Blockchain participation games model costly entry, random selection, and threshold success; their retraction variants charge completion costs only to selected contributors. We study committee tasks requiring operators to reserve computing or communication capacity before assignment, so preparation costs are incurred even when capacity remains unused. Users choose abstention, bare registration without preparation, or binding commitment to contribute if selected. Success requires sufficiently many selected contributors, creates public value, and may trigger separate rewards for registration and verified contribution. We characterize all pure Nash equilibria under homogeneous selection and analyze ordering under heterogeneous selection. The results distinguish free-riding on public value from registration that earns rewards without productive commitment; more frequently selected users can choose bare registration while less frequently selected users contribute. Our main result characterizes every homogeneous minimum-outlay scheme supporting full contribution, where every user commits, as a Nash equilibrium. When positive rewards are required, these schemes form a line segment. There is always an optimum with no registration reward. It eliminates every equilibrium containing bare registrants at minimum outlay while retaining the full-contribution equilibrium; threshold-coordination failures may remain. Under heterogeneous selection, a two-user instance has a unique optimum using both rewards, cheaper than every zero-registration-reward scheme supporting full contribution. Finally, if full contribution is a positive-welfare social optimum, the homogeneous zero-registration-reward design attains price of stability one. Under arbitrary independent selection probabilities, every full-contribution Nash equilibrium is also a strong equilibrium.

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