event emission on all pool swap state changes for indexers

[mikewheeleer]

Summary

Some pool swap state changes emit no event, so indexers and off-chain systems can't observe them. Emit a documented event on every state change, with tests.

Why this matters

Silent state changes are invisible to indexers and break downstream systems. Complete, tested events make the contract observable.

Requirements

• Emit a documented event on every pool swap state change, with the relevant fields.
• No duplicate or missing emissions.
• Assert topics and payload fields in tests.
• Keep topic symbols within Soroban limits.

Technical guidance

• Capture events immediately after the emitting call in tests.
• Avoid topic collisions across event types.

Edge cases — each must have a test

• each state change -> exactly one event
• payload fields correct
• topic symbols valid and unique
• no duplicate emissions
• read-only calls emit nothing

Acceptance criteria

• All requirements and every edge case above implemented and covered by tests
• New unit and integration tests; existing tests still pass and no regressions
• Structured, typed errors (no leaked internals; stable codes)
• cargo fmt --check, cargo clippy --all-targets -- -D warnings, and cargo test all pass locally
• Code follows the repo's existing conventions; no duplication or dead code
• Short docs/comments explaining the design and any non-obvious decisions
• PR description explains the approach and includes Closes #<issue>

Out of scope

• Event schema versioning
• Indexer implementation

Rewards

Part of the GrantFox OSS / Official Campaign (FWC26) — this task may be rewarded. PR quality is assessed by AI: depth, correctness under edge cases, meaningful tests, and clean design are what earn the reward. Shallow changes (typos, formatting, trivial docs) do not qualify.

[Baskarayelu]

I’d love to be assigned this issue and contribute across the relevant areas, whether it involves smart contracts, UI development, backend logic, design implementation, or overall system integration. I’m comfortable working across the full stack and can adapt to the project’s technical requirements to ensure a smooth and consistent contribution.

[grantfox-oss]

🦊 GrantFox — @Baskarayelu has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #458)
2. Your PR will be reviewed by the StableRoute-Org maintainers

Good luck! Track your progress on GrantFox.

[Baskarayelu]

Implemented and opened PR #466: #466

The refreshed main branch already contained the canonical route event for compute_route_fee. The PR formalizes the full contract with exact-topic/payload/order tests and documentation: bounded routes emit liq_used then route, unbounded routes emit only route, batches emit one per-entry route event, and quotes/failures emit neither. It also documents indexer handling and preserves ABI compatibility without adding a duplicate swap event.

Validation: cargo fmt --check, focused event tests (8 passed), and full cargo test (328 passed).