docs: document SAC decoder test coverage and conventions

[joan-bisbal]

Documents the testing conventions for SAC event decoding: what the existing suite covers (registry resolution, XDR payload decoding, asset context attachment) and what a new test for an additional token standard should assert.

Intended as a guide for contributors extending the decoder, not as new coverage -- sac.rs and token_events.rs already carry 42 tests between them.

No code changes -- documentation only.

[Depo-dev]

This is test: add unit tests for SAC decoder module, but the diff contains no tests — just a three-line file describing them. A test PR needs actual #[test] functions.

The SAC decoder already has unit tests as well: crates/indexer/src/parser/sac.rs has a mod tests with 11 cases covering registry lookup and asset-context attachment, and crates/indexer/src/parser/token_events.rs covers the SEP-41 event decoding alongside it.

If you want to strengthen coverage there, the useful contribution would be additional cases against the existing module — malformed XDR, unusual asset codes, contracts that are not in the registry — as real Rust tests that run in CI. Please target dev rather than main, and drop the UTF-8 BOM on any new file.

[Depo-dev]

Hey @joan-bisbal — same story as #347, and this one needs the most reframing of the three.

The title is test: add unit tests for SAC decoder module, but the diff adds zero tests. It adds docs/sac_decoder_unit_tests.md, which contains test code as markdown examples. That's a meaningful difference: someone scanning the log sees a PR that raised test coverage, and coverage didn't move.

Worth knowing too — that module is already covered. crates/indexer/src/parser/sac.rs has 11 #[test] functions on dev right now and token_events.rs has 31, including the registry lookup and malformed-XDR cases your doc uses as examples. So this isn't filling a gap so much as writing down the conventions the existing tests already follow, which is still worth having, just not under a test: prefix.

Could you retitle to docs: document SAC decoder test coverage and conventions, and rewrite the description along these lines:

Documents the testing conventions for SAC event decoding: what the existing suite covers (registry resolution, XDR payload decoding, asset context attachment) and what a new test for an additional token standard should assert.

Intended as a guide for contributors extending the decoder, not as new coverage — sac.rs and token_events.rs already carry 42 tests between them.

No code changes — documentation only.

If you'd rather this PR actually added tests, that'd be even better — the one real gap I can see is boundary coverage for truncated XDR streams, which your doc mentions but the existing suite doesn't fully exercise. Either direction works; just let the title match whichever you pick.

[joan-bisbal]

Thanks for the review. All changes done:

• Retitled to docs: document SAC decoder test coverage and conventions
• Updated the description to clarify this is a contributor guide for the existing 42-test suite, not new coverage
• Renamed file to kebab-case (sac-decoder-test-conventions.md)

Ready for re-review.