TierDecay v0.4.0

[0.4.0] - 2026-10-01

Repositioned as the per-repo learning layer for native model routers rather
than a router of its own.

Added

• benchmarks/pilot-v1: first measurement with real models — 36 graded Opus
  and Sonnet executor runs plus 3 distillation runs on a controlled fixture
  with hidden acceptance tests, exact input-side billing from transcripts,
  task-paired bootstrap contrasts, and a replay of the protocol on the
  measured outcomes. Fast tier 0.66× frontier cost at equal acceptance;
  protocol replay 24% below always-frontier; the distilled entry itself not
  significantly cheaper than a cold fast-tier attempt. Scope and limits in
  RESULTS.md; CI validates the fixture.
• Claude Code plugin (plugins/tierdecay) and marketplace
  (.claude-plugin/marketplace.json): /plugin install tierdecay@tierdecay,
  /tierdecay:init, an executor-scoped PreToolUse guard, a SessionStart
  hook that loads the protocol only in opted-in projects, and tierdecay on
  the Bash PATH. Generated from the native adapter by
  scripts/build-plugin.js; CI fails if they drift.
• tierdecay status: per-class route, hits against the risk-gated
  requirement, and the bookkeeping owed (decay, recertification, PRIORS).
• tierdecay export: routing tables for Claude Code (agent, alias, effort)
  and Cursor (model or Auto goal), JSON, and Agent Skills compiled from live
  playbook entries (quarantined entries are pruned, foreign skills untouched).
• tierdecay bench: seeded-permutation replay with in-memory playbook
  evolution (hits, decays, quarantines, recertification), order spread, and
  static/oracle baselines.
• Recertification: entries carry epoch:; a binding change routes them at
  provenance (recertify) before any further descent.
• Effort as the second binding axis: oracle xhigh, heavy-executor
high, executor medium, scout low.

Changed

• Decay is confidence-gated: a downgrade needs 3 / 4 / 5 probe hits for
  risk 0 / 1 / 2 (80% one-sided Clopper–Pearson bound on the pass rate
  reaching 0.5 / 0.6 / 0.7); risk-3 classes never decay; entries without
  risk: count as risk 2. Previously 2 hits for every class.
• Policy, enforced by tests/test-model-policy.js: no tier is bound to the
  cheapest model family; the cheap end of the ladder is sonnet at lower
  effort.
• Cursor adapter maps tiers to the router's Auto goals instead of advising
  against Auto.
• CLI defaults fall back to .claude/routing-ledger.md and the native
  playbook skill when .tierdecay/ledger.md is absent.
• SPEC §4 records when distillation pays: where the lower tier fails or
  struggles without the entry.

Fixed

• The shipped playbook templates did not parse with the advisor (the entry
  format example was read as a malformed entry), so every CLI command failed
  on a fresh install. Fenced code blocks are now documentation, and the
  templates fence their example.
• The guard script forwards its arguments to Node safely under set -u on
  Bash 3.2.