fix: recognize /api/graphql path in proxy for GHES-style gh CLI

When gh CLI uses GH_HOST for proxy mode, it sends GraphQL requests to
/api/graphql (GHES-style) instead of /api/v3/graphql. The proxy only
recognized /graphql and /api/v3/graphql, causing the GraphQL POST to
fall through to passthrough which forwarded it to
https://api.github.com/api/graphql (404) instead of /graphql.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: lpcox

internal/proxy/graphql.go

@@ -170,7 +170,9 @@ func extractOwnerRepo(variables map[string]interface{}, query string) (string, s
 }
 
 // IsGraphQLPath returns true if the request path is the GraphQL endpoint.
+// Accepts /graphql (after prefix strip), /api/v3/graphql (before strip),
+// and /api/graphql (GHES-style path used by gh CLI with GH_HOST).
 func IsGraphQLPath(path string) bool {
 	cleaned := strings.TrimSuffix(path, "/")
-	return cleaned == "/graphql" || cleaned == "/api/v3/graphql"
+	return cleaned == "/graphql" || cleaned == "/api/v3/graphql" || cleaned == "/api/graphql"
 }

internal/proxy/proxy_test.go

@@ -492,6 +492,8 @@ func TestIsGraphQLPath(t *testing.T) {
 	assert.True(t, IsGraphQLPath("/graphql/"))
 	assert.True(t, IsGraphQLPath("/api/v3/graphql"))
 	assert.True(t, IsGraphQLPath("/api/v3/graphql/"))
+	assert.True(t, IsGraphQLPath("/api/graphql"))
+	assert.True(t, IsGraphQLPath("/api/graphql/"))
 	assert.False(t, IsGraphQLPath("/repos/org/repo"))
 	assert.False(t, IsGraphQLPath("/user"))
 }