fix(resolvers): question-log session_id becomes a substitution placeholder + stale-comment sweep

The question-log block bound $_SESSION_ID, a shell variable the
consolidated fence never sets — hook-less hosts logged empty session_id,
breaking /plan-tune per-session grouping. It now uses the same
substitute-from-the-skill-start-echoes contract as the telemetry block.
Also: retired the pre-Phase-2 stop-gate docstring, repointed the
gbrain-local-status cross-reference at the script's inline jq, dropped an
orphaned section comment, documented retro-metrics' suffix-only census.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/resolvers/preamble.ts

@@ -28,8 +28,6 @@ import {
   generatePlanModeInfo,
 } from './preamble/generate-completion-status';
 
-// One-time onboarding prompts
-
 // Host-specific instructions
 import { generateBrainHealthInstruction } from './preamble/generate-brain-health-instruction';