diff --git a/actions/setup/js/create_pull_request.cjs b/actions/setup/js/create_pull_request.cjs
index 48e828c81a3..1c321ffd477 100644
--- a/actions/setup/js/create_pull_request.cjs
+++ b/actions/setup/js/create_pull_request.cjs
@@ -31,7 +31,8 @@ const { isStagedMode } = require("./safe_output_helpers.cjs");
 const { withRetry, isTransientError } = require("./error_recovery.cjs");
 const { tryEnforceArrayLimit } = require("./limit_enforcement_helpers.cjs");
 const { findAgent, getIssueDetails, assignAgentToIssue } = require("./assign_agent_helpers.cjs");
-const { globPatternToRegex } = require("./glob_pattern_helpers.cjs");
+const { generatePatchPreview } = require("./patch_preview.cjs");
+const { parseAllowedBaseBranches, isBaseBranchAllowed } = require("./pr_validation_helpers.cjs");
 
 /**
  * @typedef {import('./types/handler-factory').HandlerFactoryFunction} HandlerFactoryFunction
@@ -89,50 +90,6 @@ const LABEL_MAX_RETRIES = 3;
 /** @type {number} Initial delay in ms before the first label retry (3 seconds) */
 const LABEL_INITIAL_DELAY_MS = 3000;
 
-/**
- * Parse allowed base branch patterns from config value (array or comma-separated string)
- * @param {string[]|string|undefined} allowedBaseBranchesValue
- * @returns {Set<string>}
- */
-function parseAllowedBaseBranches(allowedBaseBranchesValue) {
-  const set = new Set();
-  if (Array.isArray(allowedBaseBranchesValue)) {
-    allowedBaseBranchesValue
-      .map(branch => String(branch).trim())
-      .filter(Boolean)
-      .forEach(branch => set.add(branch));
-  } else if (typeof allowedBaseBranchesValue === "string") {
-    allowedBaseBranchesValue
-      .split(",")
-      .map(branch => branch.trim())
-      .filter(Boolean)
-      .forEach(branch => set.add(branch));
-  }
-  return set;
-}
-
-/**
- * Check if a base branch matches an allowed pattern.
- * Supports exact matches and "*" glob patterns (e.g. "release/*").
- * @param {string} baseBranch
- * @param {Set<string>} allowedBaseBranches
- * @returns {boolean}
- */
-function isBaseBranchAllowed(baseBranch, allowedBaseBranches) {
-  if (allowedBaseBranches.has(baseBranch)) {
-    return true;
-  }
-  for (const pattern of allowedBaseBranches) {
-    if (pattern === "*") {
-      return true;
-    }
-    if (pattern.includes("*") && globPatternToRegex(pattern, { pathMode: true, caseSensitive: true }).test(baseBranch)) {
-      return true;
-    }
-  }
-  return false;
-}
-
 /**
  * Merges the required fallback label with any workflow-configured labels,
  * deduplicating and filtering empty values.
@@ -243,36 +200,6 @@ function enforcePullRequestLimits(patchContent) {
   }
 }
 
-/**
- * Generate a patch preview with max 500 lines and 2000 chars for issue body
- * @param {string} patchContent - The full patch content
- * @returns {string} Formatted patch preview
- */
-function generatePatchPreview(patchContent) {
-  if (!patchContent || !patchContent.trim()) {
-    return "";
-  }
-
-  const lines = patchContent.split("\n");
-  const maxLines = 500;
-  const maxChars = 2000;
-
-  // Apply line limit first
-  let preview = lines.length <= maxLines ? patchContent : lines.slice(0, maxLines).join("\n");
-  const lineTruncated = lines.length > maxLines;
-
-  // Apply character limit
-  const charTruncated = preview.length > maxChars;
-  if (charTruncated) {
-    preview = preview.slice(0, maxChars);
-  }
-
-  const truncated = lineTruncated || charTruncated;
-  const summary = truncated ? `Show patch preview (${Math.min(maxLines, lines.length)} of ${lines.length} lines)` : `Show patch (${lines.length} lines)`;
-
-  return `\n\n<details><summary>${summary}</summary>\n\n\`\`\`diff\n${preview}${truncated ? "\n... (truncated)" : ""}\n\`\`\`\n\n</details>`;
-}
-
 /**
  * Check whether the remote branch already exists and, if so, either fail loudly
  * (when preserve-branch-name is enabled) or rename the local branch by appending
diff --git a/actions/setup/js/patch_preview.cjs b/actions/setup/js/patch_preview.cjs
new file mode 100644
index 00000000000..ba1989b2024
--- /dev/null
+++ b/actions/setup/js/patch_preview.cjs
@@ -0,0 +1,34 @@
+// @ts-check
+
+/**
+ * Generate a patch preview with max 500 lines and 2000 chars for issue body
+ * @param {string} patchContent - The full patch content
+ * @returns {string} Formatted patch preview
+ */
+function generatePatchPreview(patchContent) {
+  if (!patchContent || !patchContent.trim()) {
+    return "";
+  }
+
+  const lines = patchContent.split("\n");
+  const maxLines = 500;
+  const maxChars = 2000;
+
+  // Apply line limit first
+  let preview = lines.length <= maxLines ? patchContent : lines.slice(0, maxLines).join("\n");
+  const lineTruncated = lines.length > maxLines;
+
+  // Apply character limit
+  const charTruncated = preview.length > maxChars;
+  if (charTruncated) {
+    preview = preview.slice(0, maxChars);
+  }
+
+  const truncated = lineTruncated || charTruncated;
+  const shownLines = preview.length > 0 ? preview.split("\n").length : 0;
+  const summary = truncated ? `Show patch preview (${shownLines} of ${lines.length} lines)` : `Show patch (${lines.length} lines)`;
+
+  return `\n\n<details><summary>${summary}</summary>\n\n\`\`\`diff\n${preview}${truncated ? "\n... (truncated)" : ""}\n\`\`\`\n\n</details>`;
+}
+
+module.exports = { generatePatchPreview };
diff --git a/actions/setup/js/patch_preview.test.cjs b/actions/setup/js/patch_preview.test.cjs
new file mode 100644
index 00000000000..64ef9f90356
--- /dev/null
+++ b/actions/setup/js/patch_preview.test.cjs
@@ -0,0 +1,45 @@
+// @ts-check
+import { describe, it, expect } from "vitest";
+import { createRequire } from "module";
+
+const require = createRequire(import.meta.url);
+const { generatePatchPreview } = require("./patch_preview.cjs");
+
+describe("patch_preview", () => {
+  it("returns empty string for empty patch content", () => {
+    expect(generatePatchPreview("")).toBe("");
+  });
+
+  it("formats non-truncated preview", () => {
+    const patch = ["diff --git a/a.txt b/a.txt", "--- a/a.txt", "+++ b/a.txt"].join("\n");
+    const preview = generatePatchPreview(patch);
+
+    expect(preview).toContain("<summary>Show patch (3 lines)</summary>");
+    expect(preview).toContain("```diff");
+    expect(preview).not.toContain("... (truncated)");
+  });
+
+  it("truncates by line count", () => {
+    const patch = Array.from({ length: 600 }, () => "x").join("\n");
+    const preview = generatePatchPreview(patch);
+
+    expect(preview).toContain("<summary>Show patch preview (500 of 600 lines)</summary>");
+    expect(preview).toContain("... (truncated)");
+  });
+
+  it("truncates by character count", () => {
+    const patch = "x".repeat(2500);
+    const preview = generatePatchPreview(patch);
+
+    expect(preview).toContain("<summary>Show patch preview (1 of 1 lines)</summary>");
+    expect(preview).toContain("... (truncated)");
+  });
+
+  it("reports shown line count accurately when truncated by characters", () => {
+    const patch = Array.from({ length: 800 }, (_, i) => `line-${i}`).join("\n");
+    const preview = generatePatchPreview(patch);
+
+    expect(preview).toMatch(/<summary>Show patch preview \(\d+ of 800 lines\)<\/summary>/);
+    expect(preview).not.toContain("<summary>Show patch preview (800 of 800 lines)</summary>");
+  });
+});
diff --git a/actions/setup/js/pr_validation_helpers.cjs b/actions/setup/js/pr_validation_helpers.cjs
new file mode 100644
index 00000000000..9610f2e9967
--- /dev/null
+++ b/actions/setup/js/pr_validation_helpers.cjs
@@ -0,0 +1,58 @@
+// @ts-check
+
+const { globPatternToRegex } = require("./glob_pattern_helpers.cjs");
+
+/**
+ * Parse allowed base branch patterns from config value (array or comma-separated string)
+ * @param {string[]|string|undefined} allowedBaseBranchesValue
+ * @returns {Set<string>}
+ */
+function parseAllowedBaseBranches(allowedBaseBranchesValue) {
+  const set = new Set();
+  if (Array.isArray(allowedBaseBranchesValue)) {
+    allowedBaseBranchesValue
+      .map(branch => String(branch).trim())
+      .filter(Boolean)
+      .forEach(branch => set.add(branch));
+  } else if (typeof allowedBaseBranchesValue === "string") {
+    allowedBaseBranchesValue
+      .split(",")
+      .map(branch => branch.trim())
+      .filter(Boolean)
+      .forEach(branch => set.add(branch));
+  }
+  return set;
+}
+
+/**
+ * Check if a base branch matches an allowed pattern.
+ * Supports exact matches and "*" glob patterns (e.g. "release/*").
+ * @param {string} baseBranch
+ * @param {Set<string>} allowedBaseBranches
+ * @returns {boolean}
+ */
+function isBaseBranchAllowed(baseBranch, allowedBaseBranches) {
+  if (allowedBaseBranches.has(baseBranch)) {
+    return true;
+  }
+  for (const pattern of allowedBaseBranches) {
+    if (pattern === "*") {
+      return true;
+    }
+    // Exact-match patterns were already handled above by Set lookup.
+    // Skip regex compilation unless the pattern is a glob.
+    if (!pattern.includes("*")) {
+      continue;
+    }
+    const regex = globPatternToRegex(pattern, { pathMode: true, caseSensitive: true });
+    if (regex.test(baseBranch)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+module.exports = {
+  parseAllowedBaseBranches,
+  isBaseBranchAllowed,
+};
diff --git a/actions/setup/js/pr_validation_helpers.test.cjs b/actions/setup/js/pr_validation_helpers.test.cjs
new file mode 100644
index 00000000000..604fee94a80
--- /dev/null
+++ b/actions/setup/js/pr_validation_helpers.test.cjs
@@ -0,0 +1,38 @@
+// @ts-check
+import { describe, it, expect } from "vitest";
+import { createRequire } from "module";
+
+const require = createRequire(import.meta.url);
+const { parseAllowedBaseBranches, isBaseBranchAllowed } = require("./pr_validation_helpers.cjs");
+
+describe("pr_validation_helpers", () => {
+  describe("parseAllowedBaseBranches", () => {
+    it("parses array values", () => {
+      const parsed = parseAllowedBaseBranches([" main ", "release/*", ""]);
+      expect([...parsed]).toEqual(["main", "release/*"]);
+    });
+
+    it("parses comma-separated values", () => {
+      const parsed = parseAllowedBaseBranches("main, release/*, ");
+      expect([...parsed]).toEqual(["main", "release/*"]);
+    });
+  });
+
+  describe("isBaseBranchAllowed", () => {
+    it("allows exact branch matches", () => {
+      expect(isBaseBranchAllowed("main", new Set(["main"]))).toBe(true);
+    });
+
+    it("allows wildcard branch matches", () => {
+      expect(isBaseBranchAllowed("release/2026.04", new Set(["release/*"]))).toBe(true);
+    });
+
+    it("allows all branches for star pattern", () => {
+      expect(isBaseBranchAllowed("feature/x", new Set(["*"]))).toBe(true);
+    });
+
+    it("rejects non-matching branches", () => {
+      expect(isBaseBranchAllowed("feature/x", new Set(["main", "release/*"]))).toBe(false);
+    });
+  });
+});