execir numeric comparisons lose integer precision above 2^53 #560

What happened

Execution-IR numeric comparisons convert every int/int64 operand to float64 before equality or ordering. Distinct integers above 2^53 therefore collapse to the same floating-point value. For example, 9007199254740992 == 9007199254740993 evaluates true, and < evaluates false.

This can select the wrong if arm, stop or continue a bounded loop incorrectly, or produce the wrong retry outcome for valid integer-valued workflow data/literals. Integer-vs-integer comparisons must remain exact; mixed integer/float comparisons need a range-aware implementation that does not round the integer before deciding equality/order.

Steps to reproduce

1. Add the focused regression below in package internal/execir.
2. Run GOCACHE=/tmp/terfyn-go-cache go test ./internal/execir -run TestLargeIntegersRemainDistinct -count=1.
3. Observe that the distinct int64 values compare equal.

Minimal project / .agent source (if applicable)

func TestLargeIntegersRemainDistinct(t *testing.T) {
	const a int64 = 9007199254740992
	const b int64 = 9007199254740993
	if valuesEqual(a, b) {
		t.Fatalf("valuesEqual(%d, %d) = true", a, b)
	}
	less, err := compareOrdered("<", a, b)
	if err != nil { t.Fatal(err) }
	if !less {
		t.Fatalf("compareOrdered(<, %d, %d) = false", a, b)
	}
}

Command output

--- FAIL: TestLargeIntegersRemainDistinct (0.00s)
    bughunt_temp_test.go:9: valuesEqual(9007199254740992, 9007199254740993) = true
FAIL

Terfyn version

d506e9f1095a625b2df70c160454cba1ed6e3709

Operating system

Linux

Go version (if built from source)

go version go1.25.0 linux/amd64

Anything else

The loss is in internal/execir/eval.go: valuesEqual and compareOrdered both delegate to toFloat. Add tests around ±2^53, math.MaxInt64, integer/float mixtures, negative values, and ordinary fractional floats. Branch-level coverage should prove the correct arm executes.

Before submitting

• I searched existing issues and this is not a duplicate.
• I can reproduce this on the latest release or main.