feat: Add Codex cross-model review and per-ticket backend routing

[seongjinpark-speak]

Summary

• Per-ticket backend routing: Tickets now have Backend (claude|codex) and ModelTier (haiku|sonnet|opus) fields. Execute skill routes codex tickets via ask_codex MCP with graceful fallback to Claude opus. Works in both Agent Teams and Subagents modes.
• Cross-model review loop: Dual parallel reviewers (Opus + Codex) with severity classification (CRITICAL/HIGH block, MEDIUM/LOW pass), synthesis with deduplication + side-by-side comparison, and re-review loop with configurable max rounds.
• New review-severity-gate.mjs script: Zero-dep ESM script that gates approval on severity levels (exit 2 on CRITICAL/HIGH, exit 0 otherwise). Invoked programmatically, not registered as a hook.

Codex is a soft dependency — all features degrade gracefully to Claude-only when unavailable.

Files changed (12)

File	Change
templates/ticket.md	Added Backend and ModelTier fields
skills/plan/SKILL.md	Backend/modelTier in ticket generation + heuristics
skills/execute/SKILL.md	Backend routing for both execution modes
skills/review/SKILL.md	Cross-model review, severity, synthesis, re-review loop
agents/takt-orchestrator.md	Codex Backend Dispatch Protocol section
templates/agents/reviewer.md	Cross-model review context + severity defs
templates/POLICY.md	Backend column in model selection table
scripts/init-project.mjs	New session.json config fields
scripts/review-severity-gate.mjs	NEW — severity gate script
docs/CONFIGURATION.md	Field references + complete example
CLAUDE.md	4 new architectural decision records
README.md	Config table + safety hook entries

Test plan

• node -c scripts/review-severity-gate.mjs — syntax check passes
• node -c scripts/init-project.mjs — syntax check passes
• Severity gate returns exit 1 when no review file exists
• Severity gate returns exit 2 on CRITICAL/HIGH findings
• Severity gate returns exit 0 on MEDIUM/LOW only findings
• Backend/ModelTier fields present in ticket template
• All new session.json fields have defaults in init-project.mjs
• CONFIGURATION.md complete example includes all new fields
• Codex fallback documented at every dispatch point

🤖 Generated with Claude Code