tests: the pins row's merged-away check (#676, PR #751) has no test for a prepare that refuses, or for both, upstream-removed and unmapped beside a merged-away row; two mutants survive #755

Goal: the tests pin every branch of refusals_ahead, the check #751 adds to the doctor's pins row for #676. A wrong return or a narrowed state list must then fail a test.

Filed by lane openRepoShape-3 under v1.1.1, on Brett Heap's word of 2026-10-16T13:35:28Z ("yes create v1.1.1"). Lane 3's reviewer RV-f found these while reviewing #751, as S1 and S2. RV-f measured the code right in every state below. Only the tests are missing.

What survives on #751's head b7312258:

• A prepare refusal returning {} instead of None (shape-doctor.py:2775): 14 tests pass.
• Counting only copy-is-link as a refusal ahead (:2777): all tests pass.

What to add in tests/test_update_shape_merged_away.py:

1. A merged-away root whose prepare refuses, for example run from shape-doctor.py and update-shape.py: run from a partial clone of the standard, the shape currency row asks without fetching whether the clone holds what the comparison reads, and is CANNOT ANSWER with a fetch for a person to run where it does not, and a read that fails is refused, never a copy called both (#683) #742's promisor = false-alone clone, or from a standard lacking the pinned commit. Assert the pins row keeps its gate and has no merged_away key.
2. One parametrized test over both, upstream-removed and unmapped beside a merged-away row. Assert the row keeps the gate and names the state, and that the printed apply, pasted, exits 2. RV-f measured all three as update-conflict. Unmapped is the cheapest to build: a pin row for a root file no upstream path maps to.

Lands after: #751.