proto: freeze the wire contract at 1.0.0

Schemas for the whole v1 surface: 38 methods, 9 events, 25 named types and the
JSON-RPC envelope, with x-privileged / x-transports / x-deadlineMs / x-errors
annotations that both generators emit as data rather than prose.

Four generators over one IR (contracts/codegen/schema_ir.py), so the C++ structs,
the TypeScript types and the OpenRPC document cannot disagree about what the
contract says:

  gen_cpp.py             -> core/generated/velox_proto.{hpp,cpp}
  gen_ts.py              -> extension/src/shared/protocol/
  gen_openrpc.py         -> contracts/openrpc.json
  gen_cpp_conformance.py -> tests/conformance/cpp/fixture_dispatcher.hpp

Inbound parsing never throws: parse<T>() returns std::expected<T, ParseError> and
nlohmann's throwing ADL from_json is deliberately not emitted. Schema constraints
(minimum, maxLength, pattern, ...) become real runtime checks in both languages —
the daemon does not trust the extension and the extension does not trust the
daemon.

59 golden fixtures: a success case per method, 12 error cases, 9 events. Replayed
by tests/conformance/ against both the generated C++ and a live server over both
transports. tools/mockd serves the same fixtures with unhappy-path flags so the
GUI and EXT lanes never wait for veloxd.

run.sh also proves capture.offer fails open: with a daemon answering slower than
750 ms the client gives up and lets Firefox take the download.

core/generated/ is libveloxproto, a separate target from libveloxcore, which
still never sees JSON — see docs/adr/0009.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_012fgjnqFCS5h5L7gZTZo3rV

contracts/schema/methods/session.hello.schema.json

@@ -0,0 +1,36 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://velox.dev/schema/methods/session.hello.schema.json",
+  "title": "session.hello",
+  "description": "First call on every connection, on every transport. The daemon compares protocolVersion majors and refuses a mismatch with -32001 so a stale GUI or extension fails loudly on connect instead of subtly at the tenth field. On the WebSocket transport a valid token is required unless the client is about to call session.pair.",
+  "x-privileged": false,
+  "x-transports": ["uds", "ws"],
+  "x-deadlineMs": 2000,
+  "x-errors": [-32001, -32002],
+  "type": "object",
+  "properties": {
+    "params": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["clientType", "clientName", "protocolVersion"],
+      "properties": {
+        "clientType":      { "type": "string", "enum": ["gui", "cli", "extension", "nmhost", "test"] },
+        "clientName":      { "type": "string", "maxLength": 64, "description": "Human-readable, shown in the pairing prompt and the logs." },
+        "protocolVersion": { "type": "string", "pattern": "^[0-9]+\\.[0-9]+\\.[0-9]+(-[0-9A-Za-z.-]+)?$" },
+        "token":           { "type": ["string", "null"], "description": "Required on the WebSocket transport once paired. Ignored on the Unix socket, where SO_PEERCRED is the authorization." }
+      }
+    },
+    "result": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["daemonVersion", "protocolVersion", "capabilities", "sessionId"],
+      "properties": {
+        "daemonVersion":   { "type": "string" },
+        "protocolVersion": { "type": "string" },
+        "capabilities":    { "type": "array", "items": { "type": "string" }, "description": "Optional features this build has, e.g. 'media', 'grabber', 'secretservice'. A client must degrade gracefully when one is absent rather than assuming it." },
+        "sessionId":       { "type": "string", "format": "uuid" },
+        "transport":       { "type": "string", "enum": ["uds", "ws"], "description": "How the daemon sees this connection. Lets a client know up front which privileged methods will be refused." }
+      }
+    }
+  }
+}