Gather/scatter emitted by gb main ci

```

%c_108 = stablehlo.constant dense<16> : tensor<256xi64> loc(#loc645)

%c_110 = stablehlo.constant dense<"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tensor<256xi64> loc(#loc645)

%c_88 = stablehlo.constant {enzymexla.non_negative = [#enzymexla]} dense<1> : tensor<256xi64> loc(#loc)

%c_109 = stablehlo.constant dense<"0x01000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"> : tensor<256xi1> loc(#loc645)

%c_85 = stablehlo.constant dense<[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94]> : tensor<95xi64> loc(#loc1135)

%c_332 = stablehlo.constant dense<16> : tensor<95xi64> loc(#loc925)

%25 = stablehlo.divide %c_110, %c_108 : tensor<256xi64> loc(#loc645)
%26 = stablehlo.negate %25 : tensor<256xi64> loc(#loc645)

%27 = stablehlo.subtract %26, %c_88 {enzymexla.non_negative = [#enzymexla]} : tensor<256xi64> loc(#loc645)

%28 = stablehlo.select %c_109, %27, %25 {enzymexla.non_negative = [#enzymexla]} : tensor<256xi1>, tensor<256xi64> loc(#loc645)

%3067 = stablehlo.multiply %c_85, %c_332 : tensor<95xi64> loc(#loc1162)

%3068 = stablehlo.broadcast_in_dim %3067, dims = [0] : (tensor<95xi64>) -> tensor<95x256xi64> loc(#loc925)
%3069 = stablehlo.broadcast_in_dim %28, dims = [1] : (tensor<256xi64>) -> tensor<95x256xi64> loc(#loc925)

%3070 = stablehlo.add %3068, %3069 : tensor<95x256xi64> loc(#loc925)
%3071 = stablehlo.reshape %3070 : (tensor<95x256xi64>) -> tensor<24320x1xi64> loc(#loc925)

%3083 = stablehlo.add %3071, %c_334 : tensor<24320x1xi64> loc(#loc925)
%3084 = "stablehlo.gather"(%arg6, %3083) <{dimension_numbers = #stablehlo.gather, indices_are_sorted = false, slice_sizes = array}> : (tensor<1536xf32>, tensor<24320x1xi64>) -> tensor<24320xf32> loc(#loc925)
```

cc @avik-pal @dkytezab . Bad regardless, may be part of the cause of current pain

Start with the StableHLO snippet in this issue and reproduce the gb main CI case that emits it. Trace the generation of the gather and preceding index computations, then compare the emitted IR with the intended gather/scatter behavior. Done means the problematic emission is explained and corrected or a focused reproducer and actionable diagnosis is added.

Written by the indexing model from the issue text.