diff --git a/actions/setup/js/create_code_scanning_alert.cjs b/actions/setup/js/create_code_scanning_alert.cjs
index e93c6e7fc9f..2ed6f4663ae 100644
--- a/actions/setup/js/create_code_scanning_alert.cjs
+++ b/actions/setup/js/create_code_scanning_alert.cjs
@@ -8,6 +8,7 @@
 const { getErrorMessage } = require("./error_helpers.cjs");
 const { logStagedPreviewInfo } = require("./staged_preview.cjs");
 const { isStagedMode } = require("./safe_output_helpers.cjs");
+const { ERR_SYSTEM } = require("./error_codes.cjs");
 const fs = require("fs");
 const path = require("path");
 
@@ -89,7 +90,7 @@ async function main(config = {}) {
     try {
       fs.writeFileSync(sarifFilePath, JSON.stringify(sarifContent, null, 2));
     } catch (err) {
-      throw new Error(`Failed to write file ${sarifFilePath}: ${String(err)}`, { cause: err });
+      throw new Error(`${ERR_SYSTEM}: Failed to write file ${sarifFilePath}: ${String(err)}`, { cause: err });
     }
     core.info(`✓ Updated SARIF file with ${validFindings.length} finding(s): ${sarifFilePath}`);
   }
diff --git a/actions/setup/js/load_experiment_state_from_repo.cjs b/actions/setup/js/load_experiment_state_from_repo.cjs
index d73cc234ac7..8e6b3476c9c 100644
--- a/actions/setup/js/load_experiment_state_from_repo.cjs
+++ b/actions/setup/js/load_experiment_state_from_repo.cjs
@@ -22,6 +22,7 @@
 const fs = require("fs");
 const path = require("path");
 const { getErrorMessage } = require("./error_helpers.cjs");
+const { ERR_SYSTEM, ERR_API } = require("./error_codes.cjs");
 
 const MAX_STATE_FILE_BYTES = 102400;
 // Keep this allowlist aligned with actions/setup/js/normalize_branch_name.cjs valid characters.
@@ -99,7 +100,7 @@ async function fetchFileFromBranch(octokit, owner, repo, branch, filePath) {
     if (errAny.status === 404) {
       return null;
     }
-    throw err;
+    throw new Error(`${ERR_API}: Failed to fetch file "${filePath}" from branch "${branch}": ${String(err)}`, { cause: err });
   }
 }
 
@@ -119,7 +120,7 @@ async function main() {
     try {
       fs.mkdirSync(stateDir, { recursive: true });
     } catch (err) {
-      throw new Error(`Failed to create directory ${stateDir}: ${String(err)}`, { cause: err });
+      throw new Error(`${ERR_SYSTEM}: Failed to create directory ${stateDir}: ${String(err)}`, { cause: err });
     }
     return;
   }
@@ -143,7 +144,7 @@ async function main() {
   try {
     fs.mkdirSync(stateDir, { recursive: true });
   } catch (err) {
-    throw new Error(`Failed to create directory ${stateDir}: ${String(err)}`, { cause: err });
+    throw new Error(`${ERR_SYSTEM}: Failed to create directory ${stateDir}: ${String(err)}`, { cause: err });
   }
 
   if (content === null) {
@@ -171,7 +172,7 @@ async function main() {
   try {
     fs.writeFileSync(stateFile, content, "utf8");
   } catch (err) {
-    throw new Error(`Failed to write file ${stateFile}: ${String(err)}`, { cause: err });
+    throw new Error(`${ERR_SYSTEM}: Failed to write file ${stateFile}: ${String(err)}`, { cause: err });
   }
   core.info(`Experiment state written to ${stateFile}`);
 }
diff --git a/actions/setup/js/safe_outputs_bootstrap.cjs b/actions/setup/js/safe_outputs_bootstrap.cjs
index 86803dfef12..f60315d9c87 100644
--- a/actions/setup/js/safe_outputs_bootstrap.cjs
+++ b/actions/setup/js/safe_outputs_bootstrap.cjs
@@ -15,6 +15,7 @@
 const fs = require("fs");
 const { loadConfig } = require("./safe_outputs_config.cjs");
 const { loadTools } = require("./safe_outputs_tools_loader.cjs");
+const { ERR_CONFIG } = require("./error_codes.cjs");
 
 /**
  * @typedef {Object} Logger
@@ -68,7 +69,7 @@ function enforceCreatePullRequestRuntimePolicy(config, logger) {
 
   const message = `create-pull-request is disabled by runtime policy: ${policyVarName}=false. ` + `Remove safe-outputs.create-pull-request or set ${policyVarName}=true.`;
   logger.debugError(message);
-  throw new Error(message);
+  throw new Error(`${ERR_CONFIG}: ${message}`);
 }
 
 /**
diff --git a/actions/setup/js/safe_outputs_config.cjs b/actions/setup/js/safe_outputs_config.cjs
index b50eba4f2a9..b6423999a54 100644
--- a/actions/setup/js/safe_outputs_config.cjs
+++ b/actions/setup/js/safe_outputs_config.cjs
@@ -2,6 +2,7 @@
 
 const { getErrorMessage } = require("./error_helpers.cjs");
 const { redactSensitiveConfig } = require("./safe_outputs_config_redact.cjs");
+const { ERR_SYSTEM } = require("./error_codes.cjs");
 
 const fs = require("fs");
 const path = require("path");
@@ -73,7 +74,7 @@ function loadConfig(server) {
     try {
       fs.mkdirSync(outputDir, { recursive: true });
     } catch (err) {
-      throw new Error(`Failed to create directory ${outputDir}: ${String(err)}`, { cause: err });
+      throw new Error(`${ERR_SYSTEM}: Failed to create directory ${outputDir}: ${String(err)}`, { cause: err });
     }
   }