Close loop-1.0 emulation gaps: momentum gate and max active insulin limit

[ps2]

Follow-up to #40. A review of the loop-1.0 preset against the Tidepool Loop 1.0 source (LoopWorkspace build-332, i.e. LoopKit bdad094 and Loop cf10ea3) found two behaviors it did not restore.

Momentum gradual-transitions gate

linearMomentumEffect called hasGradualTransitions() with its hard-coded 40 mg/dL default. So noGradualTransitionsGate only bypassed the retrospective-correction gate, even though its doc comment says it covers momentum too.

This PR:

• adds a gradualTransitionThreshold: Double? = 40.0 parameter, where nil means no gate;
• has both prediction paths pass nil when noGradualTransitionsGate is set.

1.0's linearMomentumEffect checked only continuity, calibration and provenance (LoopKit GlucoseMath.swift:97-99).

Max active insulin limit

1.0's temp-basal recommendation had no active-insulin limit (Loop DoseMath.swift:340-386). The port caps automatic dosing at maxBolus × maxActiveInsulinMultiplier. When IOB is above that limit, it caps the temp basal below scheduled even when a high is forecast.

This PR adds disableMaxActiveInsulinLimit, which is on in loop-1.0.

Documentation

The loop1 preset's doc comment now lists the 1.0 behaviors callers must set through inputs:

• recommendationType = .tempBasal
• useIntegralRetrospectiveCorrection = false
• useMidAbsorptionISF = false
• the insulin model

It also lists the dosing-side behaviors outside this package that callers must reproduce:

• override application, including 1.0's override-expiry quirk
• predictionStart at the CGM timestamp
• rate rounding and temp-basal continuation
• no recommendation while a bolus is in progress

Not addressed here

With IOB above the limit and a forecast high, the default path recommends a negative temp basal (−12.07 U/h in the new test's scenario before the flag is applied). The headroom cap pushes maxBasalRate below zero and nothing clamps it back to 0. That's worth a separate fix.

Testing

Defaults are unchanged: the 158 existing tests pass unmodified. Five new tests in AlgorithmEmulationTests cover:

• the momentum gate on, off and without a jump;
• the flag removing the temp-basal cap, matching a run with an unbounded limit;
• the preset contents.

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