fix(descriptor): use _normalize_header_name in header fast-path

spec/unit/features/descriptor.feature

@@ -44,6 +44,10 @@ Feature: Descriptor extraction and claim resolution
     Scenario: AC-7b header limit_key with hyphens matches OpenResty normalized key with underscores
       Given limit_keys is "header:x-e2e-key"
       And header "x_e2e_key" is "exhaust-abc123"
+
+    Scenario: AC-7c uppercase header limit_key matches OpenResty normalized key (lowercase + underscore)
+      Given limit_keys is "header:X-E2E-Key"
+      And header "x_e2e_key" is "exhaust-abc123"
       When I extract descriptors
       Then descriptor "header:x-e2e-key" is "exhaust-abc123"
       And missing keys are empty

src/fairvisor/descriptor.lua

@@ -249,9 +249,9 @@ function _M.extract(limit_keys, request_context)
         value = headers[name]
         if value == nil then
           -- OpenResty normalizes header names: lowercase and hyphen to underscore (e.g. X-E2E-Key -> x_e2e_key).
-          local name_underscore = string_gsub(name, "-", "_")
-          local name_lower = string_lower(name)
-          value = headers[name_underscore] or headers[name_lower]
+          -- Use _normalize_header_name so both transformations are applied together; the two-step
+          -- approach (hyphen→underscore OR lowercase separately) misses uppercase+hyphenated keys.
+          value = headers[_normalize_header_name(name)]
         end
         if value == nil then
           local name_norm = _normalize_header_name(name)