Files
my-pi/pi-permission-system/docs/plans/archive/0097-document-subagent-extension-coexistence.md
T

85 lines
4.9 KiB
Markdown

---
issue: 97
issue_title: "Document coexistence with pi-subagent extensions and their tool deny mechanisms"
---
# Document subagent extension coexistence
## Problem Statement
Three major pi-subagent extensions (nicobailon/pi-subagents, tintinweb/pi-subagents, HazAT/pi-interactive-subagents) each implement their own tool restriction mechanisms.
These compose correctly with our permission system today — subagent extensions control tool *visibility* while our extension controls tool *policy* — but users have no documentation explaining this layering.
A user might set `deny-tools: bash` in one extension and `bash: allow` in ours, or vice versa, with no guidance on how the two interact.
## Goals
- Add a "Coexistence with subagent extensions" section to `README.md`.
- Document the two-layer model: visibility (subagent extension) → policy (permission system).
- Clarify that `permission:` frontmatter is exclusive to our extension and does not conflict with `tools:`, `disallowed_tools:`, or `deny-tools:` keys.
- Note the interaction edges: hidden tools are never seen by our extension; denied tools are hidden regardless of the subagent extension's allowlist.
## Non-Goals
- Changing any runtime behavior — this is docs-only.
- Adding integration tests against third-party subagent extensions.
- Modifying frontmatter parsing to detect or warn about subagent extension keys (tracked separately in #96).
## Background
Our extension hooks into Pi's tool lifecycle at two points:
1. **Tool filtering** (`onRegisterTool`) — removes denied tools before the agent sees them and rewrites the `Available tools:` system prompt section.
2. **Permission gating** (`checkPermission`) — intercepts tool/bash/MCP/skill calls at runtime and enforces allow/ask/deny policy.
Subagent extensions operate at a different layer:
| Extension | Mechanism | Effect |
| ------------------------------ | --------------------------------------- | -------------------------------------------------- |
| nicobailon/pi-subagents | `--tools` CLI allowlist | Only listed tools are registered in the subprocess |
| tintinweb/pi-subagents | `session.setActiveToolsByName()` | Filters the active tool set in-process |
| HazAT/pi-interactive-subagents | `PI_DENY_TOOLS` env var + `--tools` CLI | Combines denylist env var with CLI allowlist |
The two layers do not conflict:
- If a subagent extension hides a tool, our extension never receives a registration or call event for it.
- If our extension denies a tool, it is removed from the active set regardless of what the subagent extension allowed.
## Design Overview
Add a new `### Coexistence with Subagent Extensions` subsection under the existing `## Technical Details` heading in `README.md`.
The section should:
1. Introduce the two-layer model with a brief diagram or table.
2. List the three known subagent extensions and their frontmatter keys.
3. Explain the interaction rules with concrete examples.
4. State that `permission:` frontmatter is exclusive to this extension.
No code, schema, or config changes are required.
## Module-Level Changes
| File | Change |
| ----------- | --------------------------------------------------------------------------- |
| `README.md` | Add `### Coexistence with Subagent Extensions` under `## Technical Details` |
No changes to `src/`, `schemas/`, `config/`, `tests/`, or `docs/architecture/`.
## TDD Order
1. **docs: document subagent extension coexistence (#97)** — Add the new README section.
No test cycle; docs-only change.
Verify with `markdownlint README.md` if available.
## Risks and Mitigations
| Risk | Mitigation |
| -------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------- |
| Documentation becomes stale if subagent extensions change their mechanisms | Keep the section descriptive of the general two-layer model; specific extension details are secondary and link to upstream repos |
| Could this silently weaken a permission? | No — this change is documentation only; no runtime behavior is altered |
| Users might misread the section as endorsing a specific subagent extension | Use neutral language; describe mechanism, not recommendation |
## Open Questions
- None.
The issue scope is clear and self-contained.