diff --git a/doc/plans/2026-11-11-staging-failures-vs-chaos-coverage.md b/doc/plans/2026-11-11-staging-failures-vs-chaos-coverage.md
index 7c0bb57e730..25714e623fb 100644
--- a/doc/plans/2026-11-11-staging-failures-vs-chaos-coverage.md
+++ b/doc/plans/2026-11-11-staging-failures-vs-chaos-coverage.md
@@ -190,6 +190,11 @@ working hours is about 40 minutes. Every native run longer than about 40 minutes
   and OpenCode) passed 2 of 2 on master. The save-back did not block the task. The harness keeps no
   evidence for passing tasks, so it is not verified that the link existed at save-back time.
 - Proposed (not built): `DF1`, which fills the sandbox disk to ENOSPC before result copy-back.
+- Built (2026-11-11): `DF1` (`--faults DF1`, `--env daytona`). A test-only server hook makes the
+  task's final saves report a full sandbox disk until the harness clears it, instead of filling a
+  real disk. See "Sandbox disk full (DF1)" in `tests/restart-chaos/README.md`. First wave
+  `w-20261111T131941-s9412` (Daytona, R1, Codex): the task rested with `sandbox_disk_full` and the
+  API offered Retry, but the board showed "Recover saved files" and no Retry button.
 
 ### E: Daytona capacity outage (18 runs, mostly self-healing)
 
@@ -274,7 +279,7 @@ working hours is about 40 minutes. Every native run longer than about 40 minutes
 | K15 redeploy into a new process space and deployment identity | R, P, L (and A with `--upgrade-from`) | `--faults K15` | Implemented, unit-tested. Five Daytona waves are recorded below. |
 | EP1 environment-provider 5xx window | E | — | Proposed |
 | F1 absolute symlink kept in the repository workspace | F (unsafe-symlink save-back) | `--workloads F1` | Implemented, unit-tested. Daytona wave: 2 of 2 pass on master. |
-| DF1 sandbox disk full | F (ENOSPC save-back) | — | Proposed |
+| DF1 sandbox disk full | F (ENOSPC save-back) | — | Built (test-only save hook) |
 
 ### Waves on master 8f6ca25976
 
diff --git a/server/src/services/remote-workspaces.ts b/server/src/services/remote-workspaces.ts
index 2920a4f6447..5e2ebec34a7 100644
--- a/server/src/services/remote-workspaces.ts
+++ b/server/src/services/remote-workspaces.ts
@@ -9,6 +9,7 @@ import os from "node:os";
 import path from "node:path";
 import { and, eq, inArray, isNull, or, sql } from "drizzle-orm";
 import { crashPoint } from "@paperclipai/shared/crash-points";
+import { sandboxDiskFullFaultTarget } from "./sandbox-disk-full-fault.js";
 import {
   companies, environmentLeases, executionWorkspaces, executionWorkspaceSnapshots, heartbeatRuns, issues, workspaceOperations, type Db,
 } from "@paperclipai/db";
@@ -912,7 +913,9 @@ export async function saveRemoteWorkspace(input: {
     const existingUpload = snapshot.status === "uploaded" ? await getWorkspaceSnapshot(input.db, { companyId: input.workspace.companyId,
       workspaceId: input.workspace.id, snapshotId: snapshot.id }) : null;
     if (existingUpload) timing.reusedUpload = true;
-    captured = existingUpload ? null : await captureRemoteWorkspaceArchive({ target, remoteCwd: expected.location.remoteCwd,
+    captured = existingUpload ? null : await captureRemoteWorkspaceArchive({ remoteCwd: expected.location.remoteCwd,
+      // Test-only DF1 hook (sandbox-disk-full-fault.ts): the target itself unless a harness armed this save.
+      target: sandboxDiskFullFaultTarget(target, { boundary, issueId: operation.issueId, runId: input.runId }),
       operationId: operation.id, timing });
     await input.assertOwned();
     const uploadStarted = performance.now();
diff --git a/server/src/services/sandbox-disk-full-fault.test.ts b/server/src/services/sandbox-disk-full-fault.test.ts
new file mode 100644
index 00000000000..af2e2ae3a3c
--- /dev/null
+++ b/server/src/services/sandbox-disk-full-fault.test.ts
@@ -0,0 +1,78 @@
+import { mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, describe, expect, it } from "vitest";
+import { REMOTE_WORKSPACE_SANDBOX_DISK_FULL, captureRemoteWorkspaceArchive, type RemoteWorkspaceTarget } from "./remote-workspace-transport.js";
+import {
+  DISK_FULL_FAULT_CONTROL_ENV, DISK_FULL_FAULT_RECEIPT_ENV, DISK_FULL_FAULT_SYNC_OUT_MESSAGE,
+  readDiskFullFaultGate, sandboxDiskFullFaultTarget, setDiskFullFaultGateForTest,
+} from "./sandbox-disk-full-fault.js";
+
+const ISSUE = "11111111-1111-4111-8111-111111111111";
+const RUN = "22222222-2222-4222-8222-222222222222";
+const OPERATION = "33333333-3333-4333-8333-333333333333";
+
+function sandboxTarget(calls: string[]): RemoteWorkspaceTarget {
+  return {
+    kind: "remote", transport: "sandbox", remoteCwd: "/workspace", providerKey: "test",
+    runner: {
+      execute: async () => { calls.push("execute"); return { exitCode: 0, signal: null, timedOut: false, stdout: "{}", stderr: "", pid: 1, startedAt: null }; },
+      syncIn: async () => { calls.push("syncIn"); return {} as never; },
+      syncOut: async () => { calls.push("syncOut"); return {} as never; },
+    },
+  } as unknown as RemoteWorkspaceTarget;
+}
+
+describe("sandbox disk-full fault gate", () => {
+  let restore: (() => void) | null = null;
+  const dirs: string[] = [];
+  afterEach(() => {
+    restore?.(); restore = null;
+    for (const dir of dirs.splice(0)) rmSync(dir, { recursive: true, force: true });
+  });
+  const scratch = () => { const dir = mkdtempSync(path.join(os.tmpdir(), "disk-full-fault-")); dirs.push(dir); return dir; };
+
+  it("is off unless the harness switch is set, and never on in production", () => {
+    expect(readDiskFullFaultGate({})).toBeNull();
+    expect(readDiskFullFaultGate({ [DISK_FULL_FAULT_CONTROL_ENV]: "  " })).toBeNull();
+    expect(readDiskFullFaultGate({ NODE_ENV: "production", [DISK_FULL_FAULT_CONTROL_ENV]: "/tmp/control" })).toBeNull();
+    expect(readDiskFullFaultGate({ NODE_ENV: "test", [DISK_FULL_FAULT_CONTROL_ENV]: "/tmp/control", [DISK_FULL_FAULT_RECEIPT_ENV]: "/tmp/receipt" }))
+      .toEqual({ controlPath: "/tmp/control", receiptPath: "/tmp/receipt" });
+  });
+
+  it("returns the save's own target when the process was started without the switch", () => {
+    const target = sandboxTarget([]);
+    expect(sandboxDiskFullFaultTarget(target, { boundary: "final", issueId: ISSUE, runId: RUN })).toBe(target);
+  });
+
+  it("faults only a final save whose issue or run is listed, and stops when cleared", async () => {
+    const dir = scratch();
+    const control = path.join(dir, "control"), receipt = path.join(dir, "receipts.jsonl");
+    restore = setDiskFullFaultGateForTest({ controlPath: control, receiptPath: receipt });
+    const calls: string[] = [];
+    const target = sandboxTarget(calls);
+    // No control file yet: disarmed.
+    expect(sandboxDiskFullFaultTarget(target, { boundary: "final", issueId: ISSUE, runId: RUN })).toBe(target);
+    writeFileSync(control, `other-issue\n${ISSUE}\n`);
+    expect(sandboxDiskFullFaultTarget(target, { boundary: "initial", issueId: ISSUE, runId: RUN })).toBe(target);
+    expect(sandboxDiskFullFaultTarget(target, { boundary: "final", issueId: "other", runId: "other-run" })).toBe(target);
+
+    const faulted = sandboxDiskFullFaultTarget(target, { boundary: "final", issueId: ISSUE, runId: RUN });
+    expect(faulted).not.toBe(target);
+    expect(await faulted.runner!.execute({ command: "node" })).toMatchObject({ exitCode: 1, stderr: REMOTE_WORKSPACE_SANDBOX_DISK_FULL });
+    await expect(faulted.runner!.syncOut!([])).rejects.toThrow(DISK_FULL_FAULT_SYNC_OUT_MESSAGE);
+    await faulted.runner!.syncIn!([]);
+    expect(calls).toEqual(["syncIn"]);
+    expect(JSON.parse(readFileSync(receipt, "utf8").trim())).toMatchObject({ issueId: ISSUE, runId: RUN, boundary: "final" });
+
+    // The save's own capture path turns the sandbox's answer into the named disk-full failure.
+    await expect(captureRemoteWorkspaceArchive({ target: faulted, remoteCwd: "/workspace", operationId: OPERATION }))
+      .rejects.toThrow(REMOTE_WORKSPACE_SANDBOX_DISK_FULL);
+
+    // A run id arms it too; clearing the file disarms the next save.
+    writeFileSync(control, `${RUN}\n`);
+    expect(sandboxDiskFullFaultTarget(target, { boundary: "final", issueId: null, runId: RUN })).not.toBe(target);
+    writeFileSync(control, "");
+    expect(sandboxDiskFullFaultTarget(target, { boundary: "final", issueId: ISSUE, runId: RUN })).toBe(target);
+  });
+});
diff --git a/server/src/services/sandbox-disk-full-fault.ts b/server/src/services/sandbox-disk-full-fault.ts
new file mode 100644
index 00000000000..0e57e22b9df
--- /dev/null
+++ b/server/src/services/sandbox-disk-full-fault.ts
@@ -0,0 +1,82 @@
+/**
+ * Test-only sandbox disk-full fault (restart-chaos DF1, tests/restart-chaos/disk-full-faults.ts).
+ *
+ * A real full sandbox disk cannot be made on demand, locally or on Daytona. This hook makes a
+ * final workspace save see what a full sandbox returns, and leaves every decision after that to
+ * the product: the save's own failure handling, finalization, saved-work recovery and Retry.
+ *
+ * Arming (test mode only), in the same style as `@paperclipai/shared/crash-points`:
+ *
+ *   PAPERCLIP_DISK_FULL_FAULT_CONTROL=<file>  each final save reads this file. A line that equals
+ *                                             the save's issue id or run id arms that save. No file,
+ *                                             or no matching line, means disarmed.
+ *   PAPERCLIP_DISK_FULL_FAULT_RECEIPT=<file>  optional; one JSON line is appended per faulted save.
+ *
+ * While a save is armed, every sandbox command its capture runs exits 1 with the exact message the
+ * in-sandbox capture script writes on ENOSPC, and the provider's file download fails with tar's
+ * "No space left on device". Restore and other operations are untouched.
+ *
+ * The variable is read once, when this module is first imported, and is ignored when
+ * `NODE_ENV=production`. Disarmed, the hook is one comparison against a module constant and
+ * returns the save's own target. Only the chaos harness sets the variable, on the server it starts.
+ *
+ * This is test instrumentation, not Telemetry or Observability: nothing is recorded or sent
+ * anywhere unless a test arms a save.
+ */
+import { appendFileSync, readFileSync } from "node:fs";
+import { REMOTE_WORKSPACE_SANDBOX_DISK_FULL, type RemoteWorkspaceTarget } from "./remote-workspace-transport.js";
+
+export const DISK_FULL_FAULT_CONTROL_ENV = "PAPERCLIP_DISK_FULL_FAULT_CONTROL";
+export const DISK_FULL_FAULT_RECEIPT_ENV = "PAPERCLIP_DISK_FULL_FAULT_RECEIPT";
+/** The provider download's failure on a full disk: tar cannot write its archive. */
+export const DISK_FULL_FAULT_SYNC_OUT_MESSAGE = "tar: workspace archive: Cannot write: No space left on device";
+
+export type DiskFullFaultReceipt = { issueId: string | null; runId: string; boundary: string; pid: number; at: string };
+
+type Gate = { controlPath: string; receiptPath: string | null };
+
+export function readDiskFullFaultGate(env: NodeJS.ProcessEnv | undefined): Gate | null {
+  if (!env || env.NODE_ENV === "production") return null;
+  const controlPath = env[DISK_FULL_FAULT_CONTROL_ENV]?.trim();
+  if (!controlPath) return null;
+  return { controlPath, receiptPath: env[DISK_FULL_FAULT_RECEIPT_ENV]?.trim() || null };
+}
+
+let gate: Gate | null = readDiskFullFaultGate(typeof process === "undefined" ? undefined : process.env);
+if (gate) process.stderr.write(`[disk-full-fault] armed from ${gate.controlPath} pid=${process.pid}\n`);
+
+function armed(current: Gate, ids: readonly string[]): boolean {
+  let text: string;
+  try { text = readFileSync(current.controlPath, "utf8"); } catch { return false; }
+  const lines = new Set(text.split("\n").map(line => line.trim()).filter(Boolean));
+  return ids.some(id => lines.has(id));
+}
+
+/**
+ * The target a workspace save captures through. Disarmed, or for any boundary other than the
+ * final copy-back, it is `target` itself.
+ */
+export function sandboxDiskFullFaultTarget<T extends RemoteWorkspaceTarget>(target: T,
+  save: { boundary: string; issueId: string | null; runId: string }): T {
+  if (gate === null) return target;
+  if (save.boundary !== "final" || !armed(gate, [save.runId, ...(save.issueId ? [save.issueId] : [])])) return target;
+  const receipt: DiskFullFaultReceipt = { issueId: save.issueId, runId: save.runId, boundary: save.boundary,
+    pid: process.pid, at: new Date().toISOString() };
+  if (gate.receiptPath) {
+    try { appendFileSync(gate.receiptPath, `${JSON.stringify(receipt)}\n`); } catch { /* the log line still records it */ }
+  }
+  process.stderr.write(`[disk-full-fault] save ${JSON.stringify(receipt)}\n`);
+  const runner = target.runner!;
+  const full = Object.create(runner) as typeof runner;
+  full.execute = async () => ({ exitCode: 1, signal: null, timedOut: false, stdout: "",
+    stderr: REMOTE_WORKSPACE_SANDBOX_DISK_FULL, pid: null, startedAt: null });
+  if (runner.syncOut) full.syncOut = async () => { throw new Error(DISK_FULL_FAULT_SYNC_OUT_MESSAGE); };
+  return { ...target, runner: full };
+}
+
+/** Replaces the gate inside a test process; returns a function that restores the previous one. */
+export function setDiskFullFaultGateForTest(next: Gate | null): () => void {
+  const previous = gate;
+  gate = next;
+  return () => { gate = previous; };
+}
diff --git a/tests/restart-chaos/README.md b/tests/restart-chaos/README.md
index 2de445fb04e..4539c747378 100644
--- a/tests/restart-chaos/README.md
+++ b/tests/restart-chaos/README.md
@@ -414,6 +414,53 @@ How the product saves the link itself (skip it, keep it, or record it) is not
 graded. F1 is meaningful with a remote workspace (`--env daytona`, with
 `--storage s3` as on staging). Locally it is a plain repository task.
 
+## Sandbox disk full (DF1)
+
+```sh
+node cli/node_modules/tsx/dist/cli.mjs tests/restart-chaos/main.ts --env daytona --daytona-image $IMG --daytona-cpu 3 \
+  --adapters codex --workloads R1 --workspace-repo "$PWD" --faults DF1 --storage s3 --concurrency 2 --tasks 2 --seed 9412
+```
+
+On staging, saving a run's result back from its sandbox failed because the sandbox disk was full
+(census class F, `doc/plans/2026-11-11-staging-failures-vs-chaos-coverage.md`). The product then
+ends saved-work recovery at once with cause `sandbox_disk_full` and offers a Retry (#20758).
+
+A full disk cannot be made on demand, so DF1 uses a test-only hook in the server
+(`server/src/services/sandbox-disk-full-fault.ts`). The harness starts its server with
+`PAPERCLIP_DISK_FULL_FAULT_CONTROL=<file>` and `PAPERCLIP_DISK_FULL_FAULT_RECEIPT=<wave>/disk-full-faults.jsonl`.
+The hook reads the variable once at startup and ignores it when `NODE_ENV=production`. Without it the
+hook is one comparison and the save uses its own target.
+
+- **Armed**: when a DF1 task launches, the harness writes its issue id to the control file. Each
+  final workspace save of that task (finalization's copy-back and recovery's re-save) then gets what
+  a full sandbox returns: every capture command exits 1 with the product's disk-full message, and
+  the provider download fails with `No space left on device`. The product's own code does the rest.
+  The server appends one receipt per faulted save.
+- **Cleared**: when the task rests with the cause `sandbox_disk_full` (or is `done`), the harness
+  records what the board shows, removes the id, and then the observer clicks Retry, as a person who
+  freed space would. A board-owned recovery can look like a rest while it still checks the saved
+  source; the harness keeps waiting there for up to 10 minutes (`DISK_FULL_REST_SETTLE_MS`) before it
+  clears the fault anyway, so that recovery's own save cannot hide the disk-full rest.
+
+The task passes when:
+
+- the fault reached at least one save (a receipt for the task);
+- it rested with recovery cause `sandbox_disk_full` and a Retry offered (T check `disk_full_fault`);
+- exactly one Retry, after the fault cleared, finished the task (R3). A needed Retry is expected
+  here, so R3 passes on it. Whether that Retry starts a new run is not graded.
+
+The ledger line records `diskFull: { faultedSaves, restedDiskFull, retryOffered, retryWorked }`.
+
+DF1 restarts nothing and needs `--env daytona --storage s3`: only a remote workspace has a sandbox
+save, so the harness refuses other setups. Use R1 with `--workspace-repo`. With the chaoscli fixture
+(B1) on Daytona, the workspace is a local worktree synced into the sandbox, so no remote save runs
+and the task fails as `not_applied` (wave `w-20261111T131314-s9411`). An unchanged workspace also
+skips the capture.
+
+The observer clicks Retry in the board UI, as for every other cell. In waves `w-20261111T131941-s9412`
+and `w-20261111T134316-s9413` the disk-full rest showed "Recover saved files", not a Retry button, while the API reported
+`canRetry: true`; R3 records this as `ui_retry_button_missing`.
+
 ## Config faults (CF1–CF3, `config-wave.ts`)
 
 ```sh
@@ -1138,6 +1185,7 @@ re-arms the task's own triggered faults instead of using their offsets.
 | `journeys.ts`, `journey-driver.ts`, `journey-oauth-app.ts`, `journey-matrix.ts` | Q2 and Q3 definitions and oracles, the board's side of each, Q3's loopback OAuth/MCP app, and the `--matrix` planner. |
 | `evidence.ts`, `ledger.ts` | Evidence bundle for each failure and the JSONL ledger plus `SUMMARY.md`. |
 | `daytona-image.ts` | Docker-free extraction of the image's runnerd and provider pack, cached per digest, and the controller/image content-ID check. |
+| `disk-full-faults.ts` | DF1: the control file for the server's test-only disk-full hook, the rest evidence, and the `disk_full_fault` check and R3 rule. |
 | `provider-faults.ts`, `provider-shim/` | PV1–PV3: the resolve hook, the Codex stdio shim, per-task rules and the `provider_fault_applied` check. |
 | `acpx-provider-faults.ts`, `provider-shim/acpx-*` | PV1–PV3 for Claude (ACPX): the stand-in runner package, the server hook, the sidecar/provider tap, and `--provider-fault-restart`. |
 | `question-handoff.ts` | Q1 saved question: the board's answer step and its oracle. |
diff --git a/tests/restart-chaos/config.ts b/tests/restart-chaos/config.ts
index 6e9ab880600..eae8f75317a 100644
--- a/tests/restart-chaos/config.ts
+++ b/tests/restart-chaos/config.ts
@@ -13,6 +13,7 @@ import { parseRepeatedRestartOptions } from "./repeated-restarts.js";
 import { daytonaRetainsSandboxes } from "./ttft-baseline-stats.js";
 import { PROVIDER_FAULT_KINDS, PROVIDER_FAULT_WORKLOADS, isProviderFault, parseProviderDelays, parseProviderMessages, type ProviderFaultKind } from "./provider-faults.js";
 import { PROVIDER_FAULT_ADAPTERS, parseProviderFaultRestart } from "./acpx-provider-faults.js";
+import { DISK_FULL_FAULT_KINDS, isDiskFullFault, type DiskFullFaultKind } from "./disk-full-faults.js";
 import {
   ADAPTER_IDS, ENVIRONMENT_KINDS, FAULT_KINDS, TRIGGER_IDS, WORKLOAD_IDS,
   type AdapterId, type EnvironmentKind, type FaultKind, type TriggerId, type WaveOptions, type WorkloadId,
@@ -174,10 +175,12 @@ export function parseCommand(argv: readonly string[], now = Date.now()): ParsedC
   }
   if (lifecycle !== undefined && lifecycle !== "per_turn" && lifecycle !== "warm" && lifecycle !== "default") throw new Error("--lifecycle must be per_turn, warm or default");
   const adapters = list<AdapterId>(values.adapters, ADAPTER_IDS, "adapters", ["codex", "claude"]);
-  // `--faults` takes restart faults (K*) and provider message faults (PV*, provider-faults.ts).
-  const allFaults = list<FaultKind | ProviderFaultKind>(values.faults, [...FAULT_KINDS, ...PROVIDER_FAULT_KINDS], "faults",
+  // `--faults` takes restart faults (K*), provider message faults (PV*, provider-faults.ts) and the
+  // sandbox disk-full fault (DF1, disk-full-faults.ts).
+  const allFaults = list<FaultKind | ProviderFaultKind | DiskFullFaultKind>(values.faults, [...FAULT_KINDS, ...PROVIDER_FAULT_KINDS, ...DISK_FULL_FAULT_KINDS], "faults",
     stormMinutes ? STORM_DEFAULT_FAULTS : crashPoint ? ["K1"] : ["K1", "K2", "K4"]);
   const providerFaults = allFaults.filter(isProviderFault);
+  const diskFullFaults = allFaults.filter(isDiskFullFault);
   const options: WaveOptions = {
     env,
     adapters,
@@ -185,8 +188,9 @@ export function parseCommand(argv: readonly string[], now = Date.now()): ParsedC
     workloads: list<WorkloadId>(values.workloads, workloadChoices, "workloads", workloadChoices.filter(id => id !== "G1" && id !== "H1" && id !== "R1" && id !== "S1" && id !== "L1" && id !== "F1" && id !== "T1"
       && !takesJourneyTriggers(id) && (id !== "M1" || adapters.length >= 2))),
     // A crash-point wave schedules no fault; K1 is the restart its self-kill gets.
-    faults: allFaults.filter((fault): fault is FaultKind => !isProviderFault(fault)),
+    faults: allFaults.filter((fault): fault is FaultKind => !isProviderFault(fault) && !isDiskFullFault(fault)),
     ...(providerFaults.length ? { providerFaults } : {}),
+    ...(diskFullFaults.length ? { diskFullFaults } : {}),
     triggers: list<TriggerId>(values.triggers, TRIGGER_IDS, "triggers", ["time"]),
     concurrency: integer(values.concurrency, "concurrency", 4, 1, 20),
     tasks: integer(values.tasks, "tasks", stormMinutes ? 200 : 8, 1, 200),
@@ -215,6 +219,14 @@ export function parseCommand(argv: readonly string[], now = Date.now()): ParsedC
     throw new Error("--fault-after-seconds fires faults by time; use it with --triggers time");
   }
   if (!crashPoint && values["crash-point-hold-ms"] !== undefined) throw new Error("--crash-point-hold-ms applies only to --crash-point");
+  if (diskFullFaults.length) {
+    if (stormMinutes) throw new Error("The disk-full fault (DF1) is planned per task; do not combine it with --storm-minutes");
+    // Only a remote sandbox workspace has a save the sandbox disk can refuse; a local run has none.
+    if (env !== "daytona" || values.storage !== "s3") throw new Error("The disk-full fault (DF1) needs a remote sandbox workspace save; run it with --env daytona --storage s3");
+    if (providerFaults.length) throw new Error("The disk-full fault (DF1) does not share a wave with provider message faults (PV*)");
+    // The matrix planner builds its cells from restart and provider faults only; DF1 would silently drop out.
+    if (values.matrix) throw new Error("The disk-full fault (DF1) is not a --matrix cell; run it as a planned wave");
+  }
   if (providerFaults.length) {
     if (stormMinutes) throw new Error("Provider message faults (PV*) are planned per task; do not combine them with --storm-minutes");
     if (env !== "local") throw new Error("Provider message faults (PV*) shim the local provider; run them with --env local");
diff --git a/tests/restart-chaos/disk-full-faults.test.ts b/tests/restart-chaos/disk-full-faults.test.ts
new file mode 100644
index 00000000000..f6bc0273840
--- /dev/null
+++ b/tests/restart-chaos/disk-full-faults.test.ts
@@ -0,0 +1,113 @@
+import { mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, describe, expect, it } from "vitest";
+import { parseCommand } from "./config.js";
+import { DISK_FULL_REST_SETTLE_MS, DiskFullFaultSeam, diskFullLedger, diskFullRest, diskFullRestReady, receiptsForIssue, withDiskFullCheck } from "./disk-full-faults.js";
+import { gradeR3 } from "./grader.js";
+import { planTasks, taskFaultSchedule } from "./scheduler.js";
+import type { TaskRecord } from "./types.js";
+
+const IMAGE = `ghcr.io/paperclipai/paperclip-daytona-runner@sha256:${"a".repeat(64)}`;
+const diskFullIssue = (label = "sandbox_disk_full", canRetry = true) => ({
+  status: "blocked", interruption: { canRetry },
+  activeRecoveryAction: { ownerType: "board", evidence: { systemRecovery: { failure: {
+    code: "export_interrupted", retryClass: "user_action_required", cause: { label, code: "ENOSPC", status: null } } } } },
+});
+
+function record(extra: Partial<TaskRecord> = {}): TaskRecord {
+  return {
+    plan: { taskId: "t01", index: 0, workload: "B1", adapter: "codex", fault: "DF1", fireAfterMs: 0, holdMs: 0, followUpAfterMs: null, nonce: "abcd1234" },
+    issueId: "issue-1", identifier: "CHA-1", createdAt: 0, launchError: null, samples: [], retry: null, restAt: 1,
+    finalStatus: "done", deadlineAt: 1, timedOut: false, followUp: null, faultIds: [], sweep: null,
+    preFaultFiles: null, lostFiles: null,
+    diskFull: { kind: "DF1", armedAt: 1, clearedAt: 2, rest: diskFullRest(diskFullIssue(), 2), appliedSaves: 2 },
+    ...extra,
+  };
+}
+const accepted = { at: 3, observedRunId: "run-1", httpStatus: 200, accepted: true, error: null };
+const passing = { verdict: "pass" as const, checks: [] };
+
+describe("DF1 planning", () => {
+  it("is a per-task fault on Daytona that schedules no restart", () => {
+    const command = parseCommand(["--env", "daytona", "--daytona-image", IMAGE, "--adapters", "codex", "--workloads", "B1",
+      "--faults", "DF1", "--storage", "s3", "--tasks", "2", "--seed", "7"]);
+    if (command.mode !== "wave") throw new Error("expected a wave");
+    expect(command.options).toMatchObject({ faults: [], diskFullFaults: ["DF1"] });
+    const tasks = planTasks(command.options);
+    expect(tasks.map(task => task.fault)).toEqual(["DF1", "DF1"]);
+    expect(tasks.map(taskFaultSchedule)).toEqual([[], []]);
+  });
+
+  it("refuses waves where no sandbox save exists or the plan cannot carry it", () => {
+    expect(() => parseCommand(["--adapters", "codex", "--workloads", "B1", "--faults", "DF1"])).toThrow(/--env daytona/);
+    expect(() => parseCommand(["--env", "daytona", "--daytona-image", IMAGE, "--adapters", "codex", "--workloads", "B1", "--faults", "DF1"])).toThrow(/--storage s3/);
+    expect(() => parseCommand(["--env", "daytona", "--daytona-image", IMAGE, "--adapters", "codex", "--faults", "DF1", "--storage", "s3", "--storm-minutes", "5"]))
+      .toThrow(/storm/);
+    expect(() => parseCommand(["--env", "daytona", "--daytona-image", IMAGE, "--adapters", "codex", "--workloads", "B1", "--faults", "DF1", "--storage", "s3", "--matrix"]))
+      .toThrow(/--matrix/);
+  });
+});
+
+describe("DF1 control file", () => {
+  let root: string | null = null;
+  afterEach(async () => { if (root) await rm(root, { recursive: true, force: true }); root = null; });
+
+  it("arms and clears issue ids atomically and reads the server's receipts", async () => {
+    root = await mkdtemp(path.join(os.tmpdir(), "df1-seam-"));
+    const receiptPath = path.join(root, "receipts.jsonl");
+    const seam = await DiskFullFaultSeam.install({ root, receiptPath });
+    expect(seam.serverEnvironment).toEqual({ PAPERCLIP_DISK_FULL_FAULT_CONTROL: seam.controlPath, PAPERCLIP_DISK_FULL_FAULT_RECEIPT: receiptPath });
+    expect(await readFile(seam.controlPath, "utf8")).toBe("");
+    await Promise.all([seam.arm("issue-1"), seam.arm("issue-2")]);
+    expect(await readFile(seam.controlPath, "utf8")).toBe("issue-1\nissue-2\n");
+    await seam.clear("issue-1");
+    expect(await readFile(seam.controlPath, "utf8")).toBe("issue-2\n");
+    await writeFile(receiptPath, `${JSON.stringify({ issueId: "issue-2", runId: "r", boundary: "final", pid: 1, at: "t" })}\nnot json\n`);
+    expect(receiptsForIssue(await seam.receipts(), "issue-2")).toHaveLength(1);
+    expect(receiptsForIssue(await seam.receipts(), "issue-1")).toHaveLength(0);
+  });
+});
+
+describe("DF1 clear timing", () => {
+  it("waits at an unfinished rest until the board names the full disk, then up to the settle bound", () => {
+    const disk = { kind: "DF1" as const, armedAt: 1, clearedAt: null, rest: null };
+    const checking = diskFullRest({ status: "blocked", interruption: { canRetry: true }, activeRecoveryAction: { ownerType: "board", evidence: {} } }, 0);
+    expect(diskFullRestReady(disk, checking, 1_000)).toBe(false);
+    expect(diskFullRestReady(disk, checking, 1_000 + DISK_FULL_REST_SETTLE_MS - 1)).toBe(false);
+    expect(diskFullRestReady(disk, diskFullRest(diskFullIssue(), 0), 2_000)).toBe(true);
+    expect(diskFullRestReady(disk, { ...checking, status: "done" }, 2_000)).toBe(true);
+    expect(diskFullRestReady(disk, checking, 1_000 + DISK_FULL_REST_SETTLE_MS)).toBe(true);
+  });
+});
+
+describe("DF1 grading", () => {
+  it("passes when the task rested on a full disk with a Retry and one Retry finished it", () => {
+    const graded = record({ retry: accepted });
+    expect(withDiskFullCheck(passing, graded.plan, graded).verdict).toBe("pass");
+    expect(gradeR3(graded)).toMatchObject({ verdict: "pass" });
+    expect(diskFullLedger(graded, "done")).toEqual({ faultedSaves: 2, restedDiskFull: true, retryOffered: true, retryWorked: true });
+  });
+
+  it("fails a fault that never reached a save, a different rest cause, or a missing Retry", () => {
+    const notApplied = record({ diskFull: { kind: "DF1", armedAt: 1, clearedAt: null, rest: null, appliedSaves: 0 } });
+    expect(withDiskFullCheck(passing, notApplied.plan, notApplied).checks[0]).toMatchObject({ ok: false, detail: expect.stringContaining("not_applied") });
+    const otherCause = record({ retry: accepted, diskFull: { kind: "DF1", armedAt: 1, clearedAt: 2, rest: diskFullRest(diskFullIssue("provider_error"), 2), appliedSaves: 1 } });
+    expect(withDiskFullCheck(passing, otherCause.plan, otherCause).checks[0]?.detail).toContain("rest_cause=provider_error");
+    const noRetryOffered = record({ diskFull: { kind: "DF1", armedAt: 1, clearedAt: 2, rest: diskFullRest(diskFullIssue("sandbox_disk_full", false), 2), appliedSaves: 1 } });
+    expect(withDiskFullCheck(passing, noRetryOffered.plan, noRetryOffered).checks[0]?.detail).toContain("retry_not_offered");
+    expect(gradeR3(record({ finalStatus: "blocked" }))).toMatchObject({ verdict: "fail", detail: expect.stringContaining("disk_full_retry_missing") });
+  });
+
+  it("fails a Retry that did not finish the task or needed a second click", () => {
+    expect(gradeR3(record({ retry: accepted, finalStatus: "blocked" }))).toMatchObject({ verdict: "fail", detail: expect.stringContaining("did_not_complete") });
+    expect(gradeR3(record({ retry: accepted, priorRetries: [accepted] }))).toMatchObject({ verdict: "fail", detail: expect.stringContaining("2_clicks") });
+    expect(gradeR3(record({ retry: { ...accepted, accepted: false } }))).toMatchObject({ verdict: "fail", detail: expect.stringContaining("retry_rejected") });
+  });
+
+  it("leaves other cells to the ordinary Retry rule", () => {
+    const plain = record({ plan: { ...record().plan, fault: "K1" }, retry: accepted, diskFull: undefined });
+    expect(withDiskFullCheck(passing, plain.plan, plain)).toBe(passing);
+    expect(gradeR3(plain)).toMatchObject({ verdict: "fail", detail: expect.stringContaining("retry_no_new_run") });
+  });
+});
diff --git a/tests/restart-chaos/disk-full-faults.ts b/tests/restart-chaos/disk-full-faults.ts
new file mode 100644
index 00000000000..10d7cc5f8ad
--- /dev/null
+++ b/tests/restart-chaos/disk-full-faults.ts
@@ -0,0 +1,183 @@
+/**
+ * DF1: the sandbox disk is full when the run's result is saved (staging census class F,
+ * doc/plans/2026-11-11-staging-failures-vs-chaos-coverage.md).
+ *
+ * A genuinely full disk cannot be made on demand, so the server carries a test-only hook
+ * (server/src/services/sandbox-disk-full-fault.ts). The harness starts its server with
+ * PAPERCLIP_DISK_FULL_FAULT_CONTROL pointing at a file it owns. While a task's issue id is in
+ * that file, each final workspace save of that task gets the answer a full sandbox gives: the
+ * capture command exits 1 with the product's disk-full message, and the provider download fails
+ * with "No space left on device". Everything after that is the product's own handling.
+ *
+ * The harness arms the task when it launches and clears it when the task first rests offering a
+ * Retry, just before the observer clicks Retry, as a person who freed space would. Grading:
+ * - the fault applied (the server wrote a receipt for the task);
+ * - the task rested with recovery cause `sandbox_disk_full` and a Retry offered;
+ * - one Retry, after the fault cleared, finished the task (R3).
+ *
+ * DF1 restarts nothing. It needs a remote sandbox workspace, so it runs with `--env daytona`.
+ */
+import { randomUUID } from "node:crypto";
+import { mkdir, readFile, rename, writeFile } from "node:fs/promises";
+import path from "node:path";
+import type { OracleResult, RuleResult, TaskPlan, TaskRecord } from "./types.js";
+
+type Json = Record<string, any>;
+
+export const DISK_FULL_FAULT_KINDS = ["DF1"] as const;
+export type DiskFullFaultKind = (typeof DISK_FULL_FAULT_KINDS)[number];
+export function isDiskFullFault(value: string): value is DiskFullFaultKind {
+  return (DISK_FULL_FAULT_KINDS as readonly string[]).includes(value);
+}
+
+/** The recovery cause the product names for a save that found the sandbox disk full. */
+export const SANDBOX_DISK_FULL_CAUSE = "sandbox_disk_full";
+
+/** Server-side receipt, one per faulted save (sandbox-disk-full-fault.ts DiskFullFaultReceipt). */
+export interface DiskFullReceipt { issueId: string | null; runId: string; boundary: string; pid: number; at: string }
+
+/** What the board showed when a DF1 task first rested. */
+export interface DiskFullRest {
+  at: number;
+  status: string | null;
+  canRetry: boolean;
+  /** `activeRecoveryAction.evidence.systemRecovery.failure.cause.label`. */
+  causeLabel: string | null;
+  retryClass: string | null;
+  ownerType: string | null;
+}
+
+export interface DiskFullRecord {
+  kind: DiskFullFaultKind;
+  armedAt: number | null;
+  clearedAt: number | null;
+  rest: DiskFullRest | null;
+  /** First rest seen while armed; the harness waits for the disk-full verdict from here (DISK_FULL_REST_SETTLE_MS). */
+  firstRestAt?: number;
+  /** Faulted saves the server recorded for the task; filled in at grading. */
+  appliedSaves?: number;
+  armError?: string;
+}
+
+export function diskFullRest(issue: Json | null, at: number): DiskFullRest {
+  const action = (issue?.activeRecoveryAction ?? null) as Json | null;
+  const failure = (action?.evidence?.systemRecovery?.failure ?? null) as Json | null;
+  return {
+    at, status: typeof issue?.status === "string" ? issue.status : null,
+    canRetry: issue?.interruption?.canRetry === true,
+    causeLabel: typeof failure?.cause?.label === "string" ? failure.cause.label : null,
+    retryClass: typeof failure?.retryClass === "string" ? failure.retryClass : null,
+    ownerType: typeof action?.ownerType === "string" ? action.ownerType : null,
+  };
+}
+
+/**
+ * A board-owned recovery can look like a rest while it is still checking the saved source
+ * ("Recovering saved files…", wave w-20261111T131941-s9412/t02). Clearing the fault there would
+ * let that recovery's own save succeed and hide the disk-full rest. While armed, the harness
+ * keeps waiting at an unfinished rest until the board names `sandbox_disk_full`, up to this long.
+ */
+export const DISK_FULL_REST_SETTLE_MS = 10 * 60_000;
+
+/** True when the harness may record this rest and clear the fault; false keeps watching. */
+export function diskFullRestReady(record: DiskFullRecord, rest: DiskFullRest, now: number): boolean {
+  if (rest.status === "done" || rest.causeLabel === SANDBOX_DISK_FULL_CAUSE) return true;
+  record.firstRestAt ??= now;
+  return now - record.firstRestAt >= DISK_FULL_REST_SETTLE_MS;
+}
+
+/** The control file the server reads and the receipts it writes. */
+export class DiskFullFaultSeam {
+  private readonly armed = new Set<string>();
+  private writes: Promise<void> = Promise.resolve();
+
+  private constructor(readonly controlPath: string, readonly receiptPath: string) {}
+
+  static async install(input: { root: string; receiptPath: string }): Promise<DiskFullFaultSeam> {
+    const directory = path.join(input.root, "disk-full-fault");
+    await mkdir(directory, { recursive: true, mode: 0o700 });
+    const seam = new DiskFullFaultSeam(path.join(directory, "control"), input.receiptPath);
+    await seam.write();
+    return seam;
+  }
+
+  get serverEnvironment(): Record<string, string> {
+    return { PAPERCLIP_DISK_FULL_FAULT_CONTROL: this.controlPath, PAPERCLIP_DISK_FULL_FAULT_RECEIPT: this.receiptPath };
+  }
+
+  arm(issueId: string): Promise<void> { this.armed.add(issueId); return this.write(); }
+  clear(issueId: string): Promise<void> { this.armed.delete(issueId); return this.write(); }
+
+  /** Atomic, so a save never reads half a file; serialized, so the last change wins. */
+  private write(): Promise<void> {
+    const body = [...this.armed].map(id => `${id}\n`).join("");
+    this.writes = this.writes.catch(() => undefined).then(async () => {
+      const temporary = `${this.controlPath}.${randomUUID()}.tmp`;
+      await writeFile(temporary, body, { mode: 0o600 });
+      await rename(temporary, this.controlPath);
+    });
+    return this.writes;
+  }
+
+  async receipts(): Promise<DiskFullReceipt[]> {
+    const text = await readFile(this.receiptPath, "utf8").catch(() => "");
+    return text.split("\n").filter(Boolean).flatMap(line => { try { return [JSON.parse(line) as DiskFullReceipt]; } catch { return []; } });
+  }
+}
+
+export function receiptsForIssue(receipts: readonly DiskFullReceipt[], issueId: string | null): DiskFullReceipt[] {
+  return issueId ? receipts.filter(receipt => receipt.issueId === issueId) : [];
+}
+
+/** Adds the `disk_full_fault` check: the fault applied and the task rested on it with a Retry. */
+export function withDiskFullCheck(oracle: OracleResult, plan: TaskPlan, record: TaskRecord): OracleResult {
+  if (!isDiskFullFault(plan.fault)) return oracle;
+  const disk = record.diskFull;
+  const applied = disk?.appliedSaves ?? 0;
+  const rest = disk?.rest ?? null;
+  const problems = [
+    ...(disk?.armError ? [`arm_failed=${disk.armError}`] : []),
+    ...(applied === 0 ? ["not_applied (no save reached the hook: an unchanged workspace, a local run or a server without the hook)"] : []),
+    ...(applied > 0 && !rest ? ["no_rest_while_armed"] : []),
+    ...(rest && rest.causeLabel !== SANDBOX_DISK_FULL_CAUSE ? [`rest_cause=${rest.causeLabel ?? "none"}`] : []),
+    ...(rest && !rest.canRetry ? ["retry_not_offered"] : []),
+  ];
+  const detail = `${plan.fault}: faultedSaves=${applied} rest=${rest ? `${rest.status}/${rest.causeLabel ?? "none"}/${rest.retryClass ?? "none"}/canRetry=${rest.canRetry}` : "none"}`
+    + (problems.length ? `; ${problems.join("; ")}` : "");
+  const checks = [...oracle.checks, { name: "disk_full_fault", ok: problems.length === 0, detail }];
+  return { verdict: checks.every(check => check.ok) ? "pass" : "fail", checks };
+}
+
+/**
+ * R3 for DF1. The product cannot free a sandbox disk, so one Retry is the expected outcome, not a
+ * failure: R3 passes when exactly one accepted Retry, after the fault cleared, finished the task.
+ * Whether the Retry started a new run is not graded: applying the already-saved result without a
+ * new turn is a correct Retry too.
+ */
+export function gradeDiskFullRetry(record: TaskRecord, expectedStatus: string): RuleResult {
+  const retry = record.retry;
+  if (!retry) {
+    return { verdict: "fail", detail: `disk_full_retry_missing: rested ${record.finalStatus ?? "unknown"}${record.timedOut ? " (timed out)" : ""} without a Retry` };
+  }
+  if (retry.error || retry.accepted !== true) {
+    return { verdict: "fail", detail: `retry_rejected: http=${retry.httpStatus ?? "none"} accepted=${String(retry.accepted)} ${retry.error ?? ""}`.trim() };
+  }
+  const clicks = 1 + (record.priorRetries?.length ?? 0);
+  if (clicks > 1) return { verdict: "fail", detail: `retry_needed_${clicks}_clicks (expected one Retry after the disk-full fault cleared)` };
+  if (record.finalStatus !== expectedStatus) {
+    return { verdict: "fail", detail: `disk_full_retry_did_not_complete (status ${record.finalStatus ?? "unknown"}${record.timedOut ? ", timed out" : ""})` };
+  }
+  return { verdict: "pass", detail: `expected Retry after ${SANDBOX_DISK_FULL_CAUSE}; Retry worked (${expectedStatus})` };
+}
+
+/** Ledger fields: needed-Retry and Retry-worked for the cell. */
+export function diskFullLedger(record: TaskRecord, expectedStatus: string) {
+  const disk = record.diskFull;
+  if (!disk) return undefined;
+  return {
+    faultedSaves: disk.appliedSaves ?? 0,
+    restedDiskFull: disk.rest?.causeLabel === SANDBOX_DISK_FULL_CAUSE,
+    retryOffered: disk.rest?.canRetry === true,
+    retryWorked: record.retry?.accepted === true && record.finalStatus === expectedStatus,
+  };
+}
diff --git a/tests/restart-chaos/grader.ts b/tests/restart-chaos/grader.ts
index 1a3730f456e..fd8e0f93893 100644
--- a/tests/restart-chaos/grader.ts
+++ b/tests/restart-chaos/grader.ts
@@ -1,5 +1,6 @@
 import { UI_RETRY_BLOCKED_BY_MODAL, UI_RETRY_BUTTON_MISSING, UI_RETRY_NO_REQUEST, type FaultReceipt, type OracleResult, type RuleId, type RuleResult, type TaskGrade, type TaskRecord, type TaskSample } from "./types.js";
 import { g1Decision } from "./workloads.js";
+import { gradeDiskFullRetry, isDiskFullFault } from "./disk-full-faults.js";
 import { enforcedUniversalFailures, gradeUniversal, type UniversalDbEvidence } from "./universal.js";
 
 /** Pure R1–R6 grading over observer samples (plan §2). No I/O. */
@@ -98,7 +99,8 @@ export function gradeR2(record: TaskRecord, oracle: OracleResult): RuleResult {
 }
 
 export function gradeR3(record: TaskRecord): RuleResult {
-  const own = gradeOwnRetry(record);
+  // DF1: a full sandbox disk needs a person, so one Retry is expected (disk-full-faults.ts).
+  const own = isDiskFullFault(record.plan.fault) ? gradeDiskFullRetry(record, expectedFinalStatus(record)) : gradeOwnRetry(record);
   const childClicks = record.childRetries?.length ?? 0;
   if (!childClicks || own.verdict === "fail") return own;
   return { verdict: "fail", detail: `retry_needed_on_subtask_${childClicks} (${record.childRetries!.map(attempt => attempt.childIssueId).join(",")})` };
diff --git a/tests/restart-chaos/ledger.ts b/tests/restart-chaos/ledger.ts
index d527fdc558b..894a23f6f46 100644
--- a/tests/restart-chaos/ledger.ts
+++ b/tests/restart-chaos/ledger.ts
@@ -2,6 +2,8 @@ import { appendFile, mkdir, readFile, writeFile } from "node:fs/promises";
 import path from "node:path";
 import { replayCommand } from "./config.js";
 import type { RuleId, TaskGrade, TaskRecord, WavePlan } from "./types.js";
+import { diskFullLedger } from "./disk-full-faults.js";
+import { expectedFinalStatus } from "./grader.js";
 
 export interface LedgerLine {
   schema: "paperclip.restart-chaos.ledger/v1";
@@ -37,6 +39,8 @@ export interface LedgerLine {
   /** Universal checks U1–U4 (universal.ts): verdict per rule, and the details of warnings that did not fail the task. */
   universal?: Record<string, string>;
   universalWarnings?: string[];
+  /** DF1: faulted saves, the disk-full rest with a Retry offered, and whether that Retry worked. */
+  diskFull?: { faultedSaves: number; restedDiskFull: boolean; retryOffered: boolean; retryWorked: boolean };
 }
 
 export function ledgerLine(plan: WavePlan, record: TaskRecord, grade: TaskGrade, gitSha: string, evidence: string | null,
@@ -55,6 +59,7 @@ export function ledgerLine(plan: WavePlan, record: TaskRecord, grade: TaskGrade,
     recordedAt: new Date().toISOString(),
     ...(plan.options.masks?.length ? { masks: [...plan.options.masks] } : {}),
     ...(plan.options.crashPoint ? { crashPoint: plan.options.crashPoint } : {}),
+    ...(record.diskFull ? { diskFull: diskFullLedger(record, expectedFinalStatus(record)) } : {}),
     ...(grade.universal ? {
       universal: Object.fromEntries(Object.entries(grade.universal).map(([id, rule]) => [id, rule.verdict])),
       universalWarnings: Object.entries(grade.universal).filter(([, rule]) => !rule.enforced && rule.verdict === "fail")
diff --git a/tests/restart-chaos/main.ts b/tests/restart-chaos/main.ts
index 86dcb0f05ec..131eafc10dd 100644
--- a/tests/restart-chaos/main.ts
+++ b/tests/restart-chaos/main.ts
@@ -23,6 +23,7 @@ import { NativeTrigger, nativeTriggerMarkdown, nativeTriggerShortfall, triggered
 import { needsCredentialRotation, startCredentialRotation, type CredentialRotation } from "./storage-credentials.js";
 import { describeProviderFault, installProviderFaultSeam, resolveRealCodex, withProviderFaultCheck, type ProviderFaultSeam } from "./provider-faults.js";
 import { installAcpxSidecarSeam, withAcpxSidecarHook, type AcpxSidecarSeam } from "./acpx-provider-faults.js";
+import { DiskFullFaultSeam, isDiskFullFault, receiptsForIssue, withDiskFullCheck } from "./disk-full-faults.js";
 import { CREDENTIAL_FOR_ADAPTER, parseCommand, replayCommand, waveIdFor } from "./config.js";
 import { assertControllerMatchesImage, defaultDaytonaImageCacheRoot, prepareDaytonaImageArtifacts } from "./daytona-image.js";
 import { PLUGIN_BUILD_STAMP, pluginBuildState } from "./plugin-build.js";
@@ -274,6 +275,7 @@ async function main(): Promise<number> {
   let storageAuditor: StorageAuditor | null = null;
   let providerFaults: ProviderFaultSeam | null = null;
   let acpxSidecarSeam: AcpxSidecarSeam | null = null;
+  let diskFullSeam: DiskFullFaultSeam | null = null;
   let speedSection: string | null = null;
   let storageSection: string | null = null;
   let harnessError: unknown;
@@ -336,6 +338,12 @@ async function main(): Promise<number> {
       timeline.add("provider_faults_installed", { realCodex: realCodex.command, codexVersion: realCodex.version,
         rules: plan.tasks.flatMap(task => task.providerFault ? [`${task.taskId}:${describeProviderFault(task.providerFault)}`] : []) });
     }
+    if (plan.tasks.some(task => isDiskFullFault(task.fault))) {
+      // DF1: the server's test-only hook reads this control file at each final workspace save.
+      diskFullSeam = await DiskFullFaultSeam.install({ root: supervisor.paths.temporaryRoot, receiptPath: path.join(waveDir, "disk-full-faults.jsonl") });
+      Object.assign(serverEnvironment, diskFullSeam.serverEnvironment);
+      timeline.add("disk_full_faults_installed", { tasks: plan.tasks.filter(task => isDiskFullFault(task.fault)).map(task => task.taskId) });
+    }
     if (plan.options.timeAgeMs) supervisor.timeAgeMs = plan.options.timeAgeMs;
     if (plan.options.rrStopOn) supervisor.rrStopOn = plan.options.rrStopOn;
     await supervisor.start(serverEnvironment);
@@ -369,6 +377,7 @@ async function main(): Promise<number> {
     board = serverEnvironment.SERVE_UI === "false" ? null
       : new BoardUi(supervisor.baseUrl, undefined, path.join(waveDir, "ui-retry-diagnostics"));
     const observers = plan.tasks.map(task => new TaskObserver(task, api, lab, timeline, supervisor, protectedRoots, board));
+    for (const observer of observers) if (isDiskFullFault(observer.plan.fault)) observer.diskFullSeam = diskFullSeam;
     const pending = [...observers];
     const launched: TaskObserver[] = [];
     const active: TaskObserver[] = [];
@@ -678,8 +687,13 @@ async function main(): Promise<number> {
       const restart = faults.find(receipt => receipt.requestedBy === observer.plan.taskId && receipt.trigger === "provider");
       const oracle = withProviderFaultCheck(graded, observer.plan, artifacts?.providerFaultEvents ?? [], restart?.startedAt ?? null,
         restart?.stoppedAt ?? restart?.startedAt ?? null);
+      if (observer.record.diskFull) {
+        observer.record.diskFull.appliedSaves = receiptsForIssue(await diskFullSeam?.receipts() ?? [], observer.record.issueId).length;
+      }
       // T1: a mid-tool fault only counts when one of the task's faults started while its loop ran (workloads.ts).
-      const toolOracle = withT1CrossingCheck(oracle, observer.plan, artifacts?.documents.brief, faults);
+      // DF1 restarts nothing, so T1's mid-tool restart check does not apply; the disk-full check replaces it.
+      const toolOracle = isDiskFullFault(observer.plan.fault) ? withDiskFullCheck(oracle, observer.plan, observer.record)
+        : withT1CrossingCheck(oracle, observer.plan, artifacts?.documents.brief, faults);
       const grade = gradeTask(observer.record, faults, observer.definition.budgetMs, toolOracle, universalByIssue ? {
         runMessages: allRunMessages, recoveryActions: universalByIssue.get(observer.record.issueId ?? "")?.recoveryActions ?? [] } : undefined);
       let evidence: string | null = null;
diff --git a/tests/restart-chaos/observer.ts b/tests/restart-chaos/observer.ts
index 8618de508c1..2a74d8bcc4c 100644
--- a/tests/restart-chaos/observer.ts
+++ b/tests/restart-chaos/observer.ts
@@ -21,6 +21,7 @@ import { taskFaultSchedule } from "./scheduler.js";
 import { g1ChildTitle, g1Decision, workloadDefinitions, type WorkloadAgents } from "./workloads.js";
 import { databaseUrlFromConfig, journeyDriverFor, type JourneyDriver } from "./journey-driver.js";
 import { withLiveStatusEvidence } from "./live-status-evidence.js";
+import { diskFullRest, diskFullRestReady, isDiskFullFault, type DiskFullFaultSeam } from "./disk-full-faults.js";
 
 const IGNORED_DIRECTORIES = new Set([".git", ".bench", "__pycache__", "node_modules"]);
 const MAX_SNAPSHOT_FILES = 2_000;
@@ -207,6 +208,8 @@ export class TaskObserver {
   private readonly faultSchedule: ScheduledFault[];
   private readonly pendingFaults: ScheduledFault[];
   done = false;
+  /** DF1 (disk-full-faults.ts): arms this task's saves at launch and clears them before its Retry. */
+  diskFullSeam: Pick<DiskFullFaultSeam, "arm" | "clear"> | null = null;
 
   /** Replaceable in tests. A Daytona run's process is remote, so only local runs are checked. */
   processAlive = (pid: number, startedAt: string) => this.lab.environmentKind === "local" && localProcessAlive(pid, startedAt);
@@ -288,6 +291,7 @@ export class TaskObserver {
       this.record.deadlineAt = this.record.createdAt + definition.budgetMs;
       this.timeline.add("task_launched", { taskId: this.plan.taskId, issueId: issue.id, identifier: issue.identifier,
         workload: this.plan.workload, adapter: this.plan.adapter, faults: this.faultSchedule });
+      await this.armDiskFull();
     } catch (error) {
       this.record.launchError = error instanceof Error ? error.message : String(error);
       this.done = true;
@@ -605,6 +609,37 @@ export class TaskObserver {
     return true;
   }
 
+  /** DF1: the task's final saves find the sandbox disk full until the fault is cleared. */
+  private async armDiskFull(): Promise<void> {
+    if (!isDiskFullFault(this.plan.fault) || !this.record.issueId) return;
+    const record = this.record.diskFull = { kind: this.plan.fault, armedAt: null as number | null, clearedAt: null as number | null, rest: null };
+    try {
+      if (!this.diskFullSeam) throw new Error("disk-full seam not installed");
+      await this.diskFullSeam.arm(this.record.issueId);
+      record.armedAt = Date.now();
+      this.timeline.add("disk_full_fault_armed", { taskId: this.plan.taskId, issueId: this.record.issueId });
+    } catch (error) {
+      (record as NonNullable<TaskRecord["diskFull"]>).armError = error instanceof Error ? error.message : String(error);
+      this.timeline.add("disk_full_fault_arm_failed", { taskId: this.plan.taskId, error: (record as NonNullable<TaskRecord["diskFull"]>).armError });
+    }
+  }
+
+  /**
+   * DF1: once the rest names the full disk (or the task is done, or the settle bound passed), record
+   * what the board shows, then clear the fault, as a person who freed space. Returns false to keep watching.
+   */
+  private async clearDiskFullAtRest(now: number): Promise<boolean> {
+    const record = this.record.diskFull;
+    if (!record || record.armedAt === null || record.clearedAt !== null || !this.record.issueId) return true;
+    const rest = diskFullRest(this.issue, now);
+    if (!diskFullRestReady(record, rest, now)) return false;
+    record.rest = rest;
+    await this.diskFullSeam!.clear(this.record.issueId);
+    record.clearedAt = Date.now();
+    this.timeline.add("disk_full_fault_cleared", { taskId: this.plan.taskId, rest: record.rest });
+    return true;
+  }
+
   private async onRest(sample: TaskSample, now: number) {
     const status = sample.issueStatus ?? null;
     // The board has not acted yet: the task waits on it, so it has not rested (and gets no Retry).
@@ -629,6 +664,7 @@ export class TaskObserver {
         return;
       }
     }
+    if (!await this.clearDiskFullAtRest(now)) { this.restCandidateSince = null; return; }
     if (status !== "done" && (!this.record.retry || faultSinceRetry) && sample.interruption?.canRetry) {
       if (this.record.retry) (this.record.priorRetries ??= []).push(this.record.retry);
       this.record.retry = await this.retry(sample, now);
diff --git a/tests/restart-chaos/scheduler.ts b/tests/restart-chaos/scheduler.ts
index 3ba1b1f4796..fdde7f8865a 100644
--- a/tests/restart-chaos/scheduler.ts
+++ b/tests/restart-chaos/scheduler.ts
@@ -1,4 +1,5 @@
 import { isProviderFault, withProviderFaultRules } from "./provider-faults.js";
+import { isDiskFullFault } from "./disk-full-faults.js";
 import { takesJourneyTriggers } from "./journeys.js";
 import { workloadDefinitions } from "./workloads.js";
 import { isTimeFault, timeFaultHoldMs } from "./time-faults-config.js";
@@ -79,8 +80,8 @@ const STORM_RESULT_FAULTS: readonly FaultKind[] = ["K1", "K2"];
  * A `result` task in a storm also fires its own K1 or K2 just after its run
  * accepts a result, the window of RC-30, RC-33 and RC-41.
  */
-function stormCellFaults(options: Pick<WaveOptions, "faults" | "stormMinutes" | "providerFaults">, trigger: TriggerId): readonly TaskFaultKind[] {
-  if (!options.stormMinutes) return [...options.faults, ...(options.providerFaults ?? [])];
+function stormCellFaults(options: Pick<WaveOptions, "faults" | "stormMinutes" | "providerFaults" | "diskFullFaults">, trigger: TriggerId): readonly TaskFaultKind[] {
+  if (!options.stormMinutes) return [...options.faults, ...(options.providerFaults ?? []), ...(options.diskFullFaults ?? [])];
   if (trigger === "time") return ["K13"];
   if (trigger !== "result") throw new Error(`A K13 storm fires on its own clock; --triggers ${trigger} does not combine with it (use time or result)`);
   const faults = options.faults.filter(fault => STORM_RESULT_FAULTS.includes(fault));
@@ -96,7 +97,7 @@ function pinnedFireAfterMs(faultAfterMs: number | undefined, drawn: number): num
   return faultAfterMs ?? drawn;
 }
 
-export function planTasks(options: Pick<WaveOptions, "seed" | "tasks" | "workloads" | "adapters" | "faults" | "triggers" | "stormMinutes" | "k4HoldMaxMs" | "k15HoldMs" | "tm1HoldMs" | "faultAfterMs" | "providerFaults" | "rrGapMs">): TaskPlan[] {
+export function planTasks(options: Pick<WaveOptions, "seed" | "tasks" | "workloads" | "adapters" | "faults" | "triggers" | "stormMinutes" | "k4HoldMaxMs" | "k15HoldMs" | "tm1HoldMs" | "faultAfterMs" | "providerFaults" | "diskFullFaults" | "rrGapMs">): TaskPlan[] {
   const rng = createRng(options.seed);
   const triggers = options.triggers?.length ? options.triggers : ["time" as const];
   for (const trigger of triggers) {
@@ -293,11 +294,11 @@ export function observedFaultSchedule(createdAt: number | null, faultIds: readon
 /** The faults a task schedules: its replayed sequence, or its one planned fault. */
 export function taskFaultSchedule(task: TaskPlan): ScheduledFault[] {
   if (task.replayFaults?.length) return task.replayFaults;
-  // A storm crosses K13 tasks; a provider fault (PV*) and a matrix baseline (K0) restart nothing, unless
+  // A storm crosses K13 tasks; a provider fault (PV*), a disk-full fault (DF1) and a matrix baseline (K0) restart nothing, unless
   // `--provider-fault-restart` asked for a K1 once the provider fault applied (the `provider` trigger).
   const restart = task.providerFault?.restart;
   if (restart) return [{ kind: restart.kind, holdMs: restart.holdMs ?? 0, atMs: 0, trigger: "provider", delayMs: restart.afterAppliedMs }];
-  if (task.fault === "K13" || task.fault === "K0" || isProviderFault(task.fault)) return [];
+  if (task.fault === "K13" || task.fault === "K0" || isProviderFault(task.fault) || isDiskFullFault(task.fault)) return [];
   const planned: ScheduledFault = { kind: task.fault, holdMs: task.holdMs, atMs: task.fireAfterMs,
     ...(task.restartSteps ? { restartSteps: task.restartSteps } : {}) };
   const trigger = task.trigger ?? "time";
diff --git a/tests/restart-chaos/types.ts b/tests/restart-chaos/types.ts
index 3622401ecf3..9e3cf8a48be 100644
--- a/tests/restart-chaos/types.ts
+++ b/tests/restart-chaos/types.ts
@@ -1,4 +1,5 @@
 /** Shared types for the control-plane restart chaos harness (plan §5). */
+import type { DiskFullFaultKind, DiskFullRecord } from "./disk-full-faults.js";
 import type { ProviderFaultEvent, ProviderFaultKind, ProviderFaultRule, ProviderMessage, ProviderRestartKind } from "./provider-faults.js";
 import type { QuestionArtifacts, QuestionRecord } from "./question-handoff.js";
 import type { RepeatedRestartRecord, RestartStep } from "./repeated-restarts.js";
@@ -20,8 +21,9 @@ export const K4_MIN_HOLD_MS = 120_000;
  * A task's planned fault. "K13" (restart storm) tasks have none of their own; the wave's storm crosses them.
  * PV1–PV3 (provider message faults, provider-faults.ts) restart nothing: the task's rule is armed in the Codex shim.
  * "K0" is a `--matrix` baseline cell: the same journey with no fault.
+ * DF1 (disk-full-faults.ts) restarts nothing either: the task's final workspace saves find the sandbox disk full.
  */
-export type TaskFaultKind = FaultKind | "K13" | "K0" | ProviderFaultKind;
+export type TaskFaultKind = FaultKind | "K13" | "K0" | ProviderFaultKind | DiskFullFaultKind;
 
 /**
  * G1: an approval-gated action across a restart. H1: a budget hard stop crossed mid-run with a restart (its own wave).
@@ -117,6 +119,8 @@ export interface WaveOptions {
   workspaceGitUrl?: string;
   /** Provider message faults from `--faults` (PV1 delay, PV2 drop, PV3 duplicate); see provider-faults.ts. */
   providerFaults?: ProviderFaultKind[];
+  /** Sandbox disk-full faults from `--faults` (DF1); see disk-full-faults.ts. */
+  diskFullFaults?: DiskFullFaultKind[];
   providerFaultMessage?: ProviderMessage;
   /** `--provider-fault-message S1=interrupt_ack,...`: a workload's own message, over `providerFaultMessage`. */
   providerFaultMessageByWorkload?: Partial<Record<WorkloadId, ProviderMessage>>;
@@ -419,6 +423,8 @@ export interface TaskRecord {
   journey?: import("./journeys.js").JourneyRecord;
   /** PV with `--provider-fault-restart`: when the shim logged the task's fault (arms the `provider` trigger). */
   providerFaultAppliedAt?: number;
+  /** DF1: when the fault was armed and cleared, and what the board showed at the disk-full rest. */
+  diskFull?: DiskFullRecord;
 }
 
 export interface TaskGrade {