# Feature Plan: Transport Capability Matrix

## Goal
Define transport feature capabilities centrally so router/policy/UI can make deterministic decisions.

## Why This Fits GIA
- GIA currently spans Signal/WhatsApp/Instagram/XMPP with uneven feature support.
- Prevents silent failures (for example reaction exists internally but cannot be sent outward).

## How It Follows Plan 1
- Plan 1 established canonical event flow as the shared source language for transport actions.
- Plan 2 uses that event flow to gate what may be attempted per transport before adapter calls.
- Interlink:
  - Canonical events define **what happened** (`reaction_added`, `message_edited`, etc.).
  - Capability matrix defines **what is allowed** on each service at execution time.
  - Together they prevent drift:
    - no silent no-op on unsupported features,
    - no adapter-specific policy branching,
    - deterministic user-visible failure reasons.

## Required Inputs From Plan 1
- Canonical event types and normalized action shapes are stable.
- Event write path exists for ingress/outbound actions.
- Traceability exists for diagnostics (`trace_id`, source transport metadata).

## Scope
- Add capability registry per transport.
- Features: reactions, edits, deletes, threaded replies, typing, media classes, read receipts, participant events.
- Runtime helper APIs used by router and compose UI.

## Implementation
1. Add `core/transports/capabilities.py` with static matrix + version field.
2. Expose query helpers: `supports(service, feature)` and `unsupported_reason(...)`.
3. Integrate checks into `core/clients/transport.py` send/reaction/edit paths.
4. Compose UI: disable unsupported actions with clear hints.
5. Add tests per service for expected behavior.

## Acceptance Criteria
- Unsupported action never calls transport adapter.
- User receives explicit, actionable error.
- Service capabilities are test-covered and easy to update.
- Capability decisions are traceable against canonical event/action context.

## Out of Scope
- Dynamic remote capability negotiation.