last_theta_ist was hardcoded to 20 in __init__, used to compute the very
first process() tick's heatrate as (theta_ist - 20)/dt*60 - a wildly bogus
spike whenever the real starting temperature wasn't actually 20 (e.g.
1200 deg/min for a 40-degree start). The exponentially-smoothed
heatrate_ist (alpha=0.1) takes several ticks to recover from that, during
which it distorts the PID's rate-error term and visibly throws off the
heating trajectory.
This was invisible everywhere this assumption was implicitly tested,
since ambient (and every start_theta used) was always exactly 20. It
surfaced once SudForecastEstimator.estimate() started being called with a
real, non-20 start_theta: it builds a fresh TempController on every call,
so its first tick always hits this bug fresh - unlike the real controller,
which only ever goes through this once near server startup and has long
since self-corrected (last_theta_ist = theta_ist runs every tick) by the
time any forecast comparison matters. That's exactly what showed up as a
forecast-vs-actual gap during the initial ramp.
last_theta_ist now starts None; process() treats the first tick's
heatrate as 0 (no real history yet) instead of computing it against a
hardcoded, usually-wrong baseline.
Verified: ambient=20 (the only case ever exercised before) is byte-
identical to before the fix. ambient=40/start=40 - reproducing the old
hardcoded-20 behavior side by side - shows the old version visibly lagging
~12 minutes behind the fixed one during the initial ramp before they
converge, matching the reported gap exactly.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DkkuG48uHFCGKe6dPSERFk
jensandClaude Sonnet 4.6
d981c36194