fix: extract ${{ }} expressions from <safe-output-tools> max: values to avoid 21KB heredoc limit

pkg/workflow/safe_outputs_prompt_tools_test.go

@@ -194,7 +194,56 @@ func TestBuildSafeOutputsSectionsCustomToolsConsistency(t *testing.T) {
 	}
 }
 
-// extractToolNamesFromSections parses the <safe-output-tools> opening section and returns
+// TestBuildSafeOutputsSectionsMaxExpressionExtraction verifies that ${{ }} expressions
+// in safe-output max: values are extracted to GH_AW_* env vars and replaced with
+// __GH_AW_*__ placeholders in the <safe-output-tools> prompt block.
+// This prevents ${{ }} from appearing in the run: heredoc, which is subject to the
+// GitHub Actions 21KB expression-size limit (regression guard for gh-aw#21158).
+func TestBuildSafeOutputsSectionsMaxExpressionExtraction(t *testing.T) {
+	maxExpr := "${{ inputs.review-comment-max }}"
+	sections := buildSafeOutputsSections(&SafeOutputsConfig{
+		CreatePullRequestReviewComments: &CreatePullRequestReviewCommentsConfig{
+			BaseSafeOutputConfig: BaseSafeOutputConfig{
+				Max: &maxExpr,
+			},
+		},
+		NoOp: &NoOpConfig{},
+	})
+
+	require.NotNil(t, sections, "Expected non-nil sections")
+
+	// Find the opening <safe-output-tools> section
+	var openingSection *PromptSection
+	for i := range sections {
+		if !sections[i].IsFile && strings.HasPrefix(sections[i].Content, "<safe-output-tools>") {
+			openingSection = &sections[i]
+			break
+		}
+	}
+	require.NotNil(t, openingSection, "Expected to find <safe-output-tools> opening section")
+
+	// The raw ${{ }} expression must NOT appear in the content (would hit the 21KB limit)
+	assert.NotContains(t, openingSection.Content, "${{",
+		"${{ }} expressions must not appear in the tools content (triggers 21KB expression-size limit)")
+
+	// A __GH_AW_*__ placeholder must appear instead
+	assert.Contains(t, openingSection.Content, "__GH_AW_",
+		"A __GH_AW_*__ placeholder should replace the ${{ }} expression")
+
+	// The EnvVars map must have an entry mapping the placeholder key to the original expression
+	require.NotEmpty(t, openingSection.EnvVars,
+		"EnvVars must be populated so the substitution step can resolve the placeholder")
+
+	var foundExpr bool
+	for _, v := range openingSection.EnvVars {
+		if v == "${{ inputs.review-comment-max }}" {
+			foundExpr = true
+			break
+		}
+	}
+	assert.True(t, foundExpr, "EnvVars must contain the original ${{ inputs.review-comment-max }} expression")
+}
+
 // the list of tool names in the order they appear, stripping any max-budget annotations
 // (e.g. "noop(max:5)" → "noop").
 func extractToolNamesFromSections(t *testing.T, sections []PromptSection) []string {

pkg/workflow/unified_prompt_step.go

@@ -543,6 +543,9 @@ func toolWithMaxBudget(name string, max *string) string {
 // buildSafeOutputsSections returns the PromptSections that form the <safe-output-tools> block.
 // The block contains:
 //  1. An inline opening tag with a compact Tools list (dynamic, depends on which tools are enabled).
+//     Any ${{ }} expressions in max: values are extracted to GH_AW_* env vars and replaced
+//     with __GH_AW_*__ placeholders so they do not appear in the run: heredoc, avoiding the
+//     GitHub Actions 21KB expression-size limit.
 //  2. File references for tools that require multi-step instructions (create_pull_request,
 //     push_to_pull_request_branch, auto-injected create_issue notice).
 //  3. An inline closing tag.
@@ -724,10 +727,28 @@ func buildSafeOutputsSections(safeOutputs *SafeOutputsConfig) []PromptSection {
 
 	var sections []PromptSection
 
-	// Inline opening: XML tag + compact tools list
+	// Build the inline opening: XML tag + compact tools list.
+	// Extract any ${{ }} expressions from max: values so they do not appear in the
+	// run: heredoc (which is subject to GitHub Actions' 21KB expression-size limit).
+	// Expressions are replaced with __GH_AW_...__  placeholders and added to EnvVars
+	// so the placeholder substitution step can resolve them at runtime.
+	toolsContent := "<safe-output-tools>\nTools: " + strings.Join(tools, ", ")
+	envVars := make(map[string]string)
+	extractor := NewExpressionExtractor()
+	exprMappings, err := extractor.ExtractExpressions(toolsContent)
+	if err == nil && len(exprMappings) > 0 {
+		safeOutputsPromptLog.Printf("Extracted %d expression(s) from safe-output-tools block", len(exprMappings))
+		toolsContent = extractor.ReplaceExpressionsWithEnvVars(toolsContent)
+		for _, mapping := range exprMappings {
+			envVars[mapping.EnvVar] = fmt.Sprintf("${{ %s }}", mapping.Content)
+		}
+	}
+
+	// Inline opening: XML tag + compact tools list (with placeholders for any expressions)
 	sections = append(sections, PromptSection{
-		Content: "<safe-output-tools>\nTools: " + strings.Join(tools, ", "),
+		Content: toolsContent,
 		IsFile:  false,
+		EnvVars: envVars,
 	})
 
 	// File sections for tools with multi-step instructions