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/download.addBatch.schema.json

@@ -0,0 +1,45 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://velox.dev/schema/methods/download.addBatch.schema.json",
+  "title": "download.addBatch",
+  "description": "Create many tasks in one call: the clipboard blob, the wildcard expander, and the extension's 'Download all links'. Partial success is normal and is reported per item rather than failing the whole batch.",
+  "x-privileged": false,
+  "x-transports": ["uds", "ws"],
+  "x-deadlineMs": 30000,
+  "x-errors": [-32011, -32012],
+  "x-wsRestrictions": ["Same saveDir restriction as download.add, applied to defaults and to every item."],
+  "type": "object",
+  "properties": {
+    "params": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["items"],
+      "properties": {
+        "items":    { "type": "array", "minItems": 1, "maxItems": 5000, "items": { "$ref": "https://velox.dev/schema/types/DownloadSpec.schema.json" } },
+        "defaults": { "oneOf": [{ "$ref": "https://velox.dev/schema/types/DownloadSpec.schema.json" }, { "type": "null" }], "description": "Applied to any field an item left unset. Its url is ignored." }
+      }
+    },
+    "result": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["taskIds", "failed"],
+      "properties": {
+        "taskIds": { "type": "array", "items": { "type": "string", "format": "uuid" }, "description": "In the same order as the accepted items." },
+        "failed": {
+          "type": "array",
+          "description": "One entry per item that could not be added. index refers to params.items.",
+          "items": {
+            "type": "object",
+            "additionalProperties": false,
+            "required": ["index", "code", "message"],
+            "properties": {
+              "index":   { "type": "integer", "minimum": 0 },
+              "code":    { "$ref": "https://velox.dev/schema/types/ErrorCode.schema.json" },
+              "message": { "type": "string" }
+            }
+          }
+        }
+      }
+    }
+  }
+}