fix(core-dart): detect C address sourceAccount and emit CONTRACT_SEND…

[Manuelshub]

Closes #74

fix(core-dart): detect C address sourceAccount and emit CONTRACT_SENDER_DETECTED warning

Problem

extractRouting in the Dart implementation ignored the sourceAccount field
on RoutingInput entirely. If a contract address (C...) was supplied as the
transaction source, it passed through silently with no warning — leaving
downstream pipeline consumers with no signal that the routing context was
invalid.

The Go implementation already handled this correctly by checking sourceAccount
at the top of ExtractRouting and returning early with a
CONTRACT_SENDER_DETECTED warning. The Dart implementation was out of parity.

Solution

Added a sourceAccount check at the entry point of extractRouting, mirroring
the Go behavior exactly. If sourceAccount is non-null, non-empty, and parses
as a C address, the function returns early with:

• routingSource: none
• warnings: [CONTRACT_SENDER_DETECTED] (severity: info)

All other routing logic is bypassed, consistent with the spec.

Files Changed

• packages/core-dart/lib/src/routing/extract.dart

Testing

All routing and spec vector tests pass.

dart test test/routing_test.dart test/spec_runner_test.dart
# +24: All tests passed!

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[codeZe-us]

@Manuelshub This is okay