Add disable-xpia-prompt feature flag

[Copilot]

Adds a frontmatter feature flag to exclude the XPIA (Cross-Prompt Injection Attack) security prompt from agent instructions.

Changes

• Added DisableXPIAPromptFeatureFlag constant (pkg/constants/constants.go)

  • Value: "disable-xpia-prompt"

• Modified prompt section collection (pkg/workflow/unified_prompt_step.go)

  • collectPromptSections() now checks feature flag via isFeatureEnabled()
  • XPIA section skipped when flag is true, included otherwise (default)

• Added test coverage (pkg/workflow/unified_prompt_step_test.go)

  • Verifies behavior with flag enabled, disabled, and absent
  • Uses xpiaPromptFile constant for robust assertion

Usage

---
engine: copilot
features:
  disable-xpia-prompt: true
---

When enabled, the compiled workflow omits xpia.md from the prompt construction:

# Without flag (default)
cat "/opt/gh-aw/prompts/xpia.md" >> "$GH_AW_PROMPT"
cat "/opt/gh-aw/prompts/temp_folder_prompt.md" >> "$GH_AW_PROMPT"

# With flag enabled
cat "/opt/gh-aw/prompts/temp_folder_prompt.md" >> "$GH_AW_PROMPT"

---

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[Copilot]

Pull request overview

This PR adds a new feature flag disable-xpia-prompt that allows workflows to opt out of the XPIA (Cross-Prompt Injection Attack) security prompt being included in agent instructions. The implementation follows the established pattern for feature flags in the codebase, using the isFeatureEnabled() function to check the flag in frontmatter and conditionally include the XPIA prompt section.

Changes:

• Added DisableXPIAPromptFeatureFlag constant in pkg/constants/constants.go with value "disable-xpia-prompt"
• Modified collectPromptSections() in pkg/workflow/unified_prompt_step.go to check the feature flag and skip the XPIA section when enabled
• Added comprehensive test coverage with three test cases covering default behavior, flag enabled, and flag explicitly disabled

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
pkg/constants/constants.go	Added the DisableXPIAPromptFeatureFlag constant with value "disable-xpia-prompt"
pkg/constants/constants_test.go	Added test case for the new feature flag constant to verify correct type and value
pkg/workflow/unified_prompt_step.go	Modified prompt section collection to conditionally include XPIA section based on feature flag using isFeatureEnabled()
pkg/workflow/unified_prompt_step_test.go	Added comprehensive test coverage for the feature flag with three scenarios: default inclusion, exclusion when enabled, and inclusion when explicitly disabled

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