style: clear two of the lint backlog items blocking every merge (fmt + GC knob kill-policy)

[proggeramlug]

lint is red repo-wide, so nothing merges. The failures are stacked — each one hides the next, which is why they surfaced one at a time:

#	step	state
1	Public benchmark evidence freshness	red — maintainer-only (needs Node v22.23.1 + Bun 1.3.14, AC power, quiet host). #7012 also reports it cannot regenerate from a clean checkout.
2	cargo fmt --all -- --check	red — fixed here
3	check_file_size.sh (2000-line cap)	red — 7 files, listed below, not touched here
4	addr_class_inventory.py	red on native_module/constants.rs:2088

This PR clears (2) and adds the knob kill-policy. It does not pretend to unblock lint on its own — (1) is not delegable and (3)/(4) are separate changes.

Part 1 — rustfmt

Four files had drifted:

crates/perry-codegen/src/lower_call/native/mod.rs
crates/perry-runtime/src/object/global_this/install_static.rs
crates/perry/src/commands/check.rs
crates/perry/src/commands/deps.rs

Pure formatting — the entire diff is four call/macro argument lists being wrapped. +12/−10.

Part 2 — GC knob kill-policy in CLAUDE.md

Every GC env knob either has a required CI arm exercising its OFF state, or it is deleted after one release of soak. At most one diagnostic-only knob, labelled untested.

Written down because this project has paid for unexercised modes three times in the last week:

• PERRY_GC_FORCE_EVACUATE was inert for every gc()-driven test — it is read only on the minor path, while gc() runs a full mark-sweep with a forced conservative scan (gc: no reachable configuration exercises an evacuating minor with unpinned runtime locals — the #6655/#6935 bug class is untestable #6942/GC testing: PERRY_GC_FORCE_EVACUATE is inert for gc()-driven tests (full mark-sweep + forced conservative scan) — stress claims may be unsupported #6946). Months of "passes under evacuation" meant nothing.
• The matrix's --pressure knob disabled the very path it was measuring — the defer hard cap and the arena-trigger ceiling share a formula and collapse together, so the default arm ran zero copying minors on all 22 rows (gc-matrix: --pressure disables the very path #7019 added — the 'default' arm runs ZERO copying minors on all 22 corpus rows #7024).
• gc_incremental_enabled's doc said "EXPERIMENTAL — default OFF" eight lines above a body comment saying "DEFAULT ON" (gc: policy gate docs state "default OFF" while the code defaults ON (gc_incremental_enabled, gc_safepoint_moving_minor) — this caused #6972 to dismiss a real concern #6987). A merge decision was made on the wrong one.

The principle: a mode that still exists is a decision that hasn't been made. When a knob's off-state stops being exercised, the off-state and the branch behind it should stop compiling, rather than lingering as an untested configuration a future bisect will trust.

For whoever takes item (3)

The 7 files over the cap:

2054  crates/perry-codegen/src/codegen/typed_abi.rs
2135  crates/perry-codegen/src/expr/index_get.rs
2013  crates/perry-runtime/src/array/generic.rs
2081  crates/perry-runtime/src/gc/tests/layout_trace.rs
2210  crates/perry-runtime/src/object/native_module/callable_export_check.rs
2255  crates/perry-runtime/src/object/native_module/callable_exports.rs
2421  crates/perry-runtime/src/object/native_module/constants.rs

Deliberately untouched: splitting seven files is a mechanical but non-trivial change and folding it into a formatting PR would make both unreviewable.

Validation

cargo fmt --all -- --check clean on this branch. No semantic change, so no behavioural verification is claimed.

Summary by CodeRabbit

• Documentation

  • Added binding guidance for managing and testing garbage-collection environment toggles.
  • Documented requirements for removing stale or untested diagnostic modes.

• Style

  • Applied Rust formatting fixes across several files and test assertions.
  • Updated the changelog to record formatting-only maintenance with no behavior changes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 7eadc21f-5e20-48ac-8696-e13a30765a38

📥 Commits

Reviewing files that changed from the base of the PR and between 926c11f and 0b0dda9.

📒 Files selected for processing (6)

• CLAUDE.md
• changelog.d/7042-lint-fmt-backlog.md
• crates/perry-codegen/src/lower_call/native/mod.rs
• crates/perry-runtime/src/object/global_this/install_static.rs
• crates/perry/src/commands/check.rs
• crates/perry/src/commands/deps.rs

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📝 Walkthrough

Walkthrough

The PR documents binding policy for GC environment knobs and reformats four Rust code locations to satisfy rustfmt checks. It also adds a changelog entry describing the formatting-only updates.

Changes

GC knob policy

Layer / File(s)	Summary
GC knob policy documentation CLAUDE.md	Documents CI coverage, soak-based removal, and limits for untested diagnostic-only GC environment knobs.

Rust formatting cleanup

Layer / File(s)	Summary
Rustfmt compliance updates crates/perry-codegen/src/lower_call/native/mod.rs, crates/perry-runtime/src/object/global_this/install_static.rs, crates/perry/src/commands/check.rs, crates/perry/src/commands/deps.rs, changelog.d/7042-lint-fmt-backlog.md	Reformats call arguments, a method tuple, and test assertions without changing values or behavior; the changelog records the formatting-only updates.

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

Possibly related PRs

• PerryTS/perry#7005: Concerns the same Reflect setPrototypeOf entry referenced by one formatting-only change.

Suggested reviewers: andrewtdiz, jdalton

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the two main changes: rustfmt cleanup and the GC knob kill-policy documentation.
Description check	✅ Passed	It covers summary, concrete changes, and validation, though the template's Related issue and checklist sections are omitted.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
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

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/lint-fmt-backlog

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