* fix(line): limit webhook request body size to prevent DoS
Add io.LimitReader with 1 MB cap on the LINE webhook handler to prevent
unauthenticated memory exhaustion via oversized POST requests.
Follows the same pattern used in the WeCom channel (io.LimitReader).
Requests exceeding the limit are rejected with 413 Request Entity Too Large.
Fixes#1407
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
* refactor(line): hoist body size const, add boundary tests
- Move maxWebhookBodySize to package-level const
- Add TestWebhookAcceptsMaxBodySize (exact limit → 403, not 413)
- Add TestWebhookRejectsOversizedBodyBeforeSignatureCheck
- Use const in test instead of magic number
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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