chore: add plan and phase reports for D1 + cron rollout

plans/260415-1010-d1-cron-infra/phase-04-retention-cron.md

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+# Phase 04 — Retention Cron
+
+**Priority:** P1
+**Status:** Complete
+**Depends on:** Phases 02 + 03
+
+## Overview
+
+Daily cron trims `trading_trades` to enforce caps:
+- **Per user:** keep newest 1000 rows, delete older.
+- **Global:** keep newest 10000 rows across all users, delete oldest (FIFO).
+
+## Requirements
+
+**Functional**
+- Schedule: `"0 17 * * *"` (daily 17:00 UTC = 00:00 ICT).
+- Per-user pass first (bounded by user count), then global FIFO.
+- Report count deleted via `console.log` (shows in Cloudflare logs).
+
+**Non-functional**
+- Safe to retry — idempotent (just deletes excess rows).
+- Bounded execution time — large backlog handled in batches of 1000 deletes per statement if needed.
+
+## Architecture
+
+Added to `src/modules/trading/index.js`:
+
+```js
+crons: [{
+  schedule: "0 17 * * *",
+  name: "trim-trades",
+  handler: trimTradesHandler,
+}]
+```
+
+### Per-user trim query
+
+```sql
+DELETE FROM trading_trades
+WHERE id IN (
+  SELECT id FROM trading_trades
+  WHERE user_id = ?
+  ORDER BY ts DESC
+  LIMIT -1 OFFSET 1000
+);
+```
+
+Run once per distinct `user_id` from a `SELECT DISTINCT user_id FROM trading_trades`.
+
+### Global FIFO trim
+
+```sql
+DELETE FROM trading_trades
+WHERE id IN (
+  SELECT id FROM trading_trades
+  ORDER BY ts DESC
+  LIMIT -1 OFFSET 10000
+);
+```
+
+## Related Code Files
+
+**Create**
+- `src/modules/trading/retention.js` — `trimTradesHandler(event, { sql })`
+- `tests/modules/trading/retention.test.js`
+
+**Modify**
+- `src/modules/trading/index.js` — wire cron entry
+- `wrangler.toml` — add `"0 17 * * *"` to `[triggers] crons`
+
+## Todo List
+
+- [x] `retention.js` with per-user + global trim
+- [x] Wire cron entry
+- [x] Tests: seed >1000 per user + >10000 global, assert trimmed counts
+
+## Success Criteria
+
+- Given 1500 rows for user A, cron leaves 1000 newest.
+- Given 15000 rows globally across users, cron leaves 10000 newest.
+- Console logs deletion counts.
+
+## Risks
+
+- Per-user pass cost scales with user count. At current scale (hobby) irrelevant; document limit for future.
+- Competing writes during trim — acceptable since trades append-only.