runbooks: make issue severity a first-class impact axis, require self-contained citations

[Savid]

Summary

Formalizes classification.severity (critical|major|minor) on the shared devnet issue contract as an impact rank — a distinct axis from confidence (evidence strength) — and threads it consistently through the investigation pipeline. Also tightens evidence-citation discipline so every ref is self-contained and re-runnable.

Changes

• devnet_issue_contract.md — owns the severity scale with per-level criteria; adds severity to the classification example and Field rules; clarifies first_bad value/at must be a concrete coordinate (never prose), with guidance for gradual/monotonic onset; requires ref to be executable and self-contained.
• devnet_issue_collation.md — adds a "rank impact" step that re-judges an incoming severity onto the scale rather than copying it verbatim, and emits within-expected issues as minor instead of dropping them; self-check enforces it.
• devnet_bug_report.md — distinguishes the board's severity thresholds from the contract-owned scale, and documents that the top-level severity is a copy of issue.classification.severity that must stay in sync (the renderer ranks/filters on the top-level field).
• evidence_discipline.md — requires each citation to be self-contained (no "same query as above"), allowing a placeholder like {dora} only when the same citation says how to resolve it.

Docs-only change (runbooks); no code paths affected.

🤖 Generated with Claude Code

[github-actions]

🐼 Smoke eval — f377b18: ✅ 8/8 pass

📊 Interactive report — tokens p50 16,536 · tokens/solve 21,349.

Reference points: master@2042fdc 100% · v0.38.6 96%.

question	result	tokens	tools
forky_node_coverage	✅	16,027	5
tracoor_node_coverage	✅	19,036	11
mainnet_block_arrival_p50	✅	16,819	10
list_datasources	✅	14,257	4
block_count_24h	✅	16,252	8
missed_slots_24h	✅	15,723	6
chartkit_default_arrival_distribution	✅	47,508	17
storage_upload_session_scoped	✅	25,167	14

🔭 Langfuse traces (8 runs; ⚠️ = failed)

• forky_node_coverage
• tracoor_node_coverage
• mainnet_block_arrival_p50
• list_datasources
• block_count_24h
• missed_slots_24h
• chartkit_default_arrival_distribution
• storage_upload_session_scoped

_{The report walks this branch's commits against the master baseline and the most recent release. A self-contained copy is in the run's eval-smoke-* artifact.}