Add AGENTS.md agent guidance and run staticcheck on the root module

[fortuna]

What

Two related sets of changes:

Agent/contributor docs

• Replace the AGENTS.md → CONTRIBUTING.md symlink with a real guidance file for AI coding agents: module structure (root vs x/, no local replace), commands (test/lint/license check), gotchas (psiphon on Go 1.25, gomobile wrapper packages, vanity import path), and workflow conventions.
• Add CLAUDE.md as a one-line @AGENTS.md import so Claude Code and other tools share the same source of truth.
• Extract the Cross-platform Development section of CONTRIBUTING.md into docs/cross-platform.md, linked from both CONTRIBUTING.md and AGENTS.md.

Staticcheck on the root module

Staticcheck was already declared as a tool in the root go.mod, but CI only ran it on x/. This adds a Staticcheck SDK CI step and fixes the findings it surfaced:

• Real bug: dns/resolver_net_test.go had // go:build nettest (extraneous space), making the build constraint ineffective — the network-dependent test was not actually gated behind -tags nettest (SA9009). Now it is; CI still runs it since it passes -tags nettest.
• Line-scoped //lint:ignore SA1019 directives in network/lwip2transport for the intentional PacketProxy compat path, pending the PacketRelay migration (Refactor PacketProxy to PacketRelay (Side-by-Side) #618).
• //lint:ignore U1000 for the happyeyeballs_test.go helper used only by the commented-out flaky "IP order" test.

Testing

• go tool staticcheck ./... passes clean on the root module
• go vet ./... and go test -race pass on the touched packages

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR adds agent guidance and brings root-module Staticcheck into CI. The main changes are:

• Replaces the AGENTS.md symlink with a standalone guidance file.
• Adds CLAUDE.md as an import of the shared agent guidance.
• Moves cross-platform development docs into docs/cross-platform.md.
• Adds a root go tool staticcheck ./... workflow step.
• Fixes the malformed nettest build tag on the DNS network tests.
• Adds targeted lint ignores for intentional deprecated PacketProxy compatibility and one unused test helper.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.
• The new Staticcheck step matches the root module tooling pattern.
• The corrected nettest tag matches the documented and CI test commands.
• The lint ignores are placed on the intended deprecated or unused declarations.

Important Files Changed

Filename	Overview
.github/workflows/test.yml	Adds root-module Staticcheck to CI before the existing x/ Staticcheck step.
AGENTS.md	Replaces the symlink with standalone agent guidance for module layout, commands, gotchas, and workflow conventions.
CLAUDE.md	Adds a one-line import pointing Claude-oriented tooling at AGENTS.md.
CONTRIBUTING.md	Replaces the embedded cross-platform section with a link to the extracted document.
docs/cross-platform.md	Adds the extracted cross-platform development guide.
dns/resolver_net_test.go	Corrects the nettest build constraint so network-dependent resolver tests are gated as documented.
network/lwip2transport/device_test.go	Adds targeted Staticcheck ignores for test-only deprecated PacketProxy compatibility helpers.
network/lwip2transport/udp.go	Adds targeted Staticcheck ignores around the intentional deprecated PacketProxy compatibility path.
network/lwip2transport/udp_test.go	Adds targeted Staticcheck ignores for deprecated PacketProxy test stubs.
transport/happyeyeballs_test.go	Adds a Staticcheck ignore for a helper retained for a commented-out flaky test.

_{Reviews (1): Last reviewed commit: "docs: add AGENTS.md guidance and extract..." | Re-trigger Greptile}

[fortuna]

Ping

[ohnorobo]

thanks!

[dosubot]

📄 Knowledge review

🆕 New pages

1 new page was drafted from this PR.

Page	Library
Outline SDK Development Guide for AI Agents and Contributors	Outline Foundation's Space

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