fix: return preflight simulation errors as 400 instead of 500

[findolor]

Motivation

When a swap calldata request fails due to a preflight simulation error (e.g. "ERC20: transfer amount exceeds balance"), the API returns a generic 500 Internal Server Error with "failed to generate calldata". This hides the actual cause from callers and makes it look like a server bug when it's really an on-chain condition the user can act on.

Solution

• Add explicit match arm for RaindexError::PreflightError in map_raindex_error() so it returns a 400 Bad Request with the readable error message instead of falling through to the catch-all 500 Internal Error.
• Export COMMIT_SHA automatically in the nix dev shell (flake.nix) so local builds no longer require manually setting the env var.
• Add dev-config.toml for local development and gitignore docs/book/ build output.

Checks

By submitting this for review, I'm confirming I've done the following:

• made this PR as small as possible
• unit-tested any new functionality
• linked any relevant issues or PRs
• included screenshots (if this involves a front-end change)

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Enhanced error handling for preflight validation failures with improved, user-friendly diagnostic messages. Users now receive clearer feedback when validation checks fail.

• Chores

  • Added development configuration file with settings for logging, database connectivity, and external registry endpoints.
  • Updated development environment setup to automatically include build metadata and commit tracking information.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between d773fed and 706b878.

📒 Files selected for processing (4)

• .gitignore
• dev-config.toml
• flake.nix
• src/routes/swap/mod.rs

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📝 Walkthrough

Walkthrough

The changes introduce development configuration, update the Nix development shell, and extend error handling. A new dev configuration file is added with paths and rate limits, the shell environment is modified to include a COMMIT_SHA variable derived from Git HEAD, error handling for preflight validation failures is added to the swap route, and the gitignore is updated to exclude documentation build artifacts.

Changes

Cohort / File(s)	Summary
Configuration & Documentation .gitignore, dev-config.toml	Added gitignore entry for docs/book/ and introduced new development configuration file with settings for logging directory, SQLite database URL, registry URL, rate limits, and documentation directory.
Build Environment flake.nix	Modified devShells.default to explicitly define shellHook, extending the base rainix shellHook with a COMMIT_SHA environment variable set to Git HEAD or "dev" as fallback.
Error Handling src/routes/swap/mod.rs	Extended map_raindex_error to handle RaindexError::PreflightError by logging a warning and returning ApiError::BadRequest with the error's readable message.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 Hops in with glee 🌿
Config files align, docs are tucked away,
COMMIT_SHA now tracks the way,
Preflight errors caught and styled so neat—
Development paths are complete! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: fixing error handling to return 400 instead of 500 for preflight simulation errors, which aligns with the primary code change in src/routes/swap/mod.rs.
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 docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/preflight-error-handling

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