diff --git a/.github/labels.yaml b/.github/labels.yaml
index 314743b5..7c35809f 100644
--- a/.github/labels.yaml
+++ b/.github/labels.yaml
@@ -73,4 +73,12 @@
 - name: agent/saffron-escalated
   color: "0052cc"
   description: Stable escalated-lane Saffron worker.
-# Repo-specific labels can be appended below. Unknown labels are not pruned.
+# Blocked / infra
+# The umbrella label is the only managed infra-blocked label. Per-attempt and
+# per-model variants (blocked/infra-attempt/N, blocked/infra-model/name) are
+# unmanaged drift emitted by an external loop and are pruned by the label-sync
+# workflow. Do NOT add them here. See AGENTS.md "Label hygiene".
+- name: blocked/infra
+  color: "e11d21"
+  description: Progress is blocked on infrastructure (umbrella; no per-attempt variants).
+# Repo-specific labels can be appended below.
diff --git a/.github/workflows/label-sync.yaml b/.github/workflows/label-sync.yaml
index 2be05b1b..19453424 100644
--- a/.github/workflows/label-sync.yaml
+++ b/.github/workflows/label-sync.yaml
@@ -12,7 +12,15 @@ on:
         default: false
   push:
     branches: ["main"]
-    paths: [".github/labels.yaml"]
+    paths:
+      - ".github/labels.yaml"
+      - ".github/workflows/label-sync.yaml"
+  # Recurring guard: an external emitter (bridge / pr-followup path) keeps
+  # creating fresh blocked/infra-attempt/<N> and blocked/infra-model/<name>
+  # labels that are never declared in labels.yaml. Prune them on a schedule so
+  # the kanban filter UI does not accumulate 100+ dead labels. See #916.
+  schedule:
+    - cron: "23 4 * * 1"
 
 permissions:
   contents: read
@@ -24,6 +32,7 @@ jobs:
     permissions:
       contents: read
       issues: write
+      labels: write
     steps:
       - name: Checkout
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
@@ -37,3 +46,27 @@ jobs:
           config-file: .github/labels.yaml
           delete-other-labels: false
           dry-run: ${{ github.event_name == 'workflow_dispatch' && inputs.dry_run || false }}
+
+      # The sync action above only manages labels declared in .github/labels.yaml
+      # and (with delete-other-labels: false) never prunes unmanaged ones. An
+      # external emitter keeps creating fresh blocked/infra-attempt/<N> and
+      # blocked/infra-model/<name> labels, so prune exactly those shapes here.
+      # The blocked/infra umbrella is kept. See #916.
+      - name: Prune unmanaged blocked/infra-attempt/* and blocked/infra-model/* labels
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          set -uo pipefail
+          labels="$(gh label list --limit 500 --json name \
+            | jq -r '.[].name' \
+            | grep -E '^blocked/infra-(attempt|model)/' || true)"
+          if [ -z "$labels" ]; then
+            echo "No unmanaged blocked/infra-attempt/* or blocked/infra-model/* labels to prune."
+            exit 0
+          fi
+          while IFS= read -r label; do
+            [ -n "$label" ] || continue
+            echo "Deleting unmanaged label: $label"
+            gh label delete "$label" --yes \
+              || echo "::warning::Could not delete $label (may be in use)"
+          done <<< "$labels"
diff --git a/AGENTS.md b/AGENTS.md
index f3ea7f6f..8fcab3a9 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -61,6 +61,24 @@ Labels follow a `category/value` pattern:
 - **Priority**: `priority/p0` through `priority/p3`
 - **Type**: `type/bug`, `type/feature`, `type/chore`, `type/research`, `type/security`
 
+#### Label hygiene
+
+`.github/labels.yaml` is the source of truth for managed labels. The label-sync
+workflow (`.github/workflows/label-sync.yaml`) keeps the repo in sync with it.
+
+- **Umbrella labels are allowed; per-attempt / per-model variants are not.**
+  `blocked/infra` is the single managed label for infrastructure-blocked work.
+  Do NOT create `blocked/infra-attempt/<N>` or `blocked/infra-model/<name>`
+  labels: an external emitter (bridge / pr-followup path) used to write a fresh
+  one per failed GHA attempt, accumulating ~95 dead labels that polluted every
+  kanban label filter, repo add-label call, and audit view (#916).
+- The label-sync workflow prunes exactly the `blocked/infra-attempt/*` and
+  `blocked/infra-model/*` shapes (on push to main touching the label files and
+  on a weekly schedule) and keeps the `blocked/infra` umbrella.
+- If you need to distinguish infra failure modes, encode them in the issue
+  body / audit log, not in a new label. A single repo failure mode does not
+  need N unique identifiers.
+
 
 ### Issue Execution Lane Classification
 
diff --git a/src/app/api/issues/label/route.test.ts b/src/app/api/issues/label/route.test.ts
index 1e119474..5bfc3b98 100644
--- a/src/app/api/issues/label/route.test.ts
+++ b/src/app/api/issues/label/route.test.ts
@@ -201,6 +201,66 @@ describe("POST /api/issues/label", () => {
     expect(mockAddLabel).toHaveBeenCalledTimes(30);
   });
 
+  it("rejects adding a blocked/infra-attempt/N label (unmanaged drift, #916)", async () => {
+    const res = await POST(
+      makeRequest({ ...validBody, label: "blocked/infra-attempt/42", action: "add" }),
+    );
+    expect(res.status).toBe(400);
+    const data = await res.json();
+    expect(data.error).toContain("blocked/infra-attempt/42");
+    expect(data.error).toContain("blocked/infra");
+    expect(mockAddLabel).not.toHaveBeenCalled();
+    expect(mockRemoveLabel).not.toHaveBeenCalled();
+    expect(mockUpdate).not.toHaveBeenCalled();
+    expect(mockAuditCreate).not.toHaveBeenCalled();
+  });
+
+  it("rejects adding a blocked/infra-model/name label (unmanaged drift, #916)", async () => {
+    const res = await POST(
+      makeRequest({ ...validBody, label: "blocked/infra-model/llama-3", action: "add" }),
+    );
+    expect(res.status).toBe(400);
+    const data = await res.json();
+    expect(data.error).toContain("blocked/infra-model/llama-3");
+    expect(mockAddLabel).not.toHaveBeenCalled();
+    expect(mockUpdate).not.toHaveBeenCalled();
+  });
+
+  it("allows adding the blocked/infra umbrella label", async () => {
+    const res = await POST(
+      makeRequest({ ...validBody, label: "blocked/infra", action: "add" }),
+    );
+    expect(res.status).toBe(200);
+    const data = await res.json();
+    expect(data.success).toBe(true);
+    expect(data.labels).toEqual(["bug", "blocked/infra"]);
+    expect(mockAddLabel).toHaveBeenCalledWith("misospace/dispatch", 42, "blocked/infra");
+  });
+
+  it("allows removing a blocked/infra-attempt/N label (cleanup of existing drift)", async () => {
+    mockFindUnique.mockResolvedValue({
+      ...validIssue,
+      labels: ["bug", "blocked/infra-attempt/7"],
+    } as never);
+    const res = await POST(
+      makeRequest({
+        ...validBody,
+        label: "blocked/infra-attempt/7",
+        action: "remove",
+      }),
+    );
+    expect(res.status).toBe(200);
+    const data = await res.json();
+    expect(data.success).toBe(true);
+    expect(data.labels).toEqual(["bug"]);
+    expect(mockRemoveLabel).toHaveBeenCalledWith(
+      "misospace/dispatch",
+      42,
+      "blocked/infra-attempt/7",
+    );
+    expect(mockAddLabel).not.toHaveBeenCalled();
+  });
+
   it("returns 400 when required fields are missing", async () => {
     const res = await POST(makeRequest({ issueId: "issue-1" }));
     expect(res.status).toBe(400);
diff --git a/src/app/api/issues/label/route.ts b/src/app/api/issues/label/route.ts
index da81aefd..33a91c44 100644
--- a/src/app/api/issues/label/route.ts
+++ b/src/app/api/issues/label/route.ts
@@ -62,6 +62,19 @@ export async function POST(request: Request) {
     const op = action === "remove" ? "remove" : "add";
     const labelName = label.trim();
 
+    // Guard (#916): an external emitter used to auto-create a fresh
+    // blocked/infra-attempt/<N> / blocked/infra-model/<name> label per failed
+    // GHA attempt, accumulating ~95 dead labels. The GitHub API auto-creates
+    // missing labels on add, so reject that shape here before it can be
+    // created. The blocked/infra umbrella is allowed, and removal is always
+    // allowed so existing drift can still be cleaned up.
+    if (op === "add" && /^blocked\/infra-(attempt|model)\//.test(labelName)) {
+      return errorResponse(
+        `Label "${labelName}" is not allowed: per-attempt/per-model infra labels are unmanaged drift. Use the "blocked/infra" umbrella label instead.`,
+        400,
+      );
+    }
+
     const actorName = getAuthorizedActor(
       auth,
       request,