Loki Mode

Bun-route parity hardening. The autonomous live route is bash today, so these
are dormant in production, but the Bun route must agree with bash byte-for-byte
before the Phase 6 bash sunset wires it in, and the cross-route parity matrix is
an enforced gate. All fixes mirror the bash source of truth exactly.

Fixed

• Bun applyMaxTierCeiling normalizes LOKI_MAX_TIER (lowercase + trim, empty
  means no ceiling) before comparing, matching claude.sh:352. A user-typed
  LOKI_MAX_TIER="Sonnet" / " haiku " is now honored instead of silently
  blown past. The sonnet ceiling now also caps a fable session tier down to
  development (claude.sh:358-362), not only planning.
• Bun claudeTierToModel reads LOKI_ALLOW_HAIKU with exact === "true",
  matching bash (claude.sh:294, claude-flags.sh:104) and Bun's own
  fallbackForPrimary. LOKI_ALLOW_HAIKU=1 no longer dispatches haiku on one
  path while bash and the rest of the Bun route resolve sonnet.
• Bun caveman cavemanActivateEnv branches on whether LOKI_CAVEMAN_LEVEL is
  SET (not merely truthy), so an exported-empty LOKI_CAVEMAN_LEVEL="" resolves
  to the full override like bash (claude-flags.sh:543/709) instead of inferring
  lite. The wenyan-* compression ranks now mirror bash exactly so a user's
  global CAVEMAN_DEFAULT_MODE=wenyan-lite is honored (no-raise), not raised to
  full.

Notes

• applyCodexMaxTier is intentionally left raw (no normalization): codex.sh
  also compares LOKI_MAX_TIER raw, so normalizing only the Bun codex side
  would create drift. Locked with a guard test.
• getProviderTierParam (rarv.ts) is unchanged: it mirrors bash's legacy
  fallback table, which applies no max-tier clamp; the clamp lives in
  applyMaxTierCeiling on the dispatch path.