docs: initialize project wiki from production hardening session

12 pages covering architecture, findings, and metrics from the
rotatingMachine + machineGroupControl hardening work:

- Overview: node inventory, what works/doesn't, current scale
- Architecture: 3D pump curves, group optimization algorithm
- Findings: BEP-Gravitation proof (0.1% of optimum), NCog behavior,
  curve non-convexity, pump switching stability
- Metrics: test counts, power comparison table, performance numbers
- Knowledge graph: structured YAML with all data points and provenance
- Session log: 2026-04-07 production hardening
- Tools: query.py, search.sh, lint.sh

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

wiki/findings/pump-switching-stability.md

@@ -0,0 +1,34 @@
+---
+title: Pump Switching Stability
+created: 2026-04-07
+updated: 2026-04-07
+status: proven
+tags: [machineGroupControl, stability, switching]
+sources: [nodes/machineGroupControl/test/integration/ncog-distribution.integration.test.js]
+---
+
+# Pump Switching Stability
+
+## Concern
+Frequent pump on/off cycling causes mechanical wear, water hammer, and process disturbance.
+
+## Test Method
+Sweep demand from 5% to 95% in 2% steps, count combination changes. Repeat in reverse to check for hysteresis.
+
+## Results — Mixed Station (2x H05K + 1x C5)
+
+Rising 5→95%: **1 switch** at 27% (H05K-1+C5 → all 3)
+Falling 95→5%: **1 switch** at 25% (all 3 → H05K-1+C5)
+
+Same transition zone, no hysteresis.
+
+## Results — Equal Station (3x H05K)
+
+Rising 5→95%: **2 switches**
+- 19%: 1 pump → 2 pumps
+- 37%: 2 pumps → 3 pumps
+
+Clean monotonic transitions, no flickering.
+
+## Why It's Stable
+The marginal-cost refinement only adjusts flow distribution WITHIN a combination — it never changes which pumps are selected. Combination selection is driven by total power comparison, which changes smoothly with demand.