04c8e4295f
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.