Design doc for azd update and auto-update

[rajeshkamal5050]

Design doc for azd update command, auto-update, and channel management.

Covers:

• azd update command with channel switching
• Auto-update with configurable check intervals
• Install method-aware update strategies
• CI/CD detection to skip auto-updates

Epic: #6721

[Copilot]

Pull request overview

Adds a draft design document describing the proposed azd update command, opt-in auto-update behavior, and stable/daily channel management as part of Epic #6721.

Changes:

• Introduces a new design doc covering update command UX, configuration keys, and channel switching behavior.
• Documents install-method-aware update strategies (package manager vs direct binary replace) and elevation handling.
• Proposes daily build version tracking (build number) and an expanded update-check cache format.

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[Copilot]

This section says to use the existing CommandRunner for elevation (sudo), but the snippet uses exec.Command directly. Consider rewriting the example to use CommandRunner (or label it as simplified pseudocode) so the guidance doesn’t conflict with the intended implementation approach.

Suggested change

	cmd := exec.Command("sudo", "mv", stagedBinary, currentBinaryPath)
	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	// commandRunner is configured to pass through stdin/stdout/stderr so sudo
	// can prompt the user for their password as usual.
	err := commandRunner.Run(ctx, "sudo", "mv", stagedBinary, currentBinaryPath)
	if err != nil {
	// handle error
	}

[Copilot]

The markdown table syntax here uses a double leading pipe (e.g., || Installer | ...), which renders as an extra empty column in most markdown renderers. Consider changing to a single leading pipe (| Installer | ...) for correct formatting (same pattern appears in other tables in this doc).

[Copilot]

This section says “Two new config keys via azd config:” but the example only shows updates.autoUpdate. Since the design also introduces updates.checkIntervalHours (and persists updates.channel), update the text to reflect the full set of keys or adjust it to match what’s being proposed.

[Copilot]

The cache location is described as ~/.azd/update-check.json, but the code uses config.GetUserConfigDir() which can be overridden via AZD_CONFIG_DIR. Consider describing it as {AZD_CONFIG_DIR or ~/.azd}/update-check.json to avoid documenting an incorrect path.

Suggested change

	- **Logic**: `main.go` → `fetchLatestVersion()` — async check at startup, cached in `~/.azd/update-check.json`
	- **Skip**: `AZD_SKIP_UPDATE_CHECK=true` disables the check
	- Already shows platform-specific upgrade instructions based on install method
	**Current cache format** (`~/.azd/update-check.json`):
	- **Logic**: `main.go` → `fetchLatestVersion()` — async check at startup, cached in `{AZD_CONFIG_DIR or ~/.azd}/update-check.json`
	- **Skip**: `AZD_SKIP_UPDATE_CHECK=true` disables the check
	- Already shows platform-specific upgrade instructions based on install method
	**Current cache format** (`{AZD_CONFIG_DIR or ~/.azd}/update-check.json`):

[Copilot]

The auto-update flow includes “Check non-interactive terminal → skip if detected”, but the explicit skip list later only mentions CI / --no-prompt / AZD_SKIP_UPDATE_CHECK. Please align these two sections by adding the non-interactive/TTY condition to the list (and defining detection) or removing it from the flow.