fix: parse SIWE Chain ID from the structured field only

[o-mid]

Summary

Hey @ignaciosantise / Reown team — getChainIdFromMessage was taking the first Chain ID: <digits> anywhere in the SIWE text.

If the statement says something like "Please use Chain ID: 137", AppKit then sends personal_sign on Polygon even when the real field is Chain ID: 1. This now only reads lines that start with Chain ID: .

Test plan

• cd packages/reown_sign && flutter test test/auth/signature_test.dart
• SIWE statement mentions another chain; signing still uses the structured Chain ID line

[Copilot]

🟡 Changes recommended

The updated chain-id parser can now return non-numeric values if the structured Chain ID: line contains trailing text, which regresses prior digits-only behavior and can break downstream chain-id validation/routing.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR fixes SIWE chain-id extraction so getChainIdFromMessage no longer picks up Chain ID: <digits> occurrences embedded in the free-form statement, and instead only considers lines that start with Chain ID: (the structured field).

Changes:

• Update AuthSignature.getChainIdFromMessage to scan line-by-line for a Chain ID: -prefixed field.
• Add a regression test where the statement mentions another chain id, ensuring the structured Chain ID is used.
• Document the fix in packages/reown_sign changelog (1.4.1).

File summaries

File	Description
packages/reown_sign/lib/utils/auth_signature.dart	Adjusts SIWE chain-id parsing to avoid matching statement text.
packages/reown_sign/test/auth/signature_test.dart	Adds coverage for statements that mention a different chain id.
packages/reown_sign/CHANGELOG.md	Notes the SIWE chain-id parsing fix in a new release entry.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

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[o-mid]

@ignaciosantise this is the greedy SIWE regex — a statement that mentions another chain was winning over the real Chain ID: line and sending personal_sign to the wrong network. Happy to tweak if you'd rather keep the old \d+ restriction as well.

[o-mid]

@ignaciosantise still merge-ready after catching latest develop. Please approve/apply when you can.