ci: make the tree rustfmt-clean and gate on it

[Steel-tech]

Closes the one deliberate gap left by the CI work: formatting was unenforced because the tree was not rustfmt-clean.

Why now, and why not a config

Before reformatting, I tested whether a rustfmt.toml could be tuned to match the existing hand-formatted style instead. It cannot:

Config	Differing hunks
defaults (baseline)	93
max_width = 110	91
max_width = 120	111
use_small_heuristics = "Max"	156–247

Nothing approaches zero. The tree is formatted case-by-case — sometimes more broken up than rustfmt wants, sometimes less — which no single config reproduces. That left a binary choice, and enforcing the standard formatter is the one that stops the drift.

Two commits, deliberately

style: apply cargo fmt across the workspace is pure cargo fmt --all output with no hand edits, so it can be skimmed as "rustfmt did this" rather than reviewed line by line. ci: gate on cargo fmt --check adds the job. Reviewing them separately is much cheaper than reviewing the squashed diff.

Verification

• cargo fmt --all --check clean, and idempotent (a second run is a no-op)
• 91 tests pass, unchanged
• cargo clippy --all-targets -- -D warnings still silent
• The new fmt job passes locally before being pushed

The fmt job skips rust-cache on purpose: rustfmt parses sources and never builds, so there is nothing to restore and the cache round-trip would cost more than the job.

Post-Deploy Monitoring & Validation

Expect four green jobs (test ×2, fmt, clippy). The fmt job should be among the fastest since it does no compilation. Going forward, a red fmt means someone committed unformatted code — the fix is always cargo fmt --all, never editing the job. rustfmt ships in the pinned toolchain, so contributors already have the matching version.

No runtime or production impact — formatting and CI configuration only.

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Summary by CodeRabbit

• Chores
  • Added an automated formatting check to continuous integration.
  • Applied consistent Rust formatting across authentication, CLI, sandbox, storage, tool, and language-model components.
  • Improved readability of expressions, function signatures, assertions, test fixtures, and chained calls without changing functionality or public interfaces.

[coderabbitai]

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 1a826fa1-5cfd-4e8e-84a1-5175f7b2d934

📥 Commits

Reviewing files that changed from the base of the PR and between 4c17fdb and b50ee68.

📒 Files selected for processing (1)

• .github/workflows/ci.yml

📝 Walkthrough

Walkthrough

This pull request adds a GitHub Actions formatting check and applies cargo fmt formatting across Rust source files and tests. No runtime behavior or public API changes are reported.

Changes

Rust formatting

Layer / File(s)	Summary
CI formatting check .github/workflows/ci.yml	Adds an Ubuntu job that installs the pinned Rust toolchain and runs cargo fmt --all --check.
Application crate formatting crates/agent/..., crates/auth/..., crates/cli/..., crates/harness/...	Reformats signatures, expressions, patterns, assertions, fixtures, and test calls without changing behavior.
LLM, sandbox, and storage formatting crates/llm/..., crates/sandbox/..., crates/store/...	Reformats parsing, sandbox, storage, recovery, and test code without changing behavior.
Tool crate formatting crates/tools/...	Reformats Bash, filesystem, registry, search, and test code without changing behavior.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• StructuPath/bullpen#2: Introduces the existing CI workflow and pinned-toolchain setup extended by this formatting job.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 79.37% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes both the rustfmt cleanup and the new CI gate, which are the main changes in the pull request.
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.

✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci/rustfmt-gate

---

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In @.github/workflows/ci.yml:
- Around line 48-54: Restrict the fmt job’s GITHUB_TOKEN permissions by adding a
job-level permissions block granting only read access to repository contents.
Keep the existing checkout configuration unchanged.

🪄 Autofix

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: 5746b3d3-f038-49cd-80ea-88b6bccf6303

📥 Commits

Reviewing files that changed from the base of the PR and between d03ec60 and 4c17fdb.

📒 Files selected for processing (21)

• .github/workflows/ci.yml
• crates/agent/src/lib.rs
• crates/auth/src/codex.rs
• crates/auth/src/lib.rs
• crates/auth/src/openrouter.rs
• crates/auth/src/pkce.rs
• crates/cli/src/agents.rs
• crates/cli/src/main.rs
• crates/harness/src/lib.rs
• crates/harness/src/pen.rs
• crates/llm/src/anthropic.rs
• crates/llm/src/chatcompletions.rs
• crates/llm/src/codex.rs
• crates/llm/src/lib.rs
• crates/sandbox/src/lib.rs
• crates/store/src/lib.rs
• crates/store/src/recovery.rs
• crates/tools/src/bash.rs
• crates/tools/src/fs.rs
• crates/tools/src/lib.rs
• crates/tools/src/search.rs