chore(tasks): model-router W1-C contract + plan (absolute tiers, breaker fallback, derived phases)

.claude/tasks/TODO.md

@@ -13,6 +13,7 @@ migration of shifters/pins/model-gate in wave 2 after proof; names model-router
 - [x] W1-B2 wiring (contract `2026-10-08-model-router-wiring-1835`, 2026-10-09): tracked symlink `skills/model-router` → `../mods/model-router` loads as `model-router@skills-dir` (fresh-process `claude plugin list --json` proves it), `.gitignore` `mods/*/tsconfig.json`, `lib/tests/mods.test.sh` (4 checks, capability probe, bounded, SKIP), doctor `── Mods ──` fail-soft, CLAUDE.md `## mods/`. Plan r2 from 3 lenses (5 MAJOR), feater DONE, gap round (4b label + unbounded probe), verifier CONFORME 8/8, security PASS
 - [ ] W1-B2 residuals (accepted): `claude plugin <unknown> --help` returns 0 → the suite's capability probe can pass on a CLI without `plugin test` and then FAIL instead of SKIP (fail-closed; fix = grep the probe output for the test usage line); doctor `claude plugin list --json` unbounded; doctor `echo -e` helpers interpolate `$_mod` (tracked folder names only); fallback timeout guard orphans grandchildren (only without coreutils timeout); `update-all.sh` runs `claude plugin update` over `@skills-dir` → one recurring warn (needs an update-all edit)
 - [x] W1 close-out (2026-10-09): doc-sync opus audit SIGNIFICANT → user go all 10 → patched (README effort routing + Explore row + /route, USAGE, ARCHITECTURE mods/, CHANGELOG Unreleased) b22f894; hot-reload link removed from `~/.claude/dev-mods/<session>/`; BDR-115 amended (a6e2003). Pending user: `/reload-plugins` in this session (new sessions load the skills-dir copy by themselves); merge decision on feature/model-router-mod (`gitflow finish`, human signal)
+- [ ] W1-C adaptive tiers (user 2026-10-09: "un système logique et optimisé", no /route typed, works on a haiku session, falls back when fable has no credit): contract `2026-10-09-model-router-tiers-1237`, plan same slug. Phases name absolute tiers (best/big/work/cheap), availability breaker (turn error/refusal + engine auto switch, 15 min cooldown), fallback chain fable→opus→sonnet→haiku, main upgrade on / downgrade gated, prompt default rules (plan/reflect keywords FR+EN) + dispatch push/pop + optional classifier
 - [ ] W2 migration (after wave 1 proven in daily use): 15 skills `Skill(effort-*)` → `route` tool calls; remove `skills/effort-*`, `lib/effort-pins.txt/.sh`, install/update steps, `effort:` frontmatter on skills and agents; repo agents into the mod's `agents` table (verify the spawn/first-step ordering first); `lib/model-gate.md` + `lib/model-check.sh` → mod rule; census tests repointed; `lib/effort-shift.md` rewritten; docs
 - [ ] W2 migration: 15 skills off `Skill(effort-*)`, remove shifters + effort-pins + model-gate, census repointed, docs
 - [ ] W3 optional: step heuristics, haiku classifier, quota-aware downgrade, A/B