🐛 fix(bdd): shouldEnableV2 wrongly matched ~@v2 as @v2 substring

Pre-existing latent bug surfaced by the new @v2-gate scenario in
greet.feature (added in PR #56 follow-up): shouldEnableV2 used
strings.Contains(tags, "@v2") which matched the negation tag `~@v2`
as a positive inclusion. Result: the greet "v1" sub-test, intended
to run with v2_enabled=false, was actually starting the test server
with v2_enabled=true. The @v2-gate scenario asserting "v2 disabled →
404" got 200 instead.

Fix: parse the GODOG_TAGS expression by splitting on `&&` / `||` /
whitespace, then check each clause for exact `@v2` match (positive
inclusion only). The negation `~@v2` no longer matches.

The new BDD scenario is the regression test — without the fix, it
fails with status 200 instead of 404. With the fix, both greet "v1"
(v2 disabled) and "v2" (v2 enabled) sub-tests pass cleanly.

Verifier verdict: APPROVE. Race-clean. Full BDD suite green.

features/greet/greet.feature

@@ -15,6 +15,16 @@ Feature: Greet Service
     When I request a greeting for "John"
     Then the response should be "{\"message\":\"Hello John!\"}"
 
+  @critical @v2-gate
+  Scenario: v2 endpoint returns 404 when api.v2_enabled is disabled
+    # In the default tag-filter run (~@v2), the test server starts with
+    # v2_enabled=false. The v2EnabledGate middleware (ADR-0023 Phase 4)
+    # returns 404 with a JSON body explaining the flag state.
+    Given the server is running
+    When I send a POST request to v2 greet with name "John"
+    Then the status code should be 404
+    And the response should contain "v2 API is currently disabled"
+
   @v2 @api
   Scenario: v2 greeting with JSON POST request
     Given the server is running with v2 enabled

pkg/bdd/testserver/server.go

@@ -741,8 +741,14 @@ func (s *Server) waitForServerReady() error {
 	}
 }
 
-// shouldEnableV2 determines if v2 API should be enabled for this test server
-// This is the ONLY place that reads FEATURE and GODOG_TAGS env vars
+// shouldEnableV2 determines if v2 API should be enabled for this test server.
+// This is the ONLY place that reads FEATURE and GODOG_TAGS env vars.
+//
+// 2026-05-05: previous version used strings.Contains(tags, "@v2") which
+// wrongly matched the negation `~@v2` as well. This made the "v1" greet
+// sub-test (tags `~@v2 && ~@skip`) actually run with v2 enabled, masking
+// the gate behavior we now test in feature `@v2-gate` scenario. Fixed
+// here by inspecting each && clause and checking for positive inclusion.
 func (s *Server) shouldEnableV2() bool {
 	feature := os.Getenv("FEATURE")
 
@@ -753,9 +759,19 @@ func (s *Server) shouldEnableV2() bool {
 		return false
 	}
 
-	// For greet feature: enable v2 if tags include @v2
+	// For greet feature: enable v2 if tags include `@v2` as a POSITIVE clause.
+	// Godog tag expression syntax: clauses separated by `&&` or `||`, negation
+	// via leading `~`. A positive clause matches exactly `@v2` (after trim).
 	tags := os.Getenv("GODOG_TAGS")
-	return strings.Contains(tags, "@v2")
+	for _, clause := range strings.FieldsFunc(tags, func(r rune) bool {
+		return r == '&' || r == '|' || r == ' '
+	}) {
+		clause = strings.TrimSpace(clause)
+		if clause == "@v2" {
+			return true
+		}
+	}
+	return false
 }
 
 // createTestConfig creates a test configuration