#1044 A duplicated attention lane in the engine's answer is summed twice

[Tevin2119]

Task pingdotgg#1044, run run-9775c43c56. Approved by Tevin Tendai Muparadzi for commit 626fa70, which passed its checks and the QA gate.

What was asked

Found by qa-attack (zhipu) while testing task task-820b4cc07e.

Steps: Run pnpm exec vp test run .qa/attack-count.test.ts (first test): a /api/lanes body with lane 'needs-decision' listed twice, 2 cards each, and an empty 'human-review'.
Expected: The reading is malformed (an engine lists each lane once) and should be rejected as null, like every other malformation boardAttentionCount guards against.
Actual: It returns 4, double-counting the 2 tasks; the badge would show an inflated number.

• Finding: find-aec2380b94, not blocking, in scope of the task it was found on, in the code that change delivered
• Run: run-15ebfccf0b
• Candidate tested: e367548
• Evidence: /Users/tevinmuparadzi/.paperclip/polymania/runs/run-15ebfccf0b/evidence

Done when

1. boardAttentionCount returns null for a development/all reading that lists 'needs-decision' twice (2 cards each) with an empty 'human-review', not 4.
2. boardAttentionCount returns null for a development/all reading that lists 'human-review' twice alongside one 'needs-decision'.
3. A well-formed reading with each attention lane listed once still returns the sum of their cards (for example 2 in 'needs-decision' and 1 in 'human-review' gives 3).
4. A well-formed reading with both attention lanes empty still returns 0, not null.
5. apps/web/src/lib/deliveryBoard.test.ts has a test for the duplicated attention lane case, and the existing boardAttentionCount tests in that file still pass.
6. With a duplicated attention lane in the engine's answer, the sidebar Board badge shows no number rather than an inflated one.

Opened by the delivery engine after a person's approval. Merging is a separate step.