diff --git a/Dockerfile.dashboard b/Dockerfile.dashboard
index 7b7e8b77..0e923738 100644
--- a/Dockerfile.dashboard
+++ b/Dockerfile.dashboard
@@ -16,6 +16,11 @@ RUN npm run build
 FROM node:22-slim AS production
 WORKDIR /app
 
+# `cascade.managed=true` is the contract the router's dangling-image cleanup
+# loop filters on (src/router/dangling-image-cleanup.ts). Without this LABEL,
+# the loop matches zero images and reclaims nothing — see PR #1256.
+LABEL cascade.managed=true
+
 # Install curl for health checks
 RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*
 
diff --git a/Dockerfile.frontend b/Dockerfile.frontend
index 45839b92..186aefa9 100644
--- a/Dockerfile.frontend
+++ b/Dockerfile.frontend
@@ -2,6 +2,11 @@
 FROM node:22-slim
 WORKDIR /app
 
+# `cascade.managed=true` is the contract the router's dangling-image cleanup
+# loop filters on (src/router/dangling-image-cleanup.ts). Without this LABEL,
+# the loop matches zero images and reclaims nothing — see PR #1256.
+LABEL cascade.managed=true
+
 # Install backend deps (needed for type imports from src/api)
 COPY package*.json .npmrc ./
 RUN npm ci --ignore-scripts
diff --git a/Dockerfile.router b/Dockerfile.router
index 1fe39de1..5d933c4a 100644
--- a/Dockerfile.router
+++ b/Dockerfile.router
@@ -15,6 +15,11 @@ RUN npm run build
 FROM node:22-slim AS production
 WORKDIR /app
 
+# `cascade.managed=true` is the contract the router's dangling-image cleanup
+# loop filters on (src/router/dangling-image-cleanup.ts). Without this LABEL,
+# the loop matches zero images and reclaims nothing — see PR #1256.
+LABEL cascade.managed=true
+
 # Install curl for health checks
 RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*
 
diff --git a/Dockerfile.selfhosted b/Dockerfile.selfhosted
index 0c58cbb8..c57c21fd 100644
--- a/Dockerfile.selfhosted
+++ b/Dockerfile.selfhosted
@@ -34,6 +34,11 @@ CMD ["npx", "drizzle-kit", "migrate"]
 FROM node:22-slim AS production
 WORKDIR /app
 
+# `cascade.managed=true` is the contract the router's dangling-image cleanup
+# loop filters on (src/router/dangling-image-cleanup.ts). Without this LABEL,
+# the loop matches zero images and reclaims nothing — see PR #1256.
+LABEL cascade.managed=true
+
 RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*
 
 COPY package*.json .npmrc ./
diff --git a/Dockerfile.worker b/Dockerfile.worker
index 664be5ed..d2db9c80 100644
--- a/Dockerfile.worker
+++ b/Dockerfile.worker
@@ -15,6 +15,11 @@ RUN npm run build
 FROM node:22-bookworm AS production
 WORKDIR /app
 
+# `cascade.managed=true` is the contract the router's dangling-image cleanup
+# loop filters on (src/router/dangling-image-cleanup.ts). Without this LABEL,
+# the loop matches zero images and reclaims nothing — see PR #1256.
+LABEL cascade.managed=true
+
 # Install pnpm globally (some repos use pnpm)
 RUN npm install -g pnpm --force
 
diff --git a/src/router/dangling-image-cleanup.ts b/src/router/dangling-image-cleanup.ts
index 6ed21a53..8f546400 100644
--- a/src/router/dangling-image-cleanup.ts
+++ b/src/router/dangling-image-cleanup.ts
@@ -15,6 +15,19 @@
  * from being reaped — see the regression test of the same name in
  * `tests/unit/router/dangling-image-cleanup.test.ts`. Never widen the scope.
  *
+ * The label is applied by the cascade Dockerfiles themselves (every
+ * `Dockerfile.<svc>` at repo root carries `LABEL cascade.managed=true` in
+ * its production stage). PR #1243 originally shipped this loop without that
+ * Dockerfile contract — the loop was a no-op for days because no built
+ * image carried the label, and dangling rebuilds accumulated unchecked.
+ * The same regression test pins both halves of the contract: the filter
+ * shape AND the per-Dockerfile LABEL directive.
+ *
+ * The CONTAINER label of the same name (`cascade.managed=true`, set in
+ * `container-manager.ts` on every `docker run`) is a separate surface used
+ * by `orphan-cleanup.ts` to scope container reaping. It does not propagate
+ * to images; the Dockerfile LABEL is the only path to image-level matching.
+ *
  * The 5-min snapshot eviction loop and the 5-min orphan-container cleanup
  * loop are unaffected; this loop runs at 30 min because dangling
  * accumulation is gradual and `force: false` rmi is cheap.
diff --git a/tests/unit/router/dangling-image-cleanup.test.ts b/tests/unit/router/dangling-image-cleanup.test.ts
index d607aa46..d478cecd 100644
--- a/tests/unit/router/dangling-image-cleanup.test.ts
+++ b/tests/unit/router/dangling-image-cleanup.test.ts
@@ -1,3 +1,5 @@
+import { readdirSync, readFileSync } from 'node:fs';
+import { join } from 'node:path';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 
 // ---------------------------------------------------------------------------
@@ -244,6 +246,52 @@ describe('dangling-image-cleanup', () => {
 		});
 	});
 
+	describe('Dockerfile LABEL contract — static guard', () => {
+		// Counterpart to the scan-filter regression guard above. The filter
+		// only matches images carrying the `cascade.managed=true` label, and
+		// the only way a built image gets that label is via a `LABEL`
+		// directive in the Dockerfile. PR #1243 shipped the cleanup loop
+		// without this contract — the loop was a no-op for days because no
+		// image carried the label. If a new `Dockerfile.<svc>` lands at the
+		// repo root without the directive, the cleanup loop silently stops
+		// reclaiming that service's dangling rebuilds. This test fails
+		// loudly the moment that happens.
+		const REPO_ROOT = join(__dirname, '..', '..', '..');
+		const dockerfiles = readdirSync(REPO_ROOT)
+			.filter((name) => name.startsWith('Dockerfile.'))
+			.sort();
+
+		it('finds the expected cascade Dockerfiles at repo root (sanity)', () => {
+			// Sanity: if this assertion fails the glob is broken or someone
+			// renamed the Dockerfiles, and the per-file assertions below
+			// would silently pass on an empty list.
+			expect(dockerfiles.length).toBeGreaterThanOrEqual(5);
+			expect(dockerfiles).toEqual(
+				expect.arrayContaining([
+					'Dockerfile.dashboard',
+					'Dockerfile.frontend',
+					'Dockerfile.router',
+					'Dockerfile.selfhosted',
+					'Dockerfile.worker',
+				]),
+			);
+		});
+
+		it.each([
+			'Dockerfile.router',
+			'Dockerfile.worker',
+			'Dockerfile.dashboard',
+			'Dockerfile.frontend',
+			'Dockerfile.selfhosted',
+		])('%s declares LABEL cascade.managed=true so dangling rebuilds match the cleanup filter', (filename) => {
+			const contents = readFileSync(join(REPO_ROOT, filename), 'utf8');
+			// Match `LABEL cascade.managed=true` (with optional quotes
+			// around the value). Tolerates `LABEL k=v k2=v2` chains.
+			const labelRegex = /^\s*LABEL\b[^\n]*\bcascade\.managed=("?)true\1/im;
+			expect(contents).toMatch(labelRegex);
+		});
+	});
+
 	describe('startDanglingImageCleanup / stopDanglingImageCleanup', () => {
 		it('starts a periodic cleanup scan', () => {
 			expect(() => startDanglingImageCleanup()).not.toThrow();