Adds Pin() and Unpin() methods to the beads wrapper that call bd pin/unpin.
Updates pinToHook() to call b.Pin() after AttachMolecule() to set the
pinned boolean field and assignee on the work issue. This should enable
bd hook to show pinned work.
NOTE: There's a known issue where bd pin via subprocess doesn't actually
set the pinned field even though it reports success. The handoff bead
attachment remains the primary mechanism until this is resolved.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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