diff --git a/changelog.d/3251-app-test-html-report.fixed.md b/changelog.d/3251-app-test-html-report.fixed.md
new file mode 100644
index 000000000..8670ad022
--- /dev/null
+++ b/changelog.d/3251-app-test-html-report.fixed.md
@@ -0,0 +1,2 @@
+- `/wheels/app/tests` now renders the TestBox-style HTML report in a browser for apps that use the built-in fallback test runner, matching `/wheels/core/tests`. The endpoint previously returned raw JSON for the no-format default and `?format=html`; `?format=json`, `?format=txt`, and `?format=junit` are unchanged, and an unrecognized `?format=` value still returns no body as before (#3251).
+- Fixed an Adobe ColdFusion `Routines cannot be declared more than once` HTTP 500 in the shared test-report template (`vendor/wheels/tests/html.cfm`) that broke the `format=html` report for both the app and core test runners on repeated requests. The recursive helper is now declared as a variables-scoped function expression, matching the core runner's existing convention (#3251).
diff --git a/vendor/wheels/tests/_assets/dispatch/TestFormatResolver.cfc b/vendor/wheels/tests/_assets/dispatch/TestFormatResolver.cfc
new file mode 100644
index 000000000..4bc3f7dfc
--- /dev/null
+++ b/vendor/wheels/tests/_assets/dispatch/TestFormatResolver.cfc
@@ -0,0 +1,87 @@
+/**
+ * Helper extracted from app-runner.cfm so the output-format rule is
+ * unit-testable without spinning up an HTTP request. app-runner.cfm reads
+ * url.format, hands it to this resolver, and uses the returned reporter /
+ * contentType / rendersHtml / recognized fields to drive the response.
+ *
+ * Issue #3251 (item 1): the html / no-format branch historically emitted
+ * application/json for the app runner — a user opening
+ * `/wheels/app/tests?format=html` (or hitting the no-format default) in a
+ * browser got raw JSON instead of the TestBox-style HTML report the core
+ * runner (`/wheels/core/tests`) renders. resolveFormat() marks that branch
+ * rendersHtml=true so the app runner falls through to html.cfm with
+ * type="App" — a branch html.cfm already supports — exactly like the core
+ * runner falls through with type="Core".
+ *
+ * Recognized formats (case-insensitive, trimmed): html | json | txt | junit,
+ * plus the no-format default (no `format` key) which is treated as html. Any
+ * other value — an empty string or an arbitrary token like "xml" — resolves
+ * to recognized=false. The app runner emits nothing for an unrecognized
+ * format, preserving the historical behavior: html.cfm must NOT be rendered
+ * for an arbitrary url.format. Its dev-tools navigation
+ * (vendor/wheels/tests/_navigation.cfm) builds format-toggle links from
+ * url.format and the framework's response content-negotiation throws a 500
+ * on Adobe when the format is unknown.
+ */
+component {
+
+	variables.REPORTER_PACKAGE = "wheels.wheelstest.system.reports";
+
+	public struct function resolveFormat(required struct url) {
+		var htmlChoice = {
+			format: "html",
+			reporter: variables.REPORTER_PACKAGE & ".JSONReporter",
+			contentType: "text/html",
+			rendersHtml: true,
+			recognized: true
+		};
+
+		// No format key at all is the no-format default → HTML report.
+		if (!StructKeyExists(arguments.url, "format")) {
+			return htmlChoice;
+		}
+
+		var format = LCase(Trim(arguments.url.format));
+
+		switch (format) {
+			case "html":
+				return htmlChoice;
+			case "json":
+				return {
+					format: "json",
+					reporter: variables.REPORTER_PACKAGE & ".JSONReporter",
+					contentType: "application/json",
+					rendersHtml: false,
+					recognized: true
+				};
+			case "txt":
+				return {
+					format: "txt",
+					reporter: variables.REPORTER_PACKAGE & ".TextReporter",
+					contentType: "text/plain",
+					rendersHtml: false,
+					recognized: true
+				};
+			case "junit":
+				return {
+					format: "junit",
+					reporter: variables.REPORTER_PACKAGE & ".ANTJUnitReporter",
+					contentType: "text/xml",
+					rendersHtml: false,
+					recognized: true
+				};
+			default:
+				// Empty value or unrecognized token: not a known format. The app
+				// runner emits nothing, matching the historical behavior and
+				// avoiding an html.cfm render for an arbitrary url.format.
+				return {
+					format: format,
+					reporter: "",
+					contentType: "",
+					rendersHtml: false,
+					recognized: false
+				};
+		}
+	}
+
+}
diff --git a/vendor/wheels/tests/app-runner.cfm b/vendor/wheels/tests/app-runner.cfm
index 5cba3d6d5..5f0166563 100644
--- a/vendor/wheels/tests/app-runner.cfm
+++ b/vendor/wheels/tests/app-runner.cfm
@@ -114,48 +114,55 @@
             bundlesDiscovered = local.bundlesDiscovered
         );
 
-        if (!StructKeyExists(url, "format") || url.format == "html") {
-            result = testBox.run(reporter = "wheels.wheelstest.system.reports.JSONReporter");
-            decoded = DeserializeJSON(result);
-            cfheader(statuscode = (decoded.totalFail > 0 || decoded.totalError > 0) ? 417 : 200);
-            // For the html case the framework runner falls through to html.cfm;
-            // for the app-runner we just emit the JSON in this branch too since
-            // app tests are typically requested over JSON (CLI/CI). Users hitting
-            // the URL in a browser still get a structured response they can read.
-            cfcontent(type="application/json");
-            writeOutput(local.dirResolver.injectScopeMetadata(
-                resultJson = result,
-                scope = local.testScope,
-                bundlesDiscovered = local.bundlesDiscovered,
-                warnings = local.scopeWarnings
-            ));
-        } else if (url.format == "json") {
-            result = testBox.run(reporter = "wheels.wheelstest.system.reports.JSONReporter");
-            decoded = DeserializeJSON(result);
-            if (decoded.totalFail > 0 || decoded.totalError > 0) {
-                if (!StructKeyExists(url, "cli") || !url.cli) {
-                    cfheader(statuscode = 417);
+        // Resolve the output format (reporter + content type + whether to
+        // render an HTML report) through TestFormatResolver so the rule is
+        // unit-testable without an HTTP request (see AppRunnerTestFormatSpec,
+        // issue #3251). An unrecognized format resolves to recognized=false:
+        // the runner emits nothing, preserving the historical behavior.
+        local.fmtResolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+        local.output = local.fmtResolver.resolveFormat(url);
+
+        if (local.output.recognized) {
+            result = testBox.run(reporter = local.output.reporter);
+
+            if (local.output.rendersHtml) {
+                // Render the TestBox-style HTML report for the html / no-format
+                // default, mirroring the core runner (vendor/wheels/tests/runner.cfm).
+                // html.cfm has a type="App" branch (package=tests.specs,
+                // route=testbox) built for exactly this. Previously this branch
+                // emitted raw JSON, so a user opening /wheels/app/tests?format=html
+                // in a browser got JSON instead of the report (issue #3251 item 1).
+                decoded = DeserializeJSON(result);
+                cfheader(statuscode = (decoded.totalFail > 0 || decoded.totalError > 0) ? 417 : 200);
+                type = "App";
+                include "html.cfm";
+            } else if (local.output.format == "json") {
+                decoded = DeserializeJSON(result);
+                if (decoded.totalFail > 0 || decoded.totalError > 0) {
+                    if (!StructKeyExists(url, "cli") || !url.cli) {
+                        cfheader(statuscode = 417);
+                    }
+                } else {
+                    cfheader(statuscode = 200);
                 }
+                cfcontent(type = local.output.contentType);
+                cfheader(name="Access-Control-Allow-Origin", value="*");
+                writeOutput(local.dirResolver.injectScopeMetadata(
+                    resultJson = result,
+                    scope = local.testScope,
+                    bundlesDiscovered = local.bundlesDiscovered,
+                    warnings = local.scopeWarnings
+                ));
             } else {
-                cfheader(statuscode = 200);
+                // txt / junit: emit the reporter output verbatim under the
+                // resolved content type.
+                cfcontent(type = local.output.contentType);
+                writeOutput(result);
             }
-            cfcontent(type="application/json");
-            cfheader(name="Access-Control-Allow-Origin", value="*");
-            writeOutput(local.dirResolver.injectScopeMetadata(
-                resultJson = result,
-                scope = local.testScope,
-                bundlesDiscovered = local.bundlesDiscovered,
-                warnings = local.scopeWarnings
-            ));
-        } else if (url.format == "txt") {
-            result = testBox.run(reporter = "wheels.wheelstest.system.reports.TextReporter");
-            cfcontent(type = "text/plain");
-            writeOutput(result);
-        } else if (url.format == "junit") {
-            result = testBox.run(reporter = "wheels.wheelstest.system.reports.ANTJUnitReporter");
-            cfcontent(type = "text/xml");
-            writeOutput(result);
         }
+        // Unrecognized format (empty value / unknown token): no output, and
+        // testBox is not run — html.cfm must not be rendered for an arbitrary
+        // url.format (it 500s on Adobe). Mirrors the pre-fix fall-through.
     } finally {
         // Restore the original datasource (via applyDataSource() so test-run cached model classes are invalidated).
         if (local.swappedDataSource) {
diff --git a/vendor/wheels/tests/html.cfm b/vendor/wheels/tests/html.cfm
index 9a89842e5..c38c2963f 100644
--- a/vendor/wheels/tests/html.cfm
+++ b/vendor/wheels/tests/html.cfm
@@ -34,12 +34,18 @@
     
     testResults.ok = (testResults.numFailures + testResults.numErrors) == 0;
     
-    // Recursive function to process nested suites
-    function processNestedSuites(suites, bundleName) {
+    // Recursive function to process nested suites. Declared as a variables-scoped
+    // function expression (not a named `function` declaration) so repeated
+    // includes of this template into the cached Public.cfc do not throw Adobe's
+    // "Routines cannot be declared more than once" — the same reason the core
+    // runner declares its helpers as closures (vendor/wheels/tests/runner.cfm).
+    // A named declaration in an included .cfm leaks into the component scope on
+    // Adobe and collides on the second request. See issue #3251.
+    variables.processNestedSuites = function(suites, bundleName) {
         for (suite in suites) {
             // Process nested suites first (deeper level)
             if (structKeyExists(suite, "suiteStats") && arrayLen(suite.suiteStats) > 0) {
-                processNestedSuites(suite.suiteStats, bundleName);
+                variables.processNestedSuites(suite.suiteStats, bundleName);
             }
             
             // Process individual specs in this suite
@@ -108,10 +114,10 @@
                 arrayAppend(testResults.results, thisResult);
             }
         }
-    }
+    };
 
     for (bundle in DeJsonResult.bundleStats) {
-        processNestedSuites(bundle.suiteStats, bundle.name);
+        variables.processNestedSuites(bundle.suiteStats, bundle.name);
     }
     
     failures = [];
diff --git a/vendor/wheels/tests/specs/dispatch/AppRunnerTestFormatSpec.cfc b/vendor/wheels/tests/specs/dispatch/AppRunnerTestFormatSpec.cfc
new file mode 100644
index 000000000..78faa5e56
--- /dev/null
+++ b/vendor/wheels/tests/specs/dispatch/AppRunnerTestFormatSpec.cfc
@@ -0,0 +1,113 @@
+component extends="wheels.WheelsTest" {
+
+	function run() {
+
+		describe("app-runner output format resolution (issue 3251)", () => {
+
+			// Issue #3251 (item 1): `/wheels/app/tests?format=html` — which is
+			// also the no-format default — historically emitted application/json.
+			// A user opening that URL in a browser reasonably expects the
+			// TestBox-style HTML report the core runner (`/wheels/core/tests`)
+			// renders. resolveFormat() centralizes the format-to-output decision
+			// so the html / no-format branch can be marked rendersHtml=true; the
+			// app runner then falls through to html.cfm (type="App", a branch
+			// html.cfm already supports) exactly like the core runner does.
+			//
+			// Recognized formats are html | json | txt | junit (plus the
+			// no-format default). An UNrecognized value (an empty string or an
+			// arbitrary token like "xml") resolves to recognized=false: the app
+			// runner emits nothing for it, preserving the historical behavior.
+			// html.cfm must NOT be rendered for an arbitrary url.format — its
+			// dev-tools navigation builds format-toggle links from url.format and
+			// the framework's response content-negotiation 500s on Adobe when the
+			// format is unknown.
+
+			it("renders HTML when url has no format key (the no-format default)", () => {
+				var resolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+				var resolved = resolver.resolveFormat(url = {});
+				expect(resolved.recognized).toBeTrue();
+				expect(resolved.rendersHtml).toBeTrue();
+				expect(resolved.format).toBe("html");
+				expect(resolved.contentType).toBe("text/html");
+			});
+
+			it("renders HTML for format=html", () => {
+				var resolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+				var resolved = resolver.resolveFormat(url = { format: "html" });
+				expect(resolved.recognized).toBeTrue();
+				expect(resolved.rendersHtml).toBeTrue();
+				expect(resolved.contentType).toBe("text/html");
+			});
+
+			it("uses the JSON reporter for the HTML branch (html.cfm needs the JSON payload to render)", () => {
+				var resolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+				expect(resolver.resolveFormat(url = { format: "html" }).reporter)
+					.toBe("wheels.wheelstest.system.reports.JSONReporter");
+			});
+
+			it("emits JSON (not HTML) for format=json", () => {
+				var resolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+				var resolved = resolver.resolveFormat(url = { format: "json" });
+				expect(resolved.recognized).toBeTrue();
+				expect(resolved.rendersHtml).toBeFalse();
+				expect(resolved.format).toBe("json");
+				expect(resolved.contentType).toBe("application/json");
+				expect(resolved.reporter).toBe("wheels.wheelstest.system.reports.JSONReporter");
+			});
+
+			it("emits text/plain for format=txt via the Text reporter", () => {
+				var resolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+				var resolved = resolver.resolveFormat(url = { format: "txt" });
+				expect(resolved.recognized).toBeTrue();
+				expect(resolved.rendersHtml).toBeFalse();
+				expect(resolved.format).toBe("txt");
+				expect(resolved.contentType).toBe("text/plain");
+				expect(resolved.reporter).toBe("wheels.wheelstest.system.reports.TextReporter");
+			});
+
+			it("emits text/xml for format=junit via the ANTJUnit reporter", () => {
+				var resolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+				var resolved = resolver.resolveFormat(url = { format: "junit" });
+				expect(resolved.recognized).toBeTrue();
+				expect(resolved.rendersHtml).toBeFalse();
+				expect(resolved.format).toBe("junit");
+				expect(resolved.contentType).toBe("text/xml");
+				expect(resolved.reporter).toBe("wheels.wheelstest.system.reports.ANTJUnitReporter");
+			});
+
+			it("matches the format token case-insensitively", () => {
+				var resolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+				expect(resolver.resolveFormat(url = { format: "JSON" }).format).toBe("json");
+				expect(resolver.resolveFormat(url = { format: "Txt" }).format).toBe("txt");
+				expect(resolver.resolveFormat(url = { format: "HTML" }).rendersHtml).toBeTrue();
+			});
+
+			it("trims surrounding whitespace before matching", () => {
+				var resolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+				expect(resolver.resolveFormat(url = { format: "  junit  " }).format).toBe("junit");
+			});
+
+			it("does NOT render HTML for an empty format value (preserves the historical no-output behavior)", () => {
+				var resolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+				var resolved = resolver.resolveFormat(url = { format: "" });
+				expect(resolved.recognized).toBeFalse();
+				expect(resolved.rendersHtml).toBeFalse();
+			});
+
+			it("does NOT render HTML for an unrecognized format token (avoids the Adobe html.cfm 500)", () => {
+				// Rendering html.cfm for an arbitrary url.format 500s on Adobe
+				// (the dev-tools nav reads url.format and response negotiation
+				// chokes on the unknown format). An unrecognized token must
+				// resolve to recognized=false so the app runner emits nothing,
+				// exactly as it did before this fix.
+				var resolver = new wheels.tests._assets.dispatch.TestFormatResolver();
+				var resolved = resolver.resolveFormat(url = { format: "xml" });
+				expect(resolved.recognized).toBeFalse();
+				expect(resolved.rendersHtml).toBeFalse();
+			});
+
+		});
+
+	}
+
+}
diff --git a/vendor/wheels/tests/specs/dispatch/HtmlReportFunctionDeclarationGuardSpec.cfc b/vendor/wheels/tests/specs/dispatch/HtmlReportFunctionDeclarationGuardSpec.cfc
new file mode 100644
index 000000000..98bd3281e
--- /dev/null
+++ b/vendor/wheels/tests/specs/dispatch/HtmlReportFunctionDeclarationGuardSpec.cfc
@@ -0,0 +1,80 @@
+/**
+ * Structural cross-engine guard for issue #3251 (item 1).
+ *
+ * vendor/wheels/tests/html.cfm renders the TestBox HTML report and is included
+ * into the cached Public.cfc singleton by both the core runner
+ * (vendor/wheels/tests/runner.cfm) and the app runner
+ * (vendor/wheels/tests/app-runner.cfm). On Adobe ColdFusion a *named* function
+ * declaration in an included .cfm leaks into the component scope, so the second
+ * request that includes the template throws "Routines cannot be declared more
+ * than once" — a hard HTTP 500. html.cfm originally declared
+ * `function processNestedSuites()`, which 500'd `/wheels/core/tests?format=html`
+ * and `/wheels/app/tests?format=html` on every Adobe engine.
+ *
+ * The fix declares the helper as a variables-scoped function EXPRESSION
+ * (`variables.processNestedSuites = function(){...}`), the same pattern the core
+ * runner already uses for its helpers to dodge Adobe's
+ * DuplicateFunctionDefinitionException. CI exercises the runners with
+ * `format=json`, never the `format=html` render path, so a regression here is
+ * invisible to the normal suite — hence this source-level guard.
+ *
+ * Scan rules (Anti-Pattern 14 spirit, line-anchored on purpose):
+ * - Only html.cfm is scanned (a .cfm view included into a component).
+ * - A named declaration matches `function <name>(`; a function EXPRESSION
+ *   (`= function(`) and the JS IIFE in the inline <script> (`(function () {`)
+ *   have no identifier after the `function` keyword and never match.
+ * - Comment-only lines are skipped via trimmed-prefix checks. Deliberately NOT
+ *   a global non-greedy comment-strip regex over the whole file — that shape
+ *   hangs Lucee 7 on large sources.
+ */
+component extends="wheels.WheelsTest" {
+
+	function run() {
+
+		describe("Cross-engine guard: html.cfm declares no named functions (issue ##3251)", () => {
+
+			it("vendor/wheels/tests/html.cfm contains no bare named function declarations", () => {
+				var templatePath = ExpandPath("/wheels/tests/html.cfm");
+				expect(FileExists(templatePath)).toBeTrue(
+					"Expected vendor/wheels/tests/html.cfm to exist at #templatePath#."
+				);
+
+				// A named declaration: the `function` keyword as a whole word,
+				// then whitespace, then an identifier character (the name). A
+				// function expression assigns `... = function(` (no name) and the
+				// inline-<script> IIFE is `(function () {` (no name), so neither
+				// matches.
+				var pattern = "\bfunction\s+[a-zA-Z_]";
+
+				var content = FileRead(templatePath);
+				var fileLines = ListToArray(content, Chr(10), true);
+				var offenders = [];
+				var lineNumber = 0;
+				for (var rawLine in fileLines) {
+					lineNumber++;
+					var trimmed = Trim(Replace(rawLine, Chr(13), "", "all"));
+					// Skip comment-only lines (this template's own doc/// lines
+					// mention the word "function").
+					if (Left(trimmed, 2) == "//" || Left(trimmed, 1) == "*" || Left(trimmed, 2) == "/*") {
+						continue;
+					}
+					if (REFindNoCase(pattern, trimmed)) {
+						ArrayAppend(offenders, "line " & lineNumber & ": " & trimmed);
+					}
+				}
+
+				expect(ArrayLen(offenders)).toBe(
+					0,
+					"Found named function declaration(s) in html.cfm at: #ArrayToList(offenders, ' | ')#. "
+					& "A named function in an included .cfm leaks into the cached Public.cfc scope on Adobe "
+					& "and throws 'Routines cannot be declared more than once' on the second request, 500ing "
+					& "the format=html test report. Declare the helper as a variables-scoped function "
+					& "expression instead (variables.name = function(){...}). See issue ##3251."
+				);
+			});
+
+		});
+
+	}
+
+}