[J2TeamNNL]

Summary

• Display As > Protobuf Schema… on binary columns takes a .proto file or a descriptor set (protoc --descriptor_set_out), then asks which message when the file has several. A --include_imports set opens on the file that imports the others. The tree names each field and badges its declared type.
• Text matches protoc --decode (libprotoc 36.2): map entries sorted by key, the last oneof member only, proto3 and editions fields at their default left out, a closed enum's undeclared number with the unknown fields, a singular message sent twice merged. Fields the schema does not name, or names with another wire type, show by number. A declared message or packed field that does not parse, or a proto3 string that is not UTF-8, fails the value as it fails protoc, so the cell stays hex and the viewer says why.
• Display As > Schema Registry, offered when the connection names a registry. Each value's prefix gives the schema ID, fetched from GET /schemas/ids/{id} with its references from /subjects/{subject}/versions/{version} (Avro and Protobuf). Protobuf picks the message by the frame's message index; JSON Schema values open in the JSON tree.
• The grid owns the fetches: it collects the column's schema IDs when rows load, rows arrive or the format is set, fetches each once, and redraws only that column when a batch lands. At most 4 fetches run at once and 256 wait, so a page of bytes that happen to start with zero cannot flood the registry. Formatting a cell never touches the network.
• Schemas are kept for the session per registry URL and credentials, so an edited registry reads from the new one after the next connect. A failed fetch is kept 30 seconds; Refresh or opening the value asks again at once. The viewer waits for the fetch, never shows the previous value meanwhile, and redraws when a schema lands. A value filter on the column, in every tab and hidden or not, follows the text from stored bytes to decoded and across a registry switch.
• Kafka connection settings gain Schema Registry URL, User and Password (Keychain) under Authentication, in the plugin and the curated snapshot. The app reads them by field id, so any driver can declare them, and an installed plugin from before them keeps the curated fields. Only http and https; responses are capped at 4 MB and 60 seconds.
• Kafka: a value that starts with a zero byte makes the column binary. With an older plugin a framed value can land in a text column; the cell, inspector and double-click all decode it from its UTF-8 bytes.
• SameOriginRedirectGuard replaces the MCP transport's private guard and is used by the registry client. It now treats http://h and http://h:80 as one origin; nothing else it allows changed.
• Schema files: SchemaFileCache holds the shared file handling for AvroSchemaStore and ProtobufSchemaStore (ProtobufSchemas/<hash>.pbschema), remembers an unreadable file instead of reading it per cell, and choosing a lost schema again redraws the grid columns that name it (Avro too).
• A .proto file is read alone (imports are not opened); a descriptor set built with --include_imports covers imported types. The registry is reached directly, not through the connection's SSH tunnel.

Test plan

• ProtobufSchemaDecoderTests: fixtures from protoc --encode, expected text from protoc --decode (libprotoc 36.2), for a .proto and the descriptor set built from it: every scalar, enums, packed and unpacked repeats, maps with repeated keys, oneof in both orders, proto3 and proto2 presence, editions features.field_presence, closed enums, groups, merged messages, --include_imports primary file, a truncated descriptor set, optional as a type name, budgets inside unknown fields and nested messages.
• SchemaRegistryTests: responses recorded from confluentinc/cp-schema-registry 7.7.1, values from confluent-kafka 2.6.1. Avro, Protobuf with a reference and message index [0] and [1], basic auth, the 404 reason, the pure cache read, one fetch per schema, the fetch bounds, the failure lifetime and reload retry, an endpoint change, no URL.
• DataGridSchemaRegistryTests: prefetch on format change, on inserted rows and from a text column; a registry change or a restored schema file clears only the affected column.
• SameOriginRedirectGuardTests, CellInteractionResolverBinaryTests, FieldEditorResolverTests, AvroSchemaStoreTests, ValueDisplayFormatTests, BinaryDisplayFormatTests, ValueDisplayFormatStorageTests, DataGridDisplayCacheTests, DataGridValueFilterTests.

Docs: TableProApp/docs#155 (draft, merges after this one).

Part of #3607