feat(p): link only OEM codes with a cross-reference match

Every OEM code was a link → unmatched codes (the majority — fasteners,
clips, body parts TecDoc doesn't carry) opened an empty "no
equivalents" page. Now the schema page batch-checks its codes against
the snapshot (POST /p/matched, one indexed query) and links ONLY the
matched ones; unmatched codes render as plain text. Copy stays for all.
No more dead-end empty pages from the parts panel.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/api/src/integrations/p/p-source-db.service.ts

@@ -64,6 +64,39 @@ export class PSourceDbService implements OnModuleInit, OnModuleDestroy {
     return code.toUpperCase().replace(/[^A-Z0-9]/g, "");
   }
 
+  /**
+   * Batch membership test for the schema page: given the OEM codes in a parts
+   * list, return the subset that has at least one OE cross-reference in the
+   * snapshot. The panel links only these (and renders the rest as plain text),
+   * so a click never lands on an empty "no equivalents" detail page. One indexed
+   * query (`code_norm` btree). Fail-open to [] (→ no links) when disabled / on
+   * error, echoing back the caller's original spelling for the matched codes.
+   */
+  async matchedCodes(rawCodes: string[]): Promise<string[]> {
+    if (!this.enabled || !this.sql || !rawCodes?.length) return [];
+    const rawByNorm = new Map<string, string>();
+    for (const raw of rawCodes) {
+      const n = PSourceDbService.norm(raw ?? "");
+      if (n.length >= PSourceDbService.MIN_NORM_LEN && !rawByNorm.has(n)) rawByNorm.set(n, raw);
+    }
+    if (rawByNorm.size === 0) return [];
+    try {
+      const norms = [...rawByNorm.keys()];
+      const rows = await this.sql<Array<{ code_norm: string }>>`
+        SELECT DISTINCT code_norm FROM article_oe_numbers
+        WHERE code_norm IN ${this.sql(norms)}
+      `;
+      return rows
+        .map((r) => rawByNorm.get(r.code_norm))
+        .filter((c): c is string => c !== undefined);
+    } catch (err) {
+      this.logger.warn(
+        `[p] matchedCodes failed (${rawByNorm.size} codes): ${(err as Error).message}`,
+      );
+      return [];
+    }
+  }
+
   async lookupByOem(rawCode: string): Promise<POemResult | null> {
     const query = (rawCode ?? "").trim();
     const queryNorm = PSourceDbService.norm(query);

apps/api/src/integrations/p/p.controller.ts

@@ -1,4 +1,4 @@
-import { Controller, Get, Query } from "@nestjs/common";
+import { Body, Controller, Get, Post, Query } from "@nestjs/common";
 import { PSourceDbService } from "./p-source-db.service";
 
 @Controller("p")
@@ -14,4 +14,15 @@ export class PController {
   async oem(@Query("code") code: string) {
     return this.p.lookupByOem(code ?? "");
   }
+
+  /**
+   * Batch: which of these OEM codes have a P cross-reference. The schema page
+   * sends the codes it's about to render and links only the returned ones, so
+   * unmatched codes stay plain text and never open an empty detail page.
+   * `POST /p/matched { codes: [...] }` → { matched: [...] }.
+   */
+  @Post("matched")
+  async matched(@Body("codes") codes: string[]) {
+    return { matched: await this.p.matchedCodes(Array.isArray(codes) ? codes : []) };
+  }
 }