fix: align common behaviour with GitHub's runner (#1413)

Closes differences from GitHub's runner that common workflows hit:

- `ACTIONS_STEP_DEBUG` set as a repository variable enables debug output as on GitHub, where a secret of the same name still takes precedence. `runner.debug` and `RUNNER_DEBUG` are now also set inside composite actions, which lost the secret.
- `github.env` and `github.path` hold the file-command paths instead of being empty, so `echo "A=1" >> "${{ github.env }}"` works.
- Remote composite actions only get a pre stage when they nest actions. That stage evaluated `with:` before earlier steps ran, so an input like `${{ fromJSON(steps.meta.outputs.json).v }}` failed the job.
- `ports` on a job container are published, they were ignored while service ports worked.
- Dockerfile action build output reaches the job log. It was logged at debug and dropped, so a failing `RUN` showed only the final error.
- Local Docker actions honor their `.dockerignore`, as `docker build` does.
- Cancelling or timing out a host-mode step sends SIGINT, then SIGTERM after 7.5 seconds and SIGKILL after 2.5 more, as GitHub's runner does, so `trap` handlers and shutdown hooks run.
- `.sh` job hooks fall back to `sh` where bash is missing, and `.ps1` hooks to `powershell` where pwsh is missing, as on GitHub.

_Written by Claude (Opus 5.5)._

Reviewed-on: https://gitea.com/gitea/runner/pulls/1413
Reviewed-by: bircni <[email protected]>
Co-authored-by: silverwind <[email protected]>

internal/pkg/process/killer_unix_test.go

@@ -6,9 +6,11 @@
 package process
 
 import (
+	"context"
 	"fmt"
 	"os"
 	"os/exec"
+	"path/filepath"
 	"strings"
 	"syscall"
 	"testing"
@@ -95,3 +97,34 @@ func TestTreeKillCancelBeforeCaptureKillsTree(t *testing.T) {
 	require.Error(t, cmd.Wait())
 	require.Eventually(t, func() bool { return !processAlive(childPID) }, 5*time.Second, 10*time.Millisecond)
 }
+
+func TestTreeKillCancelRunsInterruptTrap(t *testing.T) {
+	ctx, cancel := context.WithTimeout(t.Context(), 5*time.Second)
+	defer cancel()
+	marker := filepath.Join(t.TempDir(), "interrupted")
+	cmd := exec.CommandContext(ctx, "/bin/sh", "-c", `trap 'echo interrupted > "$1"; exit 0' INT; echo ready; read value`, "sh", marker)
+	cmd.SysProcAttr = SysProcAttr("", false)
+	input, err := cmd.StdinPipe()
+	require.NoError(t, err)
+	defer input.Close()
+	output, err := cmd.StdoutPipe()
+	require.NoError(t, err)
+	treeKill := NewTreeKill(cmd)
+	treeKill.GracefulCancel = true
+	require.NoError(t, cmd.Start())
+	killer, err := treeKill.Capture(cmd.Process)
+	require.NoError(t, err)
+	defer killer.Close()
+	t.Cleanup(func() {
+		_ = killer.Kill()
+		_ = cmd.Wait()
+	})
+	var ready string
+	_, err = fmt.Fscanln(output, &ready)
+	require.NoError(t, err)
+	require.Equal(t, "ready", ready)
+
+	cancel()
+	require.ErrorIs(t, treeKill.Wait(ctx, cmd), context.Canceled)
+	require.FileExists(t, marker)
+}