feat: complete admission workspace

.trellis/spec/backend/database.md

@@ -191,6 +191,66 @@ export async function getOrdersWithItems(params: {
 
 ## Advanced SQL Patterns
 
+## Scenario: Admission and Bed Mutations
+
+### 1. Scope / Trigger
+
+- Trigger: changing elder admission, transfer, discharge, or bed occupancy behavior.
+- These mutations span `admissions`, `beds`, and `elders`, so partial writes are not acceptable.
+
+### 2. Signatures
+
+- `POST /api/admissions`: admit an elder or transfer an active elder to a new available bed.
+- `PATCH /api/admissions/[id]`: discharge an active admission and release its bed.
+- Mutations use `getDatabase().transaction(async (transaction) => ...)`.
+
+### 3. Contracts
+
+- `POST /api/admissions` request: `{ elderId: string; bedId: string; notes?: string }`.
+- `PATCH /api/admissions/[id]` request: `{ notes?: string }`.
+- Success responses include `{ success: true, reason: string, admission }`.
+- Failure responses include `{ success: false, reason: string }`.
+
+### 4. Validation & Error Matrix
+
+- Missing active organization -> `400`.
+- Missing elder or bed -> `404`.
+- Target bed not `available` -> `409`.
+- Discharge target not found -> `404`.
+- Discharge target not `active` -> `409`.
+- Insert/update returning no row -> `500`.
+
+### 5. Good/Base/Bad Cases
+
+- Good: return a typed mutation result from inside the transaction, then convert it to `jsonFailure` or `jsonSuccess` outside the transaction.
+- Base: read-only admission lists may use the temporary `readData()` compatibility model while the domain helper layer is being extracted.
+- Bad: throw ordinary `Error` for business conflicts such as occupied beds, because it loses the structured status/reason contract.
+
+### 6. Tests Required
+
+- `pnpm lint`
+- `pnpm type-check`
+- `pnpm build`
+- Integration assertions: occupied-bed admission returns `409`; transfer closes the old active admission and frees the old bed; discharge closes the active admission, frees the bed, and marks the elder discharged.
+
+### 7. Wrong vs Correct
+
+#### Wrong
+
+```ts
+if (bed.status !== "available") {
+  throw new Error("床位不可分配");
+}
+```
+
+#### Correct
+
+```ts
+if (bed.status !== "available") {
+  return { success: false, reason: "床位不可分配", status: 409 };
+}
+```
+
 ### JSON Column Operations
 
 When using PostgreSQL JSON/JSONB columns, proper casting is required for JSON functions.