fix(self-update): improve update UX on macOS

[nadav-y]

Two small quality-of-life fixes to the apm update flow on Unix.

Changes

Fix -e garbage output on macOS during self-update

_get_installer_run_command was invoking install.sh with /bin/sh. On macOS,
/bin/sh is bash 3.2 running in POSIX compatibility mode, where the echo builtin
does not recognize the -e flag and prints it literally — so every colored output
line printed with echo -e "..." appeared prefixed with -e in the terminal.
Switching to bash (via shutil.which("bash"), falling back to /bin/bash,
raising FileNotFoundError if neither exists) respects the script's own shebang
and fixes the output.

Show a progress bar during binary download

install.sh used curl --silent --show-error, which suppresses all output including the progress bar. Replacing --silent with --progress-bar gives users visual feedback during the download without adding verbose byte-count noise.

Notes

• Windows (install.ps1) is unaffected — Invoke-WebRequest renders its own progress bar natively
• Unit and integration tests for _get_installer_run_command updated to match new behavior

[Copilot]

Pull request overview

Improves the Unix self-update experience by running the installer script under bash (to avoid macOS /bin/sh echo-flag behavior) and by showing a curl progress bar during downloads.

Changes:

• Switch _get_installer_run_command() to prefer bash on Unix.
• Update unit + integration tests to expect bash-based execution.
• Replace curl --silent with curl --progress-bar for the public download path in install.sh.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/apm_cli/commands/self_update.py	Updates the Unix installer runner to use bash.
tests/unit/test_update_command.py	Adjusts helper tests for the new bash selection behavior.
tests/integration/test_commands_config_coverage.py	Updates integration coverage assertion to require bash.
install.sh	Enables a visible progress bar for the initial unauthenticated download.

[nadav-y]

This is how the old code looked like:

~ apm update
[!] 'apm update' refreshes APM dependencies. To update the CLI binary, use 'apm self-update'. Forwarding for back-compat (deprecated).
[i] Current version: 0.20.0
[>] Checking for updates...
[*] Latest version available: 0.21.0
[>] Downloading and installing update...
[*] Running installer...
-e
+--------------------------------------------------------------+
|                         APM Installer                        |
|              The NPM for AI-Native Development               |
+--------------------------------------------------------------+
-e
-e Detected platform: darwin-arm64
-e Target binary: apm-darwin-arm64.tar.gz
-e Note: Will need sudo permissions to install to /usr/local/bin
-e Fetching latest release information...
-e Latest version: v0.21.0
-e Download URL: https://github.com/microsoft/apm/releases/download/v0.21.0/apm-darwin-arm64.tar.gz
-e Downloading APM...
-e [+] Download successful
-e Extracting binary...
-e [+] Extraction successful
-e Testing binary...
-e [+] Binary test successful
-e Installing APM CLI to /usr/local/bin...
-e [+] APM installed successfully!
-e Version: Agent Package Manager (APM) CLI version 0.21.0 (975f8f0)
-e Location: /usr/local/bin/apm -> /usr/local/lib/apm/apm

-e Installation complete!

-e Quick start:
  apm init my-app          # Create a new APM project
  cd my-app && apm install # Install dependencies
  apm run                  # Run your first prompt

-e Documentation: https://github.com/microsoft/apm
-e Need help? Create an issue at https://github.com/microsoft/apm/issues
[*] Successfully updated to version 0.21.0!

New one doesn't have the -e prefix, plus (single line)

Downloading APM...
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