feat(sof-tx): add SOF plugin-host adapters — bridge runtime signals into tx providers

[Lythaeon]

Description

Add an optional adapter layer in sof-tx that bridges live sof plugin events into RecentBlockhashProvider and LeaderProvider.

This closes the integration gap between observer runtime signals and tx submission routing without forcing sof as a default dependency for all SDK users.

Changes

• crates/sof-tx/Cargo.toml
  • Added sof-adapters feature.
  • Added optional dependency on workspace crate sof.
• crates/sof-tx/src/lib.rs
  • Exposed adapters module behind sof-adapters feature flag.
• crates/sof-tx/src/adapters/mod.rs
  • Added adapter module export surface.
• crates/sof-tx/src/adapters/plugin_host.rs
  • Added PluginHostTxProviderAdapter + PluginHostTxProviderAdapterConfig.
  • Implemented ObserverPlugin, RecentBlockhashProvider, and LeaderProvider.
  • Added state handling for:
    • observed recent blockhash events,
    • cluster topology TPU endpoint updates,
    • leader schedule updates with bounded slot retention.
  • Added helper methods:
    • prime_from_plugin_host(...)
    • set_leader_tpu_addr(...)
    • remove_leader_tpu_addr(...)
  • Added adapter unit tests for event ingestion, target resolution, bounded retention, and host priming.
• crates/sof-tx/README.md
  • Documented sof-adapters feature.
  • Added end-to-end integration snippet for PluginHostTxProviderAdapter.

For slice-related changes, include:

• Affected slices: none (sof-tx crate only).
• Cross-slice communication changes: none.
• Migration requirements: none (additive feature).

Motivation

Business motivation:

• Make sof-tx + sof composition practical for latency-sensitive users without custom glue code.

Technical motivation:

• Provide first-party adapter primitives so tx routing can consume observer-derived leader and blockhash signals.

Alternative approaches considered:

• Keep requiring downstream projects to implement providers/plugins manually.
• Add hard dependency from sof-tx to sof (rejected to preserve lightweight default SDK footprint).

Scope and impact

• Affected slices: N/A (sof-observer internals unchanged).
• Data/API changes: additive APIs under sof-adapters feature.
• Backward compatibility: preserved; default behavior unchanged.
• Performance impact: minimal; adapter uses bounded in-memory state.
• Security impact: no new privileged operations.

Testing

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

Commands/results:

cargo test -p sof-tx
cargo test -p sof-tx --features sof-adapters

Both commands passed.

Related issues and documentation

• Fixes: N/A
• Related: ADR transaction SDK integration phase
• Architecture docs: docs/architecture/README.md
• Relevant ARD/ADR: docs/architecture/adr/0006-transaction-sdk-and-dual-submit-routing.md
• Operations/runbook updates: N/A

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

• PluginHostTxProviderAdapter is intentionally feature-gated so RPC-only sof-tx users keep the current dependency surface.