feat: add CLI self-upgrade command

[alongubkin]

Summary

• add alien upgrade with a visible alien update alias
• stream and checksum-verify immutable binaries from the stable release channel before atomic replacement
• delegate npm and Homebrew installations to their package managers
• add --dry-run and --force safeguards

Research

Reviewed Alien's release workflow, stable S3/CloudFront channel, installer routes, npm wrapper, Homebrew publishing, and public installation docs. Compared Codex, Claude Code, Deno, uv, and mise update behavior. The resulting model follows the common split: standalone installs self-replace; package-managed installs delegate to their owner.

Validation

• cargo check -p alien-cli --locked
• cargo test -p alien-cli commands::upgrade --lib
• cargo test -p alien-cli update_alias_parses_as_upgrade --lib
• target/debug/alien upgrade --dry-run
• target/debug/alien update --dry-run
• npm delegation dry-run via ALIEN_INSTALL_METHOD=npm
• end-to-end local release server: streamed a checksum-tagged mock v99.0.0 executable, validated it, replaced a copied Alien binary, then executed the replaced path and confirmed alien 99.0.0

Linear: ALIEN-577

Companion docs PR follows.

[greptile-apps]

Greptile Summary

The PR adds self-upgrade support for standalone, npm, and Homebrew installations, including dry-run and forced same-version reinstall behavior.

• Downloads stable standalone binaries as a stream, verifies their release checksum and reported version, then replaces the running executable.
• Delegates package-managed upgrades to npm or Homebrew.
• Adds post-replacement synchronization and warning-based handling for durability errors.

Confidence Score: 5/5

The PR appears safe to merge because no blocking failure is established at the current revision.

No blocking failure remains.

Important Files Changed

Filename	Overview
crates/alien-cli/src/commands/upgrade.rs	Implements package-manager delegation and checksum-verified standalone replacement, including the follow-up safeguards and synchronization handling.
crates/alien-cli/src/lib.rs	Adds the upgrade command, visible update alias, parsing coverage, and early context-free dispatch.
packages/alien-cli-npm/bin/alien.js	Marks binaries launched through the npm wrapper so upgrades delegate back to npm.
crates/alien-cli/src/error.rs	Adds a structured error variant for upgrade failures.
crates/alien-cli/Cargo.toml	Enables streaming downloads and adds the semantic-versioning and executable-replacement dependencies.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[alien upgrade or update] --> B{Installation method}
    B -->|npm| C[npm install -g latest]
    B -->|Homebrew| D[brew upgrade alien]
    B -->|Standalone| E[Fetch stable version]
    E --> F{Newer or forced same version?}
    F -->|No| G[Leave installation unchanged]
    F -->|Yes| H[Stream release binary]
    H --> I[Verify checksum]
    I --> J[Execute version validation]
    J --> K[Replace current executable]
    K --> L[Synchronize replacement]
    L --> M[Report completion]

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_{Reviews (5): Last reviewed commit: "fix: report completed CLI replacements a..." | Re-trigger Greptile}

[alongubkin]

Production-channel verification passed after CI: copied the locally built PR binary to a temporary path, then ran the temporary binary with alien upgrade --force against the default https://releases.alien.dev. It fetched stable v3.3.18, verified/validated the production artifact, replaced only the temporary binary, and the replaced path executed successfully as alien 3.3.18. Binary comparison confirmed replacement: local debug build 554,816,488 bytes / SHA-256 702592ed..., installed production artifact 191,867,152 bytes / SHA-256 49579f21.... The user-installed CLI was not modified.