Change update command to override local changes by default

[Copilot]

The update command previously performed 3-way merges by default, which could produce unpredictable merge conflicts. This changes the default behavior to override local changes, with merge available via --merge flag.

Changes

• Added --merge flag to opt into 3-way merge behavior (previous default)
• Modified updateWorkflow to branch on merge mode:

  if merge {
      // Download base, current, new → 3-way merge
      mergedContent := MergeWorkflowContent(base, current, new, ...)
  } else {
      // Download latest → replace file
      newContent := downloadWorkflowContent(repo, path, latestRef)
      finalContent := updateSourceFieldAndProcessIncludes(newContent, ...)
  }

• Updated help text to explain default override behavior and merge opt-in
• Added tests for both modes

Behavior

Mode	Command	Result
Override (new default)	gh aw update	Replaces local file with upstream, no conflicts
Merge (opt-in)	gh aw update --merge	3-way merge preserving local changes, may conflict

Migration

Users wanting the previous behavior: add --merge to update commands.

Original prompt

Change the "update" command to NOT try to merge by default. The merge mode can be enabled with "--merge". Otherwise, the default behavior is to override local changes.

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[Copilot]

Pull Request Overview

This PR changes the default behavior of the update command from performing 3-way merges (which could lead to merge conflicts) to simply overriding local changes with the latest upstream version. Users who want the previous merge behavior can now opt-in using the --merge flag.

Key Changes:

• Added --merge flag to enable 3-way merge behavior (previous default)
• Modified update logic to branch between override mode (new default) and merge mode
• Updated help text and examples to document the new behavior

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
pkg/cli/update_command.go	Added --merge flag, updated help text, refactored updateWorkflow() to branch between override and merge modes, threading the merge parameter through all update functions
pkg/cli/update_command_test.go	Added two new test functions for override and merge modes (though tests lack meaningful assertions)

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