devvit: onModAction trigger re-fetches full mod log, contradicts architecture §3

[bakerboy448]

Problem

Architecture spec devvit-migration/docs/04-architecture.md:246 (§3, "Execution Model Decision") specifies the onModAction trigger:

does NOT call getModerationLog and does NOT publish. Cheap, idempotent, self-loop-safe.

The shipped trigger contradicts this:

• devvit/src/main.ts:174-191 — the ModAction trigger calls ingest(reddit, redis, cfg) on every single mod action.
• devvit/src/modlog.ts:219-246 — ingest unconditionally calls fetchActions.
• devvit/src/modlog.ts:191-202 — fetchActions issues reddit.getModerationLog({ subredditName, limit: cfg.fetchLimit, pageSize: 100 }).all(), a full listing re-fetch, not an incremental single-event ingest.

This means every moderation action on the subreddit triggers a full moderation-log re-fetch, not the cheap dirty-flag-only path the architecture decision describes. Also contradicts NFR-6 (devvit-migration/docs/01-requirements.md:149) which bounds normal-run cost assuming incremental ingest; a full re-fetch per action multiplies read-API load under active moderation and doesn't scale the way the architecture doc assumed when making the cron-primary/trigger-ingest tradeoff.

Fix

Either:

1. Make the trigger truly incremental — extract/dedup/persist the single ModAction event payload directly (no getModerationLog call), matching architecture §3's stated design, or
2. If a full re-fetch on every trigger is intentional, update 04-architecture.md §3 to reflect that and re-evaluate whether the cron-primary design still holds (it was chosen partly because the trigger was assumed cheap).

References

PR #34 (feat/devvit-migration), devvit-migration/docs/STATUS.md §7b.