In the

    United States Court of Appeals
                for the Seventh Circuit
                    ____________________
No. 22-1983
SHEMIKA D. MITCHELL, Executor
of the Estate of Tommy Harris,
                                                 Plaintiff-Appellant,

                                v.

DURHAM ENTERPRISES, INC., and DON DURHAM,
                                   Defendants-Appellants,

                               and

OHIO SECURITY INSURANCE COMPANY, et al.,

                                              Defendants-Appellees.
                    ____________________

          Appeal from the United States District Court
                for the Southern District of Illinois.
        Nos. 20-cv-72 & 21-cv-1389 — J. Phil Gilbert, Judge.
                    ____________________

    ARGUED NOVEMBER 8, 2022 — DECIDED APRIL 24, 2024
               ____________________

   Before SYKES, Chief Judge, and WOOD and SCUDDER, Circuit
Judges.
2                                                  No. 22-1983

    SYKES, Chief Judge. Tommy Harris was diagnosed with
bacterial sepsis after suffering repeated infections resulting
from his dialysis treatment at a clinic in Belleville, Illinois.
He filed a state-court malpractice action against the opera-
tors of the clinic and later added a claim against Durham
Enterprises, Inc., the janitorial company responsible for
cleaning the facility. This appeal concerns Durham’s insur-
ance coverage.
   Durham tendered the suit to Ohio Security Insurance
Company, its insurer. Ohio Security denied coverage based
on the insurance policy’s exclusion for injuries caused by
fungi or bacteria. Harris and Durham then negotiated an
agreement in which Durham promised not to mount a
defense and Harris promised to seek recovery only from the
insurer.
    Harris moved to sever his claim against Durham and set
it for a bench trial. The state trial judge granted the motion.
On the trial date, the parties disclosed their agreement to the
court. The judge then held a short, uncontested bench trial;
adopted Harris’s uncontested findings; and entered judg-
ment against Durham for more than $2 million. Though
Ohio Security was not a party and the insurance policy was
not in the record, the consent judgment includes findings on
insurance issues—notably, that the insurer breached its duty
to defend and is estopped from asserting any policy defens-
es.
   After the judgment became final, Harris filed an amend-
ed complaint purporting to add Ohio Security as a defend-
No. 22-1983                                                               3

ant. 1 Ohio Security removed the action to federal court and
sought a declaration of its coverage obligations. The district
court held that the bacteria exclusion precludes coverage.
    Aligned in interest, Harris and Durham jointly appealed,
challenging the no-coverage ruling but also raising a belated
challenge to subject-matter jurisdiction under the Rooker–
Feldman doctrine. The jurisdictional argument is meritless.
The Rooker–Feldman doctrine does not block federal jurisdic-
tion over claims by nonparties to state-court judgments. Lance
v. Dennis, 

 (2006); Johnson v. De Grandy,

 (1994). And the judge’s merits ruling was
sound; the policy’s bacteria exclusion precludes coverage for
this loss. We affirm the judgment.
                            I. Background
    In December 2015 Harris had a dialysis catheter surgical-
ly implanted and began dialysis treatment at the Metro East
Dialysis in Belleville. From February to August 2016, he
contracted multiple infections at the catheter site, necessitat-
ing several surgeries to remove and replace the catheter. The
infections, in turn, led to sepsis. During this period, Harris


1 Harris also added “Liberty Mutual Insurance” as a defendant. That was

a mistake. “Liberty Mutual Insurance” is not a legal entity; it’s a group of
affiliated underwriting companies that includes Liberty Mutual Insur-
ance Company and Ohio Security Insurance Company. The latter issued
Durham’s insurance policy. Though the policy document bears the
logomark “Liberty Mutual Insurance,” the declarations page indicates
that Ohio Security is the insurer. The district judge noted these anomalies
and permitted Harris to substitute Liberty Mutual Insurance Company
for “Liberty Mutual Insurance.” It’s not clear why Liberty Mutual
Insurance Company is in the case. Ohio Security issued the relevant
policy, so we can ignore Liberty Mutual.
4                                                            No. 22-1983

was diagnosed with both gram positive and gram negative
sepsis; both are types of bacterial sepsis.
    Several public health agencies investigated an increase in
patient infections originating from the dialysis clinic during
this six-month period in 2016. Among other discoveries, the
investigation found that Durham Enterprises, the janitorial
company responsible for cleaning the facility, was doing so
improperly.2 There is no dispute that Harris’s infections
were caused in part by Durham’s negligent cleaning of the
facility.
    In January 2017 Harris commenced a malpractice action
in St. Clair County Circuit Court against the dialysis clinic
alleging (among other things) that it failed to properly
sanitize the facility and its equipment. But he did not name
the proper defendant. In April he filed an amended com-
plaint with the correct names of the clinic operators: Renal
Life Link, Inc., and Davita, Inc. As a prerequisite for his
malpractice claims, Harris attached a certificate of merit
prepared by a medical expert pursuant to Illinois law. See
735 ILL. COMP. STAT. 5/2-622. The certificate stated that the
clinic operators deviated from acceptable standards of care
by failing to properly sanitize the facility, causing Harris’s
injuries.
    Harris’s amended complaint also added a negligence
claim against Durham Enterprises and its owner, Don
Durham. (We refer to them collectively as “Durham.”) More


2 The investigators determined that Durham improperly used vinegar as

its primary cleaning agent, used dirty mop heads to clean the floors,
failed to clean all touchable surfaces, and failed to disinfect the cleaning
cart upon entry and exit from the facility.
No. 22-1983                                                               5

specifically, Count Three of the amended complaint alleged
that the janitorial company “negligently and carelessly failed
to properly clean and sanitize said dialysis center.”
   Durham was insured during the relevant period under a
commercial general liability policy issued by Ohio Security.3
Durham sought a defense and indemnification from the
insurer, submitting the amended complaint, the certificate of
merit, and an affidavit from Harris’s counsel.
   Ohio Security promptly reviewed the materials Durham
submitted and the language of the operative insurance
policy. Relevant here is the policy’s “Fungi or Bacteria
Exclusion,” which excludes coverage for
        “Bodily Injury” … which would not have oc-
        curred, in whole or in part, but for the actual,
        alleged or threatened inhalation of, ingestion
        of, contact with, exposure to, existence of, or
        presence of, any “fungi” or bacteria on or with-
        in a building or structure, including its con-
        tents, regardless of whether any other cause,
        event, material or product contributed concur-
        rently or in any sequence to such injury or
        damage.




3 Durham also carried excess insurance under an umbrella policy issued

by Ohio Casualty Insurance Company, Ohio Security’s parent. Ohio
Casualty intervened in the district court to protect its potential exposure
under the umbrella policy. The two policies are materially identical, so
for simplicity we treat the policies as one and refer to the two insurers as
“Ohio Security.”
6                                                  No. 22-1983

But there is an exception: “This exclusion does not apply to
any ‘fungi’ or bacteria that are, are on, or are contained in, a
good or product intended for bodily consumption.”
    By letter dated May 15, 2017, Ohio Security denied cov-
erage based on the bacteria exclusion. Emily Anderson, the
claims adjuster who processed the claim, made the determi-
nation based on the materials Durham had provided; she
did not seek any additional information. She did, however,
invite Don Durham to submit further information if he
wished. She also asked him to forward any amended plead-
ings in the Harris litigation. Durham did not respond to the
invitation to submit further information. The May 15 letter
denying coverage was the last communication between
Durham and its insurer for quite some time.
    Harris’s case in state court moved forward very slowly.
At some point along the way, Harris and Durham reached
an agreement whereby Durham promised not to mount a
defense and Harris promised to seek recovery only from
Durham’s insurer. Durham did not notify Ohio Security of
this agreement.
    On March 18, 2019—nearly two years after initiating the
state-court litigation—Harris filed an uncontested motion to
sever his claim against Durham into a separate action. The
state trial judge granted the motion and assigned a new case
number, and Harris filed a new complaint under the second
case number naming only Don Durham and Durham Enter-
prises as defendants. On May 15 Harris moved for a trial to
the bench. That motion was granted, and the case against
Durham was set for a bench trial on July 30.
No. 22-1983                                                               7

    On July 18, 2019—12 days before the scheduled bench
trial—Harris and Durham formalized their agreement in a
written “Covenant Not to Execute and Limit Recovery.”
Under Missouri law, which governs this insurance dispute,
Durham had a statutory duty to notify Ohio Security of the
agreement within 30 days. MO. REV. STAT. § 537.065(2)
(2021). 4 It did not do so.
    At the start of trial on July 30, the parties told the judge
about their agreement—specifically, that Durham had
agreed not to mount a defense in exchange for Harris’s
agreement to seek recovery of any judgment only from the
insurer. The judge then held a brief, uncontested bench trial,
and on October 9 adopted Harris’s uncontested findings of
fact and conclusions of law verbatim and entered judgment
against Durham for a little over $2 million. The judgment
included findings adverse to Durham’s insurer even though
Ohio Security was not a party to the lawsuit and the insur-
ance policy was not in the record. Specifically, the judge

4 Missouri law permits agreements of this type but requires the insured

to notify the insurer within 30 days:
        If any action seeking a judgment on the claim against the
        tort-feasor is pending at the time of the execution of any
        contract entered into under this section, then, within
        thirty days after such execution, the tort-feasor shall
        provide his or her insurer or insurers with a copy of the
        executed contract and a copy of any such action.
MO. REV. STAT. § 537.065(2) (2021). The insurer is entitled to intervene in
the underlying suit within 30 days of receiving notice. See id. § 537.065(4)
(“Any insurer or insurers who receive notice pursuant to this section
shall have the unconditional right to intervene in any pending civil
action involving the claim for damages within thirty days after receipt of
such notice.”).
8                                                 No. 22-1983

found that (1) Durham’s insurer had a duty to defend the
lawsuit; (2) it was too late for the insurer to seek a declara-
tion to the contrary; (3) the insurer had breached its duty to
defend; and (4) the insurer was estopped from raising policy
defenses to coverage.
    On December 7—after the judgment became final and the
30-day time to appeal had expired, see ILL. SUP. CT. R. 303—
Harris filed an amended complaint adding Ohio Security as
a defendant and seeking satisfaction of the judgment from it
as Durham’s insurer. Before this development, the insurer
had not heard from Durham since the May 2017 letter
denying coverage. Ohio Security removed the case to federal
court based on diversity of citizenship and sought a declara-
tion concerning its coverage obligations. Harris and
Durham, aligned in interest, both moved to remand, but the
district judge denied the motion.
    The case proceeded to cross-motions for summary judg-
ment on Ohio Security’s duty to defend. The judge held that
the bacteria exclusion bars coverage, the “bodily consump-
tion” exception is inapplicable, and Ohio Security therefore
owed no duty to defend Durham in the Harris lawsuit. That
ruling appeared to resolve all other insurance issues in Ohio
Security’s favor—i.e., questions of indemnification, breach of
contract, and bad-faith denial of coverage—so the judge
issued an order to show cause why final judgment should
not be entered for the insurer.
   In response Harris argued for the first time that the court
lacked subject-matter jurisdiction under the Rooker–Feldman
doctrine. Durham’s response simply reargued the judge’s
duty-to-defend ruling. Ohio Security argued that final
No. 22-1983                                                9

judgment in its favor followed necessarily from the judge’s
conclusion that it had no duty to defend.
   The judge agreed with Ohio Security. He explained that
because the duty to defend is broader than the duty to
indemnify, his ruling on the duty to defend necessarily
resolved all remaining insurance issues in the insurer’s
favor. Without addressing Harris’s Rooker–Feldman argu-
ment, the judge entered final judgment for Ohio Security.
   Harris died shortly after judgment was entered. His at-
torney joined with Durham’s counsel to file a timely notice
of appeal. But the notice erroneously listed Harris as the
plaintiff-appellant. In compliance with Rule 43(a) of the
Federal Rules of Appellate Procedure, Harris’s counsel later
moved to substitute Shemika D. Mitchell, the executor of
Harris’s estate, as the plaintiff-appellant. We granted the
motion.
                       I. Discussion
    As we’ve just noted, Harris’s estate and Durham filed a
joint appeal. But Harris’s estate alone has shouldered the
burden of developing an appellate challenge to the district
court’s judgment. That’s not surprising. With its immunity
from collection secure, Durham was content to let the estate
fight the battle over insurance coverage, so it summarily
adopted the estate’s appellate arguments and called it a day.
   We focus then on the issues the estate raises on appeal.
There are two. The estate argues that the Rooker–Feldman
doctrine bars subject-matter jurisdiction and that the judge
wrongly concluded that Ohio Security had no duty to de-
fend Durham in the state-court lawsuit. Ohio Security
responds that the Rooker–Feldman argument is frivolous; on
10                                                 No. 22-1983

this issue it filed a separate motion for sanctions under
Rule 38 of the Federal Rules of Appellate Procedure. The
insurer also defends the judge’s no-coverage ruling on the
merits.
    We begin, as we must, with the jurisdictional argument.
But we can be brief. Rooker–Feldman does not apply here. The
doctrine “is confined to cases of the kind from which the
doctrine acquired its name: cases brought by state-court
losers complaining of injuries caused by state-court judg-
ments rendered before the district court proceedings com-
menced and inviting district court review and rejection of
those judgments.” Exxon Mobil Corp. v. Saudi Basic Indus.
Corp., 

 (2005) (explaining the limits of the
jurisdictional rule established in Rooker v. Fidelity Trust Co.,

 (1923), and District of Columbia Court of Appeals
v. Feldman, 

 (1983)). The Rooker–Feldman rule
enforces the line between original and appellate jurisdiction
in the federal judicial system. The Supreme Court has appel-
late jurisdiction to review and modify or reverse a state-
court judgment; the lower federal courts do not. 

 at 291–
92.
    In keeping with the doctrine’s rationale and narrow ap-
plication, the Supreme Court has held that Rooker–Feldman
does not apply “where the party against whom the doctrine
is invoked was not a party to the underlying state-court
proceeding.” Lance, 

. A federal litigant who
was absent from the underlying litigation and judgment in
state court is “in no position to ask [the Supreme Court] to
review the state court’s judgment” but instead is “merely
seek[ing] to litigate its … case for the first time” in federal
court. De Grandy, 

.
No. 22-1983                                                   11

    Because Ohio Security was not a party to the Harris liti-
gation in state court and is not a party to the state-court
judgment against Durham, Rooker–Feldman cannot be in-
voked against it. The estate rests its jurisdictional argument
on a footnote in Lance in which the Court declined to address
“whether there are any circumstances, however limited, in
which Rooker–Feldman may be applied against a party not
named in an earlier state proceeding.” Lance, 

n.2. The Court gave an example of a limited circumstance
that might qualify: “e.g., where an estate takes a de facto
appeal in a district court of an earlier state decision involv-
ing the decedent.” 

    The Court’s example makes sense considering the logic of
the doctrine: a decedent’s estate simply steps into the dece-
dent’s shoes and like the decedent cannot seek de facto
appellate review of a state-court judgment in district court.
But this example doesn’t remotely fit the procedural facts of
this case. Ohio Security is not stepping into the shoes of a
state-court litigant. The estate’s Rooker–Feldman argument is
clearly foreclosed by Lance and De Grandy. Subject-matter
jurisdiction is secure.
    Turning to the merits, the estate challenges the judge’s
determination that Ohio Security had no duty to defend
Durham in the state litigation. That ruling turned on the
insurance policy’s bacteria exclusion and the exclusion’s
“bodily consumption” exception. We review de novo the
judge’s interpretation and application of the Ohio Security
insurance policy. Panfil v. Nautilus Ins. Co., 

, 718–
19 (7th Cir. 2015). Everyone agrees that Missouri law governs
this insurance-coverage dispute.
12                                                 No. 22-1983

    When sitting in diversity, we are bound by controlling
decisions of the state’s highest court, and when the state’s
highest court has not yet addressed an issue, we must pre-
dict how it would rule. Smith v. RecordQuest, LLC, 

, 517–18 (7th Cir. 2021). We also “consult and follow the
decisions of intermediate appellate courts unless there is a
convincing reason to predict the state’s highest court would
disagree.” 

 (quotation marks omitted). “So while a
state supreme court’s rule would control, a state appellate
court’s decision can provide controlling guidance as well.”

 at 517–18.
    In Missouri (as elsewhere), an insurer’s duty to defend
arises “when there is a possibility or potential for coverage at
the outset of the case.” Allen v. Bryers, 

 (Mo.
2016). “The obligation … to defend a suit … is to be deter-
mined from the cause of action pleaded, at the time the
action is commenced, not from what an investigation or a
trial of the case may show the true facts to be.” Trainwreck W.
Inc. v. Burlington Ins. Co., 

 (Mo. Ct. App.
2007) (emphasis removed) (quotation marks omitted).
   The insurer’s duty to defend is determined by comparing
the facts alleged against the insured in the complaint with
the text of the insurance policy. If the complaint alleges facts
that potentially give rise to a claim within the policy’s cover-
age, the insurer has a duty to defend the insured. Allen,

. An insurer’s assessment of its duty to
defend should also consider facts that it either knows or “are
reasonably apparent [to it] at the outset of the case.” 

(quotation marks omitted).
    The insurer may also have a duty to defend based on
facts that are reasonably ascertainable at the outset of a case,
No. 22-1983                                                   13

even if they were not actually ascertained. “[I]f, at the time
the claim is made, facts … could reasonably be ascertained
by the insurer that would potentially put the claim within
the scope of the policy, the insurer must defend the insured.”

 (quoting Fostill Lake Builders, LLC v. Tudor Ins. Co.,

 (Mo. Ct. App. 2011)). When an insured
claims that facts establishing coverage were ascertainable by
the insurer through reasonable investigation, the insured
must point to evidence of what the insurer would have
found through reasonable investigation that would have
brought the claim within the policy’s coverage. Interstate
Bakeries Corp. v. OneBeacon Ins. Co., 

 (8th Cir.
2012) (applying Missouri law).
    The standard for determining an insurer’s duty to defend
is undeniably generous to the insured—the duty arises when
there is a “possibility” or “potential” for coverage based on
the facts alleged in the complaint or reasonably apparent to
the insurer when the case begins. But duty to defend is not
“boundless.” 

 The scope of the duty is limited by the
language of policy, which expresses the intent of the con-
tracting parties. 

 The insurer has the burden to establish
that it owes no duty to defend. 

; see also Allen,

.
    This case turns on the bacteria exclusion in the Ohio
Security policy, which excludes from coverage any injury
“which would not have occurred … but for … exposure
to … any … bacteria on or within a building or structure,
including its contents.” The amended complaint in the state-
court suit alleged that Harris “suffered numerous infections”
in part because Durham “negligently and carelessly failed to
properly clean and sanitize [the] dialysis center.” The com-
14                                                 No. 22-1983

plaint itself contains no specifics about what type of infec-
tions Harris suffered, but the certificate of merit accompany-
ing the complaint added the relevant details. The certificate
states that Harris was placed “at significantly increased risk
of bacterial sepsis and, in fact, [Harris] was diagnosed with
both gram positive and gram negative sepsis”; both are
types of bacterial infection. Accordingly, based on the allega-
tions in the amended complaint and the details in the at-
tached certificate of merit, the bacteria exclusion plainly
applies.
     The estate resists this conclusion, arguing that it’s inap-
propriate to consider the certificate of merit to determine the
duty to defend. Citing Garrison v. Choh, 

 (Ill. App. Ct. 1999), the estate emphasizes that a certifi-
cate of merit, though required for a malpractice claim in
Illinois, is not considered a formal part of the complaint.
That’s irrelevant in this context. The certificate of merit was
attached to the amended complaint and provided facts
known to the insurer at the outset of the case; it’s not off-
limits in the duty-to-defend calculus. See Allen, 

.
    The estate next takes issue with the insurer’s lack of in-
vestigation, criticizing the claims adjuster for denying
coverage without first seeking medical records or other
information related to the claim. This line of argument
requires the estate to identify facts that would have given
rise to a duty to defend and to support its argument with
evidence that would have been found by the insurer through
reasonable investigation. See Interstate Bakeries, 

. The estate has not identified any such facts, let alone
provided evidence to back up this argument.
No. 22-1983                                                   15

    Finally, the estate contends that this case falls within the
bacteria exclusion’s “bodily consumption” exception. To
repeat, the exception provides that the exclusion “does not
apply to any … bacteria that are, are on, or are contained in,
a good or product intended for bodily consumption.” The
estate bears the burden of showing that the exception ap-
plies. See Trans World Airlines, Inc. v. Associated Aviation
Underwriters, 

 (Mo. Ct. App. 2001).
    We note first that although Harris and Durham both
made passing references to the bodily-consumption excep-
tion in their responses to Ohio Security’s summary-judgment
motion, neither of them developed an argument about its
application. Ohio Security justifiably raises waiver. Ross v.
Fin. Asset Mgmt. Sys., Inc., 

 (7th Cir. 2023)
(“When a party fails to develop an argument in the district
court, the argument is waived, and we cannot consider it on
appeal.” (quoting Frey Corp. v. City of Peoria, 

(7th Cir. 2013))).
    Even if we were inclined to overlook the failure to ade-
quately preserve this issue, the estate made only minimal
effort in its appellate brief to explain the basis for its claim
that the bodily-consumption exception applies. The estate
never identified a “good or product intended for bodily
consumption” that might have caused Harris’s injuries.
Instead, it returned to its refrain that the claims adjuster did
not adequately investigate the applicability of the bacteria
exclusion but again did not explain why the bodily-
consumption exception might have applied or how a rea-
sonable investigation would have made that apparent.
   At oral argument the estate suggested for the first time
that the dialysis machines caused Harris’s infections and
16                                                  No. 22-1983

could be considered a good or product “intended for bodily
consumption” within the meaning of the exception. Argu-
ments first raised at oral argument are waived. Wonsey v.
City of Chicago, 

, 398–99 (7th Cir. 2019). Waiver
aside, to the extent that this new and undeveloped theory
posits that Durham was responsible for cleaning the dialysis
machines, it conflicts with Harris’s allegations in the state-
court suit. The amended complaint alleged that the clinic
operators failed to (1) “timely change the diasafe filters”;
(2) “properly maintain the premises to minimize risk of
infection to patients”; and (3) “properly maintain dialysis
machines and equipment to minimize the risk of infection in
patients.” Durham, on the other hand, was accused of failing
to properly clean and sanitize the dialysis facility. Ohio
Security was not required to imagine a wholly different and
contradictory set of allegations when evaluating its duty to
defend. Interstate Bakeries, 

 (declining to find a
duty to defend when the insured’s argument required “an
unacceptable degree of imagination”).
    In sum, the policy’s bacteria exclusion precluded cover-
age for this loss. We agree with the district judge that Ohio
Security had no duty to defend Durham in the Harris litiga-
tion.
    There is one final matter. As we’ve noted, Ohio Security
moved for Rule 38 sanctions limited to its costs to defend the
Rooker–Feldman argument, which it characterizes as frivo-
lous. An appeal is frivolous (in whole or in part) “when the
result is obvious or when the appellant’s argument is wholly
without merit.” Harris N.A. v. Hershey, 

 (7th
Cir. 2013) (quotation marks omitted). The Rooker–Feldman
argument was clearly foreclosed by the Supreme Court’s
No. 22-1983                                                17

decisions in Lance and De Grandy. The estate’s argument to
the contrary was paper thin. And neither the estate nor
Durham bothered to file a response to the Rule 38 motion or
even a reply brief.
    Still, we conclude that sanctions are unwarranted here.
“Frivolous” is not synonymous with merely “unsuccessful
or unlikely to succeed.” Dolin v. GlaxoSmithKline LLC,

 (7th Cir. 2020) (internal quotation marks
omitted). And even if an appeal is frivolous, “Rule 38 sanc-
tions are not mandatory but are left to the sound discretion
of the court of appeals.” Harris N.A., 

. We
decline to award sanctions on this discrete issue. The Rule 38
motion is denied.
                          AFFIRMED; RULE 38 MOTION DENIED.