Port the setup script to macOS

[saty-a]

macos/setup.sh is currently a stub that prints a pointer to the official guide and exits 1. This issue tracks bringing it to parity with the Windows script.

What parity means is specified in CONTRIBUTING.md → The porting contract — same flag surface (--verify-only, --skip-android, --install-root, --precache), same exit codes (0 ok / 1 missing or failed / 2 installed but flutter doctor found toolchain issues), idempotent steps that check before acting, and environment changes written to the shell profile behind a marker-delimited block instead of the Windows registry.

Rough shape of the work

• Resolve and install the latest stable Flutter SDK (same releases-JSON approach, macOS archive, SHA-256 verified)
• Install Temurin JDK 17 (Adoptium API), set JAVA_HOME
• Install Android cmdline-tools into cmdline-tools/latest, then platform-tools, platforms;android-36, build-tools;36.0.0
• Accept Android SDK licenses non-interactively
• Write PATH / ANDROID_HOME / JAVA_HOME into the shell profile idempotently (zsh is the macOS default)
• --verify-only mode that changes nothing
• Run flutter doctor and map its result to the exit-code contract

Partial work is welcome — comment here saying which step you're taking so two people don't do the same one. Apple Silicon and Intel notes both useful.

[saty-a]

Done in a958c01 — macos/setup.sh is now a full implementation, not a stub.

Every box in this issue is checked: latest stable Flutter resolved at runtime from releases_macos.json and SHA-256 verified, Temurin JDK 17 via the Adoptium API, Android cmdline-tools into cmdline-tools/latest plus platform-tools/platforms;android-36/build-tools;36.0.0, non-interactive license acceptance, a marker-delimited block in the shell profile, a read-only --verify-only mode, and flutter doctor mapped to the 0/1/2 exit-code contract.

Three things turned out to be macOS-specific and are worth recording for the Linux port (#6):

• Arch naming differs three ways — Flutter wants arm64/x64, Adoptium wants aarch64/x64, and cmdline-tools wants mac_arm64/mac_x86_64. The script maps all three from uname -m, and detects Rosetta via sysctl.proc_translated so an x86_64-reporting shell on Apple Silicon still gets the native toolchain.
• The Temurin macOS archive is .tar.gz, not .zip, and uses the Apple bundle layout — JAVA_HOME has to point at <jdk>/Contents/Home, which is detected rather than hardcoded.
• The mac cmdline-tools build is arch-specific. The Windows filename commandlinetools-mac-<build>_latest.zip returns 404; the real URLs are resolved at runtime from repository2-3.xml. Only SHA-1 is published for that package, so that is what gets verified — SHA-256 is used for Flutter and the JDK where the publisher provides it.

Tested on macOS 15.7.3, Apple Silicon, bash 3.2, in a sandboxed HOME with a clean PATH:

Scenario	Exit	Result
Fresh install	0	[✓] Flutter (3.44.9), [✓] Android toolchain (SDK 36.0.0); the [!] Xcode iOS warning correctly scoped as out-of-scope
Re-run	0	every component Already installed, nothing re-downloaded
--verify-only, clean machine	1	components MISSING, no install root created
--verify-only, installed	0	all present, no log written
Corrupted download cache + gutted cmdline-tools dir	0	checksum mismatch re-downloaded; incomplete directory removed before extract, not nested into
--skip-android	0	JDK and SDK steps skipped

Exactly one profile block after repeated runs, and sourcing ~/.zprofile in a clean environment yields working flutter, adb and java.

Linux (#6) is now the only remaining port, and it has two reference implementations to copy from.