Guardex advertised task-size tiers, but branch start still treated tier selection as a no-op during OpenSpec auto-bootstrap. Codex launches also lacked a lightweight routing gate, so small asks paid the OMX/T3 setup cost and active-session records could not explain why a sandbox was caveman or OMX.

This wires real T0/T1/T2/T3 branch-start scaffolding, adds Codex-side task routing plus routing metadata, and updates the focused regression suite and change record so the bootstrap path stays consistent without changing the documented default auto-init toggle.

Constraint: gx branch start must preserve the documented default GUARDEX_OPENSPEC_AUTO_INIT=false behavior
Rejected: Make branch-start auto-bootstrap true by default | breaks the current repo contract and existing setup coverage
Confidence: high
Scope-risk: moderate
Directive: Keep branch-start tier semantics, codex-agent routing heuristics, and session-schema metadata in sync when adding new task-size keywords or tiers
Tested: node --test test/branch.test.js test/sandbox.test.js test/vscode-active-agents-session-state.test.js; openspec validate agent-codex-codex-session-task-mode-decider-2026-04-22-12-16 --type change --strict; openspec validate --specs; git diff --check
Not-tested: live Codex CLI launch against a real operator task outside the focused harness