fix: stop inventing a false default for options without one

[dajiaohuang]

Summary

generateConfigOptionsMarkdown() falls back to the literal string 'false' when an option declares neither defaultDescription nor default:

markdown += `  - **Default:** \`${optionConfig.defaultDescription ?? optionConfig.default ?? 'false'}\`\n`;

As a result, every string, number and array config option is documented as having a default of false. Of the 45 documented options, 30 declare no default and are affected. Only 15 declare one (8 true, 6 false, and --filesystemRoot with defaultDescription: 'OS temp directory').

Relation to #2233 / #2234 — please read before merging

This fallback was introduced deliberately by #2234 (merged 2026-06-19, closing #2233 "Improve configuration section in readme with (implicit) defaults"). #2234 replaced a guarded emission with an unconditional one:

-    if (optionConfig.default !== undefined) {
-      markdown += `  - **Default:** \`${optionConfig.default}\`\n`;
-    }
+    markdown += `  - **Default:** \`${optionConfig.default ?? 'false'}\`\n`;

So this PR removes lines that #2234 intentionally added, and I'd rather flag that than present it as an unambiguous bug fix.

The reason I believe it is still a defect: #2233's motivating example was --memoryDebugging, a boolean whose implicit default genuinely is false. Generalising ?? 'false' to every option makes the output factually wrong for non-boolean options. For example --screenshotMaxWidth (type number) currently reads:

Maximum width in pixels for screenshots. ... Unset means no resize.
- **Type:** number
- **Default:** `false`

and --screenshotQuality and --experimentalScreencastFps are numbers documented as defaulting to a boolean.

If you would prefer to keep a Default: line on every option, the alternative is to emit each option's true implicit default (e.g. unset, or wording derived from the option's existing description) rather than omitting the line. I did not attempt that here because it needs per-option judgement — happy to rework the PR that way instead.

Verification

• npm run gen — completes; the only diff is the 30 removed doc lines plus the generator edit.
• Re-running npm run gen is idempotent (sha256 of docs/configuration.md unchanged), so [Required] Check docs updated stays green.
• npm run check-format — passed.
• npm run typecheck — passed.
• git diff --check — passed.

No issue is linked; reproduced on the current main (d05cbc05).

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[nattallius]

Hi, can you fix sign the CLA check? That happened because you co-authored commit with noreply@anthropic.com