diff --git a/.github/workflows/api-latency-smoke.yml b/.github/workflows/api-latency-smoke.yml
index b13205fa78..f978db4b9b 100644
--- a/.github/workflows/api-latency-smoke.yml
+++ b/.github/workflows/api-latency-smoke.yml
@@ -14,6 +14,7 @@ on:
 
 # Least privilege: this workflow only builds a wheel and probes a local
 # dashboard. It never writes to the repository or any GitHub API surface.
+# Any job needing more must elevate with its own job-level `permissions:`.
 permissions:
   contents: read
 
@@ -21,11 +22,6 @@ concurrency:
   group: api-latency-smoke-${{ github.ref }}
   cancel-in-progress: true
 
-# Least privilege: these jobs only read the repo. Any job needing more
-# must elevate with its own job-level `permissions:` block.
-permissions:
-  contents: read
-
 jobs:
   smoke:
     name: ${{ matrix.source == 'pypi' && 'PyPI nightly' || 'PR build' }}
diff --git a/.github/workflows/auto-deploy-cloud.yml b/.github/workflows/auto-deploy-cloud.yml
index 28d3580f35..f402fea9fe 100644
--- a/.github/workflows/auto-deploy-cloud.yml
+++ b/.github/workflows/auto-deploy-cloud.yml
@@ -20,6 +20,15 @@ on:
     types: [completed]
   workflow_dispatch:
 
+# Every cross-repo action below (checkout of clawmetry-cloud, branch push, PR
+# create/close/merge) authenticates as `secrets.CLOUD_REPO_PAT`, which this
+# block does not govern — a PAT carries its own scopes. The only thing that
+# rides on GITHUB_TOKEN is the checkout of THIS repo, which needs `contents:
+# read` and nothing more. Deliberately kept read-only so a future step cannot
+# quietly acquire write on clawmetry via the ambient token.
+permissions:
+  contents: read
+
 jobs:
   pin-version:
     name: Rebuild cloud with latest OSS
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 975fefab8c..bac4b551f5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,6 +5,13 @@ on:
     branches: [main, master]
   pull_request:
 
+# Every job here only reads the repository: checkout, install, run tests,
+# upload an artifact. Nothing calls the GitHub API with GITHUB_TOKEN, pushes
+# a commit, tags, comments on a PR or touches a Release, so the whole
+# workflow runs on the read-only default and no job needs an elevated block.
+permissions:
+  contents: read
+
 concurrency:
   group: ci-${{ github.event.pull_request.number || github.ref }}
   cancel-in-progress: true
diff --git a/.github/workflows/desktop-artifacts.yml b/.github/workflows/desktop-artifacts.yml
index d92fa897b2..8d62c9a0e6 100644
--- a/.github/workflows/desktop-artifacts.yml
+++ b/.github/workflows/desktop-artifacts.yml
@@ -18,6 +18,15 @@ on:
       - 'v*.*.*'
   workflow_dispatch: {}
 
+# Least-privilege floor for the three BUILD jobs (macos / linux inherit this;
+# windows re-declares it alongside id-token). The `release` job, and only that
+# job, elevates to `contents: write` so softprops/action-gh-release can attach
+# installers to the tag's Release and publish it. Keep the elevation on that
+# job — a workflow-wide `contents: write` would hand every build job, and each
+# third-party action it runs, the ability to write to the repository.
+permissions:
+  contents: read
+
 jobs:
   macos:
     name: macOS .app + .dmg (signed + notarized when secrets are set)
diff --git a/.github/workflows/release-on-merge.yml b/.github/workflows/release-on-merge.yml
index b2a2303f00..81b3ec1627 100644
--- a/.github/workflows/release-on-merge.yml
+++ b/.github/workflows/release-on-merge.yml
@@ -5,6 +5,15 @@ on:
     types: [closed]
     branches: [main]
 
+# Read-only floor. This workflow's single job re-declares its own scopes
+# below, and a job-level block REPLACES the top level rather than merging
+# with it, so this value never actually applies to `release` — it is here so
+# the default for any job added later is read-only, and so the workflow
+# stops reading as "inherits whatever the repository default happens to be".
+# The publish/tag/PR scopes stay on the job that needs them, not up here.
+permissions:
+  contents: read
+
 jobs:
   release:
     name: Bump version & publish to PyPI
diff --git a/tests/test_workflow_yaml_valid.py b/tests/test_workflow_yaml_valid.py
index 8b1a6e646f..0347a2d191 100644
--- a/tests/test_workflow_yaml_valid.py
+++ b/tests/test_workflow_yaml_valid.py
@@ -79,6 +79,58 @@ def test_workflow_parses_as_yaml(path: str) -> None:
     )
 
 
+class _DuplicateKeyLoader(yaml.SafeLoader):
+    """A SafeLoader that refuses a mapping with a repeated key.
+
+    PyYAML's own resolution is last-one-wins, silently: ``yaml.safe_load`` on a
+    file with two top-level ``permissions:`` blocks returns a perfectly good
+    dict and raises nothing. GitHub Actions does the opposite -- it rejects the
+    file outright and fails the run at startup -- so a duplicate key is exactly
+    the class of break ``test_workflow_parses_as_yaml`` cannot see.
+    """
+
+
+def _no_duplicate_keys(loader, node, deep=False):
+    seen = set()
+    for key_node, _ in node.value:
+        key = loader.construct_object(key_node, deep=deep)
+        if key in seen:
+            raise yaml.YAMLError(
+                f"duplicate key {key!r} at line {key_node.start_mark.line + 1}"
+            )
+        seen.add(key)
+    return yaml.SafeLoader.construct_mapping(loader, node, deep=deep)
+
+
+_DuplicateKeyLoader.add_constructor(
+    yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG, _no_duplicate_keys
+)
+
+
+@pytest.mark.parametrize("path", _workflow_files(), ids=os.path.basename)
+def test_workflow_has_no_duplicate_keys(path: str) -> None:
+    """No mapping may repeat a key. GitHub rejects the file if one does.
+
+    Burned by the token-permissions hardening pass: two separate PRs each
+    added a top-level ``permissions: contents: read`` block to
+    api-latency-smoke.yml. Both were individually correct, neither conflicted
+    in git, and the pre-merge check was ``yaml.safe_load`` -- which happily
+    kept the second and returned a valid dict. The workflow was dead on main
+    from the moment the second one merged, its runs listed under the file path
+    with zero jobs, and the API-latency safety net was off.
+    """
+    with open(path, encoding="utf-8") as fh:
+        source = fh.read()
+    try:
+        yaml.load(source, _DuplicateKeyLoader)
+    except yaml.YAMLError as exc:  # pragma: no cover - message is the point
+        pytest.fail(
+            f"{os.path.basename(path)} repeats a mapping key ({exc}). PyYAML "
+            "keeps the last one without complaining, but GitHub rejects the "
+            "workflow and fails every run at startup before any step executes."
+        )
+
+
 @pytest.mark.parametrize("path", _workflow_files(), ids=os.path.basename)
 def test_workflow_has_required_top_level_keys(path: str) -> None:
     """A parseable file can still be a non-workflow. Check the shape."""