diff --git a/actions/setup/js/add_reaction_and_edit_comment.cjs b/actions/setup/js/add_reaction_and_edit_comment.cjs
index 34a08807637..d8e2ef266cd 100644
--- a/actions/setup/js/add_reaction_and_edit_comment.cjs
+++ b/actions/setup/js/add_reaction_and_edit_comment.cjs
@@ -140,7 +140,14 @@ async function resolveEventEndpoints(eventName, owner, repo, payload) {
 async function main() {
   const reaction = process.env.GH_AW_REACTION || "eyes";
   const commandsJSON = process.env.GH_AW_COMMANDS;
-  const command = commandsJSON ? (JSON.parse(commandsJSON)[0] ?? null) : null; // Only present for command workflows
+  let command = null; // Only present for command workflows
+  if (commandsJSON) {
+    try {
+      command = JSON.parse(commandsJSON)[0] ?? null;
+    } catch (err) {
+      throw new Error("Failed to parse GH_AW_COMMANDS: " + getErrorMessage(err), { cause: err });
+    }
+  }
   const invocationContext = resolveInvocationContext(context);
   const runUrl = buildWorkflowRunUrl(context, invocationContext.workflowRepo);
 
diff --git a/actions/setup/js/apply_safe_outputs_replay.cjs b/actions/setup/js/apply_safe_outputs_replay.cjs
index 5583b0a1878..72b68fa52e4 100644
--- a/actions/setup/js/apply_safe_outputs_replay.cjs
+++ b/actions/setup/js/apply_safe_outputs_replay.cjs
@@ -100,7 +100,12 @@ async function downloadAgentArtifact(runId, destDir, repoSlug) {
  */
 function buildHandlerConfigFromOutput(agentOutputFile) {
   const content = fs.readFileSync(agentOutputFile, "utf8");
-  const validatedOutput = JSON.parse(content);
+  let validatedOutput;
+  try {
+    validatedOutput = JSON.parse(content);
+  } catch (err) {
+    throw new Error("Failed to parse agent output file " + agentOutputFile + ": " + getErrorMessage(err), { cause: err });
+  }
 
   if (!validatedOutput.items || !Array.isArray(validatedOutput.items)) {
     core.info("No items found in agent output; handler config will be empty");
diff --git a/actions/setup/js/artifact_client.cjs b/actions/setup/js/artifact_client.cjs
index 652f3085e27..bc7fabbf475 100644
--- a/actions/setup/js/artifact_client.cjs
+++ b/actions/setup/js/artifact_client.cjs
@@ -15,6 +15,8 @@ const { Readable } = require("stream");
 const { pipeline } = require("stream/promises");
 const { spawnSync } = require("child_process");
 
+const { getErrorMessage } = require("./error_helpers.cjs");
+
 const DEFAULT_RETRY_ATTEMPTS = 5;
 const RETRY_DELAY_MS = 5000;
 const RESULTS_SCOPE_PREFIX = "Actions.Results:";
@@ -33,7 +35,13 @@ function decodeJWTPayload(token) {
   }
   const payload = parts[1].replace(/-/g, "+").replace(/_/g, "/");
   const padded = payload + "=".repeat((4 - (payload.length % 4 || 4)) % 4);
-  return JSON.parse(Buffer.from(padded, "base64").toString("utf8"));
+  let parsed;
+  try {
+    parsed = JSON.parse(Buffer.from(padded, "base64").toString("utf8"));
+  } catch (err) {
+    throw new Error("Failed to parse JWT payload: " + getErrorMessage(err), { cause: err });
+  }
+  return parsed;
 }
 
 function getBackendIdsFromRuntimeToken() {
diff --git a/actions/setup/js/build_checkout_manifest.cjs b/actions/setup/js/build_checkout_manifest.cjs
index 3a585eaa3e5..3db58ce5c0d 100644
--- a/actions/setup/js/build_checkout_manifest.cjs
+++ b/actions/setup/js/build_checkout_manifest.cjs
@@ -10,7 +10,12 @@ const { execFileSync } = require("child_process");
 const { getErrorMessage } = require("./error_helpers.cjs");
 
 function parseManifestEntries(entriesJSON = process.env.GH_AW_CHECKOUT_MANIFEST_ENTRIES || "[]") {
-  const parsed = JSON.parse(entriesJSON);
+  let parsed;
+  try {
+    parsed = JSON.parse(entriesJSON);
+  } catch (err) {
+    throw new Error("Failed to parse GH_AW_CHECKOUT_MANIFEST_ENTRIES: " + getErrorMessage(err), { cause: err });
+  }
   if (!Array.isArray(parsed)) {
     throw new Error("GH_AW_CHECKOUT_MANIFEST_ENTRIES must be a JSON array");
   }
diff --git a/actions/setup/js/convert_gateway_config_shared.cjs b/actions/setup/js/convert_gateway_config_shared.cjs
index c539461e0ce..ea61e33a5b5 100644
--- a/actions/setup/js/convert_gateway_config_shared.cjs
+++ b/actions/setup/js/convert_gateway_config_shared.cjs
@@ -4,6 +4,8 @@
 const fs = require("fs");
 const path = require("path");
 
+const { getErrorMessage } = require("./error_helpers.cjs");
+
 /**
  * Rewrite a gateway URL to use the configured domain and port.
  * Replaces http://<anything>/mcp/ with http://<domain>:<port>/mcp/.
@@ -79,10 +81,20 @@ function loadGatewayContext(options = {}) {
   }
 
   /** @type {Set<string>} */
-  const cliServers = new Set(JSON.parse(process.env.GH_AW_MCP_CLI_SERVERS || "[]"));
+  let cliServers;
+  try {
+    cliServers = new Set(JSON.parse(process.env.GH_AW_MCP_CLI_SERVERS || "[]"));
+  } catch (err) {
+    throw new Error("Failed to parse GH_AW_MCP_CLI_SERVERS: " + getErrorMessage(err), { cause: err });
+  }
 
   /** @type {Record<string, unknown>} */
-  const config = JSON.parse(fs.readFileSync(gatewayOutput, "utf8"));
+  let config;
+  try {
+    config = JSON.parse(fs.readFileSync(gatewayOutput, "utf8"));
+  } catch (err) {
+    throw new Error("Failed to parse gateway output file " + gatewayOutput + ": " + getErrorMessage(err), { cause: err });
+  }
   const rawServers = config.mcpServers;
   /** @type {Record<string, Record<string, unknown>>} */
   let servers = {};
diff --git a/actions/setup/js/generate_safe_outputs_tools.cjs b/actions/setup/js/generate_safe_outputs_tools.cjs
index 00e49f933a2..187129b23cf 100644
--- a/actions/setup/js/generate_safe_outputs_tools.cjs
+++ b/actions/setup/js/generate_safe_outputs_tools.cjs
@@ -32,6 +32,7 @@
 const fs = require("fs");
 const path = require("path");
 const { ERR_CONFIG } = require("./error_codes.cjs");
+const { getErrorMessage } = require("./error_helpers.cjs");
 const { parseRuntimeFeatures, hasRuntimeFeature } = require("./runtime_features.cjs");
 
 const ADD_COMMENT_DEFAULT_DISCUSSIONS_NOTE =
@@ -95,7 +96,12 @@ async function main() {
     throw new Error(msg);
   }
   /** @type {Array<{name: string, description: string, inputSchema?: {properties?: Record<string, unknown>}}>} */
-  const allTools = JSON.parse(fs.readFileSync(toolsSourcePath, "utf8"));
+  let allTools;
+  try {
+    allTools = JSON.parse(fs.readFileSync(toolsSourcePath, "utf8"));
+  } catch (err) {
+    throw new Error("Failed to parse tools source file " + toolsSourcePath + ": " + getErrorMessage(err), { cause: err });
+  }
 
   // Load config to determine which tools are enabled
   if (!fs.existsSync(configPath)) {
@@ -104,13 +110,22 @@ async function main() {
     throw new Error(msg);
   }
   /** @type {Record<string, unknown>} */
-  const config = JSON.parse(fs.readFileSync(configPath, "utf8"));
+  let config;
+  try {
+    config = JSON.parse(fs.readFileSync(configPath, "utf8"));
+  } catch (err) {
+    throw new Error("Failed to parse config file " + configPath + ": " + getErrorMessage(err), { cause: err });
+  }
 
   // Load tools meta (description suffixes, repo params, dynamic tools)
   /** @type {{description_suffixes?: Record<string, string>, repo_params?: Record<string, {type: string, description: string}>, dynamic_tools?: Array<unknown>, required_field_removals?: Record<string, string[]>, required_field_additions?: Record<string, string[]>}} */
   let toolsMeta = { description_suffixes: {}, repo_params: {}, dynamic_tools: [] };
   if (fs.existsSync(toolsMetaPath)) {
-    toolsMeta = JSON.parse(fs.readFileSync(toolsMetaPath, "utf8"));
+    try {
+      toolsMeta = JSON.parse(fs.readFileSync(toolsMetaPath, "utf8"));
+    } catch (err) {
+      throw new Error("Failed to parse tools meta file " + toolsMetaPath + ": " + getErrorMessage(err), { cause: err });
+    }
   }
 
   // Build set of source tool names (predefined/static tools only)
@@ -127,7 +142,12 @@ async function main() {
     .filter(tool => enabledToolNames.has(tool.name))
     .map(tool => {
       // Deep copy to avoid modifying the original
-      const enhancedTool = JSON.parse(JSON.stringify(tool));
+      let enhancedTool;
+      try {
+        enhancedTool = JSON.parse(JSON.stringify(tool));
+      } catch (err) {
+        throw new Error("Failed to deep-copy tool " + tool.name + ": " + getErrorMessage(err), { cause: err });
+      }
 
       // Apply description suffix if available (e.g., " CONSTRAINTS: Maximum 5 issues.")
       const descSuffix = toolsMeta.description_suffixes?.[tool.name];
diff --git a/actions/setup/js/generate_workflow_overview.cjs b/actions/setup/js/generate_workflow_overview.cjs
index 126599a3322..be0346d20a1 100644
--- a/actions/setup/js/generate_workflow_overview.cjs
+++ b/actions/setup/js/generate_workflow_overview.cjs
@@ -2,6 +2,7 @@
 /// <reference types="@actions/github-script" />
 
 const { jsonObjectToMarkdown } = require("./json_object_to_markdown.cjs");
+const { getErrorMessage } = require("./error_helpers.cjs");
 
 /**
  * Generate workflow overview step that writes an agentic workflow run overview
@@ -16,7 +17,12 @@ async function generateWorkflowOverview(core) {
   const awInfoPath = "/tmp/gh-aw/aw_info.json";
 
   // Load aw_info.json
-  const awInfo = JSON.parse(fs.readFileSync(awInfoPath, "utf8"));
+  let awInfo;
+  try {
+    awInfo = JSON.parse(fs.readFileSync(awInfoPath, "utf8"));
+  } catch (err) {
+    throw new Error("Failed to parse aw_info.json at " + awInfoPath + ": " + getErrorMessage(err), { cause: err });
+  }
 
   // Build the collapsible summary label with engine_id and version
   const engineLabel = [awInfo.engine_id, awInfo.version].filter(Boolean).join(" ");
diff --git a/actions/setup/js/mcp_scripts_config_loader.cjs b/actions/setup/js/mcp_scripts_config_loader.cjs
index 9d1a607d8d8..ee0c638fa35 100644
--- a/actions/setup/js/mcp_scripts_config_loader.cjs
+++ b/actions/setup/js/mcp_scripts_config_loader.cjs
@@ -9,6 +9,7 @@
 
 const fs = require("fs");
 const { ERR_SYSTEM, ERR_VALIDATION } = require("./error_codes.cjs");
+const { getErrorMessage } = require("./error_helpers.cjs");
 
 /**
  * @typedef {Object} MCPScriptsToolConfig
@@ -40,7 +41,12 @@ function loadConfig(configPath) {
   }
 
   const configContent = fs.readFileSync(configPath, "utf-8");
-  const config = JSON.parse(configContent);
+  let config;
+  try {
+    config = JSON.parse(configContent);
+  } catch (err) {
+    throw new Error("Failed to parse config file " + configPath + ": " + getErrorMessage(err), { cause: err });
+  }
 
   // Validate required fields
   if (!config.tools || !Array.isArray(config.tools)) {
diff --git a/actions/setup/js/patch_awf_chroot_config.cjs b/actions/setup/js/patch_awf_chroot_config.cjs
index 780c3dcbd30..f7b61b879d5 100644
--- a/actions/setup/js/patch_awf_chroot_config.cjs
+++ b/actions/setup/js/patch_awf_chroot_config.cjs
@@ -4,6 +4,8 @@ const fs = require("fs");
 const os = require("os");
 const path = require("path");
 
+const { getErrorMessage } = require("./error_helpers.cjs");
+
 /**
  * Patch the AWF config file with chroot settings for ARC/DinD runners.
  *
@@ -23,7 +25,12 @@ function patchAWFChrootConfig(options = {}) {
   const identityHome = options.identityHome || process.env.GH_AW_CHROOT_IDENTITY_HOME || "/tmp/gh-aw/home";
   const configPath = path.join(runnerTemp, "gh-aw", "awf-config.json");
   const artifactConfigPath = path.join(binariesSourcePath, "awf-config.json");
-  const config = JSON.parse(fs.readFileSync(configPath, "utf8"));
+  let config;
+  try {
+    config = JSON.parse(fs.readFileSync(configPath, "utf8"));
+  } catch (err) {
+    throw new Error("Failed to parse AWF config file " + configPath + ": " + getErrorMessage(err), { cause: err });
+  }
   const userInfo = os.userInfo();
 
   config.chroot = {
diff --git a/actions/setup/js/route_slash_command.cjs b/actions/setup/js/route_slash_command.cjs
index 61712ddba4f..fd50980346e 100644
--- a/actions/setup/js/route_slash_command.cjs
+++ b/actions/setup/js/route_slash_command.cjs
@@ -6,6 +6,7 @@ const { REACTION_MAP } = require("./add_reaction.cjs");
 const { createOrReuseStatusComment } = require("./add_workflow_run_comment.cjs");
 const nodePath = require("node:path");
 const { matchesCommandName, parseSlashCommand } = require("./slash_command_matcher.cjs");
+const { getErrorMessage } = require("./error_helpers.cjs");
 // Keep this aligned with the current default stable GitHub REST API version used by workflows.
 // Update when GitHub advances the recommended version to avoid sunset/deprecation warnings.
 const GITHUB_API_VERSION = "2022-11-28";
@@ -638,8 +639,18 @@ async function main() {
   core.info("Starting centralized command routing.");
   core.info(`Incoming event name: '${context.eventName}'.`);
 
-  const slashRouteMap = JSON.parse(process.env.GH_AW_SLASH_ROUTING || "{}");
-  const labelRouteMap = JSON.parse(process.env.GH_AW_LABEL_ROUTING || "{}");
+  let slashRouteMap;
+  try {
+    slashRouteMap = JSON.parse(process.env.GH_AW_SLASH_ROUTING || "{}");
+  } catch (err) {
+    throw new Error("Failed to parse GH_AW_SLASH_ROUTING: " + getErrorMessage(err), { cause: err });
+  }
+  let labelRouteMap;
+  try {
+    labelRouteMap = JSON.parse(process.env.GH_AW_LABEL_ROUTING || "{}");
+  } catch (err) {
+    throw new Error("Failed to parse GH_AW_LABEL_ROUTING: " + getErrorMessage(err), { cause: err });
+  }
   core.info(`Configured centralized slash commands: ${Object.keys(slashRouteMap).length}.`);
   core.info(`Configured decentralized label commands: ${Object.keys(labelRouteMap).length}.`);
   const text = resolveBodyText();
diff --git a/actions/setup/js/safe_outputs_handlers.cjs b/actions/setup/js/safe_outputs_handlers.cjs
index d8db15ac063..8d272b5d1db 100644
--- a/actions/setup/js/safe_outputs_handlers.cjs
+++ b/actions/setup/js/safe_outputs_handlers.cjs
@@ -50,7 +50,13 @@ function resolveEffectiveContext(invocationContext, rawContext) {
  * @returns {any}
  */
 function readJSONFile(filePath) {
-  return JSON.parse(fs.readFileSync(filePath, "utf8"));
+  let parsed;
+  try {
+    parsed = JSON.parse(fs.readFileSync(filePath, "utf8"));
+  } catch (err) {
+    throw new Error("Failed to parse JSON file " + filePath + ": " + getErrorMessage(err), { cause: err });
+  }
+  return parsed;
 }
 
 const safeOutputsTools = readJSONFile(path.join(__dirname, "safe_outputs_tools.json"));
diff --git a/actions/setup/js/safe_outputs_tools_loader.cjs b/actions/setup/js/safe_outputs_tools_loader.cjs
index cb4d7669c75..a9e235b68b8 100644
--- a/actions/setup/js/safe_outputs_tools_loader.cjs
+++ b/actions/setup/js/safe_outputs_tools_loader.cjs
@@ -228,7 +228,11 @@ function registerPredefinedTools(server, tools, config, registerTool, normalizeT
       const isCreatePullRequestTool = tool.name === "create_pull_request" && config.create_pull_request;
       // Enrich create_pull_request tool description when target-repo is configured
       if (safetyWarning || isCreatePullRequestTool) {
-        toolToRegister = JSON.parse(JSON.stringify(tool));
+        try {
+          toolToRegister = JSON.parse(JSON.stringify(tool));
+        } catch (err) {
+          throw new Error("Failed to deep-copy tool " + tool.name + ": " + getErrorMessage(err), { cause: err });
+        }
         if (tool.handler) {
           toolToRegister.handler = tool.handler;
         }
diff --git a/actions/setup/js/start_mcp_gateway.cjs b/actions/setup/js/start_mcp_gateway.cjs
index f4e1f502b6d..5c728276037 100644
--- a/actions/setup/js/start_mcp_gateway.cjs
+++ b/actions/setup/js/start_mcp_gateway.cjs
@@ -35,6 +35,7 @@ const http = require("http");
 const path = require("path");
 const { withRetry } = require("./error_recovery.cjs");
 const { lstatGuard } = require("./symlink_guard.cjs");
+const { getErrorMessage } = require("./error_helpers.cjs");
 
 // ---------------------------------------------------------------------------
 // Timing helpers
@@ -743,7 +744,12 @@ async function main() {
   fs.chmodSync(outputPath, 0o600);
 
   // Check for error payload
-  const gatewayOutput = JSON.parse(fs.readFileSync(outputPath, "utf8"));
+  let gatewayOutput;
+  try {
+    gatewayOutput = JSON.parse(fs.readFileSync(outputPath, "utf8"));
+  } catch (err) {
+    throw new Error("Failed to parse gateway output file " + outputPath + ": " + getErrorMessage(err), { cause: err });
+  }
   if (gatewayOutput.error) {
     core.error("ERROR: Gateway returned an error payload instead of configuration");
     core.error("");