config(session-ingest): roll direct ingest to 20 percent

[pandemicsyn]

Summary

• Increase DIRECT_INGEST_PERCENT from 0 to 20.
• Retain the explicit user allowlist from Add Florian userid to direct session ingest gate #4541.
• Keep the 4 MiB direct-ingest body cap unchanged.

This PR is stacked on #4541 so its reviewable diff is the percentage change only. After #4541 merges, retarget this PR to main.

Rollout checks

Use the Axiom Session Ingest — Health & Direct Path Rollout dashboard and Cloudflare Queue metrics for session-ingest-processing. Monitor direct writes, fallback/reject/error signals, HTTP 5xx, queue backlog/lag/retries, and DLQ writes.

Validation

• pnpm format
• git diff --check

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (1 files)

• services/session-ingest/wrangler.jsonc

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_{Reviewed by gpt-5.6-sol · Input: 43.2K · Output: 6.2K · Cached: 377.7K}

_{Review guidance: REVIEW.md from base branch florian/config/session-ingest-allowlist}