diff --git a/deploy/run-staging-deploy.sh b/deploy/run-staging-deploy.sh
index 4bffa70a..c5ec0858 100755
--- a/deploy/run-staging-deploy.sh
+++ b/deploy/run-staging-deploy.sh
@@ -143,6 +143,16 @@ export SITE_ADDRESS='https://staging.jyotisha.chat'
 export GITHUB_SHA="$DEPLOY_SHA"
 
 "${compose[@]}" config --quiet
+# Exact-SHA images accumulate after each deploy. Pulling a new digest then
+# fails with containerd "no space left on device" (run 2841 / f9685f28).
+# Running jyotisha-staging containers keep their layers; unused tags go.
+# Do not prune named volumes: that would risk the Postgres data volume.
+echo "staging host docker disk before image reclaim"
+"${docker_command[@]}" system df || true
+"${docker_command[@]}" image prune --force
+"${docker_command[@]}" image prune --all --force
+echo "staging host docker disk after image reclaim"
+"${docker_command[@]}" system df || true
 "${compose[@]}" pull api web
 "${compose[@]}" up -d --no-build --pull never --wait postgres
 
diff --git a/deploy/run-staging-migration.sh b/deploy/run-staging-migration.sh
index 6cb35c54..9fba41fb 100755
--- a/deploy/run-staging-migration.sh
+++ b/deploy/run-staging-migration.sh
@@ -85,6 +85,16 @@ bash deploy/validate-staging-database-env.sh .env.staging.database
 
 export DATABASE_ENV_FILE='../.env.staging.database'
 compose=("${docker_command[@]}" compose -p jyotisha-staging -f deploy/docker-compose.postgres.yml)
+# Exact-SHA images accumulate after each deploy. Pulling a new digest then
+# fails with containerd "no space left on device" (run 2841 / f9685f28).
+# Running jyotisha-staging containers keep their layers; unused tags go.
+# Do not prune named volumes: that would risk the Postgres data volume.
+echo "staging host docker disk before image reclaim"
+"${docker_command[@]}" system df || true
+"${docker_command[@]}" image prune --force
+"${docker_command[@]}" image prune --all --force
+echo "staging host docker disk after image reclaim"
+"${docker_command[@]}" system df || true
 "${docker_command[@]}" pull "$WEB_IMAGE"
 "${compose[@]}" up -d --no-build --pull never --wait postgres
 "${compose[@]}" exec -T postgres psql -v ON_ERROR_STOP=1 -U postgres -d jyotisha \
diff --git a/docs/BUG_HISTORY.md b/docs/BUG_HISTORY.md
index a77cba1a..3219f58c 100644
--- a/docs/BUG_HISTORY.md
+++ b/docs/BUG_HISTORY.md
@@ -13166,4 +13166,20 @@
 - 防复发：会话标题和行内操作必须共享同一个行级状态面。不得给 `.session-menu-trigger` 单独的 canvas/选中底。
 - 相关记录：BUG-024
 - 复发自：BUG-024（旧测试没锁住 trigger 的 canvas 悬停底）
-- 修复版本：待本修复合入 staging
+- 修复版本：`f9685f28`（已进 staging；部署被 BUG-994 / migrate run 2841 磁盘写满挡住）
+
+## BUG-994 | staging 迁移拉 digest 镜像时 containerd 磁盘写满
+
+- 状态：investigating
+- 首次发现：2026-09-21
+- 最近更新：2026-09-21
+- 影响面：`deploy/run-staging-migration.sh`、`deploy/run-staging-deploy.sh`、staging 主机 Docker 镜像层、`migrate-staging-database` run 2841
+- 用户现象：无终端用户可见功能回归。`f9685f28` 门禁 validate 全绿、镜像已发布，但测试站没有切到该 SHA：迁移在主机 `docker pull` 新 web digest 时失败，后续 `deploy-staging` 未执行。当时线上仍是上一版 `d2cec179`。
+- 触发条件：向 staging 推送会触发门禁的改动后，publish 派发 `migrate-staging-database`，主机再拉一枚新的 exact-SHA web 镜像。
+- 根因：每次部署留下不可变 digest 镜像，脚本在 pull 前不回收未使用镜像。run 2841 在 `Apply digest-pinned migration under host lock` 拉 `copse/jyotisha@sha256:a00887de…` 时，containerd ingest 报 `write /var/lib/containerd/io.containerd.content.v1.content/ingest/631c40bfaf7318a3ce6ca6ead3b0f8ce0eb25e2a2e93851c76bfc9eb5060c25d/data: no space left on device`。门禁 runner 的 `reclaim-runner-disk.sh` 只管构建机，不管 staging 主机。
+- 修复：迁移与部署脚本在 pull 前打印 `docker system df`，执行 `image prune --force` 再 `image prune --all --force`。正在跑的 `jyotisha-staging` 容器会保住当前层。禁止 `volume prune`，避免误删 Postgres 数据卷。
+- 验证：源码合同 `staging-backend-workflows.test.ts` 锁定 prune 出现在 pull 之前且不得 `volume prune`。端到端证据待本轮门禁的 migrate / deploy 转绿；转绿前不得标 resolved。
+- 防复发：staging 主机拉 digest 前必须先回收未使用镜像。不得用 `volume prune` 换磁盘。
+- 相关记录：BUG-150、BUG-993
+- 复发自：无
+- 修复版本：待本轮含 prune-before-pull 的提交合入 staging 且 migrate 转绿
diff --git a/frontend/tests/staging-backend-workflows.test.ts b/frontend/tests/staging-backend-workflows.test.ts
index 756eea4e..52592dba 100644
--- a/frontend/tests/staging-backend-workflows.test.ts
+++ b/frontend/tests/staging-backend-workflows.test.ts
@@ -1008,7 +1008,13 @@ test("normal deployment checks migrations but never applies them", () => {
   for (const workflow of stagingWorkflows) {
     assert.doesNotMatch(workflow, /SERVICE_RUNTIME_PASSWORD|SERVICE_DATABASE_URL/);
   }
+  // 原值: pull api web 前不回收镜像
+  // 新值: image prune --all --force 必须出现在 pull 之前，且不得 volume prune
+  // 原因: BUG-994 / migrate run 2841 在 staging 主机拉 digest 时 containerd 写满
+  assert.match(runner, /image prune --all --force/);
+  assert.doesNotMatch(runner, /volume prune --/);
   assertOrder(runner, [
+    "image prune --all --force",
     "pull api web",
     "up -d --no-build --pull never --wait postgres",
     "--profile migration-check run --rm migration-checker",
@@ -1036,6 +1042,15 @@ test("manual migration uses only PostgreSQL and the digest-pinned migrator", ()
   assert.match(workflow, /^on:\n\s+workflow_dispatch:/m);
   assert.doesNotMatch(workflow, /workflow_run:|\n\s+push:/);
   assert.match(runner, /"\$\{docker_command\[@\]\}" pull "\$WEB_IMAGE"/);
+  // 原值: docker pull "$WEB_IMAGE" 前不回收镜像
+  // 新值: image prune --all --force 必须出现在 pull 之前，且不得 volume prune
+  // 原因: BUG-994 / migrate run 2841 在 staging 主机拉 digest 时 containerd 写满
+  assert.match(runner, /image prune --all --force/);
+  assert.doesNotMatch(runner, /volume prune --/);
+  assertOrder(runner, [
+    "image prune --all --force",
+    '"${docker_command[@]}" pull "$WEB_IMAGE"',
+  ]);
   assert.match(runner, /up -d --no-build --pull never --wait postgres/);
   assert.match(runner, /-f deploy\/docker-compose\.postgres\.yml/);
   assertOrder(runner, [