Add eth_sendPrivateTransaction support (closes #40)

[koko1123]

What

Implements MEV-Share's eth_sendPrivateTransaction on flashbots.Relay per #40: submit a single private transaction with configurable searcher hints.

• SendPrivateTxOpts: raw signed tx, optional max_block_number (omitted = relay default of current+25), optional TxPreferences (fast mode, calldata/contract_address/logs/function_selector hint flags, builder list)
• Wire format matches the MEV-Share spec: preferences.fast + preferences.privacy.{hints,builders}; the privacy object is omitted when no hints/builders are set
• New parseTxHashResult for the bare-string result shape (bundle methods return an object)
• Reuses the existing X-Flashbots-Signature authenticated request path

Tests

Param-builder tests (minimal, full preferences, fast-only) with exact-JSON assertions, and result-parser tests (success, RPC error, null result). Pass on 0.16.0 and 0.17.0-dev.

Sets up MevShareClient.sendTransaction for #34.

Closes #40

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Added support for sending private transactions with customizable privacy preferences, including hint options (calldata, contract address, logs, function selector), builder selection, fast mode, and inclusion block targeting.

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Project	Deployment	Actions	Updated (UTC)
eth-zig	Ready	Preview, Comment	Jun 10, 2026 2:04pm

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 09091de8-c619-4958-b405-a73ff078eb72

📥 Commits

Reviewing files that changed from the base of the PR and between d07f3b8 and a47d11e.

📒 Files selected for processing (2)

• CHANGELOG.md
• src/flashbots.zig

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📝 Walkthrough

Walkthrough

This PR adds MEV-Share's eth_sendPrivateTransaction capability to the Flashbots Relay client, enabling submission of single private transactions with configurable privacy hint preferences and builder selection. It introduces new request and response types, a public relay method, JSON-RPC parameter builders, response parsing, and comprehensive unit tests.

Changes

MEV-Share Private Transaction Submission

Layer / File(s)	Summary
Request and response types src/flashbots.zig	SendPrivateTxOpts defines transaction bytes, optional max block number, and optional TxPreferences with hint flags (calldata, contract_address, logs, function_selector) and optional builders list. SendPrivateTxResult contains the returned transaction hash.
Relay method and JSON-RPC implementation src/flashbots.zig	Relay.sendPrivateTransaction constructs JSON-RPC params, sends an authenticated Flashbots-signed HTTP request, and parses the response. buildSendPrivateTxParams hex-encodes the transaction, conditionally emits maxBlockNumber, and generates a preferences object with fast flag and optional privacy sub-object containing hints and/or builders. parseTxHashResult validates the JSON-RPC response shape and extracts the hex transaction-hash string into SendPrivateTxResult.
Tests and changelog src/flashbots.zig, CHANGELOG.md	Unit tests assert minimal JSON output, full preferences with privacy.hints and privacy.builders, fast-only omission of the privacy object, and response parsing success/error paths. Changelog documents the new eth_sendPrivateTransaction capability with hint preferences and builder selection.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 A little hop through MEV-Share's gate,
Where privacy preferences now dictate,
Hints and builders configured just right,
Private txs bundled and out of sight! 🌙

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Add eth_sendPrivateTransaction support' clearly and concisely describes the main change in the PR, which adds MEV-Share support for eth_sendPrivateTransaction to the flashbots.Relay.
Linked Issues check	✅ Passed	All objectives from issue #40 are met: SendPrivateTxOpts and SendPrivateTxResult types are implemented with correct fields, TxPreferences struct includes all required hint flags and builders list, wire format follows MEV-Share spec with proper preferences/privacy structure, X-Flashbots-Signature auth is reused, and tests validate the implementation.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to issue #40: CHANGELOG.md documents the new feature, src/flashbots.zig implements the required types and sendPrivateTransaction method with supporting helpers and tests. No extraneous modifications detected.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/send-private-tx

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