Extension Proposal: LAR-1 Semantic Overlay (v0.3, published SDK)

## Summary

Proposal for a community extension to A2A: **LAR-1 Semantic Overlay** — a compact, machine-readable semantic layer for agent messages.

LAR-1 adds 6 optional dimensions via the standard `extensions[]` field:

| Field | Meaning | Example |
|-------|---------|---------|
| T | Time | now, past, recall, future |
| S | Space | here, there, meta |
| C | Cognition | obs, hyp, inf, rev |
| E | Evidence | direct, derived, reported |
| L | Likelihood | 0.0–1.0 |
| V | Verification | unverified, verified_tool |

**Non-breaking**: agents that donʼt understand LAR-1 silently ignore the extension.

## Why

A2A handles agent↔agent coordination but does not answer: how is a given message situated — observation or inference, live or recalled, verified or not? LAR-1 replaces guessing with ~80 bytes of structured metadata.

## Published SDK

| Language | Package | Registry |
|----------|---------|----------|
| TypeScript | @lar-1/core | [npm](https://www.npmjs.com/package/@lar-1/core) |
| TypeScript | @lar-1/a2a | [npm](https://www.npmjs.com/package/@lar-1/a2a) |
| Python | lar1semantic | [PyPI](https://pypi.org/project/lar1semantic/) |

79+ automated conformance + round-trip tests passing.

## Wire Format

```json
{
"role": "agent",
"parts": [{ "text": "Revenue grew 12%" }],
"extensions": [
{
"uri": "https://raw.githubusercontent.com/carlsonchik/larone/main/SPEC/extension-v0.3.json",
"LAR-1": {
"T": "now",
"C": "obs",
"E": "direct",
"L": 0.98,
"V": "verified_tool"
}
}
]
}
```

Compact string format: `LAR:T=now,C=obs,E=direct,L=0.98,V=verified_tool`

## Resources

- **Extension descriptor (v0.3):** https://github.com/carlsonchik/larone/blob/main/SPEC/extension-v0.3.json
- **Full proposal:** https://github.com/carlsonchik/larone/blob/main/proposal/extension_proposal.md
- **Repository:** https://github.com/carlsonchik/larone
- **SPEC:** https://github.com/carlsonchik/larone/blob/main/SPEC.md

## Questions for the Working Group

1. Should A2A recognize `application/lar+json` as a community extension type?
2. Is semantic annotation best in `extensions[]` or message `metadata`?
3. Would the WG adopt LAR-1 field vocabulary as a recommended convention?

Discussion draft — feedback welcome. We are prepared to contribute conformance fixtures upstream.

Review the LAR-1 specification and SDKs at the linked repository. Understand the A2A protocol's extension mechanism. The work involves evaluating the proposal for integration, considering message format changes and community adoption. 'Done' means providing feedback on the three questions posed to the working group, based on the protocol's design goals.

索引モデルが issue の本文から書いたものです。