agent: Add more Rust code examples, update TODO check (#28737)

Release Notes:

- N/A

crates/eval/examples/lhs_join_update_callbacks/prompt.md

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+Add a new test case to validate join subscription updates when the **LHS table is updated**, and ensure correct invocation of reducer callbacks. The test should:
+
+- Subscribe to a join query with a filter involving fields from both tables (e.g., `SELECT p.* FROM pk_u32 p JOIN unique_u32 u ON p.n = u.n WHERE u.data > 0 AND u.data < 5`).
+- Insert rows into both LHS (`pk_u32`) and RHS (`unique_u32`) that satisfy the join condition.
+- Verify the initial subscription callback is triggered via `on_insert`.
+- Update the LHS (`pk_u32`) such that the row remains part of the join result.
+- Validate that:
+  - `on_update` is invoked correctly.
+  - An immediate follow-up update back to the original value also triggers `on_update`.
+- Repeat the above with disjoint filters (e.g., `u.n != 1`) and confirm behavior remains correct.
+
+Also, ensure that literal-first SQL expressions like `3 < x` are correctly interpreted and inverted in the physical execution plan (converted to `x > 3`) and behave identically during query evaluation and execution.