fix: resolve coverage generation conflicts with stdio transport

Fix CI coverage generation failures caused by stdio transport test:

Coverage Issue:
- go test -coverprofile with ./... fails when tests capture stdout
- TestRunWithTransport_Stdio uses stdio transport which takes over stdout
- This conflicts with coverage output being written to stdout
- Error: "write /dev/stdout: file already closed"

Solutions Applied:
1. Skip stdio transport test when coverage is enabled (testing.CoverMode())
2. Split coverage generation by package to avoid conflicts
3. Merge coverage files manually in CI workflow

CI Workflow Changes:
- Separate "Run tests" (race detector) from coverage generation
- Generate coverage per package and merge into single file
- Use atomic mode for accurate concurrent coverage

Test Changes (transport_test.go):
- Added coverage detection with testing.CoverMode()
- Skip TestRunWithTransport_Stdio when coverage is enabled
- Test still runs normally without coverage flag

This allows full test coverage reporting while avoiding the stdout
conflict. The stdio transport test is still run during normal testing
and race detection, just skipped during coverage generation.

Author: Rihoj

.github/workflows/ci.yml

@@ -55,9 +55,15 @@ jobs:
           args: --timeout=3m
 
       - name: Run tests
+        run: go test -race ./...
+          
+      - name: Generate coverage
         run: |
-          go test -race ./...
-          go test -coverprofile=coverage.out -covermode=atomic ./...
+          echo 'mode: atomic' > coverage.out
+          go test -coverprofile=coverage.tmp -covermode=atomic . && tail -n +2 coverage.tmp >> coverage.out || true
+          go test -coverprofile=coverage.tmp -covermode=atomic ./cache && tail -n +2 coverage.tmp >> coverage.out || true
+          go test -coverprofile=coverage.tmp -covermode=atomic ./httpx && tail -n +2 coverage.tmp >> coverage.out || true
+          rm coverage.tmp
 
       - name: Upload coverage report
         if: always()

transport_test.go

@@ -20,6 +20,12 @@ func TestRunWithTransport_Stdio(t *testing.T) {
 		t.Fatalf("failed to create server: %v", err)
 	}
 
+	// Skip actual transport test when running with coverage
+	// because stdio transport captures stdout, breaking coverage output
+	if testing.CoverMode() != "" {
+		t.Skip("Skipping stdio transport test when coverage is enabled")
+	}
+
 	// We can't actually run the server in a test (it would block),
 	// but we can verify the function accepts the correct transport type
 	ctx, cancel := context.WithCancel(context.Background())