docs: refresh windup writeup to past tense, link architecture diagram

overshoot_hold_windup.md read like a live plan ("not yet implemented")
even though the fix had already shipped; reworks it into a past-tense
record with corrected line numbers and test descriptions matching what
was actually built. Fixes a stale pid_heat reference in
temp_control_calibration.md.

TODO.md's windup item still claimed test coverage was "outstanding"
from before the test suite was added; corrects that and the "No
automated tests" item above it to reflect current coverage. Both docs
now link docs/fsm_states.png (durable) and the Claude Artifact URL
(session-scoped) for the cascade architecture diagram.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DGQhVQ2Y3yXAQTXhrxVd5u

docs/overshoot_hold_windup.md

@@ -1,10 +1,12 @@
-# HOLD-state overshoot from a disturbance: root cause and fix plan
+# HOLD-state overshoot from a disturbance: root cause and fix
 
 Investigation of the overshoot visible in `docs/overshoot.png`: a cold-water
 disturbance during a steady HOLD at 30°C caused `theta_ist` to overshoot to
 ~30.5°C and stay there, rather than settling back at soll. This document
-records the diagnosis and the (not yet implemented) fix plan. Numbers below
-are pulled from `logs/log_latest.json`.
+records the diagnosis, the fix that shipped for it, and the test coverage
+added alongside it. Numbers in the incident summary below are pulled from
+`logs/log_latest.json`; names in that section (`pid_hold`/`pid_heat`) are
+the *pre-fix* names — see "Rename for honesty" below for what they became.
 
 ## Incident summary
 
@@ -88,23 +90,24 @@ on which state is currently active.
 
 ### Rename for honesty
 
-The current names don't match what actually runs when:
-- `pid_hold` already runs unconditionally *every* tick regardless of state
-  (`process_pid()`'s first line, `temp_controller_base.py:134`) — it's the
-  outer loop, not "the HOLD-state PID". Rename to **`pid_outer`**.
-- `pid_heat` already runs in *both* `HOLD` and `HEAT` today (only `IDLE`/
-  `COOL` skip it, `temp_controller_base.py:151-158`) — it's the inner loop
-  for the heating direction. Rename to **`pid_inner`**.
-- `pid_cool` only ever runs in `COOL` — no `HOLD`-time ambiguity, since a
+The pre-fix names didn't match what actually ran when:
+- `pid_hold` already ran unconditionally *every* tick regardless of state
+  (`process_pid()`'s first line, `temp_controller_base.py:137`) — it's the
+  outer loop, not "the HOLD-state PID". Renamed to **`pid_outer`**.
+- `pid_heat` already ran in *both* `HOLD` and `HEAT` (only `IDLE`/`COOL`
+  skip it, `temp_controller_base.py:154-163`) — it's the inner loop for
+  the heating direction. Renamed to **`pid_inner`**.
+- `pid_cool` only ever ran in `COOL` — no `HOLD`-time ambiguity, since a
   disturbance that pushes temp *above* soll during `HOLD` is still handled
-  by `pid_inner` (the outer loop's `max(0.0, pid_hold_y)` floor sends
+  by `pid_inner` (the outer loop's `max(0.0, pid_outer_y)` floor sends
   `heatrate_soll` to 0, and `pid_inner` reacts to the resulting negative
   `heatrate_err` — the state only escalates to real `COOL` past
-  `Thresholds.HoldCool`). Rename to **`pid_inner_cool`** for symmetry, kept
-  as its own instance — today's explicit `reset()` calls when crossing
+  `Thresholds.HoldCool`). Renamed to **`pid_inner_cool`** for symmetry, kept
+  as its own instance — the explicit `reset()` calls when crossing
   between heat-direction and cool-direction states
-  (`temp_controller_fsm.py:104,108,115,123`) stay exactly as they are; there
-  is no reason to share integrator state across a heater/chiller boundary.
+  (`temp_controller_fsm.py:104,108,115,123`) stay exactly as they were;
+  there is no reason to share integrator state across a heater/chiller
+  boundary.
 
 ### Config: `Hold`/`Heat`/`Cool` → `Outer` / `Inner.{Heat,Hold,Cool}`
 
@@ -131,31 +134,31 @@ The current names don't match what actually runs when:
   cooling-side incident. `pid_inner_cool` never runs during `HOLD`, so it
   doesn't need its own `Hold` variant the way `Heat` does; one params block
   is enough.
-- **This is a breaking config change** — no backward-compat shim for the
+- **This was a breaking config change** — no backward-compat shim for the
   old flat `Hold`/`Heat`/`Cool` keys (per the "no compat hacks" convention).
-  Every deployed `config.json` needs migrating, not just the repo's
+  Every deployed `config.json` needed migrating, not just the repo's
   `config-real.json.tpl`/`config-sim.json.tpl` templates.
 
-### Code changes (planned, not yet implemented)
+### Code changes (implemented)
 
-1. **`components/pid/pid.py`** — add the symmetric `yi_max` clamp inside
-   `process()` (already planned): `self.yi = max(-yi_max, min(yi_max,
-   self.yi))` when `self.params.get('yi_max')` is set, applied right after
+1. **`components/pid/pid.py`** — the symmetric `yi_max` clamp lives inside
+   `process()` (line 40): `self.yi = max(-yi_max, min(yi_max, self.yi))`
+   when `self.params.get('yi_max')` is set, applied right after
    accumulating `yi` and before it's summed into `y`.
-2. **`components/pid/temp_controller_fsm.py`** — rename `self.pid_hold` →
+2. **`components/pid/temp_controller_fsm.py`** — `self.pid_hold` →
    `self.pid_outer`, `self.pid_heat` → `self.pid_inner`, `self.pid_cool` →
-   `self.pid_inner_cool` (constructor at lines 33-34/40, all `reset()` call
+   `self.pid_inner_cool` (constructor at lines 33/34/40, all `reset()` call
    sites and comments at lines 11-12, 83, 87-89, 99, 104, 108, 111, 115,
-   118-119, 123).
+   119, 123).
 3. **`components/pid/temp_controller_base.py`**:
-   - `set_params()` (line 28-34): `self.pid_outer.set_params(params['Outer'])`;
-     store `self._inner_heat_params = params['Inner']['Heat']` and
+   - `set_params()` (lines 30-37): `self.pid_outer.set_params(params['Outer'])`;
+     stores `self._inner_heat_params = params['Inner']['Heat']` and
      `self._inner_hold_params = params['Inner']['Hold']` for the per-tick
      lookup below; `self.pid_inner_cool.set_params(params['Inner']['Cool'])`.
-   - `process_pid()` (lines 133-160): rename `pid_hold_y` → `pid_outer_y`
-     and the `self.pid_hold.process(...)` call. In the combined `HOLD`/`HEAT`
-     branch (today's `else`, lines 156-158), select the active param set
-     before processing:
+   - `process_pid()` (lines 136-163): `pid_hold_y` → `pid_outer_y`, and the
+     `self.pid_hold.process(...)` call. In the combined `HOLD`/`HEAT`
+     branch (lines 159-163), the active param set is selected before
+     processing:
      ```python
      else:
          inner_params = self._inner_heat_params if self.state == States.HEAT else self._inner_hold_params
@@ -165,60 +168,65 @@ The current names don't match what actually runs when:
      ```
      `set_params()` is a cheap dict-reference assignment (`pid.py:22-23`),
      so calling it every tick has no meaningful cost. Because `kp`/`ki`/`kd`/
-     `kt` are identical between `Inner.Heat` and `Inner.Hold` in the starting
-     config, switching the active set at a `HOLD↔HEAT` transition changes
-     no term of `y` at that instant — only the `yi_max` ceiling going
-     forward. No bump at the transition, unlike the freeze/thaw approach.
+     `kt` are identical between `Inner.Heat` and `Inner.Hold` in the
+     shipped config, switching the active set at a `HOLD↔HEAT` transition
+     changes no term of `y` at that instant — only the `yi_max` ceiling
+     going forward, with one caveat noted in Status below.
 4. **Config files** — `config.json`, `config-real.json.tpl`,
-   `config-sim.json.tpl`: restructure into `Outer`/`Inner.{Heat,Hold,Cool}`
-   as above. Inline `"Cool": {...}` dicts in `scripts/demos/pid/
-   demo_temp_controller_smith.py:21`, `demo_temp_controller.py:21`, and
-   `scripts/demos/sud/demo_sud.py:32` need the same restructure.
+   `config-sim.json.tpl` restructured into `Outer`/`Inner.{Heat,Hold,Cool}`
+   as above. The inline `"Cool": {...}` dicts in `scripts/demos/pid/
+   demo_temp_controller_smith.py`, `demo_temp_controller.py`, and
+   `scripts/demos/sud/demo_sud.py` got the same restructure.
 5. **`utils/replay_sim.py`** — `_apply_gain_overrides()` and the CLI flag
-   loop (lines 50, 214-222) iterate `('Hold','hold'), ('Heat','heat'),
-   ('Cool','cool')`; becomes `('Outer','outer'), ('Inner.Heat','inner-heat'),
-   ('Inner.Hold','inner-hold'), ('Inner.Cool','inner-cool')` (nested dict
-   access needed since these aren't flat top-level keys any more). The
-   `for section in ('Hold','Heat','Cool')` print loop at line 284 and the
-   `_infer_heatrate_soll_set()` docstring's "hold PID" reference (line 66)
-   need the same rename.
-6. **`components/pid/TODO.md`** — update the cross-link entry added for the
-   previous (superseded) plan to point at this rewritten section instead.
+   loop now iterate the shared `GAIN_SECTIONS = (('Outer','outer'),
+   ('Inner.Heat','inner-heat'), ('Inner.Hold','inner-hold'),
+   ('Inner.Cool','inner-cool'))`, with nested dict access for the
+   `Inner.*` entries. The params print loop and
+   `_infer_heatrate_soll_set()`'s docstring were updated to match
+   (`pid_outer.get_y()` instead of "the hold PID").
+6. **`components/pid/TODO.md`** — the windup entry is marked `[x]` and
+   points at this section.
 
-## Test plan (not yet implemented)
+## Tests
 
-Stdlib `unittest`, no pytest — `tests/components/pid/test_pid.py`,
-discoverable via `python -m unittest discover -t . -s tests/components/pid`.
-Simpler than the FSM-gating plan's test plan: no engage/disengage hysteresis
-or threshold-relationship behavior to cover, since the loop is never turned
-off — only its `yi_max` ceiling changes with state.
+Stdlib `unittest`, no pytest — `tests/components/pid/test_pid.py` and
+`test_temp_controller_closed_loop.py`, discoverable via
+`python -m unittest discover -t . -s tests/components/pid` (or `-s tests`
+for the whole repo suite). Simpler than the FSM-gating plan's test plan
+would have needed: no engage/disengage hysteresis or threshold-relationship
+behavior to cover, since the loop is never turned off — only its `yi_max`
+ceiling changes with state.
 
-**A. Unit-level, isolated `Pid`** — no plant involved. Feed a synthetic
-`err` sequence shaped like the incident (positive `heatrate_err ≈ 0.3` held
-for ~130 ticks, then decaying/negative tail, matching the real
-`rate_soll - rate_ist` pulled from the log) into two `Pid` instances with
-identical gains, one with `yi_max` set (the `Inner.Hold` case) and one
-without (`Inner.Heat`). Assert: recovery time (ticks after error goes
-negative until `y` drops back under a small threshold) is measurably
-shorter when clamped; `yi` never exceeds the configured bound.
+**A. Unit-level, isolated `Pid`** (`test_pid.py`) — no plant involved. Feeds
+a synthetic `err` sequence shaped like the incident (positive
+`heatrate_err = 0.3` held for 130 ticks, matching the outer loop's real
+demand during the disturbance, then a flat `-0.3` tail for 200 ticks,
+matching the real `rate_soll - rate_ist` gap once the outer loop had
+zeroed its target) into two `Pid` instances with identical gains, one with
+`yi_max` set (the `Inner.Hold` case) and one without (`Inner.Heat`).
+Asserts: recovery time (ticks after the error goes negative until `y`
+drops back under a small threshold) is measurably shorter when clamped;
+`yi` never exceeds the configured bound; the unclamped instance's `yi`
+does exceed it (sanity-checks the test itself isn't vacuous).
 
-**B. Closed-loop, self-contained synthetic scenario** — no dependency on
-the multi-MB log file. Real numbers from `PlantParams`/`config.json`:
-`Pot(dt)` with `M=27.96, C=3403.43, L=0.2, Td=17`, ambient from
-`config.json`; `TempController` via `PidFactory.create('Smith', dt)` with
-the real `Outer`/`Inner.*` gains. Run closed-loop (controller's own `y`
-drives the plant, unlike `utils/replay_sim.py`'s open-loop observe-only
-mode):
+**B. Closed-loop** (`test_temp_controller_closed_loop.py`) — real `Pot(dt)`
+plant with `M=27.96, C=3403.43, L=0.2, Td=17`, ambient `20`°C, driven by a
+real `TempController(Smith)` with the shipped `Outer`/`Inner.*` gains.
+Controller's own `y` feeds back into the plant each tick (unlike
+`utils/replay_sim.py`'s open-loop observe-only mode):
 - **Disturbance case**: hold at 30°C until settled, knock `plant.temp` down
-  ~0.5°C to emulate the cold-water event, keep ticking for several minutes.
-  Assert peak overshoot above 30.0°C is measurably smaller with `Inner.Hold`'s
-  `yi_max` set than without.
-- **Ramp case**: command a genuine 1.5 K/min ramp (state reaches `HEAT`) and
-  assert the sustained heat rate actually reaches ~1.5 K/min — guards against
-  reintroducing the flat-clamp regression from the rejected approach above.
-- **Transition case**: drive a `HOLD→HEAT→HOLD` sequence and assert `y` has
-  no discontinuity at either transition beyond what the changing `heatrate_err`
-  itself would explain — confirms the per-state param swap is truly bumpless.
+  0.5°C to emulate the cold-water event, keep ticking for 600 more ticks —
+  confirms the state stays in `HOLD` throughout, matching the incident.
+  Asserts peak overshoot above 30.0°C is measurably smaller with
+  `Inner.Hold`'s `yi_max` set than with an unclamped copy of `Inner.Heat`.
+- **Ramp case**: commands a genuine 1.5 K/min ramp to 40°C (state reaches
+  `HEAT`) and asserts the sustained heat rate actually exceeds 1.4 K/min —
+  guards against reintroducing the flat-clamp regression from the rejected
+  approach above.
+- **Transition case**: drives a `HOLD→HEAT→HOLD` sequence and asserts the
+  `y` step at either transition stays under `0.1` — see the retroactive-clamp
+  caveat in Status below for why this isn't a stricter "no discontinuity"
+  assertion.
 
 ## Status
 
@@ -238,3 +246,12 @@ the `HEAT→HOLD` transition clamps `yi` back down immediately, producing a
 small (~0.07 in testing, well below the pre-fix disturbance's ~0.74 peak)
 step in `y` rather than the fully bumpless transfer described above. Not
 addressed here — flagged for awareness, not a blocker.
+
+## Architecture diagram
+
+A full signal-flow diagram of the cascade (`Outer`/`Inner.*` PIDs, FSM
+state gating, Smith-predictor feedback) exists as a Claude Artifact:
+https://claude.ai/code/artifact/a32e4752-b4a6-4153-b344-eb2423eb6512 — this
+is a session-scoped link, not a durable one, so it may not resolve for
+everyone with repo access. `docs/fsm_states.png` is a static screenshot of
+just the diagram's FSM-states panel, checked in as the durable copy.

docs/temp_control_calibration.md

@@ -143,7 +143,7 @@ Two problems compound:
    differentiating is the least effective arrangement: noise has already been
    amplified before the filter sees it.
 
-The noisy `heatrate_err` feeds into `pid_heat.process()` as the proportional
+The noisy `heatrate_err` feeds into `pid_inner.process()` as the proportional
 error. With `kp=0.08`, ±1 K/min rate ripple produces ±8% power output noise.
 
 ### Options