Plan for changes to CDP monitor

[archandatta]

Note

Low Risk
Documentation-only change that proposes a future refactor; no runtime behavior, APIs, or tests are modified in this PR.

Overview
Adds a new design doc (plans/cdp-decode.md) proposing a two-layer CDP decode approach: first decode wire events into PDL-faithful structs (retaining all fields, with complex sub-objects kept as json.RawMessage), then project those typed structs into monitor events.Event payloads.

The plan outlines intended file changes (new cdp_proto.go, handler signature shifts, centralized decode in dispatch) and a golden round-trip fixture test strategy to detect dropped/incorrect fields, but does not implement these code changes.

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[rgarcia]

i think you want to compare normalized full JSON after decode/re-marshal and not just top level keys, to get a full structurual round trip check

you could also consider some light codegen around the json schema in json/js_protocol.json in the devtools repo