diff --git a/actions/setup/js/checkout_pr_branch.cjs b/actions/setup/js/checkout_pr_branch.cjs
index f07f9c3b00..5f9b8ea3ef 100644
--- a/actions/setup/js/checkout_pr_branch.cjs
+++ b/actions/setup/js/checkout_pr_branch.cjs
@@ -30,6 +30,37 @@ const { renderTemplateFromFile } = require("./messages_core.cjs");
 const { detectForkPR } = require("./pr_helpers.cjs");
 const { ERR_API } = require("./error_codes.cjs");
 
+/**
+ * Build an environment for gh CLI commands that ensures GH_HOST matches the
+ * actual GITHUB_SERVER_URL, preventing "none of the git remotes correspond to
+ * GH_HOST" errors when GH_HOST is set to a different host in the environment.
+ *
+ * @returns {object} Environment object for exec options
+ */
+function buildGHExecEnv() {
+  const serverUrl = process.env.GITHUB_SERVER_URL || "https://github.com";
+  let serverHost = "github.com";
+  try {
+    serverHost = new URL(serverUrl).hostname;
+  } catch {
+    // GITHUB_SERVER_URL is malformed; fall back to github.com so gh can still run
+  }
+
+  const env = { ...process.env };
+  if (serverHost === "github.com") {
+    // Unset GH_HOST so gh uses github.com (the default).
+    // If GH_HOST is set to a different host, gh will error with:
+    // "none of the git remotes configured for this repository correspond
+    //  to the GH_HOST environment variable"
+    delete env.GH_HOST;
+  } else {
+    // Set GH_HOST to match the actual GitHub Enterprise server
+    env.GH_HOST = serverHost;
+  }
+
+  return env;
+}
+
 /**
  * Log detailed PR context information for debugging
  */
@@ -176,7 +207,7 @@ async function main() {
       }
 
       core.info(`Checking out PR #${prNumber} using gh CLI`);
-      await exec.exec("gh", ["pr", "checkout", prNumber.toString()]);
+      await exec.exec("gh", ["pr", "checkout", prNumber.toString()], { env: buildGHExecEnv() });
 
       // Log the resulting branch after checkout
       let currentBranch = "";
@@ -285,4 +316,4 @@ Pull request #${pullRequest.number} is closed. The checkout failed because the b
   }
 }
 
-module.exports = { main };
+module.exports = { main, buildGHExecEnv };
diff --git a/actions/setup/js/checkout_pr_branch.test.cjs b/actions/setup/js/checkout_pr_branch.test.cjs
index 7899e786b5..ff6338df7b 100644
--- a/actions/setup/js/checkout_pr_branch.test.cjs
+++ b/actions/setup/js/checkout_pr_branch.test.cjs
@@ -109,7 +109,10 @@ describe("checkout_pr_branch.cjs", () => {
             let isFork = false;
             let reason = "same repository";
 
-            if (!pullRequest.head?.repo) {
+            if (!pullRequest.head) {
+              isFork = false;
+              reason = "head information not available";
+            } else if (!pullRequest.head.repo) {
               isFork = true;
               reason = "head repository deleted (was likely a fork)";
             } else if (pullRequest.head.repo.fork === true) {
@@ -163,7 +166,7 @@ If the pull request is still open, verify that:
 
     // Execute the script in a new context with our mocks
     const AsyncFunction = Object.getPrototypeOf(async function () {}).constructor;
-    const wrappedScript = new AsyncFunction("core", "exec", "context", "require", scriptContent.replace(/module\.exports = \{ main \};?\s*$/s, "await main();"));
+    const wrappedScript = new AsyncFunction("core", "exec", "context", "require", scriptContent.replace(/module\.exports = \{[^}]+\};?\s*$/s, "await main();"));
 
     try {
       await wrappedScript(mockCore, mockExec, mockContext, mockRequire);
@@ -249,7 +252,7 @@ If the pull request is still open, verify that:
       expect(mockCore.info).toHaveBeenCalledWith("Reason: pull_request event from fork repository; head branch exists only in fork, not in origin");
 
       // Verify gh pr checkout is used instead of git fetch
-      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"]);
+      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"], expect.objectContaining({ env: expect.any(Object) }));
       expect(mockExec.exec).not.toHaveBeenCalledWith("git", ["fetch", "origin", "feature-branch", "--depth=2"]);
 
       expect(mockCore.setFailed).not.toHaveBeenCalled();
@@ -268,7 +271,7 @@ If the pull request is still open, verify that:
       expect(mockCore.info).toHaveBeenCalledWith("Reason: pull_request event from fork repository; head branch exists only in fork, not in origin");
 
       // Verify gh pr checkout is used
-      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"]);
+      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"], expect.objectContaining({ env: expect.any(Object) }));
       expect(mockExec.exec).not.toHaveBeenCalledWith("git", ["fetch", "origin", "feature-branch", expect.anything()]);
 
       expect(mockCore.setFailed).not.toHaveBeenCalled();
@@ -309,8 +312,8 @@ If the pull request is still open, verify that:
 
       expect(mockCore.info).toHaveBeenCalledWith("Checking out PR #123 using gh CLI");
 
-      // Updated expectation: no env options passed, GH_TOKEN comes from step environment
-      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"]);
+      // GH_HOST is now explicitly managed: set from GITHUB_SERVER_URL to prevent mismatch errors
+      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"], expect.objectContaining({ env: expect.any(Object) }));
 
       expect(mockCore.info).toHaveBeenCalledWith("✅ Successfully checked out PR #123");
       expect(mockCore.setFailed).not.toHaveBeenCalled();
@@ -332,19 +335,71 @@ If the pull request is still open, verify that:
       expect(mockCore.setFailed).toHaveBeenCalledWith(`${ERR_API}: Failed to checkout PR branch: gh pr checkout failed`);
     });
 
-    it("should pass environment variables to gh command", async () => {
-      // This test is no longer relevant since we don't pass env options explicitly
-      // The GH_TOKEN is now set at the step level, not in the exec options
-      // Keeping the test but updating to verify the call without env options
+    it("should pass correct GH_HOST env to gh command based on GITHUB_SERVER_URL", async () => {
+      // GH_HOST is now explicitly derived from GITHUB_SERVER_URL to prevent
+      // "none of the git remotes correspond to GH_HOST" errors.
       process.env.CUSTOM_VAR = "custom-value";
 
       await runScript();
 
-      // Verify exec is called without env options
-      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"]);
+      // Verify exec is called with env options containing the correct GH_HOST handling
+      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"], expect.objectContaining({ env: expect.any(Object) }));
 
       delete process.env.CUSTOM_VAR;
     });
+
+    it("should unset GH_HOST in exec env when GITHUB_SERVER_URL is github.com", async () => {
+      // Simulate a user-set GH_HOST that conflicts with the git remotes
+      process.env.GH_HOST = "my-enterprise.ghe.com";
+      process.env.GITHUB_SERVER_URL = "https://github.com";
+
+      await runScript();
+
+      const execCall = mockExec.exec.mock.calls.find(call => call[0] === "gh" && call[1][0] === "pr");
+      expect(execCall).toBeDefined();
+      const execEnv = execCall[2].env;
+      // GH_HOST should be removed so gh targets github.com (the default)
+      expect(execEnv).not.toHaveProperty("GH_HOST");
+
+      delete process.env.GH_HOST;
+      delete process.env.GITHUB_SERVER_URL;
+    });
+
+    it("should set correct GH_HOST in exec env for GitHub Enterprise", async () => {
+      process.env.GITHUB_SERVER_URL = "https://my-enterprise.ghe.com";
+      delete process.env.GH_HOST;
+
+      await runScript();
+
+      const execCall = mockExec.exec.mock.calls.find(call => call[0] === "gh" && call[1][0] === "pr");
+      expect(execCall).toBeDefined();
+      const execEnv = execCall[2].env;
+      // GH_HOST should be set to the GHE hostname so gh targets the right server
+      expect(execEnv.GH_HOST).toBe("my-enterprise.ghe.com");
+
+      delete process.env.GITHUB_SERVER_URL;
+    });
+
+    it("should use gh pr checkout with no fork warning when issue_comment has no full PR data", async () => {
+      // Simulate the real issue_comment event where context.payload.pull_request is null
+      // and the PR is constructed from context.payload.issue
+      mockContext.payload = {
+        issue: {
+          number: 302,
+          state: "open",
+          pull_request: {}, // Presence of this field indicates the issue is a PR
+        },
+      };
+
+      await runScript();
+
+      expect(mockCore.info).toHaveBeenCalledWith("Detected issue_comment event on PR #302, will use gh pr checkout");
+      // Should NOT emit a false-positive fork warning
+      expect(mockCore.warning).not.toHaveBeenCalledWith(expect.stringContaining("Fork PR detected"));
+      // Should still use gh pr checkout
+      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "302"], expect.objectContaining({ env: expect.any(Object) }));
+      expect(mockCore.setFailed).not.toHaveBeenCalled();
+    });
   });
 
   describe("no pull request context", () => {
@@ -387,8 +442,7 @@ If the pull request is still open, verify that:
 
       expect(mockCore.info).toHaveBeenCalledWith("Event: pull_request_target");
       // pull_request_target uses gh pr checkout, not git
-      // Updated expectation: no third argument (env options removed)
-      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"]);
+      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"], expect.objectContaining({ env: expect.any(Object) }));
     });
 
     it("should handle pull_request_review event", async () => {
@@ -398,8 +452,7 @@ If the pull request is still open, verify that:
 
       expect(mockCore.info).toHaveBeenCalledWith("Event: pull_request_review");
       // pull_request_review uses gh pr checkout, not git
-      // Updated expectation: no third argument (env options removed)
-      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"]);
+      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"], expect.objectContaining({ env: expect.any(Object) }));
     });
 
     it("should handle pull_request_review_comment event", async () => {
@@ -407,8 +460,8 @@ If the pull request is still open, verify that:
 
       await runScript();
 
-      // Updated expectation: no third argument (env options removed)
-      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"]);
+      // Updated expectation: env options are now passed with correct GH_HOST
+      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"], expect.objectContaining({ env: expect.any(Object) }));
     });
   });
 
@@ -508,7 +561,7 @@ If the pull request is still open, verify that:
       // Verify fork detection logging with reason
       expect(mockCore.info).toHaveBeenCalledWith("Is fork PR: true (different repository names)");
       expect(mockCore.warning).toHaveBeenCalledWith("⚠️ Fork PR detected - gh pr checkout will fetch from fork repository");
-      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"]);
+      expect(mockExec.exec).toHaveBeenCalledWith("gh", ["pr", "checkout", "123"], expect.objectContaining({ env: expect.any(Object) }));
     });
 
     it("should detect fork using GitHub's fork flag", async () => {
diff --git a/actions/setup/js/pr_helpers.cjs b/actions/setup/js/pr_helpers.cjs
index 039b5bf97f..0829a08bdf 100644
--- a/actions/setup/js/pr_helpers.cjs
+++ b/actions/setup/js/pr_helpers.cjs
@@ -15,8 +15,13 @@ function detectForkPR(pullRequest) {
   let isFork = false;
   let reason = "same repository";
 
-  if (!pullRequest.head?.repo) {
-    // Head repo is null - likely a deleted fork
+  if (!pullRequest.head) {
+    // No head information at all - cannot determine fork status.
+    // This happens for issue_comment events where only number and state are available.
+    isFork = false;
+    reason = "head information not available";
+  } else if (!pullRequest.head.repo) {
+    // Head exists but repo is null - likely a deleted fork
     isFork = true;
     reason = "head repository deleted (was likely a fork)";
   } else if (pullRequest.head.repo.fork === true) {
diff --git a/actions/setup/js/pr_helpers.test.cjs b/actions/setup/js/pr_helpers.test.cjs
index 05548a79db..b3a248525d 100644
--- a/actions/setup/js/pr_helpers.test.cjs
+++ b/actions/setup/js/pr_helpers.test.cjs
@@ -72,6 +72,20 @@ describe("pr_helpers.cjs", () => {
       expect(result.reason).toBe("head repository deleted (was likely a fork)");
     });
 
+    it("should not detect fork when head information is entirely missing (issue_comment events)", () => {
+      // Simulates issue_comment events where pullRequest is constructed
+      // with only number and state (no head/base data)
+      const pullRequest = {
+        number: 302,
+        state: "open",
+      };
+
+      const result = detectForkPR(pullRequest);
+
+      expect(result.isFork).toBe(false);
+      expect(result.reason).toBe("head information not available");
+    });
+
     it("should detect non-fork when repos match and fork flag is false", () => {
       const pullRequest = {
         head: {