diff --git a/packages/adapter-utils/src/workspace-restore-diagnostics.test.ts b/packages/adapter-utils/src/workspace-restore-diagnostics.test.ts
index 936b68e302c..492d09ed8ee 100644
--- a/packages/adapter-utils/src/workspace-restore-diagnostics.test.ts
+++ b/packages/adapter-utils/src/workspace-restore-diagnostics.test.ts
@@ -113,6 +113,13 @@ describe("workspace restore diagnostics", () => {
     },
   );
 
+  it("keeps an allowlisted ENAMETOOLONG code", async () => {
+    const sink = vi.fn();
+    const error = Object.assign(new Error("private"), { code: "ENAMETOOLONG" });
+    await expect(withWorkspaceRestoreDiagnostics("workspace", async () => { throw error; }, sink)).rejects.toBe(error);
+    expect(sink.mock.calls[0]?.[0]).toContain('"errorCode":"ENAMETOOLONG"');
+  });
+
   it("bounds cause traversal even when it cycles", async () => {
     const error = Object.assign(new Error("private"), { cause: null as unknown, code: "ENOENT" });
     error.cause = error;
diff --git a/packages/adapter-utils/src/workspace-restore-diagnostics.ts b/packages/adapter-utils/src/workspace-restore-diagnostics.ts
index 8ac378374f8..ab5d42d509d 100644
--- a/packages/adapter-utils/src/workspace-restore-diagnostics.ts
+++ b/packages/adapter-utils/src/workspace-restore-diagnostics.ts
@@ -40,7 +40,7 @@ export interface WorkspaceRestoreDiagnostic {
   rpcCode?: number;
 }
 const ERROR_CODES = new Set([
-  "ENOENT", "EACCES", "EPERM", "ENOSPC", "EIO", "EXDEV", "ENOTDIR", "EISDIR",
+  "ENOENT", "EACCES", "EPERM", "ENOSPC", "EIO", "EXDEV", "ENOTDIR", "EISDIR", "ENAMETOOLONG",
   "ECONNRESET", "ECONNREFUSED", "ETIMEDOUT", "EPIPE", "ENOTFOUND", "EAI_AGAIN",
   "ABORT_ERR", "UND_ERR_CONNECT_TIMEOUT", "UND_ERR_SOCKET",
 ]);
diff --git a/packages/plugins/sandbox-providers/daytona/src/file-sync-diagnostics.test.ts b/packages/plugins/sandbox-providers/daytona/src/file-sync-diagnostics.test.ts
index 4e5e2da1cee..e761e460fbd 100644
--- a/packages/plugins/sandbox-providers/daytona/src/file-sync-diagnostics.test.ts
+++ b/packages/plugins/sandbox-providers/daytona/src/file-sync-diagnostics.test.ts
@@ -54,6 +54,53 @@ it.each([
   });
 });
 
+it.each([
+  ["tar: ./private-file: Cannot open: Permission denied\ntar: Exiting with failure status due to previous errors", "EACCES"],
+  ["tar: ./private-dir: Cannot savedir: Operation not permitted", "EPERM"],
+  ["tar: ./private-file: Cannot stat: No such file or directory", "ENOENT"],
+  ["tar: ./private-dir/private-file: Cannot open: File name too long", "ENAMETOOLONG"],
+  ["tar: ./private-file: Read error at byte 0, while reading 512 bytes: Input/output error", "EIO"],
+  // A vanished file must not hide the error that stopped tar.
+  ["tar: ./private-file: Cannot stat: No such file or directory\ntar: ./private-dir: Cannot open: Permission denied", "EACCES"],
+  ["private-command-output mentions Permission denied mid-line only", "unknown"],
+] as const)("classifies a failed sandbox tar's output as a bounded errno: %s", async (output, errorCode) => {
+  const sandbox = {
+    process: { executeCommand: async (command: string) =>
+      command.includes("tar -c") ? { exitCode: 2, result: output } : { exitCode: 0 } },
+    fs: { downloadFiles: async () => [], deleteFile: async () => undefined },
+  };
+  await withEnvironmentSyncErrorCapture(async () => {
+    let caught: unknown;
+    try {
+      await performSyncOut({ sandbox: sandbox as never, remoteDir: "/workspace", timeoutSeconds: 30,
+        operations: [{ operationId: "fixture", files: [{ sourcePath: "/workspace/private-path", targetPath: "/unused", kind: "directory" }] }],
+      });
+    } catch (error) { caught = error; }
+    expect(caught).toBeInstanceOf(Error);
+    const diagnostic = readEnvironmentSyncErrorDiagnostic({ data: environmentSyncErrorData(caught) });
+    expect(diagnostic).toEqual({ errorCode, transferStep: "archive_create", transferFailureKind: "command_failed", exitCode: 2 });
+    expect(JSON.stringify(diagnostic)).not.toContain("private");
+  });
+});
+
+it("classifies a full sandbox disk at the guard step without recording output", async () => {
+  const sandbox = {
+    process: { executeCommand: async () => ({ exitCode: 1, result: "mkdir: cannot create directory '/workspace/private-path': No space left on device" }) },
+    fs: { downloadFiles: async () => [], deleteFile: async () => undefined },
+  };
+  await withEnvironmentSyncErrorCapture(async () => {
+    let caught: unknown;
+    try {
+      await performSyncOut({ sandbox: sandbox as never, remoteDir: "/workspace", timeoutSeconds: 30,
+        operations: [{ operationId: "fixture", files: [{ sourcePath: "/workspace/private-path", targetPath: "/unused", kind: "directory" }] }],
+      });
+    } catch (error) { caught = error; }
+    const diagnostic = readEnvironmentSyncErrorDiagnostic({ data: environmentSyncErrorData(caught) });
+    expect(diagnostic).toMatchObject({ errorCode: "ENOSPC", transferFailureKind: "command_failed", exitCode: 1 });
+    expect(JSON.stringify(diagnostic)).not.toContain("private");
+  });
+});
+
 it("keeps a thrown download exception identical and its nested safe code", async () => {
   const original = Object.freeze(new Error("private-download-error", { cause: { code: "ECONNRESET", token: "private-token" } }));
   const sandbox = {
diff --git a/packages/plugins/sandbox-providers/daytona/src/file-sync.ts b/packages/plugins/sandbox-providers/daytona/src/file-sync.ts
index f067a29130d..8ea41f23363 100644
--- a/packages/plugins/sandbox-providers/daytona/src/file-sync.ts
+++ b/packages/plugins/sandbox-providers/daytona/src/file-sync.ts
@@ -418,6 +418,31 @@ async function countHostFiles(root: string, exclude?: string[]): Promise<number>
   return total;
 }
 
+// Fatal causes first: tar can warn about a vanished file before the error that
+// stopped it. Daytona's executeCommand result already includes stderr.
+const SANDBOX_ERRNO_MESSAGES: ReadonlyArray<readonly [string, string]> = [
+  ["ENOSPC", "No space left on device"],
+  ["EIO", "Input/output error"],
+  ["ENAMETOOLONG", "File name too long"],
+  ["EACCES", "Permission denied"],
+  ["EPERM", "Operation not permitted"],
+  ["ENOTDIR", "Not a directory"],
+  ["EISDIR", "Is a directory"],
+  ["ENOENT", "No such file or directory"],
+];
+
+/**
+ * Map the strerror suffix of a failed command's output to an allowlisted errno.
+ * Reads only a bounded tail in memory; the output text itself is never recorded.
+ */
+function sandboxCommandErrorCode(output: string): string | undefined {
+  const lines = output.slice(-16 * 1024).split(/\r?\n/).map((line) => line.trimEnd());
+  for (const [code, message] of SANDBOX_ERRNO_MESSAGES) {
+    if (lines.some((line) => line.endsWith(`: ${message}`))) return code;
+  }
+  return undefined;
+}
+
 /**
  * Run one sandbox command and return its stdout on success. Throws the same
  * shaped error as {@link assertSandboxCommandOk} on a non-zero exit. Used by
@@ -434,7 +459,7 @@ async function assertSandboxCommandOkWithOutput(
   if ((result.exitCode ?? 1) !== 0) {
     const detail = (result.result ?? result.artifacts?.stdout ?? "").toString().trim();
     throw recordEnvironmentSyncError(new Error(`Daytona ${label} command failed (exit ${result.exitCode ?? "unknown"})${detail ? `: ${detail}` : ""}`), {
-      transferFailureKind: "command_failed", exitCode: result.exitCode,
+      transferFailureKind: "command_failed", exitCode: result.exitCode, errorCode: sandboxCommandErrorCode(detail),
     });
   }
   return (result.result ?? result.artifacts?.stdout ?? "").toString();
diff --git a/packages/plugins/sdk/src/environment-sync-error.ts b/packages/plugins/sdk/src/environment-sync-error.ts
index a630bb126e1..7d6a51a95da 100644
--- a/packages/plugins/sdk/src/environment-sync-error.ts
+++ b/packages/plugins/sdk/src/environment-sync-error.ts
@@ -68,7 +68,7 @@ const SCHEMA = "paperclip/environment-sync-error/v1";
 // Match the host's workspace restore diagnostic allowlist. Both sides validate
 // independently: plugin-supplied data must never widen the host's log surface.
 const ERROR_CODES = new Set([
-  "ENOENT", "EACCES", "EPERM", "ENOSPC", "EIO", "EXDEV", "ENOTDIR", "EISDIR",
+  "ENOENT", "EACCES", "EPERM", "ENOSPC", "EIO", "EXDEV", "ENOTDIR", "EISDIR", "ENAMETOOLONG",
   "ECONNRESET", "ECONNREFUSED", "ETIMEDOUT", "EPIPE", "ENOTFOUND", "EAI_AGAIN",
   "ABORT_ERR", "UND_ERR_CONNECT_TIMEOUT", "UND_ERR_SOCKET",
 ]);
diff --git a/packages/plugins/sdk/tests/environment-sync-error.test.ts b/packages/plugins/sdk/tests/environment-sync-error.test.ts
index c2480a707ce..f86196f0ba3 100644
--- a/packages/plugins/sdk/tests/environment-sync-error.test.ts
+++ b/packages/plugins/sdk/tests/environment-sync-error.test.ts
@@ -34,6 +34,7 @@ describe("environment sync diagnostic envelope", () => {
     const wrap = (cause: unknown) => ({ cause });
     expect(environmentSyncErrorData(wrap(wrap(wrap({ code: "EIO" }))))).toEqual({ schema, diagnostic: { errorCode: "EIO" } });
     expect(environmentSyncErrorData(wrap(wrap(wrap(wrap({ code: "EIO" })))))).toBeUndefined();
+    expect(environmentSyncErrorData({ code: "ENAMETOOLONG" })).toEqual({ schema, diagnostic: { errorCode: "ENAMETOOLONG" } });
   });
 
   it("revalidates worker fields and ignores arbitrary payload and protocol versions", () => {