feat(SNNBot): force learning on input change for fast re-acquisition

When enemy starts moving after stationary phase, the dead zone keeps error
low and skips learning. Now learn when input pattern changes significantly
(Hamming distance > 2 bits), forcing immediate re-adaptation regardless of
error magnitude. Balances stability vs. responsiveness.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

SNNBot_garage/src/SNNBot.nim

@@ -214,6 +214,7 @@ type
     velSpeed:        float64            # speed (units/tick) from last scan delta
     lastDecideGunDir: float             # gun heading captured at DECIDE time for EVALUATE
     lastBinInput:    BitVec80           # DECIDE-time binary input, reused in EVALUATE
+    lastInput:       BitVec80           # previous EVALUATE-time input (for change detection)
 
 # ── aimTo helper ──────────────────────────────────────────────────────────────
 
@@ -410,10 +411,14 @@ method run*(bot: SNNBot) =
 
         when USE_RESERVOIR:
           let aimRaw = bot.res.forward(bot.lastBinInput)
-          # Only learn if aim error exceeds adaptive dead zone
+          # Detect significant input change via Hamming distance
+          let hammingDist = popcount(bot.lastBinInput[0] xor bot.lastInput[0]) + popcount(bot.lastBinInput[1] xor bot.lastInput[1])
+          let inputChanged = hammingDist > 2  # 3+ bits flipped = situation changed
+
+          # Learn if: error > dead zone OR input pattern changed significantly
           if aimRaw >= 0.0:
             let aimErr = abs(normalizeRelativeAngle(aimRaw - correctAngle))
-            if aimErr > adaptiveDeadZone:
+            if aimErr > adaptiveDeadZone or inputChanged:
               bot.res.learn(bot.lastBinInput, correctAngle)
           else:
             # Cold start: always learn
@@ -423,6 +428,8 @@ method run*(bot: SNNBot) =
                " aim=" & (if aimRaw >= 0.0: formatFloat(aimRaw, ffDecimal, 1) else: "cold") &
                " correct=" & formatFloat(correctAngle, ffDecimal, 1) &
                " err=" & (if aimRaw >= 0.0: formatFloat(aimErr, ffDecimal, 1) else: "n/a") &
+               " hammingDist=" & $hammingDist &
+               " inputChanged=" & $inputChanged &
                " exemplars=" & $bot.res.count
         else:
           let targetRel = normalizeRelativeAngle(correctAngle - bot.lastDecideGunDir)
@@ -445,6 +452,9 @@ method run*(bot: SNNBot) =
             meanWout += abs(w)
           meanWout /= float(2 * N_HID)
           echo "tick=" & $bot.tick & " err=" & formatFloat(err, ffDecimal, 1) & "° infer_spk=" & $spikeCount & "/" & $(N_INFER * N_HID) & " maxV=" & formatFloat(maxV, ffDecimal, 3) & " |wih|=" & formatFloat(meanWih, ffDecimal, 4) & " |wOut|=" & formatFloat(meanWout, ffDecimal, 4) & " sin=" & formatFloat(bot.snn.lastSinOut, ffDecimal, 3) & " cos=" & formatFloat(bot.snn.lastCosOut, ffDecimal, 3) & " snnAngle=" & formatFloat(bot.snn.lastSnnAngle, ffDecimal, 1)
+
+      # Update lastInput for next EVALUATE cycle's change detection
+      bot.lastInput = bot.lastBinInput
       bot.phase = DECIDE
 
     # Radar lock