Add storyboard handout for split-loop-with-lambda mechanics

Step-by-step refactoring instructions as a single markdown handout with
one diagram per step (legend + steps 0-3, overload inset, pure test,
debrief slides for the dead call and the drift anti-pattern). Derived
from the pattern draft, the learning hour plan, and the rehearsal
findings; slide-ready for later.

ideas/split-loop-with-lambda/storyboard/storyboard.md

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+# Split Loop with Lambda — storyboard / handout
+
+Step-by-step mechanics of the **Split Loop with Lambda** refactoring, one diagram per
+step, each step followed by the exact code (full before/after, highlights as `←`
+comments). Written to be sliced into slides later; until then it works as a handout.
+
+Sources: `../zeroth-draft-of-refactoring-pattern.md` (the mechanics),
+`../split-loop-with-lambda-learning-hour.md` (where we stop: after step 3 + the test),
+`../exercise/rehearsal-findings.md` (the drift anti-pattern and the "both calls!"
+caution). Java only. Pristine start: `../exercise/java`, end state: `../exercise/solution`.
+
+## How to read the diagrams
+
+![](svg/legend.svg)
+
+---
+
+## Step 0 — Where we start: one method, three loops, one unwanted dependency
+
+**Goal:** see the problem before touching anything. `longRangeForecast()` resets, looks
+up weather, and scores — and the weather part calls `scorer`, which stands for an
+external weather service (it uses `Random`, so the approval test is red *and* flaky).
+
+![](svg/00-pristine.svg)
+
+**Before:**
+
+```java
+public Map<IceCream, Integer> longRangeForecast() {
+    var result = new HashMap<IceCream, Integer>();
+    for (IceCream flavour : IceCream.values()) {
+        result.put(flavour, 0);
+    }
+    List<Boolean> expectedWeather = new ArrayList<>();
+    for (Instant interestingDate : DATES) {
+        scorer.updateSelection();                                    // ← unwanted dependency (void)
+        long daysForward = ChronoUnit.DAYS.between(ANCHOR_DATE, interestingDate);
+        Boolean weather = scorer.lookupWeather(daysForward);         // ← unwanted dependency (value)
+        expectedWeather.add(weather);
+    }
+    for (IceCream flavour : result.keySet()) {
+        result.put(flavour, result.get(flavour) + 10);
+        var sunnyHolidays = expectedWeather.stream().filter(s -> s).count();
+        if (sunnyHolidays > 2 && flavour == IceCream.Vanilla) {
+            result.put(flavour, result.get(flavour) + 5);
+        }
+        if (sunnyHolidays > 1 && expectedWeather.get(1)) {
+            result.put(flavour, result.get(flavour) + 2);
+        }
+    }
+    return result;
+}
+```
+
+**Checkpoint:**
+
+- Run the approval test. It fails or flakes. Why? (`Scorer` calls `Random` — it *is*
+  the unwanted dependency.)
+- Plain **Split Loop** can identify the three loops — but it cannot cut the weather
+  loop loose, because the thing you would introduce and slide is not a value, it is a
+  *call on an object you don't want*. That is where this pattern starts.
+
+---
+
+## Step 1 — Extract the dependency-using code into a lambda
+
+**Goal:** make the laziness explicit. Instead of asking the weather service now, we
+inject *a function that can answer the weather question when asked*. Both `scorer`
+calls go inside the lambda — the void one too (see the anti-pattern slide for what
+happens if you leave it behind). This step is a small manual edit: no refactoring tool
+does it.
+
+![](svg/01-extract-lambda.svg)
+
+**After:**
+
+```java
+public Map<IceCream, Integer> longRangeForecast() {
+    var result = new HashMap<IceCream, Integer>();
+    for (IceCream flavour : IceCream.values()) {
+        result.put(flavour, 0);
+    }
+    List<Boolean> expectedWeather = new ArrayList<>();
+    LongFunction<Boolean> dayOffsetToWeather = daysForward -> {   // ← NEW: the lambda...
+        scorer.updateSelection();                                 // ← ...holds BOTH scorer calls
+        return scorer.lookupWeather(daysForward);
+    };
+    for (Instant interestingDate : DATES) {
+        long daysForward = ChronoUnit.DAYS.between(ANCHOR_DATE, interestingDate);
+        expectedWeather.add(dayOffsetToWeather.apply(daysForward)); // ← invocation replaced lookupWeather
+    }
+    for (IceCream flavour : result.keySet()) {
+        // ... scoring loop unchanged ...
+    }
+    return result;
+}
+```
+
+(IDE will offer to add `import java.util.function.LongFunction;` — take it.)
+
+**Checkpoint:**
+
+- Compiles; behaviour unchanged; test still flaky — the lambda still calls `Scorer`
+  for now, that is fine.
+- The lambda's parameter (`daysForward`) is *only* in scope inside the lambda. The
+  loop still computes its own `daysForward` and hands it to the invocation.
+
+---
+
+## Step 2 — Slide the lambda definition to the top of the method
+
+**Goal:** *slide, don't move.* The **definition** of the lambda slides to the top of
+the method; the **invocation** (`.apply(...)`) stays exactly where the code used to
+be. This is the Split Loop "slide statement" move — except what slides is a
+function, not a value.
+
+![](svg/02-slide-lambda.svg)
+
+**After:**
+
+```java
+public Map<IceCream, Integer> longRangeForecast() {
+    LongFunction<Boolean> dayOffsetToWeather = daysForward -> {   // ← SLID to the top...
+        scorer.updateSelection();
+        return scorer.lookupWeather(daysForward);
+    };
+    var result = new HashMap<IceCream, Integer>();
+    for (IceCream flavour : IceCream.values()) {
+        result.put(flavour, 0);
+    }
+    List<Boolean> expectedWeather = new ArrayList<>();
+    for (Instant interestingDate : DATES) {
+        long daysForward = ChronoUnit.DAYS.between(ANCHOR_DATE, interestingDate);
+        expectedWeather.add(dayOffsetToWeather.apply(daysForward)); // ← ...invocation stays here
+    }
+    for (IceCream flavour : result.keySet()) {
+        // ... scoring loop unchanged ...
+    }
+    return result;
+}
+```
+
+**Checkpoint:**
+
+- Compiles; behaviour unchanged; test still flaky.
+- Read the method out loud: everything it needs from outside the weather loop is
+  now "given a day offset, is it sunny?" — the loop body itself no longer mentions
+  `Scorer`.
+
+---
+
+## Step 3 — Extract the weather loop; the lambda becomes a parameter
+
+**Goal:** select from the `expectedWeather` declaration through the end of the
+weather loop and Extract Method. The IDE infers the parameter type
+(`LongFunction<Boolean>`) from the lambda variable. The extracted method has no
+field dependencies left — `DATES` and `ANCHOR_DATE` are constants — so it can be
+`static` right away.
+
+![](svg/03-extract-method.svg)
+
+**Before:** end state of step 2 (above).
+
+**After:**
+
+```java
+public Map<IceCream, Integer> longRangeForecast() {
+    LongFunction<Boolean> dayOffsetToWeather = daysForward -> {
+        scorer.updateSelection();
+        return scorer.lookupWeather(daysForward);
+    };
+    var result = new HashMap<IceCream, Integer>();
+    for (IceCream flavour : IceCream.values()) {
+        result.put(flavour, 0);
+    }
+    List<Boolean> expectedWeather = collectExpectedWeather(dayOffsetToWeather); // ← EXTRACTED
+    for (IceCream flavour : result.keySet()) {
+        result.put(flavour, result.get(flavour) + 10);
+        var sunnyHolidays = expectedWeather.stream().filter(s -> s).count();
+        if (sunnyHolidays > 2 && flavour == IceCream.Vanilla) {
+            result.put(flavour, result.get(flavour) + 5);
+        }
+        if (sunnyHolidays > 1 && expectedWeather.get(1)) {
+            result.put(flavour, result.get(flavour) + 2);
+        }
+    }
+    return result;
+}
+
+private static List<Boolean> collectExpectedWeather(              // ← NEW — and already static
+        LongFunction<Boolean> dayOffsetToWeather) {
+    var expectedWeather = new ArrayList<Boolean>();
+    for (Instant interestingDate : DATES) {
+        long daysForward = ChronoUnit.DAYS.between(ANCHOR_DATE, interestingDate);
+        expectedWeather.add(dayOffsetToWeather.apply(daysForward));
+    }
+    return expectedWeather;
+}
+```
+
+**Checkpoint — the drift test.** This is where the refactoring can silently fail:
+
+- `grep -n scorer src/main/java/codingdojo/LongRangeForecasts.java` — the new method
+  must contain **no** hits.
+- Try to make `collectExpectedWeather` `static` (it already is here). If any field
+  reference remained, it would not compile.
+- If `scorer.updateSelection()` is still in the loop instead of inside the lambda,
+  the dependency travelled *with* the extraction and the split is cosmetic. Put it
+  in the lambda and start this step again.
+
+### Inset — the overload: let the λ come from outside
+
+**Goal:** right now the lambda is a local variable — the test still cannot reach the
+seam. Change Signature on the big method: *add* the lambda as a parameter and *drop*
+the local. Then give callers a no-arg overload that bakes in the "real" lambda.
+
+![](svg/03b-overload.svg)
+
+**After:**
+
+```java
+public Map<IceCream, Integer> longRangeForecast() {               // ← no-arg overload: callers unchanged
+    return longRangeForecast(daysForward -> {
+        scorer.updateSelection();
+        return scorer.lookupWeather(daysForward);
+    });
+}
+
+public Map<IceCream, Integer> longRangeForecast(                  // ← the seam: λ is a parameter
+        LongFunction<Boolean> dayOffsetToWeather) {
+    var expectedWeather = collectExpectedWeather(dayOffsetToWeather);
+    // ... reset loop + scoring loop, unchanged ...
+    return result;
+}
+```
+
+**Checkpoint:** compiles; existing callers (and the old flaky test, if you keep it)
+still work through the no-arg overload.
+
+---
+
+## Step 5-lite — test through the seam with a pure lambda
+
+**Goal:** replace the weather service with a pure function in the test. Deterministic,
+glanceable, and `Scorer` is never touched.
+
+![](svg/04-pure-test.svg)
+
+**The test (end of document version — this is the whole thing):**
+
+```java
+package codingdojo;
+
+import org.approvaltests.Approvals;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Map;
+import java.util.function.LongFunction;
+
+public class LongRangeForecastsTest {
+
+    @Test
+    void longRangeForecast() {
+        // pure weather implementation: every holiday is sunny
+        LongFunction<Boolean> alwaysSunny = daysForward -> true;
+        var actual = new LongRangeForecasts().longRangeForecast(alwaysSunny);
+        Approvals.verify(printIceCreamForecast(actual));
+    }
+
+    private static String printIceCreamForecast(Map<IceCream, Integer> actual) {
+        var printedResult = new StringBuilder();
+        printedResult.append("{");
+        var sortedKeys = new ArrayList<>(actual.keySet());
+        Collections.sort(sortedKeys);
+        for (IceCream key : sortedKeys) {
+            printedResult.append(key);
+            printedResult.append(":");
+            printedResult.append(actual.get(key));
+            printedResult.append(", ");
+        }
+        printedResult.append("}");
+        return printedResult.toString();
+    }
+}
+```
+
+Approved output:
+
+```
+{Strawberry:12, Chocolate:12, Vanilla:17, }
+```
+
+**Checkpoint:** `mvn test` is green — deterministically. Nothing in the test path
+touches `Scorer`. *What just became testable that was not before?*
+
+---
+
+## Debrief
+
+### The dead call the lambda exposed
+
+![](svg/05-debrief-dead-call.svg)
+
+`scorer.updateSelection()` re-rolls `Scorer.flavour` — state that nothing in this
+method ever reads (its only real consumer is the unrelated `salesForecast()`; it is
+copy-paste residue in the long-range loop). Delete it from the lambda: the approved
+file does not change. The refactoring didn't just hide the dependency — it exposed
+that one of the two calls was dead all along.
+
+### Anti-pattern — the drift: scorer left behind in the extracted method
+
+![](svg/06-anti-pattern-drift.svg)
+
+If you lambda-ize only the value-producing call and leave `updateSelection()` as
+"loop machinery", the extraction carries the `scorer` field into the new method:
+
+```java
+// DRIFTED — the method still depends on the field; step 4 (move it
+// to another class) would be blocked, and the split is cosmetic.
+private List<Boolean> collectExpectedWeather(
+        LongFunction<Boolean> dayOffsetToWeather) {
+    var expectedWeather = new ArrayList<Boolean>();
+    for (Instant interestingDate : DATES) {
+        scorer.updateSelection();          // ← LEFT BEHIND
+        long daysForward = ChronoUnit.DAYS.between(ANCHOR_DATE, interestingDate);
+        expectedWeather.add(dayOffsetToWeather.apply(daysForward));
+    }
+    return expectedWeather;
+}
+```
+
+Worse: the test still passes (the stray call only mutates state nothing reads), so
+**green ≠ drift-free**. Catch it mechanically: `grep scorer` on the extracted method
+must return nothing, or try to make it `static` — it won't compile with a field
+reference.
+
+---
+
+## Next moves (not storyboarded yet)
+
+These are steps 4 and 6 of the full pattern — the learning hour stops before them:
+
+- **Step 4:** move `collectExpectedWeather` to a class where `Scorer` is unknown.
+  (It is already `static` and scorer-free — the move is now unblocked.)
+- **Step 6:** more pure-lambda combinations are now one line each:
+  `daysForward -> false` (no sunny holidays → all flavours 10),
+  `daysForward -> daysForward == 5` (exactly one sunny holiday, not at index 1 → all 10).
+- The design view: the lambda is the smallest **Port** (function signature) +
+  **Adapter** (the extracted code with the unwanted dependency) that could work —
+  see the Role Interface discussion in the pattern draft.

ideas/split-loop-with-lambda/storyboard/svg/00-pristine.svg

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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 460" font-family="Helvetica, Arial, sans-serif">
+  <defs>
+    <marker id="arrR" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#dc2626"/>
+    </marker>
+  </defs>
+  <rect width="760" height="460" fill="#ffffff"/>
+  <text x="24" y="34" font-size="20" font-weight="bold" fill="#0f172a">Step 0 — one method, three loops, one unwanted dependency</text>
+  <text x="24" y="56" font-size="13" fill="#475569">The weather loop reaches outside the method to Scorer (which uses Random) — that is why the test is red &amp; flaky.</text>
+
+  <!-- method -->
+  <rect x="60" y="74" width="340" height="356" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="76" y="98" font-size="14" font-weight="bold" fill="#0f172a">longRangeForecast()</text>
+
+  <!-- reset loop -->
+  <rect x="80" y="112" width="300" height="56" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="94" y="134" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (IceCream flavour : IceCream.values())</text>
+  <text x="94" y="154" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">    result.put(flavour, 0);</text>
+
+  <!-- weather loop -->
+  <rect x="80" y="184" width="300" height="112" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="94" y="206" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (Instant interestingDate : DATES)</text>
+  <text x="94" y="228" font-size="11" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#dc2626">scorer.updateSelection();</text>
+  <text x="94" y="248" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">daysForward = DAYS.between(ANCHOR, date)</text>
+  <text x="94" y="268" font-size="11" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#dc2626">weather = scorer.lookupWeather(daysForward);</text>
+
+  <!-- scoring loop -->
+  <rect x="80" y="312" width="300" height="104" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="94" y="334" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (flavour : keySet) result += 10</text>
+  <text x="94" y="356" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">if (sunnyHolidays &gt; 2 &amp;&amp; Vanilla) += 5</text>
+  <text x="94" y="376" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">if (sunnyHolidays &gt; 1 &amp;&amp; weather[1]) += 2</text>
+  <text x="94" y="402" font-size="10" fill="#64748b">scoring loop</text>
+
+  <!-- Scorer -->
+  <rect x="580" y="200" width="150" height="80" rx="8" fill="#fef2f2" stroke="#dc2626" stroke-width="1.5"/>
+  <text x="655" y="230" font-size="14" font-weight="bold" fill="#dc2626" text-anchor="middle">Scorer</text>
+  <text x="655" y="250" font-size="11" fill="#7f1d1d" text-anchor="middle">stands for the weather</text>
+  <text x="655" y="266" font-size="11" fill="#7f1d1d" text-anchor="middle">service — uses Random</text>
+
+  <line x1="384" y1="228" x2="572" y2="222" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+  <line x1="384" y1="268" x2="572" y2="254" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+
+  <!-- test -->
+  <rect x="580" y="330" width="150" height="60" rx="8" fill="#ffffff" stroke="#94a3b8" stroke-dasharray="4 3"/>
+  <text x="655" y="354" font-size="12" fill="#334155" text-anchor="middle">approval test</text>
+  <text x="655" y="372" font-size="12" font-weight="bold" fill="#dc2626" text-anchor="middle">red &amp; flaky ✗</text>
+</svg>

ideas/split-loop-with-lambda/storyboard/svg/01-extract-lambda.svg

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+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 460" font-family="Helvetica, Arial, sans-serif">
+  <defs>
+    <marker id="arrR" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#dc2626"/>
+    </marker>
+  </defs>
+  <rect width="760" height="460" fill="#ffffff"/>
+  <text x="24" y="34" font-size="20" font-weight="bold" fill="#0f172a">Step 1 — extract the dependency-using code into a lambda</text>
+  <text x="24" y="56" font-size="13" fill="#dc2626" font-weight="bold">Both scorer calls go inside the lambda — the void one too. The invocation stays in the loop.</text>
+
+  <!-- method -->
+  <rect x="60" y="74" width="340" height="356" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="76" y="98" font-size="14" font-weight="bold" fill="#0f172a">longRangeForecast()</text>
+
+  <!-- reset loop -->
+  <rect x="80" y="112" width="300" height="56" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="94" y="134" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (IceCream flavour : IceCream.values())</text>
+  <text x="94" y="154" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">    result.put(flavour, 0);</text>
+
+  <!-- weather loop -->
+  <rect x="80" y="184" width="300" height="144" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="94" y="204" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (Instant interestingDate : DATES)</text>
+
+  <!-- lambda (inside loop, where the code used to be) -->
+  <rect x="94" y="214" width="256" height="74" rx="8" fill="#faf5ff" stroke="#9333ea" stroke-width="1.5"/>
+  <text x="106" y="234" font-size="12" font-weight="bold" fill="#9333ea">λ dayOffsetToWeather</text>
+  <text x="106" y="254" font-size="11" font-family="Menlo, Consolas, monospace" fill="#dc2626">scorer.updateSelection();</text>
+  <text x="106" y="272" font-size="11" font-family="Menlo, Consolas, monospace" fill="#dc2626">return scorer.lookupWeather(days);</text>
+
+  <!-- invocation -->
+  <circle cx="90" cy="308" r="4" fill="#9333ea"/>
+  <text x="102" y="312" font-size="11" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#6b21a8">expectedWeather.add(λ.apply(daysForward));</text>
+
+  <!-- scoring loop -->
+  <rect x="80" y="344" width="300" height="80" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="94" y="368" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (flavour : keySet) result += 10</text>
+  <text x="94" y="388" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">+5 / +2 ifs, unchanged</text>
+  <text x="94" y="410" font-size="10" fill="#64748b">scoring loop</text>
+
+  <!-- Scorer -->
+  <rect x="580" y="200" width="150" height="80" rx="8" fill="#fef2f2" stroke="#dc2626" stroke-width="1.5"/>
+  <text x="655" y="230" font-size="14" font-weight="bold" fill="#dc2626" text-anchor="middle">Scorer</text>
+  <text x="655" y="250" font-size="11" fill="#7f1d1d" text-anchor="middle">still called —</text>
+  <text x="655" y="266" font-size="11" fill="#7f1d1d" text-anchor="middle">but only via the λ now</text>
+
+  <line x1="354" y1="244" x2="572" y2="228" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+  <line x1="354" y1="272" x2="572" y2="256" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+</svg>

ideas/split-loop-with-lambda/storyboard/svg/02-slide-lambda.svg

@@ -0,0 +1,56 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 460" font-family="Helvetica, Arial, sans-serif">
+  <defs>
+    <marker id="arrR" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#dc2626"/>
+    </marker>
+    <marker id="arrP" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#9333ea"/>
+    </marker>
+  </defs>
+  <rect width="760" height="460" fill="#ffffff"/>
+  <text x="24" y="34" font-size="20" font-weight="bold" fill="#0f172a">Step 2 — slide the lambda definition to the top of the method</text>
+  <text x="24" y="56" font-size="13" fill="#9333ea" font-weight="bold">Slide, don't move: the definition slides up, the invocation stays exactly where it was.</text>
+
+  <!-- method -->
+  <rect x="60" y="74" width="340" height="356" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="76" y="98" font-size="14" font-weight="bold" fill="#0f172a">longRangeForecast()</text>
+
+  <!-- lambda at top -->
+  <rect x="94" y="104" width="256" height="74" rx="8" fill="#faf5ff" stroke="#9333ea" stroke-width="1.5"/>
+  <text x="106" y="124" font-size="12" font-weight="bold" fill="#9333ea">λ dayOffsetToWeather</text>
+  <text x="106" y="144" font-size="11" font-family="Menlo, Consolas, monospace" fill="#dc2626">scorer.updateSelection();</text>
+  <text x="106" y="162" font-size="11" font-family="Menlo, Consolas, monospace" fill="#dc2626">return scorer.lookupWeather(days);</text>
+
+  <!-- reset loop -->
+  <rect x="80" y="196" width="300" height="56" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="94" y="218" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (IceCream flavour : IceCream.values())</text>
+  <text x="94" y="238" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">    result.put(flavour, 0);</text>
+
+  <!-- weather loop -->
+  <rect x="80" y="268" width="300" height="100" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="94" y="290" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (Instant interestingDate : DATES)</text>
+
+  <!-- ghost of old position -->
+  <rect x="94" y="300" width="256" height="28" rx="6" fill="none" stroke="#9333ea" stroke-width="1" stroke-dasharray="4 3"/>
+  <text x="106" y="318" font-size="10" fill="#9333ea" font-style="italic">λ used to be defined here</text>
+
+  <circle cx="90" cy="352" r="4" fill="#9333ea"/>
+  <text x="102" y="356" font-size="11" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#6b21a8">expectedWeather.add(λ.apply(daysForward));</text>
+
+  <!-- scoring loop -->
+  <rect x="80" y="384" width="300" height="40" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="94" y="409" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">scoring loop: += 10 / +5 / +2</text>
+
+  <!-- slide arrow -->
+  <line x1="219" y1="298" x2="219" y2="184" stroke="#9333ea" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrP)"/>
+  <text x="232" y="192" font-size="12" font-weight="bold" fill="#9333ea">slide</text>
+
+  <!-- Scorer -->
+  <rect x="580" y="200" width="150" height="80" rx="8" fill="#fef2f2" stroke="#dc2626" stroke-width="1.5"/>
+  <text x="655" y="230" font-size="14" font-weight="bold" fill="#dc2626" text-anchor="middle">Scorer</text>
+  <text x="655" y="250" font-size="11" fill="#7f1d1d" text-anchor="middle">still called —</text>
+  <text x="655" y="266" font-size="11" fill="#7f1d1d" text-anchor="middle">but only via the λ now</text>
+
+  <line x1="354" y1="130" x2="572" y2="226" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+  <line x1="354" y1="160" x2="572" y2="250" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+</svg>

ideas/split-loop-with-lambda/storyboard/svg/03-extract-method.svg

@@ -0,0 +1,67 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 460" font-family="Helvetica, Arial, sans-serif">
+  <defs>
+    <marker id="arrR" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#dc2626"/>
+    </marker>
+    <marker id="arrP" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#9333ea"/>
+    </marker>
+  </defs>
+  <rect width="760" height="460" fill="#ffffff"/>
+  <text x="24" y="34" font-size="20" font-weight="bold" fill="#0f172a">Step 3 — extract the weather loop; the lambda becomes a parameter</text>
+  <text x="24" y="56" font-size="13" fill="#475569">Extract Method on the expectedWeather block. Checkpoint: grep scorer → no hits; try static → compiles.</text>
+
+  <!-- left: original method -->
+  <rect x="50" y="74" width="300" height="356" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="66" y="96" font-size="14" font-weight="bold" fill="#0f172a">longRangeForecast()</text>
+
+  <!-- lambda at top -->
+  <rect x="64" y="104" width="272" height="68" rx="8" fill="#faf5ff" stroke="#9333ea" stroke-width="1.5"/>
+  <text x="78" y="126" font-size="12" font-weight="bold" fill="#9333ea">λ dayOffsetToWeather</text>
+  <text x="78" y="146" font-size="10" font-family="Menlo, Consolas, monospace" fill="#dc2626">scorer.updateSelection();</text>
+  <text x="78" y="162" font-size="10" font-family="Menlo, Consolas, monospace" fill="#dc2626">return scorer.lookupWeather(daysForward);</text>
+
+  <!-- reset loop -->
+  <rect x="64" y="188" width="272" height="44" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="78" y="214" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">reset loop: result.put(flavour, 0)</text>
+
+  <!-- call site -->
+  <rect x="64" y="248" width="272" height="48" rx="8" fill="#ffffff" stroke="#475569" stroke-width="1.5"/>
+  <text x="78" y="268" font-size="11" font-family="Menlo, Consolas, monospace" fill="#0f172a">expectedWeather =</text>
+  <text x="78" y="286" font-size="11" font-family="Menlo, Consolas, monospace" fill="#0f172a">collectExpectedWeather(<tspan fill="#9333ea" font-weight="bold">λ</tspan>)</text>
+
+  <!-- scoring loop -->
+  <rect x="64" y="312" width="272" height="84" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="78" y="334" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (flavour : keySet) result += 10</text>
+  <text x="78" y="354" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">if (sunny &gt; 2 &amp;&amp; Vanilla) += 5</text>
+  <text x="78" y="374" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">if (sunny &gt; 1 &amp;&amp; weather[1]) += 2</text>
+
+  <!-- purple arrow: lambda becomes parameter -->
+  <line x1="340" y1="272" x2="452" y2="146" stroke="#9333ea" stroke-width="1.5" marker-end="url(#arrP)"/>
+  <text x="396" y="214" font-size="10" font-weight="bold" fill="#9333ea" text-anchor="middle" transform="rotate(-48 396 214)">λ becomes a parameter</text>
+
+  <!-- right: extracted method -->
+  <rect x="440" y="74" width="290" height="280" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="456" y="96" font-size="13" font-weight="bold" fill="#0f172a">collectExpectedWeather</text>
+  <text x="456" y="112" font-size="11" fill="#475569">static — no fields, all inputs are parameters</text>
+
+  <!-- parameter pill -->
+  <rect x="456" y="122" width="258" height="32" rx="16" fill="#faf5ff" stroke="#9333ea" stroke-width="1.5"/>
+  <text x="585" y="142" font-size="11" font-weight="bold" fill="#9333ea" text-anchor="middle">λ  LongFunction&lt;Boolean&gt; dayOffsetToWeather</text>
+
+  <!-- weather loop -->
+  <rect x="456" y="166" width="258" height="110" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="470" y="190" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (Instant d : DATES)</text>
+  <text x="470" y="212" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">daysForward = between(ANCHOR, d)</text>
+  <text x="470" y="234" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">expected.add(<tspan fill="#9333ea" font-weight="bold">λ</tspan>.apply(daysForward))</text>
+  <text x="470" y="260" font-size="10" fill="#64748b">no scorer reference in here</text>
+
+  <text x="456" y="308" font-size="11" font-family="Menlo, Consolas, monospace" fill="#0f172a">return expectedWeather;</text>
+
+  <!-- scorer, out of reach -->
+  <rect x="560" y="386" width="160" height="50" rx="8" fill="#fef2f2" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="4 3"/>
+  <text x="640" y="408" font-size="12" font-weight="bold" fill="#dc2626" text-anchor="middle">Scorer</text>
+  <text x="640" y="426" font-size="10" fill="#7f1d1d" text-anchor="middle">out of reach from in here</text>
+  <line x1="640" y1="384" x2="640" y2="360" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+  <text x="650" y="376" font-size="10" font-weight="bold" fill="#dc2626">✗ cannot reach in</text>
+</svg>

ideas/split-loop-with-lambda/storyboard/svg/03b-overload.svg

@@ -0,0 +1,53 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 460" font-family="Helvetica, Arial, sans-serif">
+  <defs>
+    <marker id="arrR" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#dc2626"/>
+    </marker>
+    <marker id="arrG" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#475569"/>
+    </marker>
+  </defs>
+  <rect width="760" height="460" fill="#ffffff"/>
+  <text x="24" y="34" font-size="20" font-weight="bold" fill="#0f172a">Inset — the overload: let the λ come from outside</text>
+  <text x="24" y="56" font-size="13" fill="#475569">Add the λ as a parameter (Change Signature), drop the local. A no-arg overload bakes in the real λ — callers unchanged.</text>
+
+  <!-- left: no-arg overload -->
+  <rect x="50" y="90" width="320" height="250" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="66" y="114" font-size="13" font-weight="bold" fill="#0f172a">longRangeForecast()</text>
+  <text x="66" y="130" font-size="10" fill="#475569">no-arg overload — existing callers keep working</text>
+
+  <rect x="66" y="144" width="288" height="92" rx="8" fill="#faf5ff" stroke="#9333ea" stroke-width="1.5"/>
+  <text x="80" y="166" font-size="11" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#9333ea">daysForward -&gt; {</text>
+  <text x="80" y="186" font-size="11" font-family="Menlo, Consolas, monospace" fill="#dc2626">  scorer.updateSelection();</text>
+  <text x="80" y="206" font-size="11" font-family="Menlo, Consolas, monospace" fill="#dc2626">  return scorer.lookupWeather(days);</text>
+  <text x="80" y="226" font-size="11" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#9333ea">}</text>
+
+  <text x="66" y="278" font-size="11" font-family="Menlo, Consolas, monospace" fill="#0f172a">return longRangeForecast(<tspan fill="#9333ea" font-weight="bold">λ</tspan>);</text>
+  <text x="66" y="316" font-size="10" fill="#64748b">the "real" weather lambda lives here</text>
+
+  <!-- delegate arrow -->
+  <line x1="374" y1="150" x2="424" y2="150" stroke="#475569" stroke-width="1.5" marker-end="url(#arrG)"/>
+  <text x="376" y="140" font-size="10" fill="#475569">delegates</text>
+
+  <!-- right: the seam -->
+  <rect x="430" y="90" width="300" height="250" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="446" y="114" font-size="12" font-weight="bold" fill="#0f172a">longRangeForecast(<tspan fill="#9333ea">λ</tspan>)</text>
+  <text x="446" y="132" font-size="10" fill="#475569">the seam: weather is a parameter now</text>
+
+  <rect x="446" y="150" width="268" height="40" rx="8" fill="#ffffff" stroke="#475569" stroke-width="1"/>
+  <text x="460" y="166" font-size="11" font-family="Menlo, Consolas, monospace" fill="#0f172a">expectedWeather =</text>
+  <text x="460" y="182" font-size="11" font-family="Menlo, Consolas, monospace" fill="#0f172a">  collectExpectedWeather(<tspan fill="#9333ea" font-weight="bold">λ</tspan>)</text>
+
+  <rect x="446" y="206" width="268" height="40" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="460" y="230" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">reset loop: result.put(flavour, 0)</text>
+
+  <rect x="446" y="262" width="268" height="56" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="460" y="284" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">scoring loop: += 10 / +5 / +2</text>
+  <text x="460" y="304" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">return result;</text>
+
+  <!-- scorer still reachable from the no-arg overload only -->
+  <rect x="80" y="380" width="180" height="56" rx="8" fill="#fef2f2" stroke="#dc2626" stroke-width="1.5"/>
+  <text x="170" y="402" font-size="12" font-weight="bold" fill="#dc2626" text-anchor="middle">Scorer</text>
+  <text x="170" y="422" font-size="10" fill="#7f1d1d" text-anchor="middle">only the no-arg overload knows it</text>
+  <line x1="170" y1="378" x2="170" y2="346" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+</svg>

ideas/split-loop-with-lambda/storyboard/svg/04-pure-test.svg

@@ -0,0 +1,51 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 460" font-family="Helvetica, Arial, sans-serif">
+  <defs>
+    <marker id="arrR" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#dc2626"/>
+    </marker>
+    <marker id="arrGr" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#16a34a"/>
+    </marker>
+  </defs>
+  <rect width="760" height="460" fill="#ffffff"/>
+  <text x="24" y="34" font-size="20" font-weight="bold" fill="#0f172a">Step 5-lite — test through the seam with a pure lambda</text>
+  <text x="24" y="56" font-size="13" fill="#16a34a" font-weight="bold">The test passes alwaysSunny. Scorer is never touched: no Random, deterministic, glanceable.</text>
+
+  <!-- test -->
+  <rect x="50" y="160" width="230" height="130" rx="10" fill="#f0fdf4" stroke="#16a34a" stroke-width="1.5"/>
+  <text x="66" y="186" font-size="13" font-weight="bold" fill="#14532d">LongRangeForecastsTest</text>
+  <text x="66" y="210" font-size="10" fill="#475569">LongFunction&lt;Boolean&gt;</text>
+  <text x="66" y="232" font-size="12" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#16a34a">alwaysSunny = days -&gt; true</text>
+  <text x="66" y="258" font-size="11" font-family="Menlo, Consolas, monospace" fill="#14532d">longRangeForecast(alwaysSunny)</text>
+
+  <!-- middle: overload -->
+  <rect x="340" y="150" width="180" height="170" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="354" y="176" font-size="11" font-weight="bold" fill="#0f172a">longRangeForecast(<tspan fill="#9333ea">λ</tspan>)</text>
+  <text x="354" y="204" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">collectExpected-</text>
+  <text x="354" y="220" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">Weather(<tspan fill="#9333ea" font-weight="bold">λ</tspan>)</text>
+  <text x="354" y="248" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">reset loop</text>
+  <text x="354" y="274" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">scoring loop</text>
+  <text x="354" y="296" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">+= 10 / +5 / +2</text>
+
+  <!-- right: extracted method -->
+  <rect x="560" y="150" width="170" height="170" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="574" y="176" font-size="10" font-weight="bold" fill="#0f172a">collectExpectedWeather(λ)</text>
+  <text x="574" y="204" font-size="10" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for d : DATES</text>
+  <text x="574" y="226" font-size="10" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">expected.add(<tspan fill="#9333ea" font-weight="bold">λ</tspan>.apply(d))</text>
+  <text x="574" y="252" font-size="10" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">return expectedWeather</text>
+  <text x="574" y="290" font-size="10" fill="#16a34a" font-weight="bold">pure ✓</text>
+
+  <!-- green arrows -->
+  <line x1="284" y1="225" x2="334" y2="225" stroke="#16a34a" stroke-width="1.5" marker-end="url(#arrGr)"/>
+  <text x="286" y="214" font-size="10" fill="#16a34a">alwaysSunny</text>
+  <line x1="524" y1="225" x2="554" y2="225" stroke="#16a34a" stroke-width="1.5" marker-end="url(#arrGr)"/>
+
+  <!-- scorer, never called -->
+  <rect x="560" y="370" width="170" height="56" rx="8" fill="#f8fafc" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="4 3" opacity="0.8"/>
+  <text x="645" y="392" font-size="12" font-weight="bold" fill="#94a3b8" text-anchor="middle">Scorer</text>
+  <text x="645" y="412" font-size="10" fill="#64748b" text-anchor="middle">never called by the test ✗</text>
+  <line x1="645" y1="368" x2="645" y2="326" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+  <text x="655" y="350" font-size="11" font-weight="bold" fill="#dc2626">✗</text>
+
+  <text x="50" y="430" font-size="12" fill="#475569">Approved: {Strawberry:12, Chocolate:12, Vanilla:17, } — every run, not just a lucky roll.</text>
+</svg>

ideas/split-loop-with-lambda/storyboard/svg/05-debrief-dead-call.svg

@@ -0,0 +1,24 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 460" font-family="Helvetica, Arial, sans-serif">
+  <rect width="760" height="460" fill="#ffffff"/>
+  <text x="24" y="34" font-size="20" font-weight="bold" fill="#0f172a">Debrief — the lambda made dead code visible</text>
+  <text x="24" y="56" font-size="13" fill="#475569">updateSelection() re-rolls Scorer.flavour — state nothing in this method ever reads. Delete it; the approved file is unchanged.</text>
+
+  <!-- lambda box -->
+  <rect x="200" y="110" width="360" height="124" rx="10" fill="#faf5ff" stroke="#9333ea" stroke-width="1.5"/>
+  <text x="216" y="136" font-size="11" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#9333ea">daysForward -&gt; {</text>
+  <text x="216" y="162" font-size="11" font-family="Menlo, Consolas, monospace" fill="#dc2626">scorer.updateSelection();</text>
+  <line x1="216" y1="157" x2="408" y2="157" stroke="#dc2626" stroke-width="1.5"/>
+  <text x="420" y="162" font-size="10" font-weight="bold" fill="#dc2626">✗ delete me</text>
+  <text x="216" y="188" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">return scorer.lookupWeather(daysForward);</text>
+  <text x="216" y="212" font-size="11" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#9333ea">}</text>
+
+  <!-- result -->
+  <text x="200" y="290" font-size="13" font-weight="bold" fill="#16a34a">✓ approved file unchanged:</text>
+  <text x="200" y="316" font-size="13" font-family="Menlo, Consolas, monospace" fill="#166534">{Strawberry:12, Chocolate:12, Vanilla:17, }</text>
+
+  <!-- explanation -->
+  <rect x="200" y="350" width="360" height="72" rx="8" fill="#f8fafc" stroke="#94a3b8" stroke-width="1"/>
+  <text x="216" y="374" font-size="11" fill="#334155">Why: Scorer.flavour's only real consumer is the unrelated</text>
+  <text x="216" y="392" font-size="11" fill="#334155">salesForecast(). In the long-range loop it was copy-paste</text>
+  <text x="216" y="410" font-size="11" fill="#334155">residue — visible only once the lambda made it explicit.</text>
+</svg>

ideas/split-loop-with-lambda/storyboard/svg/06-anti-pattern-drift.svg

@@ -0,0 +1,40 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 460" font-family="Helvetica, Arial, sans-serif">
+  <defs>
+    <marker id="arrR" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#dc2626"/>
+    </marker>
+  </defs>
+  <rect width="760" height="460" fill="#ffffff"/>
+  <text x="24" y="34" font-size="20" font-weight="bold" fill="#0f172a">Anti-pattern — the drift: scorer left behind in the extracted method</text>
+  <text x="24" y="56" font-size="13" fill="#dc2626" font-weight="bold">Lambda-ize only the value-producing call, and the dependency travels with the extraction.</text>
+  <text x="24" y="74" font-size="13" fill="#dc2626" font-weight="bold">Happened in 2 of 6 agent rehearsal runs — behaviour passed, design goal silently failed.</text>
+
+  <!-- drifted extracted method -->
+  <rect x="250" y="110" width="300" height="190" rx="10" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="266" y="134" font-size="12" font-weight="bold" fill="#0f172a">collectExpectedWeather(<tspan fill="#9333ea">λ</tspan>)</text>
+  <text x="516" y="136" font-size="22" font-weight="bold" fill="#dc2626">✗</text>
+
+  <rect x="266" y="148" width="268" height="110" rx="8" fill="#eef2ff" stroke="#818cf8"/>
+  <text x="280" y="172" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">for (Instant d : DATES)</text>
+  <text x="280" y="196" font-size="11" font-family="Menlo, Consolas, monospace" font-weight="bold" fill="#dc2626">scorer.updateSelection();   ✗</text>
+  <text x="280" y="218" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">daysForward = between(ANCHOR, d)</text>
+  <text x="280" y="240" font-size="11" font-family="Menlo, Consolas, monospace" fill="#1e1b4b">expected.add(<tspan fill="#9333ea" font-weight="bold">λ</tspan>.apply(daysForward))</text>
+
+  <text x="266" y="284" font-size="10" fill="#dc2626">not static anymore — it uses the field</text>
+
+  <!-- scorer, still wired in -->
+  <rect x="600" y="140" width="130" height="56" rx="8" fill="#fef2f2" stroke="#dc2626" stroke-width="1.5"/>
+  <text x="665" y="162" font-size="12" font-weight="bold" fill="#dc2626" text-anchor="middle">Scorer</text>
+  <text x="665" y="182" font-size="10" fill="#7f1d1d" text-anchor="middle">still wired in</text>
+  <line x1="552" y1="192" x2="594" y2="172" stroke="#dc2626" stroke-width="1.5" marker-end="url(#arrR)"/>
+
+  <!-- what it breaks -->
+  <text x="250" y="330" font-size="12" fill="#475569">Behaviour looks fine (the test can still pass) — but the split is cosmetic:</text>
+  <text x="250" y="350" font-size="12" fill="#475569">step 4, moving the method to a class without Scorer, is now blocked.</text>
+
+  <!-- catch it -->
+  <rect x="250" y="374" width="310" height="72" rx="8" fill="#fffbeb" stroke="#d97706" stroke-width="1.5"/>
+  <text x="266" y="398" font-size="11" font-weight="bold" fill="#92400e">Catch it mechanically:</text>
+  <text x="266" y="418" font-size="11" fill="#92400e">• grep scorer on the extracted method → no hits</text>
+  <text x="266" y="436" font-size="11" fill="#92400e">• try static → won't compile with a field ref</text>
+</svg>

ideas/split-loop-with-lambda/storyboard/svg/legend.svg

@@ -0,0 +1,41 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 760 470" font-family="Helvetica, Arial, sans-serif">
+  <defs>
+    <marker id="arrR" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#dc2626"/>
+    </marker>
+    <marker id="arrP" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#9333ea"/>
+    </marker>
+    <marker id="arrG" viewBox="0 0 10 10" refX="9" refY="5" markerWidth="7" markerHeight="7" orient="auto-start-reverse">
+      <path d="M0,0 L10,5 L0,10 z" fill="#475569"/>
+    </marker>
+  </defs>
+  <rect width="760" height="470" fill="#ffffff"/>
+  <text x="24" y="34" font-size="20" font-weight="bold" fill="#0f172a">How to read the diagrams</text>
+
+  <rect x="50" y="58" width="110" height="32" rx="8" fill="#f8fafc" stroke="#64748b" stroke-width="1.5"/>
+  <text x="180" y="79" font-size="13" fill="#334155">composed method / class under test</text>
+
+  <rect x="50" y="106" width="110" height="32" rx="8" fill="#eef2ff" stroke="#818cf8" stroke-width="1.5"/>
+  <text x="180" y="127" font-size="13" fill="#334155">loop — the thing we split / extract</text>
+
+  <rect x="50" y="154" width="110" height="32" rx="8" fill="#fef2f2" stroke="#dc2626" stroke-width="1.5"/>
+  <text x="180" y="175" font-size="13" fill="#334155">unwanted dependency — Scorer ≈ weather service</text>
+
+  <line x1="50" y1="216" x2="160" y2="216" stroke="#dc2626" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrR)"/>
+  <text x="180" y="221" font-size="13" fill="#334155">dependency call — the thing that wants to disappear</text>
+
+  <rect x="50" y="250" width="110" height="32" rx="8" fill="#faf5ff" stroke="#9333ea" stroke-width="1.5"/>
+  <text x="180" y="271" font-size="13" fill="#334155">λ — a function value</text>
+
+  <rect x="50" y="298" width="110" height="32" rx="8" fill="#f0fdf4" stroke="#16a34a" stroke-width="1.5"/>
+  <text x="180" y="319" font-size="13" fill="#334155">pure / test</text>
+
+  <line x1="50" y1="360" x2="160" y2="360" stroke="#9333ea" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrP)"/>
+  <text x="180" y="365" font-size="13" fill="#334155">slide — definition moves, invocation stays</text>
+
+  <line x1="50" y1="408" x2="160" y2="408" stroke="#475569" stroke-width="1.5" stroke-dasharray="5 4" marker-end="url(#arrG)"/>
+  <text x="180" y="413" font-size="13" fill="#334155">extraction / other motion</text>
+
+  <text x="24" y="452" font-size="12" fill="#64748b">Code lines inside boxes are monospace. Red = the unwanted dependency; purple = the lambda and everything it makes possible.</text>
+</svg>