When branching_strategy is "phase" or "milestone", the branch was only
created during execute-phase — but discuss-phase, plan-phase, and
new-milestone all commit artifacts before that, landing them on main.
Move branch creation into cmdCommit() so the strategy branch is created
at the first commit point in any workflow. execute-phase's existing
handle_branching step becomes a harmless no-op (checkout existing branch).
Also fixes websearch test mocks broken by #1276 (fs.writeSync change).
Closes#1278
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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