Bound diagnostic config file read with size cap (#110591)

* Bound diagnostic config read with size cap

* fix: use buffer.toString for readRegularFileSync result in diagnostic export

* test: verify normal and oversized diagnostic config export behavior

PR #110591 — Add focused regression coverage for the bounded diagnostic config read:
- Test: normal config file (<8MB) produces parseOk: true in config/shape.json
- Test: oversized config file (>8MB) produces parseOk: false with graceful error handling
- Both tests verify the support bundle zip is still written with all expected contents

* refactor(logging): clarify support export config limit

Co-authored-by: 陈宪彪0668000387 <chen.xianbiao@xydigit.com>

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

src/logging/diagnostic-support-export.test.ts

@@ -912,4 +912,50 @@ describe("diagnostic support export", () => {
     expect(combined).toContain("config stat failed with token");
     expect(combined).toContain("Attach this zip to the bug report");
   });
+
+  it("finishes the support export when the config exceeds its read limit", async () => {
+    const configPath = path.join(tempDir, "openclaw.json");
+    const outputPath = path.join(tempDir, "support-oversized-config.zip");
+    fs.writeFileSync(configPath, Buffer.alloc(8 * 1024 * 1024 + 1, "{"));
+
+    await writeDiagnosticSupportExport({
+      env: {
+        ...process.env,
+        HOME: tempDir,
+        OPENCLAW_CONFIG_PATH: configPath,
+        OPENCLAW_STATE_DIR: tempDir,
+      },
+      stateDir: tempDir,
+      outputPath,
+      now: new Date("2026-07-18T12:00:01.000Z"),
+      readLogTail: async () => ({
+        file: path.join(tempDir, "logs", "openclaw.log"),
+        cursor: 0,
+        size: 0,
+        truncated: false,
+        reset: false,
+        lines: [],
+      }),
+    });
+
+    const entries = await readZipTextEntries(outputPath);
+    const configShape = JSON.parse(entries["config/shape.json"] ?? "{}") as {
+      parseOk?: boolean;
+      error?: string;
+    };
+    expect(configShape.parseOk).toBe(false);
+    expect(configShape.error).toContain("File exceeds 8388608 bytes");
+    expect(entries["config/sanitized.json"]).toBe("null\n");
+    expect(Object.keys(entries).toSorted()).toEqual([
+      "config/sanitized.json",
+      "config/shape.json",
+      "diagnostics.json",
+      "logs/openclaw-sanitized.jsonl",
+      "manifest.json",
+      "summary.md",
+    ]);
+
+    const combined = Object.values(entries).join("\n");
+    expect(combined).toContain("Attach this zip to the bug report");
+  });
 });

src/logging/diagnostic-support-export.ts

@@ -8,6 +8,7 @@ import { resolveConfigPath, resolveStateDir } from "../config/paths.js";
 import { redactConfigObject } from "../config/redact-snapshot.js";
 import { buildConfigSchema } from "../config/schema.js";
 import { resolveHomeRelativePath } from "../infra/home-dir.js";
+import { readRegularFileSync } from "../infra/regular-file.js";
 import { VERSION } from "../version.js";
 import {
   readDiagnosticStabilityBundleFileSync,
@@ -38,6 +39,9 @@ const DIAGNOSTIC_SUPPORT_EXPORT_VERSION = 1;
 
 const DEFAULT_LOG_LIMIT = 5000;
 const DEFAULT_LOG_MAX_BYTES = 1_000_000;
+// Support export must remain usable when the config is corrupt or unexpectedly
+// large. This defensive ceiling is not the product's general config-file limit.
+const SUPPORT_EXPORT_CONFIG_MAX_BYTES = 8 * 1024 * 1024;
 const SUPPORT_EXPORT_PREFIX = "openclaw-diagnostics-";
 const SUPPORT_EXPORT_SUFFIX = ".zip";
 type Awaitable<T> = T | Promise<T>;
@@ -343,7 +347,11 @@ function readConfigExport(options: {
   let stat: fs.Stats | undefined;
   try {
     stat = fs.statSync(options.configPath);
-    const parsed = parseConfigJson5(fs.readFileSync(options.configPath, "utf8"));
+    const { buffer } = readRegularFileSync({
+      filePath: options.configPath,
+      maxBytes: SUPPORT_EXPORT_CONFIG_MAX_BYTES,
+    });
+    const parsed = parseConfigJson5(buffer.toString("utf8"));
     if (!parsed.ok) {
       return {
         shape: configShapeReadFailure({