[2026 Testing] Add a nightly testnet smoke suite for real Horizon and RPC flows

[Nanle-code]

Objective

Catch breakage from network upgrades, testnet resets and SDK drift that mocked tests miss.

Target area

tests/e2e, .github/workflows

Context

Most e2e tests use fixtures and mocks, which is right for PRs but hides real-network regressions like protocol changes, RPC behaviour and Friendbot outages.

Acceptance criteria

• A scheduled workflow funds a fresh testnet account and runs: payment, trustline, path payment, contract deploy and invoke, event read.
• Failures open or update a tracking issue automatically, with logs.
• Transient network failures are retried and reported separately from assertion failures.
• The suite runs in under 10 minutes and has no mainnet access.
• Automated tests cover the primary flow, at least one boundary case, and at least one failure case.
• User-facing documentation or developer guidance is updated, including compatibility, security, or migration notes where applicable.

Pull request requirements

• All continuous integration checks must pass before a pull request may be merged.
• The branch must be free of merge conflicts with the target branch at the time of merge.
• Do not request merge with failing workflows, skipped required checks, or unresolved conflicts.

[drips-wave]

@Nanle-code This issue could not be added to the Stellar Wave Program because the per-repo points budget would be exceeded (25000 / 25000 points already used). The label has been automatically removed.

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