diff --git a/.github/workflows/smoke-codex.lock.yml b/.github/workflows/smoke-codex.lock.yml
index e17af58f820..b075d7af731 100644
--- a/.github/workflows/smoke-codex.lock.yml
+++ b/.github/workflows/smoke-codex.lock.yml
@@ -977,7 +977,7 @@ jobs:
                   "rationale": {
                     "type": "string",
                     "sanitize": true,
-                    "maxLength": 1024
+                    "maxLength": 280
                   },
                   "repo": {
                     "type": "string",
diff --git a/.github/workflows/smoke-copilot-aoai-apikey.lock.yml b/.github/workflows/smoke-copilot-aoai-apikey.lock.yml
index 5eca1511cf7..3e5fdd0c01f 100644
--- a/.github/workflows/smoke-copilot-aoai-apikey.lock.yml
+++ b/.github/workflows/smoke-copilot-aoai-apikey.lock.yml
@@ -1169,7 +1169,7 @@ jobs:
                   "rationale": {
                     "type": "string",
                     "sanitize": true,
-                    "maxLength": 1024
+                    "maxLength": 280
                   },
                   "repo": {
                     "type": "string",
diff --git a/.github/workflows/smoke-copilot-aoai-entra.lock.yml b/.github/workflows/smoke-copilot-aoai-entra.lock.yml
index 6e15c6a8a32..fb3e0751df3 100644
--- a/.github/workflows/smoke-copilot-aoai-entra.lock.yml
+++ b/.github/workflows/smoke-copilot-aoai-entra.lock.yml
@@ -1170,7 +1170,7 @@ jobs:
                   "rationale": {
                     "type": "string",
                     "sanitize": true,
-                    "maxLength": 1024
+                    "maxLength": 280
                   },
                   "repo": {
                     "type": "string",
diff --git a/.github/workflows/smoke-copilot.lock.yml b/.github/workflows/smoke-copilot.lock.yml
index 7f948cd4f86..686118986ed 100644
--- a/.github/workflows/smoke-copilot.lock.yml
+++ b/.github/workflows/smoke-copilot.lock.yml
@@ -1185,7 +1185,7 @@ jobs:
                   "rationale": {
                     "type": "string",
                     "sanitize": true,
-                    "maxLength": 1024
+                    "maxLength": 280
                   },
                   "repo": {
                     "type": "string",
diff --git a/actions/setup/js/issue_intents.cjs b/actions/setup/js/issue_intents.cjs
index 73d6865382b..c489539b40e 100644
--- a/actions/setup/js/issue_intents.cjs
+++ b/actions/setup/js/issue_intents.cjs
@@ -7,7 +7,7 @@ const { sanitizeLabelContent } = require("./sanitize_label_content.cjs");
 const { hasRuntimeFeature, parseRuntimeFeatures } = require("./runtime_features.cjs");
 
 const ISSUE_INTENTS_FEATURE = "issue_intents";
-const ISSUE_INTENT_RATIONALE_MAX_LENGTH = 1024;
+const ISSUE_INTENT_RATIONALE_MAX_LENGTH = 280;
 
 function hasIssueIntentsRuntimeFeature() {
   if (typeof global.hasRuntimeFeature === "function") {
@@ -25,7 +25,10 @@ function normalizeIssueIntentMetadata(source) {
   const metadata = {};
 
   if (typeof source.rationale === "string") {
-    const rationale = sanitizeContent(source.rationale, { maxLength: ISSUE_INTENT_RATIONALE_MAX_LENGTH }).trim();
+    const sanitizedRationale = sanitizeContent(source.rationale, { maxLength: ISSUE_INTENT_RATIONALE_MAX_LENGTH }).trim();
+    // sanitizeContent appends "\n[Content truncated due to length]" when it truncates,
+    // so clamp again to guarantee the GitHub API hard limit.
+    const rationale = sanitizedRationale.length > ISSUE_INTENT_RATIONALE_MAX_LENGTH ? sanitizedRationale.slice(0, ISSUE_INTENT_RATIONALE_MAX_LENGTH) : sanitizedRationale;
     if (rationale) {
       metadata.rationale = rationale;
     }
diff --git a/actions/setup/js/safe_output_type_validator.cjs b/actions/setup/js/safe_output_type_validator.cjs
index fc377c08d0d..d743ef1cd4d 100644
--- a/actions/setup/js/safe_output_type_validator.cjs
+++ b/actions/setup/js/safe_output_type_validator.cjs
@@ -24,6 +24,7 @@ const MAX_BODY_LENGTH = 65000;
  * Reference: https://github.com/dead-claudia/github-limits
  */
 const MAX_GITHUB_USERNAME_LENGTH = 39;
+const ISSUE_INTENT_RATIONALE_MAX_LENGTH = 280;
 
 /**
  * @typedef {{ allowedAliases?: string[], maxBotMentions?: number, normalizeIssueClosingKeywords?: boolean }} ValidateOptions
@@ -64,6 +65,25 @@ function normalizeIssueClosingKeywordBackticks(content) {
   return normalized.replace(ISSUE_CLOSING_REFERENCE_BACKTICK_PATTERN, "$1$2$3");
 }
 
+/**
+ * Normalize issue-intent rationale text while enforcing the GitHub API hard limit.
+ * sanitizeContent appends a truncation marker when it shortens content, so this
+ * helper slices again to ensure the final payload never exceeds 280 characters.
+ * @param {string} rationale
+ * @param {ValidateOptions} [options]
+ * @returns {string}
+ */
+function normalizeIssueIntentRationale(rationale, options) {
+  const sanitizedRationale = sanitizeContent(unfenceMarkdown(rationale), {
+    maxLength: ISSUE_INTENT_RATIONALE_MAX_LENGTH,
+    allowedAliases: options?.allowedAliases || [],
+    maxBotMentions: options?.maxBotMentions,
+  }).trim();
+  // sanitizeContent appends "\n[Content truncated due to length]" when it truncates,
+  // so clamp again to guarantee the GitHub API hard limit.
+  return sanitizedRationale.length > ISSUE_INTENT_RATIONALE_MAX_LENGTH ? sanitizedRationale.slice(0, ISSUE_INTENT_RATIONALE_MAX_LENGTH) : sanitizedRationale;
+}
+
 /**
  * Validate and normalize issue-intent-aware label arrays.
  * @param {any[]} value
@@ -132,11 +152,7 @@ function validateIssueIntentLabels(value, lineNum, itemType, fieldName, options)
           error: `Line ${lineNum}: ${itemType} ${fieldName}[${i}].rationale must be a string`,
         };
       }
-      const rationale = sanitizeContent(unfenceMarkdown(label.rationale), {
-        maxLength: 1024,
-        allowedAliases: options?.allowedAliases || [],
-        maxBotMentions: options?.maxBotMentions,
-      }).trim();
+      const rationale = normalizeIssueIntentRationale(label.rationale, options);
       if (rationale) {
         normalizedLabel.rationale = rationale;
       }
diff --git a/actions/setup/js/safe_output_type_validator.test.cjs b/actions/setup/js/safe_output_type_validator.test.cjs
index 6474570afba..5ee9e59c01d 100644
--- a/actions/setup/js/safe_output_type_validator.test.cjs
+++ b/actions/setup/js/safe_output_type_validator.test.cjs
@@ -116,7 +116,7 @@ const SAMPLE_VALIDATION_CONFIG = {
     fields: {
       issue_number: { issueOrPRNumber: true },
       issue_type: { required: true, type: "string", sanitize: true, maxLength: 128 },
-      rationale: { type: "string", sanitize: true, maxLength: 1024 },
+      rationale: { type: "string", sanitize: true, maxLength: 280 },
       confidence: { type: "string", enum: ["LOW", "MEDIUM", "HIGH"] },
       suggest: { type: "boolean" },
     },
@@ -129,7 +129,7 @@ const SAMPLE_VALIDATION_CONFIG = {
       field_name: { type: "string", sanitize: true, maxLength: 128 },
       field_node_id: { type: "string", maxLength: 256 },
       value: { required: true, type: "string", sanitize: true, maxLength: 256 },
-      rationale: { type: "string", sanitize: true, maxLength: 1024 },
+      rationale: { type: "string", sanitize: true, maxLength: 280 },
       confidence: { type: "string", enum: ["LOW", "MEDIUM", "HIGH"] },
       suggest: { type: "boolean" },
     },
@@ -329,6 +329,21 @@ describe("safe_output_type_validator", () => {
       expect(result.normalizedItem.labels).toEqual([{ name: "bug", rationale: "Known failure mode", confidence: "HIGH", suggest: true }]);
     });
 
+    it("should truncate structured label rationale for all issue-intent label mutations", async () => {
+      const { validateItem } = await import("./safe_output_type_validator.cjs");
+
+      for (const [type, item] of [
+        ["add_labels", { type: "add_labels", item_number: 123, labels: [{ name: "bug", rationale: "a".repeat(350) }] }],
+        ["remove_labels", { type: "remove_labels", item_number: 123, labels: [{ name: "bug", rationale: "a".repeat(350) }] }],
+        ["update_issue", { type: "update_issue", issue_number: 123, labels: [{ name: "bug", rationale: "a".repeat(350) }] }],
+      ]) {
+        const result = validateItem(item, type, 1);
+
+        expect(result.isValid).toBe(true);
+        expect(result.normalizedItem.labels[0].rationale).toBe("a".repeat(280));
+      }
+    });
+
     it("should fail add_labels when structured label entry is invalid", async () => {
       const { validateItem } = await import("./safe_output_type_validator.cjs");
 
diff --git a/actions/setup/js/safe_outputs_tools.json b/actions/setup/js/safe_outputs_tools.json
index 7bf35a642bc..bd789c3fff2 100644
--- a/actions/setup/js/safe_outputs_tools.json
+++ b/actions/setup/js/safe_outputs_tools.json
@@ -602,7 +602,8 @@
                   },
                   "rationale": {
                     "type": "string",
-                    "description": "Optional rationale for the change."
+                    "maxLength": 280,
+                    "description": "Optional rationale for the change (max 280 characters)."
                   },
                   "confidence": {
                     "type": "string",
@@ -662,7 +663,8 @@
                   },
                   "rationale": {
                     "type": "string",
-                    "description": "Optional rationale for the change."
+                    "maxLength": 280,
+                    "description": "Optional rationale for the change (max 280 characters)."
                   },
                   "confidence": {
                     "type": "string",
@@ -922,7 +924,8 @@
                   },
                   "rationale": {
                     "type": "string",
-                    "description": "Optional rationale for the change."
+                    "maxLength": 280,
+                    "description": "Optional rationale for the change (max 280 characters)."
                   },
                   "confidence": {
                     "type": "string",
@@ -1350,7 +1353,8 @@
         },
         "rationale": {
           "type": "string",
-          "description": "Optional rationale for the change."
+          "maxLength": 280,
+          "description": "Optional rationale for the change (max 280 characters)."
         },
         "confidence": {
           "type": "string",
@@ -1401,7 +1405,8 @@
         },
         "rationale": {
           "type": "string",
-          "description": "Optional rationale for the change."
+          "maxLength": 280,
+          "description": "Optional rationale for the change (max 280 characters)."
         },
         "confidence": {
           "type": "string",
diff --git a/actions/setup/js/set_issue_type.test.cjs b/actions/setup/js/set_issue_type.test.cjs
index 7170242a6f1..7dbf07c7fe8 100644
--- a/actions/setup/js/set_issue_type.test.cjs
+++ b/actions/setup/js/set_issue_type.test.cjs
@@ -384,4 +384,75 @@ describe("set_issue_type (Handler Factory Architecture)", () => {
       delete process.env.GH_AW_RUNTIME_FEATURES;
     }
   });
+
+  it("should truncate issue_intents rationale to 280 characters", async () => {
+    process.env.GH_AW_RUNTIME_FEATURES = "issue_intents";
+
+    const issueNodeId = "I_kwDO_testissue";
+    const issueTypeNodeId = "IT_kwDO_bug";
+    const longRationale = "a".repeat(350);
+
+    mockGithub.rest.issues.get.mockResolvedValueOnce({ data: { node_id: issueNodeId } });
+    mockGithub.graphql.mockImplementation(async query => {
+      if (query.includes("repository(owner")) {
+        return {
+          repository: {
+            issueTypes: {
+              nodes: [{ id: issueTypeNodeId, name: "Bug" }],
+            },
+          },
+        };
+      }
+      if (query.includes("updateIssue")) {
+        return { updateIssue: { issue: { id: issueNodeId } } };
+      }
+      return {};
+    });
+
+    try {
+      const { main } = require("./set_issue_type.cjs");
+      const featureHandler = await main({ max: 5 });
+
+      const result = await featureHandler(
+        {
+          type: "set_issue_type",
+          issue_number: 42,
+          issue_type: "Bug",
+          rationale: longRationale,
+        },
+        {}
+      );
+
+      expect(result.success).toBe(true);
+      const mutationCall = mockGithub.graphql.mock.calls.find(([query]) => typeof query === "string" && query.includes("IssueTypeUpdateInput"));
+      expect(mutationCall).toBeDefined();
+      expect(mutationCall[1].issueType.rationale).toBe("a".repeat(280));
+    } finally {
+      delete process.env.GH_AW_RUNTIME_FEATURES;
+    }
+  });
+
+  it("should preserve issue_intents rationale of exactly 280 characters", () => {
+    const { normalizeIssueIntentMetadata } = require("./issue_intents.cjs");
+
+    const metadata = normalizeIssueIntentMetadata({ rationale: "a".repeat(280) });
+
+    expect(metadata.rationale).toBe("a".repeat(280));
+  });
+
+  it("should truncate issue_intents rationale of 281 characters", () => {
+    const { normalizeIssueIntentMetadata } = require("./issue_intents.cjs");
+
+    const metadata = normalizeIssueIntentMetadata({ rationale: "a".repeat(281) });
+
+    expect(metadata.rationale).toBe("a".repeat(280));
+  });
+
+  it("should omit empty issue_intents rationale after sanitization", () => {
+    const { normalizeIssueIntentMetadata } = require("./issue_intents.cjs");
+
+    const metadata = normalizeIssueIntentMetadata({ rationale: "   " });
+
+    expect(metadata).not.toHaveProperty("rationale");
+  });
 });
diff --git a/pkg/workflow/js/safe_outputs_tools.json b/pkg/workflow/js/safe_outputs_tools.json
index 763abf7ba55..ce02572644e 100644
--- a/pkg/workflow/js/safe_outputs_tools.json
+++ b/pkg/workflow/js/safe_outputs_tools.json
@@ -770,7 +770,8 @@
                   },
                   "rationale": {
                     "type": "string",
-                    "description": "Optional rationale for the change."
+                    "maxLength": 280,
+                    "description": "Optional rationale for the change (max 280 characters)."
                   },
                   "confidence": {
                     "type": "string",
@@ -843,7 +844,8 @@
                   },
                   "rationale": {
                     "type": "string",
-                    "description": "Optional rationale for the change."
+                    "maxLength": 280,
+                    "description": "Optional rationale for the change (max 280 characters)."
                   },
                   "confidence": {
                     "type": "string",
@@ -1169,7 +1171,8 @@
                   },
                   "rationale": {
                     "type": "string",
-                    "description": "Optional rationale for the change."
+                    "maxLength": 280,
+                    "description": "Optional rationale for the change (max 280 characters)."
                   },
                   "confidence": {
                     "type": "string",
@@ -1707,7 +1710,8 @@
         },
         "rationale": {
           "type": "string",
-          "description": "Optional rationale for the change."
+          "maxLength": 280,
+          "description": "Optional rationale for the change (max 280 characters)."
         },
         "confidence": {
           "type": "string",
@@ -1773,7 +1777,8 @@
         },
         "rationale": {
           "type": "string",
-          "description": "Optional rationale for the change."
+          "maxLength": 280,
+          "description": "Optional rationale for the change (max 280 characters)."
         },
         "confidence": {
           "type": "string",
diff --git a/pkg/workflow/safe_output_validation_config_test.go b/pkg/workflow/safe_output_validation_config_test.go
index f8a1b6349ba..f04139df6db 100644
--- a/pkg/workflow/safe_output_validation_config_test.go
+++ b/pkg/workflow/safe_output_validation_config_test.go
@@ -229,6 +229,16 @@ func TestFieldValidationMarshaling(t *testing.T) {
 	}
 }
 
+func TestIssueIntentRationaleMaxLength(t *testing.T) {
+	if got := ValidationConfig["set_issue_type"].Fields["rationale"].MaxLength; got != 280 {
+		t.Fatalf("set_issue_type rationale maxLength = %d, want 280", got)
+	}
+
+	if got := ValidationConfig["set_issue_field"].Fields["rationale"].MaxLength; got != 280 {
+		t.Fatalf("set_issue_field rationale maxLength = %d, want 280", got)
+	}
+}
+
 func TestUpdateDiscussionValidationConfig(t *testing.T) {
 	// Verify update_discussion accepts label-only updates (regression test for
 	// https://github.com/github/gh-aw/issues/24979 where label-only updates were
diff --git a/pkg/workflow/safe_outputs_validation_config.go b/pkg/workflow/safe_outputs_validation_config.go
index 143bb17aa71..9257e5f1409 100644
--- a/pkg/workflow/safe_outputs_validation_config.go
+++ b/pkg/workflow/safe_outputs_validation_config.go
@@ -135,7 +135,7 @@ var ValidationConfig = map[string]TypeValidationConfig{
 		Fields: map[string]FieldValidation{
 			"issue_number": {IssueOrPRNumber: true},
 			"issue_type":   {Required: true, Type: "string", Sanitize: true, MaxLength: 128}, // Empty string clears the type
-			"rationale":    {Type: "string", Sanitize: true, MaxLength: 1024},
+			"rationale":    {Type: "string", Sanitize: true, MaxLength: 280},
 			"confidence":   {Type: "string", Enum: []string{"LOW", "MEDIUM", "HIGH"}},
 			"suggest":      {Type: "boolean"},
 			"repo":         {Type: "string", MaxLength: 256}, // Optional: target repository in format "owner/repo"
@@ -149,7 +149,7 @@ var ValidationConfig = map[string]TypeValidationConfig{
 			"field_name":    {Type: "string", Sanitize: true, MaxLength: 128},
 			"field_node_id": {Type: "string", MaxLength: 256},
 			"value":         {Required: true, Type: "string", Sanitize: true, MaxLength: 256},
-			"rationale":     {Type: "string", Sanitize: true, MaxLength: 1024},
+			"rationale":     {Type: "string", Sanitize: true, MaxLength: 280},
 			"confidence":    {Type: "string", Enum: []string{"LOW", "MEDIUM", "HIGH"}},
 			"suggest":       {Type: "boolean"},
 			"repo":          {Type: "string", MaxLength: 256}, // Optional: target repository in format "owner/repo"