feat(update): add self-update command with checksum verification

[juandiii]

No description provided.

[greptile-apps]

Greptile Summary

This PR adds a floci update self-update command that fetches the latest (or a pinned) release binary from GitHub, verifies it against the published sha256sums.txt via a streaming SHA-256 digest, and atomically replaces the running binary using the rename-over trick. A --check flag lets scripts test for staleness without installing.

• UpdateCommand: resolves the running executable path, guards against Homebrew-managed installs, checks parent-directory writability, downloads the platform-specific asset, streams the checksum without heap-loading the binary, and stages + atomically renames to replace the binary.
• ReleaseChannel: provides env-overridable GitHub API and download base URLs, making the flow testable against a local server.
• FlociCli: registers UpdateCommand in the subcommand list.

Confidence Score: 5/5

Safe to merge — the update flow is well-guarded with checksum verification, atomic replacement, and correct cleanup paths throughout.

The three changed files are self-contained: registration in FlociCli is trivial, ReleaseChannel is a thin URL factory, and UpdateCommand handles all the meaningful logic. The atomic rename trick is implemented correctly, staged-file cleanup is properly placed in a catch block, directory (not binary) writability is checked, and the SHA-256 is computed incrementally. Only minor polish items remain.

No files require special attention.

Important Files Changed

Filename	Overview
src/main/java/io/floci/cli/commands/UpdateCommand.java	New self-update command: downloads platform binary from GitHub releases, verifies SHA-256 checksum via streaming DigestInputStream, and atomically replaces the running binary. Previous-thread issues (directory-only write check, staged-file cleanup, heap-loading checksum) are all addressed in this version.
src/main/java/io/floci/cli/update/ReleaseChannel.java	Utility class that constructs GitHub API and release-asset URLs; both are env-overridable for testing and air-gapped setups. Simple and correct.
src/main/java/io/floci/cli/FlociCli.java	One-line registration of UpdateCommand in the subcommand list; no issues.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant User
    participant UpdateCommand
    participant GitHub API
    participant GitHub CDN

    User->>UpdateCommand: floci update [--check] [--version X]
    UpdateCommand->>GitHub API: GET /repos/floci-io/floci-cli/releases/latest
    GitHub API-->>UpdateCommand: {tag_name: "0.1.9"}
    UpdateCommand->>UpdateCommand: compare target vs current version
    alt versions equal
        UpdateCommand-->>User: ✓ floci 0.1.9 is up to date (exit 0)
    else "update available & --check"
        UpdateCommand-->>User: update available (exit 1)
    else update available
        UpdateCommand->>UpdateCommand: resolveSelf(), requireNotBrewManaged(), requireWritable()
        UpdateCommand->>UpdateCommand: detectPlatform() → e.g. darwin-arm64
        UpdateCommand->>GitHub CDN: GET /releases/download/0.1.9/floci-darwin-arm64
        GitHub CDN-->>UpdateCommand: binary (streamed to temp dir)
        UpdateCommand->>GitHub CDN: GET /releases/download/0.1.9/sha256sums.txt
        GitHub CDN-->>UpdateCommand: checksums file
        UpdateCommand->>UpdateCommand: verifyChecksum() via DigestInputStream
        UpdateCommand->>UpdateCommand: replaceAtomically() — stage + ATOMIC_MOVE
        UpdateCommand-->>User: ✓ updated 0.1.8 → 0.1.9 (exit 0)
    end

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sequenceDiagram
    participant User
    participant UpdateCommand
    participant GitHub API
    participant GitHub CDN

    User->>UpdateCommand: floci update [--check] [--version X]
    UpdateCommand->>GitHub API: GET /repos/floci-io/floci-cli/releases/latest
    GitHub API-->>UpdateCommand: {tag_name: "0.1.9"}
    UpdateCommand->>UpdateCommand: compare target vs current version
    alt versions equal
        UpdateCommand-->>User: ✓ floci 0.1.9 is up to date (exit 0)
    else "update available & --check"
        UpdateCommand-->>User: update available (exit 1)
    else update available
        UpdateCommand->>UpdateCommand: resolveSelf(), requireNotBrewManaged(), requireWritable()
        UpdateCommand->>UpdateCommand: detectPlatform() → e.g. darwin-arm64
        UpdateCommand->>GitHub CDN: GET /releases/download/0.1.9/floci-darwin-arm64
        GitHub CDN-->>UpdateCommand: binary (streamed to temp dir)
        UpdateCommand->>GitHub CDN: GET /releases/download/0.1.9/sha256sums.txt
        GitHub CDN-->>UpdateCommand: checksums file
        UpdateCommand->>UpdateCommand: verifyChecksum() via DigestInputStream
        UpdateCommand->>UpdateCommand: replaceAtomically() — stage + ATOMIC_MOVE
        UpdateCommand-->>User: ✓ updated 0.1.8 → 0.1.9 (exit 0)
    end

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_{Reviews (2): Last reviewed commit: "fix(update): harden self-update checksum..." | Re-trigger Greptile}