feat(tx): add typed Jito transport — fuzzed submit coverage

[Lythaeon]

Description

This PR adds typed Jito transport support to sof-tx, adds standalone fuzz coverage for the major submit and routing paths, and updates the docs so SOF is described as low-latency market infrastructure rather than a generic observer framework.

It matters because Jito is now a first-class submit path alongside RPC/direct/hybrid, the configuration surface is typed and documented with defaults, and the new fuzz package gives sof-tx the same kind of sustained hot-path validation the observer side already had.

Changes

• crates/sof-tx/src/submit/jito.rs, crates/sof-tx/src/submit/types.rs, and crates/sof-tx/src/submit/client.rs: typed Jito transport/config surface with a default mainnet endpoint, typed auth token/endpoint types, and client wiring for JitoOnly submit mode.
• crates/sof-tx/src/builder.rs: add explicit reset helpers for compute-unit-limit and priority-fee instructions so callers can toggle those knobs without rebuilding the builder from scratch.
• crates/sof-tx/fuzz/*: add a standalone sof-tx fuzz package with one target per hot path: submit_jito_mode, submit_rpc_only, submit_direct_only, submit_hybrid, routing_select_targets, signature_deduper, and tx_builder_toggles.
• README.md, crates/sof-observer/README.md, crates/sof-tx/README.md, and docs/README.md: update the framing and docs copy to position SOF as low-latency market/financial infrastructure and document Jito defaults/configuration more explicitly.

For slice-related changes:

• Affected slices: sof-tx submit/routing/builder plus top-level crate/docs surfaces.
• Cross-slice communication changes: none; this stays within sof-tx and documentation layers.
• Migration requirements: none; the Jito surface is additive.

Motivation

Business motivation:

• Make Jito submission a first-class path for users who need block-engine delivery without pushing them into stringly configuration or private local patches.
• Tighten the public framing so SOF reads like the kind of infrastructure it is being used as in production.

Technical motivation:

• Replace string-based Jito setup with typed endpoint/auth/config types and a default constructor that works out of the box.
• Add dedicated fuzz coverage for the sof-tx hot paths, not just observer-side fuzzing.
• Provide builder reset helpers so the builder API supports explicit on/off tuning transitions cleanly.

Alternative approaches considered:

• Leaving Jito setup as ad hoc strings: rejected because it weakens the API and embedding UX.
• Reusing one combined fuzz target for all submit modes: rejected because it makes crash ownership and corpus management worse.

Scope and impact

• Affected slices: sof-tx submit, routing, and builder surfaces; top-level docs.
• Data/API changes: additive JitoOnly transport/config API and additive builder reset helpers.
• Backward compatibility: preserved; existing RPC/direct/hybrid flows continue to work.
• Performance impact: neutral in normal operation, positive in validation coverage; fuzz targets now exercise the submit and routing hot paths directly.
• Security impact: no new privileged behavior; Jito auth stays explicit and typed.

Testing

• Unit tests
• Integration tests
• Manual verification
• Performance checks (if applicable)
• Security checks (if applicable)

Commands/results:

cargo make ci
cargo check --manifest-path crates/sof-tx/fuzz/Cargo.toml --bins
cd crates/sof-tx/fuzz && cargo +nightly fuzz run submit_jito_mode -- -max_total_time=300
cd crates/sof-tx/fuzz && cargo +nightly fuzz run submit_rpc_only -- -max_total_time=300
cd crates/sof-tx/fuzz && cargo +nightly fuzz run submit_direct_only -- -max_total_time=300
cd crates/sof-tx/fuzz && cargo +nightly fuzz run submit_hybrid -- -max_total_time=300
cd crates/sof-tx/fuzz && cargo +nightly fuzz run routing_select_targets -- -max_total_time=300
cd crates/sof-tx/fuzz && cargo +nightly fuzz run signature_deduper -- -max_total_time=300
cd crates/sof-tx/fuzz && cargo +nightly fuzz run tx_builder_toggles -- -max_total_time=300

All of the above passed. The 5-minute fuzz runs completed without surfacing crashes.

Related issues and documentation

• Fixes:
• Related:
• Architecture docs: docs/architecture/README.md
• Relevant ARD/ADR: docs/architecture/adr/0004-static-dispatch-and-performance-layout.md, docs/architecture/adr/0006-transaction-sdk-and-dual-submit-routing.md
• Operations/runbook updates: README/docs positioning and Jito configuration defaults updated in crate docs.

Reviewer checklist

• Code follows project standards and architecture constraints
• Slice boundaries are respected (docs/architecture/ard/0003-slice-dependency-contracts.md)
• Tests added/updated and passing
• Documentation updated (README/docs/operations as needed)
• No undocumented breaking change
• Performance trade-offs documented where relevant
• Security considerations addressed where relevant

Additional notes

• GitHub repository metadata was also updated out-of-band so the short description now matches the project positioning in the docs.