backlog: user-facing ticket descriptions + drafts for pinned native container gaps

[ahrzb]

Board-only change (backlog/**). No code touched.

Rewrote descriptions around what a user actually hits

Every open ticket and draft now opens with a concrete scenario — real column names, the SQL a user would write, the symptom they'd see — before any engine internals. Previously they were written engine-inward and read as implementation notes.

Covers: TASK-3, TASK-15, TASK-16, TASK-29, TASK-34 and DRAFT-7 through DRAFT-13.

New drafts for the pinned native gaps

Ritchie's TASK-29 container work left 4 strict xfail_on_native markers in tests/test_diff_types.py with no tickets tracking them. Per the standing native-bug process (xfail-strict + a ticket, never fix inline), the xfail half was done and the ticket half was missing. Filed as two drafts, split by severity:

• DRAFT-12 (Medium) — native has no dispatch for struct(...) / make_array(...). Fails loudly: works in transform(), breaks in infer(). Bracket literal [a, b] still works, so lists have an alternative spelling; structs don't.
• DRAFT-13 (High) — native doesn't widen mixed int/float list elements. Fails silently: SELECT [bedrooms, price_per_sqft] gives [3.0, 12.5] at training and [3, 12.5] at serving, no error. Silent cross-engine divergence on the default serving engine, hence the higher rating.

Also DRAFT-11, recording Wren's measured finding that SQL named arguments are unreachable from Python (a per-function Rust ScalarUDF capability the bindings don't expose) — captured so nobody re-derives it.

Both new drafts are pending AmirHossein's review of scope and priority.

🤖 Generated with Claude Code

[ahrzb]

Redundant — the entire contents of this branch (5f6bd0b) is already on master, having reached it via the merge of #10. A diff of this branch against master shows no backlog/ changes at all.

Cause: I branched from a stale origin/master ref (git fetch was silently failing on SSH), not realising my board commit had already been carried to master. Closing rather than merging; nothing is lost.