docs(plans): generated examples build the encrypted type from what the engine returned

The plan says the whole struct crosses the binding both ways and nothing
is rebuilt from parts on either side. The generated examples still copied
passthrough fields from the Go value into the encrypted type, so one side
rebuilt. Seal now takes only the record the engine returned, reads each
passthrough field from it, and returns an error for a value of the wrong
type rather than asserting. The README row that said generated code
assembles EQL types says the guest returns them.

Claude-Session: https://claude.ai/code/session_014jiJy4WhYH2LXojK2jSoxi

Author: auxesis

docs/plans/2026-10-04-plan-builder/README.md

@@ -43,7 +43,7 @@ The `users` example uses `TextEq`, which is the one EQL type the engine produces
 | The guest returns an EQL value for a field with `encrypt_into` | Not run. The target form and the dispatch do not exist. |
 | `stashgen` checks a declaration with the embedded guest | Not run. |
 | The code works with a database, GORM or pgx | Not run. Nothing here has connected to a database. |
-| The EQL types, and how generated code assembles them | Not run. `eql-codegen` does not write Go yet, and the examples use a stub of `eql.TextEq`. |
+| The EQL types, and the value the guest returns for them | Not run. `eql-codegen` does not write Go yet, and the examples use a stub of `eql.TextEq`. |
 | The steps in "Use the SDK" | Not run. Nobody has followed them. |
 
 ## Generate the protobuf package