docs: update agent guidance

[kdy1]

Description:

Adds agent guidance requested from PR review feedback:

• Respect the project MSRV when writing Rust code.
• Keep new swc_ecma_minifier regression coverage out of tests/terser and prefer SWC-owned fixtures such as tests/fixture/issues.

This is documentation-only and helps future automated edits choose the right compatibility and fixture behavior.

BREAKING CHANGE:

None.

Related issue (if exists):

Refs #11830 (comment)

[changeset-bot]

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Latest commit: 410c301

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[github-actions]

Binary Sizes

File	Size
swc.linux-x64-gnu.node	27M (27759688 bytes)

Commit: aa68740

[codspeed-hq]

Merging this PR will not alter performance

✅ 219 untouched benchmarks
⏩ 31 skipped benchmarks¹

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_{Comparing kdy1/docs-agent-guidance (410c301) with main (9101c71)}

Footnotes

1. 31 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[claude]

Review

Documentation-only change to AGENTS.md files. Both additions look reasonable and address concrete pain points raised in PR #11830. A few constructive observations:

MSRV rule (root AGENTS.md)

Respect the project's MSRV. Do not rely on Rust language features or standard library APIs newer than the MSRV unless the change intentionally raises the MSRV.

The guidance is sound, but it isn't actionable as written because the repo doesn't appear to declare an MSRV anywhere I can find:

• No rust-version field in the workspace Cargo.toml or in any per-crate Cargo.toml.
• rust-toolchain pins nightly-2026-04-10, which conflicts with the spirit of an MSRV.
• No MSRV mention in docs.

An agent reading this rule has no concrete version to compare against. Two options to make it enforceable:

1. Add rust-version = "..." to the workspace [workspace.package] (and inherit per-crate), then this rule has a single source of truth.
2. Or amend the rule to point at the canonical reference, e.g. "check <file> for the MSRV" or name the version inline.

Without one of those, this rule is hard to follow consistently.

tests/terser rule (crates/swc_ecma_minifier/AGENTS.md)

Do not add new regression coverage to tests/terser. Use SWC-owned fixtures such as tests/fixture/issues instead.

Good clarification, and dropping tests/terser from preferred fixture roots is consistent. One small suggestion: a one-line why would harden the rule against future drift — e.g. that tests/terser mirrors upstream Terser fixtures and shouldn't be augmented with SWC-specific cases. Future agents (and humans) won't have to re-derive the rationale, and edge-case judgments get easier.

Other notes

• Diff is clean, no formatting issues.
• No code changes, so no test/perf/security implications.
• The crate-local AGENTS.md edit is consistent with how other crate-local AGENTS.md files are structured.

Overall: useful guidance — recommend tightening the MSRV bullet so it's actually enforceable.

[Copilot]

Pull request overview

This PR updates repository guidance for automated and human contributors so future changes stay within SWC’s supported Rust compatibility range and add minifier regressions to the preferred fixture suites. It fits the codebase by refining the project’s existing AGENTS.md instructions rather than changing runtime behavior.

Changes:

• Add a repository-wide instruction to respect the project’s Rust MSRV when writing new Rust code.
• Clarify swc_ecma_minifier fixture guidance by removing tests/terser from preferred roots for new regression additions.
• Direct new minifier regression coverage toward SWC-owned fixtures such as tests/fixture/issues.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
AGENTS.md	Adds top-level contributor guidance to keep new Rust code compatible with the project MSRV.
crates/swc_ecma_minifier/AGENTS.md	Refines crate-specific testing guidance so new regressions go into SWC-owned fixture suites instead of tests/terser.

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