feat: support --platform and --pull in container.options (#1104)

Fixes https://gitea.com/gitea/runner/issues/667
Fixes https://gitea.com/gitea/runner/pulls/1103

`container.options` is parsed with docker/cli's `addFlags`, which omits the flags docker/cli registers on the `create` and `run` commands themselves. Those were rejected as unknown — most visibly `--platform`.

| Flag | Behavior | Why |
| --- | --- | --- |
| `--platform` | overrides the runner-wide container architecture | the only way to pick an image architecture per job, e.g. across a matrix |
| `--pull always\|missing\|never` | `always` forces a pull, `never` skips it | `force_pull` is runner-wide config today, with no per-job control |

Both are resolved in `NewContainer` because the image pull runs before the container is created and the two have to agree.

`--name`, `--quiet` and `--disable-content-trust` are now accepted and ignored, and `--use-api-socket` is rejected pointing at `container.docker_host`, so a valid `docker create` line no longer fails outright.

<sub>Written by Claude (Opus 4.8).</sub>

---------

Co-authored-by: bircni <bircni@icloud.com>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1104
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

act/container/docker_create_flags.go

@@ -0,0 +1,86 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build !(WITHOUT_DOCKER || !(linux || darwin || windows || netbsd))
+
+package container
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"slices"
+
+	"github.com/kballard/go-shellquote"
+	"github.com/spf13/pflag"
+)
+
+const (
+	pullPolicyAlways  = "always"
+	pullPolicyMissing = "missing"
+	pullPolicyNever   = "never"
+)
+
+var pullPolicies = []string{pullPolicyAlways, pullPolicyMissing, pullPolicyNever}
+
+// createFlags are the flags docker/cli registers on the `create` and `run` commands
+// instead of in addFlags, so they are not part of containerOptions.
+type createFlags struct {
+	platform     string
+	pull         string
+	name         string
+	useAPISocket bool
+}
+
+func registerCreateFlags(flags *pflag.FlagSet) *createFlags {
+	cf := new(createFlags)
+	flags.StringVar(&cf.platform, "platform", "", "Set platform if server is multi-platform capable")
+	flags.StringVar(&cf.pull, "pull", pullPolicyMissing, `Pull image before creating ("always", "missing", "never")`)
+	flags.StringVar(&cf.name, "name", "", "Assign a name to the container")
+	flags.BoolVar(&cf.useAPISocket, "use-api-socket", false, "Bind mount Docker API socket and required auth")
+	// Accepted without effect: pull progress is only logged at debug level, and docker
+	// no longer implements content trust.
+	flags.BoolP("quiet", "q", false, "Suppress the pull output")
+	flags.Bool("disable-content-trust", true, "Skip image verification (deprecated)")
+	return cf
+}
+
+// parseContainerOptions parses a container options string. The flags are returned even
+// on error, holding whatever was read before the failure.
+func parseContainerOptions(options string) (*pflag.FlagSet, *containerOptions, *createFlags, error) {
+	flags := pflag.NewFlagSet("container_flags", pflag.ContinueOnError)
+	flags.SetOutput(io.Discard)
+	copts := addFlags(flags)
+	cf := registerCreateFlags(flags)
+
+	args, err := shellquote.Split(options)
+	if err != nil {
+		return flags, copts, cf, fmt.Errorf("Cannot split container options: '%s': '%w'", options, err)
+	}
+
+	if err := flags.Parse(args); err != nil {
+		return flags, copts, cf, fmt.Errorf("Cannot parse container options: '%s': '%w'", options, err)
+	}
+
+	return flags, copts, cf, nil
+}
+
+// createFlagsFromOptions reads the create-level flags that have to be known before the
+// container is created. Malformed options keep the defaults here and are reported by
+// mergeContainerConfigs at create time.
+func createFlagsFromOptions(options string) *createFlags {
+	_, _, cf, _ := parseContainerOptions(options)
+	return cf
+}
+
+func (cf *createFlags) validate() error {
+	if !slices.Contains(pullPolicies, cf.pull) {
+		return fmt.Errorf("invalid --pull option %q: must be one of %q", cf.pull, pullPolicies)
+	}
+
+	if cf.useAPISocket {
+		return errors.New("--use-api-socket is not supported, use the runner's container.docker_host setting to expose a docker socket")
+	}
+
+	return nil
+}