From 0defaeb00c4b7e4a1833ef4dd6f8d96ff60d355f Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 18 Mar 2026 18:28:15 +0000
Subject: [PATCH 1/3] Initial plan


From 06c55d143b5962a9a6e58e00decb6398deb60eed Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 18 Mar 2026 18:33:43 +0000
Subject: [PATCH 2/3] fix: preserve trailing slash in route joining when it
 would not result in double slash

Co-authored-by: timotheeguerin <1031227+timotheeguerin@users.noreply.github.com>
---
 packages/http/src/route.ts        | 15 +++++++++------
 packages/http/test/routes.test.ts | 19 +++++++++++++++++++
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/packages/http/src/route.ts b/packages/http/src/route.ts
index 6a49a332498..2360d77312c 100644
--- a/packages/http/src/route.ts
+++ b/packages/http/src/route.ts
@@ -36,22 +36,25 @@ function needsSlashPrefix(fragment: string) {
   );
 }
 
-function normalizeFragment(fragment: string, trimLast = false) {
+function normalizeFragment(fragment: string) {
   if (needsSlashPrefix(fragment)) {
     // Insert the default separator
     fragment = `/${fragment}`;
   }
 
-  if (trimLast && fragment[fragment.length - 1] === "/") {
-    return fragment.slice(0, -1);
-  }
   return fragment;
 }
 
 export function joinPathSegments(rest: string[]) {
   let current = "";
-  for (const [index, segment] of rest.entries()) {
-    current += normalizeFragment(segment, index < rest.length - 1);
+  for (const segment of rest) {
+    const normalized = normalizeFragment(segment);
+    // Merge trailing and leading slashes to avoid double slashes
+    if (current.endsWith("/") && normalized.startsWith("/")) {
+      current += normalized.slice(1);
+    } else {
+      current += normalized;
+    }
   }
   return current;
 }
diff --git a/packages/http/test/routes.test.ts b/packages/http/test/routes.test.ts
index bdb1e60ac5f..39cec8801f5 100644
--- a/packages/http/test/routes.test.ts
+++ b/packages/http/test/routes.test.ts
@@ -346,6 +346,25 @@ describe("http: routes", () => {
 
       deepStrictEqual(routes, [{ verb: "get", path: `/abc${sep}restype=container`, params: [] }]);
     });
+
+    it("keeps trailing / on parent route when joining with child route", async () => {
+      const routes = await getRoutesFor(
+        `
+      @route("{blobName}/")
+      interface Container {
+        @put @route("${sep}some-query=true") op foo(blobName: string): void;
+      }
+      `,
+      );
+
+      deepStrictEqual(routes, [
+        {
+          verb: "put",
+          path: `/{blobName}/${sep}some-query=true`,
+          params: ["blobName"],
+        },
+      ]);
+    });
   });
 
   describe("joinPathSegments", () => {

From 96d0848fb22bcd981e64a4d6a0c2d70d97a32fda Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 18 Mar 2026 18:34:13 +0000
Subject: [PATCH 3/3] chore: add changelog entry for trailing slash route fix

Co-authored-by: timotheeguerin <1031227+timotheeguerin@users.noreply.github.com>
---
 ...opilot-fix-regression-http-1-10-1-2026-2-18-18-33-49.md | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 .chronus/changes/copilot-fix-regression-http-1-10-1-2026-2-18-18-33-49.md

diff --git a/.chronus/changes/copilot-fix-regression-http-1-10-1-2026-2-18-18-33-49.md b/.chronus/changes/copilot-fix-regression-http-1-10-1-2026-2-18-18-33-49.md
new file mode 100644
index 00000000000..0d220f1033f
--- /dev/null
+++ b/.chronus/changes/copilot-fix-regression-http-1-10-1-2026-2-18-18-33-49.md
@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http"
+---
+
+Fix route joining to preserve trailing `/` when it would not result in `//`
\ No newline at end of file