feat: Add max-parallel Support for Gitea Actions (#36357)

Add support for `strategy.max-parallel` on Gitea Actions matrix jobs.

**How it works**
Jobs over the limit are inserted as `Blocked` instead of `Waiting`, so
runners never see them. When a job finishes, the job-status resolver
promotes one `Blocked` job per freed slot, in job order. Slots are
counted per `JobID` and scoped by reusable-workflow caller. A
`Cancelling` job still owns its runner, so it keeps its slot.

The cap is applied wherever a job can become `Waiting`: initial insert,
rerun, approval, and resolver promotion.

Best effort, not a hard invariant: two concurrent emitter passes can
each promote into the last slot, overshooting by one. It does not
compound, since every later pass recounts.

**Parsing**
Any YAML number, cast to an int as GitHub does (`1.5` → 1). `0` or
negative means unlimited. Expressions (`${{ ... }}`) are not evaluated
yet and fall back to unlimited.

**Migration**
Adds the `max_parallel` column on `action_run_job`. No index or
constraint changes.

**Compatibility**
Existing rows default to `0`, so behaviour is unchanged. No runner
changes needed: the runner protocol is untouched, and since the server
splits the matrix each runner still receives a single job.

Closes https://github.com/go-gitea/gitea/issues/35561
Signed-off-by: Pascal Zimmermann <pascal.zimmermann@theiotstudio.com>
Signed-off-by: ZPascal <pascal.zimmermann@theiotstudio.com>
Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>

modelmigration/migrations.go

@@ -28,6 +28,7 @@ import (
 	"gitea.dev/modelmigration/v1_25"
 	"gitea.dev/modelmigration/v1_26"
 	"gitea.dev/modelmigration/v1_27"
+	"gitea.dev/modelmigration/v1_28"
 	"gitea.dev/modelmigration/v1_6"
 	"gitea.dev/modelmigration/v1_7"
 	"gitea.dev/modelmigration/v1_8"
@@ -421,6 +422,8 @@ func prepareMigrationTasks() []*migration {
 		newMigration(341, "Convert legacy MSSQL DATETIME columns to DATETIME2", v1_27.FixLegacyMSSQLDateTimeColumns),
 		newMigration(342, "Add scoped workflows schema", v1_27.AddScopedWorkflowsSchema),
 		// Gitea 1.27.0 ends at migration ID number 342 (database version 343)
+
+		newMigration(343, "Add max_parallel column to action_run_job", v1_28.AddMaxParallelToActionRunJob),
 	}
 	return preparedMigrations
 }

modelmigration/v1_28/main_test.go

@@ -0,0 +1,14 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_28
+
+import (
+	"testing"
+
+	"gitea.dev/modelmigration/migrationtest"
+)
+
+func TestMain(m *testing.M) {
+	migrationtest.MainTest(m)
+}

modelmigration/v1_28/v343.go

@@ -0,0 +1,22 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_28
+
+import (
+	"gitea.dev/modelmigration/base"
+
+	"xorm.io/xorm"
+)
+
+func AddMaxParallelToActionRunJob(x base.EngineMigration) error {
+	type ActionRunJob struct {
+		MaxParallel int `xorm:"NOT NULL DEFAULT 0"`
+	}
+
+	_, err := x.SyncWithOptions(xorm.SyncOptions{
+		IgnoreConstrains:  true,
+		IgnoreDropIndices: true,
+	}, new(ActionRunJob))
+	return err
+}

modelmigration/v1_28/v343_test.go

@@ -0,0 +1,37 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package v1_28
+
+import (
+	"testing"
+
+	"gitea.dev/modelmigration/migrationtest"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestAddMaxParallelToActionRunJob(t *testing.T) {
+	type ActionRunJob struct {
+		ID   int64  `xorm:"pk autoincr"`
+		Name string `xorm:"VARCHAR(255)"`
+	}
+
+	x, deferable := migrationtest.PrepareTestEnv(t, 0, new(ActionRunJob))
+	defer deferable()
+	if x == nil || t.Failed() {
+		return
+	}
+
+	_, err := x.Insert(&ActionRunJob{Name: "job-a"})
+	require.NoError(t, err)
+
+	require.NoError(t, AddMaxParallelToActionRunJob(x))
+
+	// pre-existing rows must default to unlimited
+	var maxParallel int
+	has, err := x.SQL("SELECT max_parallel FROM action_run_job WHERE id = ?", 1).Get(&maxParallel)
+	require.NoError(t, err)
+	require.True(t, has)
+	require.Equal(t, 0, maxParallel)
+}