claude_mac/lib/model-gate.md

Model gate — reflection requires a big model (BLOCKING)

Shared include. Runs FIRST in any orchestrator whose reflection — brainstorming, planning, contract, audit judgment, loop decisions — executes inline or in inherit-model subagents. Sonnet-pinned executors are not what this gate protects; it protects the thinking around them (BDR-066).

1. Self-check

Your system prompt names the model powering this session. Fable or Opus → big. Sonnet, Haiku, anything else → small.

2. Witness — deterministic check

bash "$HOME/.claude/lib/model-check.sh"

Output <class>:<raw>; exit 0 = big, 2 = small, 3 = unknown. The witness reads the PERSISTED model (settings.json — the file /model rewrites, LRN-098). It can lag reality (session launched with --model, settings not yet rewritten) — that is why the self-check exists alongside it.

3. Verdict

self-check	witness	action
big	big (0)	proceed, SILENT — the nominal path prints nothing
small	any	STOP
big	small (2)	disagreement — STOP, surface BOTH values; the user confirms or relaunches
big	unknown (3)	fail-visible: print model gate: witness unknown (<raw>) — self-check says <model> and ask the user to confirm before continuing (BDR-025: unknown never silently passes)

STOP means: print exactly

⛔ MODEL GATE — session on <model>. Reflection steps of this skill
require Fable or Opus. Switch with /model, then relaunch the skill.

then end the turn. No later step runs, no agent is dispatched, nothing is edited.

4. Dispatch tiers (BDR-077 — no inherit)

The gate guards the MAIN loop only. Dispatched work NEVER inherits the session model: typed agents run on their frontmatter pin; built-ins (general-purpose / Explore / Plan) carry an explicit model= at every call site — model: "fable" when the child performs reflection/orchestration on the main loop's behalf (skill-runners), otherwise its complexity tier (opus = dispatched judgment, sonnet = execution/collection, haiku = short mechanical probes).

Effort is the second axis of the same table (BDR-107): every typed agent carries an effort: pin next to model:, and the main loop shifts per phase through lib/effort-shift.md. No typed agent inherits either axis; built-ins inherit the effort in force at dispatch, so an orchestrator shifts before dispatching them (lib/effort-shift.md, wiring point 5).