diff --git a/.github/workflows/grant-paper-executor-permissions.yml b/.github/workflows/grant-paper-executor-permissions.yml
index b733172..dc79a06 100644
--- a/.github/workflows/grant-paper-executor-permissions.yml
+++ b/.github/workflows/grant-paper-executor-permissions.yml
@@ -64,27 +64,55 @@ jobs:
               'PAPER_IAM_BOOTSTRAP_SERVICE_ACCOUNT', 'PAPER_IAM_BOOTSTRAP_WIF_PROVIDER'
             ];
             const mappings = [];
-            try {
-              for (const name of names) {
-                let data;
+            for (const name of names) {
+              let scope = 'environment';
+              let category = 'transport_error';
+              const read = async (route, args) => {
+                let response;
                 try {
-                  ({data} = await github.request(
-                    'GET /repos/{owner}/{repo}/environments/{environment_name}/variables/{name}',
-                    {...context.repo, environment_name: 'longbridge-paper', name}));
+                  response = await github.request(route, args);
                 } catch (error) {
-                  if (error.status !== 404) throw error;
-                  ({data} = await github.request(
-                    'GET /repos/{owner}/{repo}/actions/variables/{name}',
-                    {...context.repo, name}));
+                  const status = error?.status;
+                  if (status === 401 || status === 403 || status === 429) {
+                    category = `http_${status}`;
+                  } else if (status === 404) {
+                    category = scope === 'repository' ? 'http_404_both' : 'other_http';
+                  } else if (Number.isInteger(status) && status >= 500 && status <= 599) {
+                    category = 'http_5xx';
+                  } else if (Number.isInteger(status)) {
+                    category = 'other_http';
+                  } else {
+                    category = 'transport_error';
+                  }
+                  // Only an Environment HTTP 404 permits the same-name fallback.
+                  if (scope === 'environment' && status === 404) return null;
+                  throw new Error('Mapping lookup failed');
+                }
+                const data = response?.data;
+                if (!data || typeof data.value !== 'string') {
+                  category = 'malformed_response';
+                  throw new Error('Invalid mapping response');
                 }
-                if (typeof data.value !== 'string' || !data.value.trim()) {
-                  throw new Error('Missing mapping');
+                if (!data.value.trim()) {
+                  category = 'blank_value';
+                  throw new Error('Empty mapping');
+                }
+                return data;
+              };
+              try {
+                let data = await read(
+                  'GET /repos/{owner}/{repo}/environments/{environment_name}/variables/{name}',
+                  {...context.repo, environment_name: 'longbridge-paper', name});
+                if (data === null) {
+                  scope = 'repository';
+                  data = await read('GET /repos/{owner}/{repo}/actions/variables/{name}',
+                    {...context.repo, name});
                 }
                 core.setSecret(data.value);
                 mappings.push([name, data.value]);
+              } catch {
+                throw new Error(`Protected mapping read failed: name=${name} scope=${scope} category=${category}; stop before authentication`);
               }
-            } catch {
-              throw new Error('Protected mapping read failed; stop before authentication');
             }
             for (const [name, value] of mappings) core.exportVariable(name, value);
       - name: Verify Environment approval protection remains configured
diff --git a/docs/iam/paper-scheduler-get.md b/docs/iam/paper-scheduler-get.md
index 045a870..7b08db9 100644
--- a/docs/iam/paper-scheduler-get.md
+++ b/docs/iam/paper-scheduler-get.md
@@ -225,6 +225,16 @@ workflow definition. Variable API access by the workflow token is a separate
 prerequisite and is not established by local tests; an inaccessible mapping
 blocks the route and does not authorize provisioning a token or changing access.
 
+A mapping-read failure reports only the failing fixed variable name, lookup
+scope (`environment` or `repository`) and an allowlisted category: `http_401`,
+`http_403`, `http_404_both`, `http_429`, `http_5xx`, `other_http`, `blank_value`,
+`malformed_response` or `transport_error`. `http_404_both` means that both
+same-name lookups returned HTTP 404. A non-string or absent value is a malformed
+response; an empty or whitespace-only string is a blank value. No raw exception,
+URL, response, headers or mapping value is included. If any read fails, no
+mapping is exported, including previously read values. This diagnostic does not
+prove a permission repair or authorize a retry, grant, or PAPER start.
+
 Role permission responses are checked for exact membership and cardinality,
 independent of order. Fresh role snapshots normalize permission ordering while
 retaining etag and every other field for concurrent-drift detection.
diff --git a/tests/test_paper_executor_grant.py b/tests/test_paper_executor_grant.py
index e9dd403..884e125 100644
--- a/tests/test_paper_executor_grant.py
+++ b/tests/test_paper_executor_grant.py
@@ -255,3 +255,72 @@ def test_mapping_masks_precede_all_step_details():
 .catch(() => process.exit(1));
 """.replace("SCRIPT", json.dumps(script)).replace("KEYS", json.dumps(mappings))
     subprocess.run(["node", "-e", harness], check=True, capture_output=True)
+
+
+@pytest.mark.parametrize("index", range(6))
+@pytest.mark.parametrize("scope", ["environment", "repository"])
+@pytest.mark.parametrize("failure,category", [
+    (401, "http_401"), (403, "http_403"), (429, "http_429"),
+    (500, "http_5xx"), (599, "http_5xx"), (400, "other_http"),
+    (302, "other_http"), (600, "other_http"), ("403", "transport_error"),
+    ("transport", "transport_error"), ("null_error", "transport_error"),
+    ("blank", "blank_value"), ("null", "malformed_response"),
+    ("missing", "malformed_response"), ("wrong_type", "malformed_response"),
+    ("null_response", "malformed_response"),
+    (404, "http_404_both"),
+])
+def test_mapping_failure_diagnostic_is_allowlisted_and_exports_nothing(index, scope, failure, category):
+    # Execute the actual inline action offline, including failures after partial success.
+    workflow = (Path(__file__).parents[1] /
+        ".github/workflows/grant-paper-executor-permissions.yml").read_text()
+    first = workflow.split("      - name:")[1]
+    script = textwrap.dedent(first.split("          script: |\n", 1)[1])
+    harness = r"""
+const assert = require('node:assert/strict');
+const keys = ['GCP_PROJECT_ID', 'PAPER_SCHEDULER_GET_PROJECT_ID',
+  'GCP_WORKLOAD_IDENTITY_SERVICE_ACCOUNT', 'PAPER_IAM_GRANT_RECIPIENT',
+  'PAPER_IAM_BOOTSTRAP_SERVICE_ACCOUNT', 'PAPER_IAM_BOOTSTRAP_WIF_PROVIDER'];
+const [index, scope, failure, category] = CASE;
+const calls = [], masks = [], exports = [];
+const core = {setSecret: value => masks.push(value),
+  exportVariable: (...args) => exports.push(args)};
+const github = {request: async (route, args) => {
+  assert.equal(exports.length, 0);
+  const actualScope = route.includes('/environments/') ? 'environment' : 'repository';
+  calls.push([args.name, actualScope]);
+  if (args.name !== keys[index]) return {data: {value: 'fake-' + args.name}};
+  if (actualScope === 'environment' && (scope === 'repository' || failure === 404)) {
+    throw {status: 404, message: 'fake-private-payload'};
+  }
+  if (failure === 'blank') return {data: {value: '   '}};
+  if (failure === 'null') return {data: null};
+  if (failure === 'missing') return {};
+  if (failure === 'wrong_type') return {data: {value: 17}};
+  if (failure === 'null_response') return null;
+  if (failure === 'null_error') throw null;
+  const error = new Error('fake-private-payload');
+  error.response = {data: 'fake-private-payload', headers: {'fake': 'fake-private-payload'}};
+  error.request = {url: 'fake-private-payload'};
+  if (failure !== 'transport') error.status = failure;
+  throw error;
+}};
+const context = {repo: {owner: 'fake-owner', repo: 'fake-repo'}};
+const run = new Function('github', 'core', 'context', 'return (async () => {' + SCRIPT + '})()');
+(async () => {
+  await assert.rejects(run(github, core, context), error => {
+    const expectedScope = failure === 404 ? 'repository' : scope;
+    assert.equal(error.message, 'Protected mapping read failed: name=' + keys[index] +
+      ' scope=' + expectedScope + ' category=' + category + '; stop before authentication');
+    assert.equal(error.cause, undefined);
+    return true;
+  });
+  assert.deepEqual(exports, []);
+  assert.equal(masks.length, index);
+  const expected = keys.slice(0, index).map(name => [name, 'environment']);
+  expected.push([keys[index], 'environment']);
+  if (scope === 'repository' || failure === 404) expected.push([keys[index], 'repository']);
+  assert.deepEqual(calls, expected);
+})().catch(error => { console.error(error); process.exit(1); });
+""".replace("SCRIPT", json.dumps(script)).replace("CASE", json.dumps([index, scope, failure, category]))
+    result = subprocess.run(["node", "-e", harness], capture_output=True, text=True)
+    assert result.returncode == 0, result.stderr