[Agora] Generate experiment_proposal artifacts from unresolved debate cruxes done

Goal

The existing experiment_proposal_generator
(scidex/agora/experiment_proposal_generator.py) takes a hypothesis as input,
but the richest source of falsifiable, time-stamped, controversial questions
on the platform is the unresolved-crux corpus inside completed debate_sessions (see api.py:15515 for the polymorphic artifact_debates
junction). Add a new entry path: scan recent debates whose outcome is unresolved or split, extract the disagreement crux from the synthesis
round, and emit one experiment_proposal artifact per crux.

Acceptance Criteria

--source debate_cruxes --since 7d --dry-run lists candidate cruxes. full schema (aims, hypotheses, dataset_dependencies,
protocol_summary, predicted_observations, falsification_criteria,
est_cost_usd, est_duration_weeks). with link_type='resolves_crux_of' (new link_type — register in
artifact_links.link_type enum or document the new value). toward the persona that lost or split the debate. cross-link per proposal visible in artifact_links.

Approach

Add _load_crux_candidates() to the existing

experiment_proposal_generator.py that joins debate_sessions (recent,
unresolved/split) with the synthesis round content.

Reuse _select_persona, _log_invocation, and the SYSTEM_PROMPT scaffold;

swap in a crux-specific user prompt that quotes both sides of the
disagreement.

Register link resolves_crux_of from proposal → debate.

Backfill: run once with --since 30d to seed initial proposals.

Dependencies

• scidex.agora.experiment_proposal_generator — extend, don't fork.
• scidex.agora.synthesis_engine — supplies crux text.

Work Log