'
         uses: actions/dependency-review-action@a1d282b36b6f3519aa1f3fc636f609c47dddb294 # v5.0.0
         with:
           fail-on-severity: moderate
diff --git a/ARCHITECTURE.md b/ARCHITECTURE.md
index 3e2e70b58..7ada146d3 100644
--- a/ARCHITECTURE.md
+++ b/ARCHITECTURE.md
@@ -104,6 +104,31 @@ sequenceDiagram
 - Rust remains the psychometric arithmetic owner. Repair never substitutes
   Python for scoring math.
 
+## Dependency-review evidence
+
+The central `Security Scan` job treats GitHub's exact `BASE_SHA...HEAD_SHA`
+comparison as a hard supply-chain evidence boundary. Revisions must be 40- or
+64-character hex and the repository must be canonical `owner/name` before the
+probe opens a socket. Only transport exit `0` plus HTTP `200` may reach the
+immutably pinned dependency-review action. A `403`, `404`, timeout, truncated
+transfer, malformed status, or malformed identity fails closed and records
+allowlisted repository visibility with the exact revisions. Other scanners
+are complementary; they are not substitutes.
+
+```mermaid
+flowchart TD
+  Probe["Exact base/head compare probe"]
+  Transport{"curl exit 0 and HTTP 200?"}
+  Action["Pinned dependency-review action"]
+  Fail["Fail closed with repo, visibility, SHAs, status"]
+
+  Probe --> Transport
+  Transport -->|"yes"| Action
+  Transport -->|"no"| Fail
+```
+
+See [`docs/doctoring/dependency-review-fail-closed.md`](docs/doctoring/dependency-review-fail-closed.md).
+
 ## Quality gates
 
 `scripts/ci/` ships with 100% statement/branch coverage and 100% docstrings.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7bf8ad766..09fd56ce0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -48,6 +48,9 @@ Semantic Versioning where the repository publishes a release.
 
 ### Security
 
+- Fail closed when GitHub dependency-review evidence is unavailable (non-200, transport failure, or truncated compare) instead of treating HTTP 403/404 as a clean skip; the probe records allowlisted repository visibility with the exact head SHA and never prints the API body.
+- Reject malformed dependency-review revisions and repository names before the compare request so an empty SHA or `../` repository cannot mint a green `supported=true` from a forged HTTP 200.
+
 - Reject `.github/` and `scripts/ci/` from review-thread-derived autofix path authority so an untrusted inline reviewer cannot authorize the write-capable repair agent to modify workflows, CODEOWNERS, actions, scheduler code, or CI helpers that govern its own control plane.
 - Require the model-write snapshot and exact-path allowlist to remain outside the pull-request worktree, checking both absolute and resolved locations so repository-local controls and outside-looking symlinks resolving into the repository fail closed before they can authorize or verify model changes.
 - Snapshot the complete pre-model worktree for ordinary and conflict repair and reject every model-caused created, deleted, modified, mode-changed, retargeted, ignored, dangling, directory-backed, external-link, metadata-race, or out-of-scope path before staging or push.
diff --git a/docs/doctoring/dependency-review-fail-closed.md b/docs/doctoring/dependency-review-fail-closed.md
new file mode 100644
index 000000000..c8941dc40
--- /dev/null
+++ b/docs/doctoring/dependency-review-fail-closed.md
@@ -0,0 +1,64 @@
+# Dependency review fail-closed operations
+
+Status: `active_pr` until the matching workflow and regression contract are present on protected `main`; thereafter `implemented_on_protected_main`.
+
+## Decision
+
+Dependency review is a hard supply-chain gate. The central workflow accepts only HTTP `200` from GitHub's exact `BASE_SHA...HEAD_SHA` comparison before invoking the immutably pinned dependency-review action. A `403`, `404`, empty or malformed status, timeout, transport failure, truncated exchange, or other unexpected outcome is unavailable evidence and fails closed.
+
+The support probe has a 10-second connection limit and 30-second total limit. It preserves curl's transport exit code separately from the bounded HTTP status and requires transport exit `0` plus exact HTTP `200`. It rejects a base or head revision that is not exactly 40 or 64 hexadecimal characters, and a repository name that is not `owner/name`, before any network call (curl exit `uncalled`). It discards the response body and logs only repository identity, allowlisted visibility (`public`, `private`, `internal`, or `unknown`), exact base/head revisions, the normalized HTTP status, and the numeric transport exit. Credentials, response bodies, and raw untrusted visibility strings are never diagnostic output. After a successful probe the pinned action is not independently skippable. Executable regressions record the exact compare argv so a hardcoded `supported=true` path cannot satisfy the success contract.
+
+RFC 9110 §15.3.1 defines `200` as a completed successful representation, not as a status that can be inferred after a truncated transfer (Fielding et al., 2022). RFC 3986 forbids unvalidated path segments in a request-target (Berners-Lee et al., 2005). CWE-20 requires rejecting malformed identity before it is interpolated into that target (MITRE, n.d.). NIST SP 800-53 Rev. 5 RA-5 and SA-12 require that vulnerability and supply-chain evidence be obtained, not assumed absent (National Institute of Standards and Technology, 2020). SLSA v1.0 likewise treats missing provenance as unverified rather than passing (SLSA, 2023). An HTTP `403` or `404` is therefore unavailable evidence, not a clean skip.
+
+## Identity and authority
+
+The dependency-review job checks out the pull request's explicit head repository and immutable head SHA with persisted credentials disabled. The API comparison independently binds the event's exact base and head revisions. The job retains `contents: read` and `pull-requests: read`; it receives no write, OIDC, model, release, package, or deployment authority.
+
+Checks, status contexts, review submissions, and merge authorization remain separate evidence classes. OSV, Trivy, CodeQL, Semgrep, Secret Scan, Scorecard, and Dependabot are complementary controls and are not semantic substitutes for dependency review.
+
+## Failure classification and remediation
+
+- Transport exit `0` plus HTTP `200`: proceed to the pinned dependency-review action.
+- Malformed revision or repository: fail closed with HTTP `unavailable` and curl exit `uncalled` before opening a socket. Re-supply the pull request's exact hex SHAs and canonical `owner/name`, then rerun.
+- Any other result: fail the job and retain exact repository, allowlisted visibility, base/head, status, and transport-exit evidence. An HTTP `200` emitted by a failed or partial transfer is unavailable evidence. Do not infer a root cause from HTTP `403` or `404`.
+- Public repository failure: verify dependency graph and security configuration, organization policy, token read access, and GitHub service health.
+- Private or internal exception: require a separately reviewed organization policy with explicit entitlement evidence and compensating controls. Never infer `not-applicable` from an unavailable response.
+
+Retries are operator-initiated only after the capability or service condition changes. Do not rerun unchanged evidence repeatedly and do not convert an unavailable endpoint into a green skip.
+
+## Known canary
+
+ContextualWisdomLab/EgressWeave#66, Security Scan run `31108241013`, job `92638903658`, compared `10d0c51daf2ad278d66f43be479df8cf6b08ba6d...c038a9509d1a8eae8561cc9081e67e12bd373d42` and received HTTP `403`. The required workflow printed the skip warning, omitted `actions/dependency-review-action`, and still concluded success. Downstream tracking: ContextualWisdomLab/EgressWeave#76. Keep ContextualWisdomLab/.github#810 open until a protected-main public consumer run proves a non-200 or failed-transfer comparison cannot green this job.
+
+## Acceptance and rollback
+
+Acceptance requires the permanent queue contract to reject the former `supported=false` path, require bounded probing and discarded bodies, require exact-head checkout, reject malformed revisions and repository names before the network call, prove the success path invoked the exact compare URL, and prove that only `200` reaches the action. Exact-head CI/security evidence, current review, protected integration, and a real protected-main consumer run remain required.
+
+Rollback requires an independently reviewed revert and fresh exact-head evidence. A rollback must not restore the `403`/`404` success path or print an API response body.
+
+## References
+
+Berners-Lee, T., Fielding, R., & Masinter, L. (2005). *Uniform Resource
+Identifier (URI): Generic syntax* (RFC 3986). Internet Engineering Task
+Force. https://doi.org/10.17487/RFC3986
+
+Fielding, R., Nottingham, M., & Reschke, J. (Eds.). (2022). *HTTP semantics*
+(RFC 9110). Internet Engineering Task Force. https://doi.org/10.17487/RFC9110
+
+GitHub. (n.d.). *Dependency review*. GitHub Docs. Retrieved August 9, 2026, from https://docs.github.com/en/code-security/concepts/supply-chain-security/dependency-review
+
+GitHub. (n.d.). *REST API endpoints for dependency review*. GitHub Docs. Retrieved August 9, 2026, from https://docs.github.com/en/rest/dependency-graph/dependency-review
+
+GitHub. (n.d.). *Dependency graph*. GitHub Docs. Retrieved August 9, 2026, from https://docs.github.com/en/code-security/concepts/supply-chain-security/dependency-graph
+
+GitHub. (n.d.). *Webhook events and payloads*. GitHub Docs. Retrieved August 16, 2026, from https://docs.github.com/en/webhooks/webhook-events-and-payloads#repository
+
+MITRE. (n.d.). *CWE-20: Improper input validation*. Retrieved August 16,
+2026, from https://cwe.mitre.org/data/definitions/20.html
+
+National Institute of Standards and Technology. (2020). *Security and
+privacy controls for information systems and organizations* (NIST SP
+800-53 Rev. 5). https://doi.org/10.6028/NIST.SP.800-53r5
+
+SLSA. (2023). *SLSA v1.0: Supply-chain Levels for Software Artifacts*.
+Open Source Security Foundation. https://slsa.dev/spec/v1.0/
diff --git a/tests/test_required_workflow_queue_contract.py b/tests/test_required_workflow_queue_contract.py
index 233c08584..bd533f4de 100644
--- a/tests/test_required_workflow_queue_contract.py
+++ b/tests/test_required_workflow_queue_contract.py
@@ -27,6 +27,115 @@ def workflow_step(workflow: str, name: str) -> str:
     return workflow[start:end]
 
 
+PROBE_TOKEN = "synthetic-read-token"
+PROBE_BASE_SHA = "a" * 40
+PROBE_HEAD_SHA = "b" * 40
+
+
+def run_dependency_review_support_probe(
+    tmp_path: Path,
+    *,
+    curl_script: str,
+    repository_visibility: str = "public",
+    repository: str = "ContextualWisdomLab/.github",
+    base_sha: str = PROBE_BASE_SHA,
+    head_sha: str = PROBE_HEAD_SHA,
+) -> subprocess.CompletedProcess:
+    """Run the workflow support probe against a controlled curl binary.
+
+    The helper places a fake ``curl`` first on ``PATH`` so the extracted
+    workflow script cannot call the real binary, records the exact argv
+    the probe used, then supplies only the synthetic environment
+    variables the support step reads.
+    """
+
+    fake_bin = tmp_path / "bin"
+    fake_bin.mkdir()
+    fake_curl = fake_bin / "curl"
+    argv_path = tmp_path / "curl-argv"
+    shebang, separator, rest = curl_script.partition("\n")
+    if not shebang.startswith("#!"):
+        shebang = "#!/usr/bin/env bash"
+        rest = curl_script
+    elif not separator:
+        rest = ""
+    recorder = f"printf '%s\\0' \"$0\" \"$@\" > {shlex.quote(str(argv_path))}\n"
+    fake_curl.write_text(f"{shebang}\n{recorder}{rest}\n", encoding="utf-8")
+    fake_curl.chmod(0o755)
+    script = textwrap.dedent(
+        workflow_step(
+            workflow_text("security-scan.yml"),
+            "Check dependency review support",
+        ).split("        run: |\n", 1)[1]
+    )
+    bash = shutil.which("bash")
+    assert bash is not None
+    return subprocess.run(
+        [bash, "-c", script],
+        env={
+            "PATH": f"{fake_bin}{os.pathsep}{os.environ.get('PATH', '/usr/bin')}",
+            "HOME": str(tmp_path),
+            "GITHUB_API_URL": "https://api.example.invalid",
+            "GITHUB_OUTPUT": str(tmp_path / "github-output"),
+            "GH_TOKEN": PROBE_TOKEN,
+            "BASE_SHA": base_sha,
+            "HEAD_SHA": head_sha,
+            "REPOSITORY": repository,
+            "REPOSITORY_VISIBILITY": repository_visibility,
+        },
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+
+
+def assert_dependency_review_compare_invoked(
+    tmp_path: Path,
+    *,
+    repository: str = "ContextualWisdomLab/.github",
+    base_sha: str = PROBE_BASE_SHA,
+    head_sha: str = PROBE_HEAD_SHA,
+) -> None:
+    """Require the probe to request the exact base/head compare URL."""
+
+    argv = [
+        part.decode("utf-8")
+        for part in (tmp_path / "curl-argv").read_bytes().split(b"\0")
+        if part
+    ]
+    expected = (
+        f"https://api.example.invalid/repos/{repository}/"
+        f"dependency-graph/compare/{base_sha}...{head_sha}"
+    )
+    assert expected in argv
+    assert "-o" in argv
+    assert "/dev/null" in argv
+
+
+def assert_dependency_review_probe_failed(
+    result: subprocess.CompletedProcess,
+    tmp_path: Path,
+    *,
+    expected_http: str,
+    expected_curl_exit: str,
+    expected_visibility: str = "public",
+    expected_base_sha: str = PROBE_BASE_SHA,
+    expected_head_sha: str = PROBE_HEAD_SHA,
+) -> None:
+    """Require a failed probe that records identity without leaking secrets."""
+
+    combined = f"{result.stdout}{result.stderr}"
+    assert result.returncode == 1
+    assert f"HTTP {expected_http}; curl exit {expected_curl_exit}" in result.stdout
+    assert f"visibility {expected_visibility}" in result.stdout
+    assert (
+        f"exact base {expected_base_sha} and head {expected_head_sha}" in result.stdout
+    )
+    assert PROBE_TOKEN not in combined
+    assert "Authorization:" not in combined
+    assert not (tmp_path / "github-output").exists()
+
+
 def test_merge_scheduler_dispatches_one_review_by_default() -> None:
     workflow = workflow_text("pr-review-merge-scheduler.yml")
 
@@ -826,16 +935,286 @@ def test_fix_scheduler_cancels_superseded_cron_runs() -> None:
     assert "cancel-in-progress: true" in workflow
 
 
-def test_security_scan_skips_dependency_review_when_dependency_graph_is_unavailable() -> (
-    None
-):
+def test_security_scan_fails_closed_when_dependency_review_is_unavailable() -> None:
     workflow = workflow_text("security-scan.yml")
+    support_probe = workflow_step(workflow, "Check dependency review support")
+    action_first_line = workflow.split(
+        "      - name: Dependency review\n",
+        1,
+    )[1].splitlines()[0]
 
     assert "id: dependency_review_support" in workflow
     assert "/dependency-graph/compare/${BASE_SHA}...${HEAD_SHA}" in workflow
-    assert '"$status" = "403"' in workflow
-    assert '"$status" = "404"' in workflow
-    assert "steps.dependency_review_support.outputs.supported == 'true'" in workflow
+    assert "repository: ${{ github.event.pull_request.head.repo.full_name }}" in workflow
+    assert "ref: ${{ github.event.pull_request.head.sha }}" in workflow
+    assert (
+        "REPOSITORY_VISIBILITY: ${{ github.event.repository.visibility }}"
+        in support_probe
+    )
+    assert "public|private|internal)" in support_probe
+    assert "visibility ${visibility}" in support_probe
+    assert 'revision_pattern=' in support_probe
+    assert 'repository_pattern=' in support_probe
+    assert "Malformed revision" in support_probe
+    assert "Malformed repository" in support_probe
+    assert 'if [ "$curl_status" -ne 0 ] || [ "$http_status" != "200" ]; then' in workflow
+    assert "--connect-timeout 10" in workflow
+    assert "--max-time 30" in workflow
+    assert "-o /dev/null" in workflow
+    assert "curl_status=$?" in support_probe
+    assert "set +e" in support_probe
+    assert "set -e" in support_probe
+    assert "|| true" not in support_probe
+    assert "HTTP ${http_status}; curl exit ${curl_status}" in workflow
+    assert "supported=false" not in workflow
+    assert "skipping dependency-review hard gate" not in workflow
+    assert 'cat "$response_file"' not in support_probe
+    assert "fail-on-severity: moderate" in workflow
+    assert action_first_line.startswith(
+        "        uses: actions/dependency-review-action@"
+    )
+    action_step = workflow.split("      - name: Dependency review\n", 1)[1].split(
+        "\n  trivy-fs:",
+        1,
+    )[0]
+    assert "if:" not in action_step
+    osv_job_header = workflow.split("  osv-scan:\n", 1)[1].split("    steps:", 1)[0]
+    trivy_job_header = workflow.split("  trivy-fs:\n", 1)[1].split("    steps:", 1)[0]
+    dependency_job_header = workflow.split("  dependency-review:\n", 1)[1].split(
+        "    steps:",
+        1,
+    )[0]
+    assert "continue-on-error: true" not in osv_job_header
+    assert "continue-on-error: true" not in trivy_job_header
+    assert "continue-on-error: true" not in dependency_job_header
+
+
+def test_dependency_review_http_403_skip_cannot_go_green(tmp_path: Path) -> None:
+    """The EgressWeave #66 canary must not be a green skip.
+
+    ContextualWisdomLab/EgressWeave#66 Security Scan run ``31108241013``,
+    job ``92638903658``, compared ``10d0c51d…c038a950`` and received HTTP
+    403. Current ``main`` printed the skip warning, omitted the pinned
+    action, and still exited 0. That path is forbidden.
+    """
+
+    result = run_dependency_review_support_probe(
+        tmp_path,
+        curl_script="#!/usr/bin/env bash\nprintf '403'\nexit 0\n",
+    )
+
+    assert_dependency_review_probe_failed(
+        result,
+        tmp_path,
+        expected_http="403",
+        expected_curl_exit="0",
+    )
+    assert "skipping dependency-review hard gate" not in result.stdout
+    assert_dependency_review_compare_invoked(tmp_path)
+
+
+def test_dependency_review_transport_failure_cannot_hide_behind_http_200(
+    tmp_path: Path,
+) -> None:
+    """A failed curl transport must not make HTTP 200 acceptable evidence."""
+
+    result = run_dependency_review_support_probe(
+        tmp_path,
+        curl_script="#!/usr/bin/env bash\nprintf '200'\nexit 18\n",
+    )
+
+    assert_dependency_review_probe_failed(
+        result,
+        tmp_path,
+        expected_http="200",
+        expected_curl_exit="18",
+    )
+
+
+def test_dependency_review_transport_failure_fails_closed(tmp_path: Path) -> None:
+    """A transport failure with no HTTP status must fail the hard gate."""
+
+    result = run_dependency_review_support_probe(
+        tmp_path,
+        curl_script="#!/usr/bin/env bash\nprintf ''\nexit 28\n",
+    )
+
+    assert_dependency_review_probe_failed(
+        result,
+        tmp_path,
+        expected_http="unavailable",
+        expected_curl_exit="28",
+    )
+
+
+@pytest.mark.parametrize(
+    ("curl_script", "expected_http"),
+    [
+        ("#!/usr/bin/env bash\nprintf '404'\nexit 0\n", "404"),
+        ("#!/usr/bin/env bash\nprintf ''\nexit 0\n", "unavailable"),
+        ("#!/usr/bin/env bash\nprintf 'OK'\nexit 0\n", "malformed"),
+    ],
+)
+def test_dependency_review_non_200_status_fails_closed(
+    tmp_path: Path,
+    curl_script: str,
+    expected_http: str,
+) -> None:
+    """HTTP 404, empty, and malformed statuses must fail closed."""
+
+    result = run_dependency_review_support_probe(
+        tmp_path,
+        curl_script=curl_script,
+    )
+
+    assert_dependency_review_probe_failed(
+        result,
+        tmp_path,
+        expected_http=expected_http,
+        expected_curl_exit="0",
+    )
+
+
+def test_dependency_review_success_writes_supported_true(tmp_path: Path) -> None:
+    """Only a complete HTTP 200 with transport exit 0 may emit supported=true."""
+
+    result = run_dependency_review_support_probe(
+        tmp_path,
+        curl_script="#!/usr/bin/env bash\nprintf '200'\nexit 0\n",
+    )
+
+    combined = f"{result.stdout}{result.stderr}"
+    assert result.returncode == 0
+    assert (tmp_path / "github-output").read_text(encoding="utf-8") == (
+        "supported=true\n"
+    )
+    assert PROBE_TOKEN not in combined
+    assert_dependency_review_compare_invoked(tmp_path)
+
+
+def test_dependency_review_accepts_sha256_object_ids(tmp_path: Path) -> None:
+    """A 64-character hex object id is a legal Git revision and may be compared."""
+
+    base_sha = "c" * 64
+    head_sha = "d" * 64
+    result = run_dependency_review_support_probe(
+        tmp_path,
+        curl_script="#!/usr/bin/env bash\nprintf '200'\nexit 0\n",
+        base_sha=base_sha,
+        head_sha=head_sha,
+    )
+
+    assert result.returncode == 0
+    assert (tmp_path / "github-output").read_text(encoding="utf-8") == (
+        "supported=true\n"
+    )
+    assert_dependency_review_compare_invoked(
+        tmp_path,
+        base_sha=base_sha,
+        head_sha=head_sha,
+    )
+
+
+def test_dependency_review_records_unknown_visibility_when_unset(
+    tmp_path: Path,
+) -> None:
+    """Missing or unrecognized visibility must be recorded as unknown."""
+
+    result = run_dependency_review_support_probe(
+        tmp_path,
+        curl_script="#!/usr/bin/env bash\nprintf '403'\nexit 0\n",
+        repository_visibility="",
+    )
+
+    assert_dependency_review_probe_failed(
+        result,
+        tmp_path,
+        expected_http="403",
+        expected_curl_exit="0",
+        expected_visibility="unknown",
+    )
+    assert_dependency_review_compare_invoked(tmp_path)
+
+
+@pytest.mark.parametrize("visibility", ["public", "private", "internal"])
+def test_dependency_review_records_allowlisted_visibility(
+    tmp_path: Path,
+    visibility: str,
+) -> None:
+    """Allowlisted visibility values must appear in fail-closed diagnostics."""
+
+    result = run_dependency_review_support_probe(
+        tmp_path,
+        curl_script="#!/usr/bin/env bash\nprintf '403'\nexit 0\n",
+        repository_visibility=visibility,
+    )
+
+    assert_dependency_review_probe_failed(
+        result,
+        tmp_path,
+        expected_http="403",
+        expected_curl_exit="0",
+        expected_visibility=visibility,
+    )
+    assert_dependency_review_compare_invoked(tmp_path)
+
+
+@pytest.mark.parametrize(
+    ("base_sha", "head_sha"),
+    [
+        ("", PROBE_HEAD_SHA),
+        (PROBE_BASE_SHA, ""),
+        ("not-a-revision", PROBE_HEAD_SHA),
+        (PROBE_BASE_SHA, "../" + ("c" * 37)),
+        ("d" * 39, PROBE_HEAD_SHA),
+    ],
+)
+def test_dependency_review_rejects_malformed_revision_before_network(
+    tmp_path: Path,
+    base_sha: str,
+    head_sha: str,
+) -> None:
+    """Empty or non-hex revisions must fail closed without calling curl."""
+
+    result = run_dependency_review_support_probe(
+        tmp_path,
+        curl_script="#!/usr/bin/env bash\nprintf '200'\nexit 0\n",
+        base_sha=base_sha,
+        head_sha=head_sha,
+    )
+
+    assert_dependency_review_probe_failed(
+        result,
+        tmp_path,
+        expected_http="unavailable",
+        expected_curl_exit="uncalled",
+        expected_base_sha=base_sha,
+        expected_head_sha=head_sha,
+    )
+    assert "Malformed revision" in result.stdout
+    assert not (tmp_path / "curl-argv").exists()
+
+
+def test_dependency_review_rejects_malformed_repository_before_network(
+    tmp_path: Path,
+) -> None:
+    """A repository name that cannot form a compare URL must not reach curl."""
+
+    result = run_dependency_review_support_probe(
+        tmp_path,
+        curl_script="#!/usr/bin/env bash\nprintf '200'\nexit 0\n",
+        repository="../evil/repo",
+    )
+
+    assert_dependency_review_probe_failed(
+        result,
+        tmp_path,
+        expected_http="unavailable",
+        expected_curl_exit="uncalled",
+        expected_visibility="public",
+    )
+    assert "Malformed repository" in result.stdout
+    assert not (tmp_path / "curl-argv").exists()
 
 
 def test_security_scan_allows_repositories_without_supported_lockfiles() -> None: