Fix __GH_AW_WIKI_NOTE__ placeholder not substituted when Wiki is disabled

actions/setup/sh/validate_prompt_placeholders.sh

@@ -13,6 +13,18 @@ fi
 
 echo "🔍 Validating prompt placeholders..."
 
+# Fallback: substitute __GH_AW_WIKI_NOTE__ with an empty string if still present.
+# This handles workflows compiled before GH_AW_WIKI_NOTE was added to the substitution
+# step for non-wiki repos. The wiki note is always optional (empty = no wiki note),
+# so it is safe to clear it here rather than failing with a confusing placeholder error.
+# If you see this message, run `gh aw update` to recompile your workflow and avoid the fallback.
+if grep -q "__GH_AW_WIKI_NOTE__" "$PROMPT_FILE"; then
+    echo "⚠️  Warning: __GH_AW_WIKI_NOTE__ was not substituted by the substitution step."
+    echo "   Applying fallback: replacing with empty string."
+    echo "   To resolve this permanently, run 'gh aw update' to recompile your workflow."
+    sed 's/__GH_AW_WIKI_NOTE__//g' "$PROMPT_FILE" > "$PROMPT_FILE.tmp" && mv "$PROMPT_FILE.tmp" "$PROMPT_FILE"
+fi
+
 # Check for unreplaced environment variable placeholders (format: __GH_AW_*__)
 if grep -q "__GH_AW_" "$PROMPT_FILE"; then
     echo "❌ Error: Found unreplaced placeholders in prompt file:"

actions/setup/sh/validate_prompt_placeholders_test.sh

@@ -95,3 +95,59 @@ fi
 echo ""
 
 echo "🎉 All validation tests passed!"
+
+# Test 5: Prompt with __GH_AW_WIKI_NOTE__ placeholder (fallback should apply, not fail)
+echo "Test 5: Prompt with unsubstituted __GH_AW_WIKI_NOTE__ (fallback should apply)"
+cat > "$TEST_DIR/prompt_wiki_note.txt" << 'EOF'
+<system>
+# Repo Memory
+You have access to a persistent repo memory folder at `/tmp/gh-aw/repo-memory/default/`
+where you can read and write files that are stored in a git branch.__GH_AW_WIKI_NOTE__
+</system>
+
+# User Task
+Do something useful.
+EOF
+
+export GH_AW_PROMPT="$TEST_DIR/prompt_wiki_note.txt"
+OUTPUT=$(bash "$SCRIPT_PATH" 2>&1)
+STATUS=$?
+if [ $STATUS -eq 0 ]; then
+    echo "✅ Test 5 passed: Prompt with __GH_AW_WIKI_NOTE__ handled by fallback"
+    if echo "$OUTPUT" | grep -q "Warning.*__GH_AW_WIKI_NOTE__"; then
+        echo "   (fallback warning message shown as expected)"
+    fi
+    # Verify __GH_AW_WIKI_NOTE__ was actually removed from the file
+    if grep -q "__GH_AW_WIKI_NOTE__" "$TEST_DIR/prompt_wiki_note.txt"; then
+        echo "❌ Test 5 failed: __GH_AW_WIKI_NOTE__ was not removed by fallback"
+        exit 1
+    fi
+else
+    echo "❌ Test 5 failed: Prompt with __GH_AW_WIKI_NOTE__ caused unexpected failure"
+    echo "Output: $OUTPUT"
+    exit 1
+fi
+echo ""
+
+# Test 6: Prompt with OTHER unreplaced placeholder (should still fail)
+echo "Test 6: Prompt with other unreplaced placeholder (should still fail)"
+cat > "$TEST_DIR/prompt_other_placeholder.txt" << 'EOF'
+<system>
+# System Instructions
+Memory directory: __GH_AW_MEMORY_DIR__
+</system>
+
+# User Task
+Do something useful.
+EOF
+
+export GH_AW_PROMPT="$TEST_DIR/prompt_other_placeholder.txt"
+if bash "$SCRIPT_PATH" 2>&1; then
+    echo "❌ Test 6 failed: Prompt with __GH_AW_MEMORY_DIR__ was accepted"
+    exit 1
+else
+    echo "✅ Test 6 passed: Prompt with other unreplaced placeholder rejected"
+fi
+echo ""
+
+echo "🎉 All validation tests passed!"

pkg/workflow/unified_prompt_creation_test.go

@@ -561,6 +561,76 @@ func TestGenerateUnifiedPromptCreationStep_CacheAndRepoMemory(t *testing.T) {
 	assert.Less(t, systemClosePos, userPos, "User task should be after system tag closes")
 }
 
+// TestGenerateUnifiedPromptCreationStep_WikiNoteInSubstitution verifies that GH_AW_WIKI_NOTE
+// is always present in the placeholder substitution step for repo-memory, regardless of wiki mode.
+// Regression test for: __GH_AW_WIKI_NOTE__ placeholder not substituted when Wiki is disabled.
+func TestGenerateUnifiedPromptCreationStep_WikiNoteInSubstitution(t *testing.T) {
+	tests := []struct {
+		name          string
+		wiki          bool
+		expectEmpty   bool
+		expectContain string
+	}{
+		{
+			name:        "non-wiki mode has empty GH_AW_WIKI_NOTE in substitution",
+			wiki:        false,
+			expectEmpty: true,
+		},
+		{
+			name:          "wiki mode has non-empty GH_AW_WIKI_NOTE in substitution",
+			wiki:          true,
+			expectEmpty:   false,
+			expectContain: "GitHub Wiki",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			compiler := &Compiler{}
+			data := &WorkflowData{
+				ParsedTools: NewTools(map[string]any{}),
+				RepoMemoryConfig: &RepoMemoryConfig{
+					Memories: []RepoMemoryEntry{
+						{ID: "default", BranchName: "memory/default", Wiki: tt.wiki},
+					},
+				},
+			}
+
+			builtinSections := compiler.collectPromptSections(data)
+			userPromptChunks := []string{"# User Task"}
+
+			var yamlBuf strings.Builder
+			allExpressionMappings := compiler.generateUnifiedPromptCreationStep(&yamlBuf, builtinSections, userPromptChunks, nil, data)
+
+			require.NotEmpty(t, allExpressionMappings, "Expected non-empty expression mappings")
+
+			// Verify GH_AW_WIKI_NOTE is always in the substitution mappings
+			var wikiNoteMapping *ExpressionMapping
+			for _, m := range allExpressionMappings {
+				if m.EnvVar == "GH_AW_WIKI_NOTE" {
+					wikiNoteMapping = m
+					break
+				}
+			}
+			require.NotNil(t, wikiNoteMapping, "GH_AW_WIKI_NOTE must be present in substitution mappings (required to substitute __GH_AW_WIKI_NOTE__ in repo_memory_prompt.md)")
+
+			// Verify the substitution step YAML contains the env var
+			var substYaml strings.Builder
+			generatePlaceholderSubstitutionStep(&substYaml, allExpressionMappings, "      ")
+			substOutput := substYaml.String()
+
+			assert.Contains(t, substOutput, "GH_AW_WIKI_NOTE:", "Substitution step must declare GH_AW_WIKI_NOTE env var")
+			assert.Contains(t, substOutput, "GH_AW_WIKI_NOTE: process.env.GH_AW_WIKI_NOTE", "Substitution step must pass GH_AW_WIKI_NOTE to substitutePlaceholders")
+
+			if tt.expectEmpty {
+				assert.Contains(t, substOutput, "GH_AW_WIKI_NOTE: ''", "Non-wiki mode should have empty GH_AW_WIKI_NOTE env var")
+			} else {
+				assert.Contains(t, substOutput, tt.expectContain, "Wiki mode should have wiki note content in GH_AW_WIKI_NOTE env var")
+			}
+		})
+	}
+}
+
 // TestGenerateUnifiedPromptCreationStep_PRContextConditional tests that PR context uses shell conditions
 func TestGenerateUnifiedPromptCreationStep_PRContextConditional(t *testing.T) {
 	compiler := &Compiler{