protocol: add canonical Phase 3A contract sources

AGENTS.md

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+# VerseVDI Protocol repository guidance
+
+This repository is the sole source of the VerseVDI Phase 3 wire contract. It
+contains OpenAPI, JSON Schema, Protobuf, registries, fixtures, and generated
+language bindings. It contains no Connection Server business policy,
+database/auth implementation, provider credentials, or media implementation.
+
+## Source and generation rules
+
+- Edit `schemas/`, `openapi/`, `proto/`, `registries/`, and `fixtures/` only as
+  protocol sources. Never hand-edit `gen/`; run `python3 tools/generate.py`.
+- `VERSION` and `compatibility.json` are the version authority. Current, N-1,
+  and N-2 fixtures must remain executable.
+- `make verify` runs schema/fixture checks, Protobuf lint/descriptor checks,
+  the historical-descriptor breaking check, deterministic generation, Go tests,
+  and native conformance runners.
+- Generated output must be byte-for-byte clean after a second generation.
+- `gen/protobuf/phase3a-baseline.binpb` is a generated historical descriptor used
+  only by Buf breaking checks; regenerate it from an approved baseline tag,
+  never by hand.
+- The Connection Server consumes generated Go types through adapters; it does
+  not own a competing wire schema.
+
+## Scope boundaries
+
+Phase 3A covers control, authorization, resources, broker session actions,
+gateway-only grants/manifests, resumable control events, registered control
+datagrams, and bounded text clipboard. It does not implement a gateway,
+provider transport, video/audio forwarding, file transfer, or a second auth or
+datastore path.
+
+## Git and release safety
+
+Keep private Gitea work and public-source boundaries explicit. Preserve dirty
+work from other owners. Do not push, merge, publish, or change release
+credentials unless the task separately authorizes it. A local immutable
+candidate tag is allowed only after matching Go/Rust/Swift fixture hashes and
+clean-checkout evidence; it is not a publication.