chore: update rust to nightly build

[jwilger]

Summary by CodeRabbit

• Chores
  • Updated development environment configuration and dependencies for improved consistency
  • Switched Rust compiler to nightly channel to leverage advanced language features
  • Simplified development shell initialization by streamlining automatic setup processes
  • Standardized build dependencies through Nix for better cross-platform compatibility

[coderabbitai]

📝 Walkthrough

Walkthrough

The Nix development shell is simplified by removing nodePackages.prettier, git, and gh from build inputs and eliminating automatic cargo-mcp installation from the shell hook. The Rust toolchain channel is switched from stable to nightly while maintaining all existing components.

Changes

Cohort / File(s)	Summary
Development Shell Configuration flake.nix	Removed nodePackages.prettier, git, and gh from buildInputs; removed automatic cargo install --locked cargo-mcp from shellHook; pre-commit setup retained.
Rust Toolchain Channel rust-toolchain.toml	Switched Rust toolchain channel from stable to nightly; component list (rustfmt, clippy, rust-src, rust-analyzer) and profile unchanged.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🐰 twitches whiskers excitedly

The shell grows lean, dependencies shed,
Prettier finds its Nix-native bed,
Nightly Rust now takes the lead—
A simpler dev setup, indeed!

🚥 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 accurately reflects the main change: switching the Rust toolchain from stable to nightly in rust-toolchain.toml.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch deps

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

flake.nix (1)

46-64: Clarify Cargo MCP Server setup expectations in docs.

README.md mentions "Cargo MCP Server" features (line 384), but the dev shell doesn't auto-install cargo-mcp. Update onboarding docs or bootstrap instructions to explicitly describe the manual setup process or state the feature is optional.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@flake.nix` around lines 46 - 64, The README references "Cargo MCP Server" but
the dev shell (shellHook) doesn't provide or install cargo-mcp; either document
the manual setup or make shellHook install it. Update README.md near the "Cargo
MCP Server" mention to add a short onboarding note with the exact manual command
(e.g., use cargo install cargo-mcp with CARGO_HOME set) and mark the feature as
optional, or modify the shellHook to check for cargo-mcp and run cargo install
--root "$PWD/.dependencies/rust/cargo" cargo-mcp when missing; refer to
shellHook, cargo-mcp, and CARGO_HOME/CARGO_HOME environment in your change.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@rust-toolchain.toml`:
- Line 2: Local toolchain uses nightly (rust-toolchain.toml channel = "nightly")
but CI workflows hardcode stable (dtolnay/rust-toolchain@stable) and the nightly
matrix is marked optional, causing CI drift; update the CI and release workflows
to match the repository toolchain: replace dtolnay/rust-toolchain@stable with
dtolnay/rust-toolchain@nightly (or read the repo toolchain dynamically) in the
ci.yml and release-plz.yml jobs, and remove or disable continue-on-error for the
nightly entry in toolchain-matrix.yml so nightly failures block merges; search
for dtolnay/rust-toolchain, ci.yml, release-plz.yml, and toolchain-matrix.yml to
locate and change the relevant job definitions.

---

Nitpick comments:
In `@flake.nix`:
- Around line 46-64: The README references "Cargo MCP Server" but the dev shell
(shellHook) doesn't provide or install cargo-mcp; either document the manual
setup or make shellHook install it. Update README.md near the "Cargo MCP Server"
mention to add a short onboarding note with the exact manual command (e.g., use
cargo install cargo-mcp with CARGO_HOME set) and mark the feature as optional,
or modify the shellHook to check for cargo-mcp and run cargo install --root
"$PWD/.dependencies/rust/cargo" cargo-mcp when missing; refer to shellHook,
cargo-mcp, and CARGO_HOME/CARGO_HOME environment in your change.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 3678067d-7c76-4823-b544-fef0c4a698e3

📥 Commits

Reviewing files that changed from the base of the PR and between 352ec23 and c64a899.

⛔ Files ignored due to path filters (1)

• flake.lock is excluded by !**/*.lock

📒 Files selected for processing (2)

• flake.nix
• rust-toolchain.toml

[coderabbitai]

⚠️ Potential issue | 🟠 Major

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "== rust-toolchain.toml =="
rg -n '^\s*channel\s*=' rust-toolchain.toml

echo
echo "== Workflow toolchain pins and gating =="
rg -n -C2 --iglob '.github/workflows/*.yml' \
  'dtolnay/rust-toolchain@|matrix\.toolchain|continue-on-error|cargo clippy --all-targets --all-features -- -D warnings'

Repository: jwilger/caxton

Length of output: 315

---

🏁 Script executed:

# List all workflow files
find .github/workflows -type f -name "*.yml" -o -name "*.yaml" | head -20

Repository: jwilger/caxton

Length of output: 312

---

🏁 Script executed:

# Search for toolchain configuration patterns in workflows
rg -n 'dtolnay/rust-toolchain|toolchain' .github/workflows/ -A 2 -B 2

Repository: jwilger/caxton

Length of output: 6696

---

Toolchain channel change is not propagated to CI/release workflows.

Local development is set to nightly, but critical workflows hardcode stable: ci.yml uses dtolnay/rust-toolchain@stable in 4 jobs (lines 25, 49, 74, 97), and release-plz.yml uses it in 3 jobs (lines 230, 330, 409). The toolchain-matrix.yml does test nightly but marks non-stable as optional (continue-on-error: true on line 19), so failures won't block merges. This creates local-vs-CI drift where nightly-specific issues or failures may be missed.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@rust-toolchain.toml` at line 2, Local toolchain uses nightly
(rust-toolchain.toml channel = "nightly") but CI workflows hardcode stable
(dtolnay/rust-toolchain@stable) and the nightly matrix is marked optional,
causing CI drift; update the CI and release workflows to match the repository
toolchain: replace dtolnay/rust-toolchain@stable with
dtolnay/rust-toolchain@nightly (or read the repo toolchain dynamically) in the
ci.yml and release-plz.yml jobs, and remove or disable continue-on-error for the
nightly entry in toolchain-matrix.yml so nightly failures block merges; search
for dtolnay/rust-toolchain, ci.yml, release-plz.yml, and toolchain-matrix.yml to
locate and change the relevant job definitions.