The sessionToAgentID function was missing handling for polecat sessions,
causing gt sling to fail to update the agent bead's hook_bead field.
Before: gt-gastown-nux -> gt-gastown-nux (unchanged, no match)
After: gt-gastown-nux -> gastown/polecats/nux (correct format)
This enables updateAgentHookBead to properly convert to the agent bead ID
(gt-polecat-gastown-nux) and update the hook_bead field, which is
required for agents to know they have work on their hook.
Found via E2E test (gt-j0gx2) - nux wasn't picking up slung work because
hook_bead was null despite the task being pinned.
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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