decoupled module system with exchange rates

AGENTS.md

@@ -2,7 +2,7 @@
 
 - When creating a new Rust file, format ONLY that new file with the Cargo formatter (`rustfmt --edition 2024 --config skip_children=true path/to/new_file.rs`). Use the file’s actual Rust edition. Never run workspace-wide or package-wide `cargo fmt`, and never format existing files unless explicitly requested.
 - Do not run other automatic code-formatting commands unless explicitly requested.
-- Write new or changed SQL in a human-readable layout. Use indented multiline queries, put SQL clauses and JOIN conditions on separate lines, and indent subqueries. Rust formatting does not format SQL inside strings; review that SQL manually.
+- Keep SQL easy to scan and preserve existing readable layouts. Short queries and simple subqueries may stay on one line; for example, keep each simple `EXISTS (SELECT 1 FROM ... WHERE ...)` condition together, with successive `OR EXISTS` conditions on separate lines. Use multiline layout and indentation when query complexity or line length warrants it, especially for long SELECT lists, multiple JOINs, or nested logic. Do not mechanically put every clause on its own line or expand compact SQL just to satisfy a formatting rule. Review SQL inside Rust strings manually; do not reformat unrelated queries.
 - Preserve existing formatting. Make only the smallest hand-edited changes required for the task.
 - Do not run builds, checks, linters, or pre-existing tests. Only run tests that an agent wrote or modified as part of the current task; if the agent did not write or modify any tests, run no tests.
 - Check if what you are doing is running. Server can be running, tauri app might be running. No need to turn on redundant systems.