Walking skeleton validating the whole echo architecture end to end; the
Command→SQL renderer currently covers `create table`, with the rest of
Bucket A / B / category-3 to follow (ADR-0038 §8).
- Channel (ADR-0037): the three-way EffectiveMode (reusing the existing
enum, not a new SubmissionMode — recorded in the ADR) rides on
Action::ExecuteDsl to the runtime. `replay` bypasses the interactive
spawn, so it never echoes (silent, for free).
- Echo (ADR-0038): built at the runtime's ExecuteDsl dispatch — the worker
gets decomposed calls, not the Command, so ADR §4's "worker builds it"
was corrected to the dispatch layer. Gated by echo_for (advanced
effective mode + DSL-form). Carried on DslSucceeded; rendered by
note_ok_summary as `Executing SQL: …` immediately beneath `[ok]`. New
src/echo.rs renderer; echo.executing_sql i18n key.
- command_to_sql: `create table` → `CREATE TABLE T (id serial PRIMARY KEY)`
(single inline / compound table-level PK), playground type vocabulary,
round-trip-verified against the advanced walker (the §1 contract).
Tests: echo.rs (render, round-trip contract, mode gate, Sql*-not-echoed);
app.rs (submit carries the 3-way mode; echo renders beneath [ok]).
Suite 1970/0/1; clippy clean.