feat: remove default job-level concurrency (none is now the default)

docs/src/content/docs/reference/concurrency.md

@@ -24,13 +24,17 @@ This ensures workflows on different issues, PRs, or branches run concurrently wi
 
 ## Per-Engine Concurrency
 
-The default per-engine pattern `gh-aw-{engine-id}` ensures only one agent job runs per engine across all workflows, preventing AI resource exhaustion. The group includes only the engine ID and `gh-aw-` prefix - workflow name, issue/PR numbers, and branches are excluded.
+By default, no job-level concurrency is applied to agent jobs (`engine.concurrency: none` is the default). This allows multiple agent jobs — even across different workflows — to execute in parallel without any engine-level serialization.
+
+To opt in to job-level concurrency and limit how many agent jobs run simultaneously, set `engine.concurrency` explicitly:
 
 ```yaml wrap
-jobs:
-  agent:
-    concurrency:
-      group: "gh-aw-{engine-id}"
+---
+engine:
+  id: copilot
+  concurrency:  # Limit to one agent job per engine across all workflows
+    group: "gh-aw-copilot-${{ github.workflow }}"
+---
 ```
 
 ## Custom Concurrency
@@ -53,6 +57,34 @@ tools:
 ---
 ```
 
+## Disabling Job-Level Concurrency
+
+Since `engine.concurrency: none` is the default, no action is required to run workflow dispatches in parallel. The workflow-level `concurrency` block is sufficient for per-issue isolation:
+
+```yaml wrap
+---
+on:
+  workflow_dispatch:
+    inputs:
+      issue_number:
+        required: true
+concurrency:
+  group: issue-triage-${{ github.event.inputs.issue_number }}
+  cancel-in-progress: true
+engine:
+  id: copilot
+  # No engine.concurrency needed - none is the default
+---
+```
+
+You can also be explicit by setting `engine.concurrency: none`:
+
+```yaml wrap
+engine:
+  id: copilot
+  concurrency: none  # Explicit opt-out of job-level concurrency
+```
+
 ## Related Documentation
 
 - [AI Engines](/gh-aw/reference/engines/) - Engine configuration and capabilities

pkg/parser/schemas/main_workflow_schema.json

@@ -7438,7 +7438,7 @@
               "oneOf": [
                 {
                   "type": "string",
-                  "description": "Simple concurrency group name. Gets converted to GitHub Actions concurrency format with the specified group."
+                  "description": "Simple concurrency group name, or 'none' to disable the default job-level concurrency. Use 'none' when the workflow-level concurrency already provides the desired isolation (e.g., per-issue dispatch workflows). Gets converted to GitHub Actions concurrency format with the specified group."
                 },
                 {
                   "type": "object",
@@ -7457,7 +7457,7 @@
                   "additionalProperties": false
                 }
               ],
-              "description": "Agent job concurrency configuration. Defaults to single job per engine across all workflows (group: 'gh-aw-{engine-id}'). Supports full GitHub Actions concurrency syntax."
+              "description": "Agent job concurrency configuration. Defaults to single job per engine across all workflows (group: 'gh-aw-{engine-id}'). Set to 'none' to disable the default job-level concurrency and rely solely on workflow-level concurrency. Supports full GitHub Actions concurrency syntax."
             },
             "user-agent": {
               "type": "string",

pkg/workflow/concurrency.go

@@ -38,71 +38,26 @@ func GenerateConcurrencyConfig(workflowData *WorkflowData, isCommandTrigger bool
 }
 
 // GenerateJobConcurrencyConfig generates the agent concurrency configuration
-// for the agent job based on engine.concurrency field
+// for the agent job based on engine.concurrency field.
+// By default, no job-level concurrency is applied (equivalent to engine.concurrency: none).
+// Set engine.concurrency to a group name or object to opt in to job-level concurrency.
 func GenerateJobConcurrencyConfig(workflowData *WorkflowData) string {
 	concurrencyLog.Print("Generating job-level concurrency config")
 
 	// If concurrency is explicitly configured in engine, use it
 	if workflowData.EngineConfig != nil && workflowData.EngineConfig.Concurrency != "" {
+		// "none" is a special value to opt out of job-level concurrency (also the default)
+		if workflowData.EngineConfig.Concurrency == "none" {
+			concurrencyLog.Print("Engine concurrency set to none, skipping job concurrency")
+			return ""
+		}
 		concurrencyLog.Print("Using engine-configured concurrency")
 		return workflowData.EngineConfig.Concurrency
 	}
 
-	// Check if this workflow has special trigger handling (issues, PRs, discussions, push, command)
-	// For these cases, no default concurrency should be applied at agent level
-	if hasSpecialTriggers(workflowData) {
-		concurrencyLog.Print("Workflow has special triggers, skipping default job concurrency")
-		return ""
-	}
-
-	// For generic triggers like workflow_dispatch, apply default concurrency
-	// Pattern: gh-aw-{engine-id}-${{ github.workflow }}
-	engineID := ""
-	if workflowData.EngineConfig != nil && workflowData.EngineConfig.ID != "" {
-		engineID = workflowData.EngineConfig.ID
-	}
-
-	if engineID == "" {
-		// If no engine ID is available, skip default concurrency
-		return ""
-	}
-
-	// Build the default concurrency configuration
-	groupValue := fmt.Sprintf("gh-aw-%s-${{ github.workflow }}", engineID)
-	concurrencyConfig := fmt.Sprintf("concurrency:\n  group: \"%s\"", groupValue)
-
-	return concurrencyConfig
-}
-
-// hasSpecialTriggers checks if the workflow has special trigger types that require
-// workflow-level concurrency handling (issues, PRs, discussions, push, command)
-func hasSpecialTriggers(workflowData *WorkflowData) bool {
-	// Check for specific trigger types that have special concurrency handling
-	on := workflowData.On
-
-	// Check for issue-related triggers
-	if isIssueWorkflow(on) {
-		return true
-	}
-
-	// Check for pull request triggers
-	if isPullRequestWorkflow(on) {
-		return true
-	}
-
-	// Check for discussion triggers
-	if isDiscussionWorkflow(on) {
-		return true
-	}
-
-	// Check for push triggers
-	if isPushWorkflow(on) {
-		return true
-	}
-
-	// If none of the special triggers are detected, return false
-	// This means workflow_dispatch and other generic triggers will get default concurrency
-	return false
+	// Default: no job-level concurrency
+	concurrencyLog.Print("No engine concurrency configured, skipping job concurrency (default)")
+	return ""
 }
 
 // isPullRequestWorkflow checks if a workflow's "on" section contains pull_request triggers

pkg/workflow/concurrency_test.go

@@ -316,24 +316,22 @@ func TestGenerateJobConcurrencyConfig(t *testing.T) {
 		description  string
 	}{
 		{
-			name: "Default concurrency for workflow_dispatch with copilot engine",
+			name: "No default concurrency for workflow_dispatch with copilot engine",
 			workflowData: &WorkflowData{
 				On:           "on:\n  workflow_dispatch:",
 				EngineConfig: &EngineConfig{ID: "copilot"},
 			},
-			expected: `concurrency:
-  group: "gh-aw-copilot-${{ github.workflow }}"`,
-			description: "Copilot with workflow_dispatch should get default concurrency",
+			expected:    "",
+			description: "Copilot with workflow_dispatch should NOT get default job-level concurrency",
 		},
 		{
-			name: "Default concurrency for workflow_dispatch with claude engine",
+			name: "No default concurrency for workflow_dispatch with claude engine",
 			workflowData: &WorkflowData{
 				On:           "on:\n  workflow_dispatch:",
 				EngineConfig: &EngineConfig{ID: "claude"},
 			},
-			expected: `concurrency:
-  group: "gh-aw-claude-${{ github.workflow }}"`,
-			description: "Claude with workflow_dispatch should get default concurrency",
+			expected:    "",
+			description: "Claude with workflow_dispatch should NOT get default job-level concurrency",
 		},
 		{
 			name: "No default concurrency for push workflows",
@@ -382,14 +380,22 @@ func TestGenerateJobConcurrencyConfig(t *testing.T) {
 			description: "Should preserve cancel-in-progress when specified",
 		},
 		{
-			name: "Default concurrency for schedule with codex engine",
+			name: "No default concurrency for schedule with codex engine",
 			workflowData: &WorkflowData{
 				On:           "on:\n  schedule:\n    - cron: '0 0 * * *'",
 				EngineConfig: &EngineConfig{ID: "codex"},
 			},
-			expected: `concurrency:
-  group: "gh-aw-codex-${{ github.workflow }}"`,
-			description: "Codex with schedule should get default concurrency",
+			expected:    "",
+			description: "Codex with schedule should NOT get default job-level concurrency",
+		},
+		{
+			name: "No concurrency when engine.concurrency is set to none",
+			workflowData: &WorkflowData{
+				On:           "on:\n  workflow_dispatch:",
+				EngineConfig: &EngineConfig{ID: "copilot", Concurrency: "none"},
+			},
+			expected:    "",
+			description: "engine.concurrency: none should disable default job-level concurrency",
 		},
 	}
 

pkg/workflow/engine.go

@@ -119,8 +119,13 @@ func (c *Compiler) ExtractEngineConfig(frontmatter map[string]any) (string, *Eng
 			// Extract optional 'concurrency' field (string or object format)
 			if concurrency, hasConcurrency := engineObj["concurrency"]; hasConcurrency {
 				if concurrencyStr, ok := concurrency.(string); ok {
-					// Simple string format (group name)
-					config.Concurrency = fmt.Sprintf("concurrency:\n  group: \"%s\"", concurrencyStr)
+					if concurrencyStr == "none" {
+						// Special value to opt out of default job-level concurrency
+						config.Concurrency = "none"
+					} else {
+						// Simple string format (group name)
+						config.Concurrency = fmt.Sprintf("concurrency:\n  group: \"%s\"", concurrencyStr)
+					}
 				} else if concurrencyObj, ok := concurrency.(map[string]any); ok {
 					// Object format with group and optional cancel-in-progress
 					var parts []string