[Shellghostt]

What this changes

Completes M2 collectors and rules: runtime, requested TCP-port, Git and local Docker inspection; diagnostic rules ENV001–ENV006; --port; and offline --fixture-dir diagnosis. Adds 54 Windows/Linux/macOS golden cases, built-CLI tests and rule documentation. Fixes collector deadlines, home-path redaction and degraded PATH inspection.

Why

M1 collected environment facts but lacked the first actionable diagnostic rules. M2 identifies Python/Node conflicts, broken or shadowed PATH entries, occupied requested ports and unavailable Docker engines. ADR 0004 defines collection, evidence and offline diagnosis. Diagnosis remains read-only.

How it was verified

Executed commands and selected output:

$ go test -race -count=1 -timeout=120s ./...
ok  github.com/shellghostt/envdoctor/internal/diagnostic  1.069s
ok  github.com/shellghostt/envdoctor/internal/system      2.207s
ok  github.com/shellghostt/envdoctor/tests/integration   2.739s

$ golangci-lint run --timeout=10m
0 issues.

$ govulncheck ./...
No vulnerabilities found.

All CI jobs passed, including Windows/Linux/macOS race tests. Validation also covered all 54 fixture cases through the built CLI, live TCP ownership checks and snapshot builds for six platform/architecture targets.

Checklist

• Tests added or updated for the new behaviour
• Formatting, vet and golangci-lint checks used by make lint pass
• Documentation updated (docs/, README roadmap, snapshot schema and CHANGELOG)
• Documented decision changes recorded in docs/adr/0004-m2-collectors-and-rules.md
• No claims of unverified behaviour: status fields still match reality
• No secrets, tokens or customer data added; fixtures are synthetic