POST /api/testcasesimport/?action=import_md&tproject_id=<pid> with hit_criteria=externalID or hit_criteria=internalID always returned HTTP 400 {"status":"error","message":"Invalid hit_criteria"}. Only hit_criteria=name was accepted. Even before the validation fix, the MD duplicate-detection block never consulted hit_criteria, so ID-based duplicate matching was unreachable.

Two coupled defects, both in api/testcasesimport/index.php:

1. Validation case-mismatch (lines 225-233). $hitCriteria = strtolower(trim($_POST['hit_criteria'] ?? 'name')) lowercased the incoming value to externalid/internalid, which never matched the mixed-case allow-list ['name','internalID','externalID']. Any non-name criterion was rejected with 400, making $hitCriteria unreachable.

2. tcId numeric extraction missing (lines 335-344). Even after the validation was relaxed (canonical re-casing), the duplicate detection used intval($c['tcId']) but the markdown parser (lib/functions/markdown_tc_import.class.php:113) stores tcId in TC-<N> format. intval("TC-1") returns 0 in PHP (stops at the first non-numeric char), so the externalID/internalID lookups always decoded to 0 and fell through to the name-based duplicate match.

Legacy parity reference: lib/testcases/tcImport.php:280-296 switches on hitCriteria (name → getDuplicatesByName, internalID → get_node_hierarchy_info, externalID → get_by_external). The modernized MD loop must mirror that switch.

Two-step correction:

1. Canonical re-casing (already landed, commit 91075141). Validate against the lowercased set ['name','internalid','externalid'], then map back to canonical name/internalID/externalID before passing downstream so the legacy XML switch (case 'externalID':) still matches. Applied to both import_md (line 225-233) and import_xml (line 555-562).

2. Numeric tcId extraction (this run, commit 385a377). Before the externalID/internalID index lookups, extract the trailing digit run from tcId:

   $tcNumericId = 0;
   if (preg_match('/(\d+)\s*$/', strval($c['tcId'] ?? ''), $idMatch)) {
       $tcNumericId = intval($idMatch[1]);
   }

   and use $tcNumericId (instead of intval('TC-N')) as the index key. The by-external and by-node indexes were already built by commit 91075141 (lines 260-286).

• php -l api/testcasesimport/index.php → no syntax errors
• hit_criteria=externalID accepted (400 gone), duplicate detected → skipped
• hit_criteria=internalID accepted (400 gone), duplicate detected → skipped
• hit_criteria=name → no regression, duplicate skipped
• hit_criteria=externalID + action_on_hit=generate_new → bypasses duplicate detection
• Non-matching external ID (TC-999, ext_id 999) → creates new (no false match)
• Invalid hit_criteria=invalid → still 400
• Event Viewer: no new Error/Warning entries
• Regression test suite: tmp/TLU_Test_Cases.md — TC-849.1 … TC-849.9, 9/9 PASS

• api/testcasesimport/index.php:332-347 — numeric tcId extraction in the externalID/internalID duplicate branch (this run)
• api/testcasesimport/index.php:225-233, 260-286, 555-562 — canonical re-casing + by-external/by-node index build (prior CI commit 91075141)