docs: root ERD.md (SQLite ERD, Mermaid), merge docs/do-erd.md

ERD.md

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+# ERD — karung counter (SQLite)
+
+Data model for the karung feedmill counter. SQLite DB at
+`$OUTPUT_DIR/jetson_counter.db` (`config.yaml` `output.dir`,
+default `/opt/jetson-counter/`; env override `DB_PATH`).
+
+**No DB foreign keys enforced** (zero `FOREIGN KEY` in code) — all relationships
+are soft, by naming/best-effort writes.
+
+```mermaid
+erDiagram
+    batches ||--o{ delivery_orders : "soft via batch_id / do_numbers"
+    batches ||--o{ daily_summaries : "rollup by counting_date"
+
+    batches {
+        INTEGER id PK
+        TEXT counting_date "NOT NULL, YYYY-MM-DD, cutoff-shifted"
+        INTEGER batch_number "NOT NULL, per date+camera+label"
+        TEXT camera_name "NOT NULL, default CC1"
+        TEXT object_label "NOT NULL, default karung-pakan"
+        INTEGER count "NOT NULL, gross sack loading"
+        TEXT start_time "NOT NULL, ISO datetime"
+        TEXT end_time "NOT NULL, ISO datetime"
+        TIMESTAMP created_at "default CURRENT_TIMESTAMP"
+        INTEGER box_loading "NOT NULL, default 0"
+        INTEGER box_unloading "NOT NULL, default 0"
+        TEXT model_mode "NOT NULL, default A"
+        TEXT plate "NOT NULL, default ''"
+        TEXT do_numbers "NOT NULL, JSON array of No. DO"
+        INTEGER expected_sack "NOT NULL, default 0"
+        INTEGER expected_box "NOT NULL, default 0"
+        INTEGER net_sack "NOT NULL, default 0"
+        INTEGER net_box "NOT NULL, default 0"
+    }
+
+    delivery_orders {
+        INTEGER id PK
+        TEXT counting_date "NOT NULL"
+        TEXT photo_path "NOT NULL, relative under do_photos/"
+        TEXT no_do "default ''"
+        TEXT plate "default ''"
+        INTEGER expected_sack "default 0"
+        INTEGER expected_box "default 0"
+        TEXT ocr_raw "nullable JSON: no_do, plate, ocr_text, engine, ocr_ok, ocr_error"
+        TEXT status "default 'draft'"
+        INTEGER batch_id "soft ref to batches.id, nullable"
+        TIMESTAMP created_at "default CURRENT_TIMESTAMP"
+        TIMESTAMP updated_at "default CURRENT_TIMESTAMP"
+    }
+
+    daily_summaries {
+        INTEGER id PK
+        TEXT counting_date "NOT NULL"
+        TEXT camera_name "NOT NULL"
+        TEXT object_label "NOT NULL"
+        INTEGER total_count "NOT NULL, default 0, SUM(batches.count)"
+        INTEGER total_batches "NOT NULL, default 0, COUNT(batches.id)"
+        TIMESTAMP updated_at "default CURRENT_TIMESTAMP"
+    }
+```
+
+## Keys
+
+- `batches`: `UNIQUE(counting_date, batch_number, camera_name, object_label)`
+- `daily_summaries`: `UNIQUE(counting_date, camera_name, object_label)`
+- `delivery_orders`: `idx_do_date_status` on `(counting_date, status)`
+
+## Relationships (logical)
+
+| From | To | How |
+|---|---|---|
+| `delivery_orders` → `batches` | N—1 | On stop: `batches.do_numbers` JSON array of `No. DO`; `delivery_orders.batch_id` set best-effort. Active batch: `current_batch.json.do_ids`. |
+| `batches` → `daily_summaries` | N—1 | Same `(counting_date, camera_name, object_label)`; stop recompute `SUM(count)`, `COUNT(id)`. |
+
+## Derived columns
+
+- `net_sack = count − sack unloading`, `net_box = box_loading − box_unloading`
+  (`src/do_batch.py:37`).
+- **Sack unloading has no column** — it only survives inside `net_sack`
+  (legacy rows with `net_sack=0` from the `ALTER TABLE ... DEFAULT 0`
+  migration are not backfillable).
+- History UI shows gross `count` / `box_loading` only (no Net).
+
+## Status (`delivery_orders.status`)
+
+`draft` (photo upload) → `staged` (saved/edited) → `attached` (in
+active/stopped batch). Discard stop with both nets 0 returns DOs to
+`staged`. `discarded` appears in older notes but **no code writes it** —
+discard is a `DELETE`.
+
+## Hazards
+
+- `INSERT OR REPLACE` on `batches` (UNIQUE match = delete+insert) changes
+  `id` on re-stop → can orphan `delivery_orders.batch_id`.
+- Schema divergence: `predict.py init_db()` creates only `batches` +
+  `daily_summaries` (3 extra cols, no `delivery_orders`); full 3-table
+  schema (9 extra `batches` cols) comes from `counter_dashboard.py`
+  `_ensure_db()` at import. Fresh DB touched only by `predict.py` is
+  incomplete; its DO updates fail silently (`try/except: pass`).
+
+## JSON sidecars + photo tree (not in SQLite)
+
+| Path | Role |
+|---|---|
+| `$OUTPUT_DIR/batch_mode.json` | `{mode: auto\|do_manual\|manual}` |
+| `$OUTPUT_DIR/current_batch.json` | active batch + `do_ids`, plate, expected_*, nets inputs |
+| `$OUTPUT_DIR/do_settings.json` | `require_plate`, `require_do`, `ocr_engine` |
+| `$OUTPUT_DIR/do_photos/YYYY-MM-DD/do_<uuid>.jpg` | source photos (7-day retention) |
+
+## Sources
+
+- DDL: `counter_dashboard.py:123-198` (`_ensure_db`, superset),
+  `predict.py:117-166` (`init_db`, partial).
+- Writes: `predict.py:249-306`, `counter_dashboard.py:610-668`.
+- Doc flow: `docs/do-erd.md` (merged into this file).