修复铁路OCR空金额回退（07-28-travel-reimbursement-guide）

.trellis/spec/hyb-oa/reimbursement-invoice-ocr.md

@@ -165,6 +165,9 @@ const ocrRan = invoice.ocr_attempts > 0
     `sellerName`.
   - `electronic_train_ticket`: `invoiceNumber`, `invoiceDate`, `totalAmount`,
     `buyerName`.
+- Railway `totalAmount` uses the first individually parseable value from
+  Tencent `Total`, then `Fare`. Parse each field before applying fallback:
+  an empty or otherwise unparseable `Total` must not block a parseable `Fare`.
 - Never invent an invoice code from an invoice number or vice versa. Known
   no-code full-VAT and railway tickets use invoice-number-only duplicate
   detection; other categories retain code-plus-number semantics.
@@ -225,6 +228,9 @@ const ocrRan = invoice.ocr_attempts > 0
 - OCR service/job tests assert category-specific required fields,
   number-only dedupe only for known no-code categories, and no retry on terminal
   errors.
+- Railway adapter tests must cover an empty `Total` with a parseable `Fare` and
+  assert that normalized `totalAmount` uses `Fare` without emitting the source
+  amount in diagnostics.
 - Cache tests seed a legacy Tencent result containing `raw` and sensitive
   fields, then assert both normal and race cache paths return and persist only
   the allow-listed shape.
@@ -251,6 +257,16 @@ const persisted = sanitizeOcrResultForPersistence("tencent", normalized);
 await prisma.ocrResult.create({ data: { result_json: persisted } });
 ```
 
+For railway amount fallback, do not choose the raw source before parsing:
+
+```js
+// Wrong: an empty string is not nullish, so it blocks Fare.
+toNumberString(info?.Total ?? info?.Fare);
+
+// Correct: only a successfully parsed Total blocks Fare.
+toNumberString(info?.Total) ?? toNumberString(info?.Fare);
+```
+
 ## Scenario: Live OCR Sample Stdin Probe
 
 ### 1. Scope / Trigger