idd-route-backfill still has a private `### Complexity` parse with a "fall back Simple" default — fifth narrowing outside the #316 convergence

[kiki830621]

Problem

plugins/idd-route/skills/idd-route-backfill/SKILL.md:67 reads ### Complexity from the Diagnosis comment on its own and states "找不到 fall back Simple" — the exact "when unsure, assume Simple" default that references/actionability-gate.md (#316) forbids for the four routing consumers. It is telemetry only (writes routing-stats jsonl, never routes, never writes to GitHub), and the real parser lives in the idd-route Swift binary in another repo, so it is not one of the four consumers #316 converged — but it is a fifth private narrowing of the same field, and its fallback silently records wrong tiers into the stats that idd-diagnose later uses for data-driven recommendation.

Source

• Verify report on PR feat: actionability gate round 2 — prefix tier + deferral vocabulary, wired into all four consumers (#316) #318 (round 2), finding 21 (regression L5).

Expected

idd-route-backfill either sources scripts/lib/actionability.sh and records idd_parse_complexity's tier (exit 3/4/5 → record unknown, never Simple), or documents that its column is a best-effort mirror that must not be read as the gate's verdict.

Acceptance criteria

• No "fall back Simple" path remains in idd-route-backfill
• Non-routable diagnoses are recorded as unknown (or the column is documented as non-authoritative)

Complexity

Simple — one SKILL.md plus, if the Swift side needs a value, a one-line contract note; no new abstraction.