feat(editor): add a simulation panel and an element inspector

- ResultsPanel: a Simulate panel that charts every Stock over time (hand-built
  SVG), with start/stop/dt run controls and a divergence warning
- Inspector: edit a selected Stock's initial value or a Flow/Converter's rule
- store: undoable setInitialValue / setRule / setSimSpec actions

src/components/Editor.vue

@@ -33,8 +33,10 @@ import { canConnect } from "@/model/validation"
 import { useModelStore } from "@/store/model"
 import { NODE_DND_MIME, type PlaceableKind } from "./palette-dnd"
 import GlossPanel from "./GlossPanel.vue"
+import Inspector from "./Inspector.vue"
 import LoopOverlay from "./LoopOverlay.vue"
 import Palette from "./Palette.vue"
+import ResultsPanel from "./ResultsPanel.vue"
 import InfoLinkEdge from "./edges/InfoLinkEdge.vue"
 import PipeEdge from "./edges/PipeEdge.vue"
 import CloudNode from "./nodes/CloudNode.vue"
@@ -48,6 +50,10 @@ const graph = computed(() => project(store.model))
 const nodes = computed(() => graph.value.nodes)
 const edges = computed(() => graph.value.edges)
 
+// The simulation results panel (phase 2). Toggled from the header; the panel runs
+// the Model and recomputes reactively while open.
+const showResults = ref(false)
+
 // Explicit shared id: useVueFlow() runs here in the parent setup, before
 // <VueFlow> mounts. Pinning both to the same id guarantees they resolve to one
 // store instance, so the event hooks below actually fire.
@@ -358,6 +364,13 @@ onBeforeUnmount(() => {
             </li>
           </ul>
         </div>
+        <button
+          class="btn btn-primary btn-sm"
+          :class="{ 'btn-active': showResults }"
+          @click="showResults = !showResults"
+        >
+          Simulate
+        </button>
         <button class="btn btn-ghost btn-sm" @click="exportModel">Export</button>
         <button class="btn btn-ghost btn-sm" @click="fileInput?.click()">Import</button>
         <input
@@ -420,6 +433,8 @@ onBeforeUnmount(() => {
       <Palette class="absolute top-3 left-3 z-20" @add="addNode" />
       <LoopOverlay />
       <GlossPanel />
+      <Inspector />
+      <ResultsPanel v-if="showResults" @close="showResults = false" />
 
       <!-- Self-dismissing teaching hint, e.g. when a Flow is dragged back onto its
            own Stock to "close the loop". Click to dismiss early; z-30 keeps it above

src/components/Inspector.vue

@@ -0,0 +1,146 @@
+<script setup lang="ts">
+/**
+ * Inspector (phase 2, ADR-0004) — equips the *selected* element with the numbers
+ * a simulation needs, so a Model becomes more than samples: a Stock gets its
+ * initial value, a Flow/Converter its rule. Editing is deliberately small —
+ * choose a rule from the fixed vocabulary and type one or two numbers; there is
+ * no formula box, so the Model stays valid by construction.
+ *
+ * It reads selection from the shared Vue Flow instance (as GlossPanel does), then
+ * resolves the *live* domain node from the store so edits round-trip through
+ * undoable store actions. Operands for a rule are the element's inbound
+ * Information Links picked by Polarity — set those by wiring, not here.
+ */
+import { useVueFlow } from "@vue-flow/core"
+import { computed } from "vue"
+import type { EdgeData } from "@/model/projection"
+import type { ConverterNode, FlowNode, Rule, StockNode } from "@/model/types"
+import { useModelStore } from "@/store/model"
+
+const store = useModelStore()
+const { getSelectedNodes, getSelectedEdges } = useVueFlow("meadows")
+
+/** The single selected element's id — a node directly, or a Flow via its pipe edge. */
+const selectedId = computed<string | null>(() => {
+  const nodes = getSelectedNodes.value
+  const edges = getSelectedEdges.value
+  if (nodes.length === 1 && edges.length === 0) return nodes[0].id
+  if (edges.length === 1 && nodes.length === 0) {
+    const edge = edges[0]
+    if ((edge.data as EdgeData | undefined)?.kind === "pipe") return edge.id.split("::")[0]
+  }
+  return null
+})
+
+/** The live, editable domain node behind the selection (Clouds are not editable). */
+const element = computed<StockNode | FlowNode | ConverterNode | null>(() => {
+  const id = selectedId.value
+  if (!id) return null
+  const node = store.model.nodes.find((n) => n.id === id)
+  if (node?.kind === "stock" || node?.kind === "flow" || node?.kind === "converter") return node
+  return null
+})
+
+const KIND_LABEL = { stock: "Stock", flow: "Flow", converter: "Converter" } as const
+
+/** Every rule carries exactly one number (a value or a factor); read it uniformly. */
+function ruleNumber(rule?: Rule): number {
+  if (!rule) return 0
+  return rule.kind === "constant" ? rule.value : rule.factor
+}
+
+function buildRule(kind: Rule["kind"], n: number): Rule {
+  return kind === "constant" ? { kind, value: n } : { kind, factor: n }
+}
+
+function onInitial(event: Event): void {
+  const el = element.value
+  if (el?.kind !== "stock") return
+  const raw = (event.target as HTMLInputElement).value.trim()
+  if (raw === "") return store.setInitialValue(el.id, undefined)
+  const n = Number(raw)
+  if (Number.isFinite(n)) store.setInitialValue(el.id, n)
+}
+
+function onKind(event: Event): void {
+  const el = element.value
+  if (el?.kind !== "flow" && el?.kind !== "converter") return
+  const kind = (event.target as HTMLSelectElement).value as Rule["kind"] | ""
+  if (!kind) return
+  // Carry the existing number across a kind change; default a fresh rule sensibly.
+  const n = el.rule ? ruleNumber(el.rule) : kind === "constant" ? 0 : 1
+  store.setRule(el.id, buildRule(kind, n))
+}
+
+function onParam(event: Event): void {
+  const el = element.value
+  if ((el?.kind !== "flow" && el?.kind !== "converter") || !el.rule) return
+  const n = Number((event.target as HTMLInputElement).value)
+  store.setRule(el.id, buildRule(el.rule.kind, Number.isFinite(n) ? n : 0))
+}
+
+/** One-line reminder of where a rule reads its operands (they come from links). */
+const RULE_HINT: Record<Rule["kind"], string> = {
+  constant: "A fixed number — no inputs.",
+  proportional: "rate = factor × its “+” inputs.",
+  gap: "rate = factor × (level − target): the “+” input is the level, the “−” the target.",
+}
+</script>
+
+<template>
+  <div
+    v-if="element"
+    class="absolute top-3 right-3 z-20 w-60 rounded-box border border-base-300 bg-base-100/95 p-3 shadow-md backdrop-blur"
+  >
+    <div class="flex items-baseline gap-2">
+      <span class="text-sm font-semibold">{{ element.name }}</span>
+      <span class="text-xs text-base-content/50">{{ KIND_LABEL[element.kind] }}</span>
+    </div>
+
+    <!-- Stock: the quantity it starts from. -->
+    <label v-if="element.kind === 'stock'" class="mt-2 block">
+      <span class="text-xs text-base-content/60">Initial value</span>
+      <input
+        type="number"
+        class="input input-sm input-bordered mt-1 w-full"
+        :value="element.initialValue ?? ''"
+        placeholder="—"
+        @change="onInitial"
+      />
+    </label>
+
+    <!-- Flow / Converter: pick a rule, then its number. -->
+    <template v-else>
+      <label class="mt-2 block">
+        <span class="text-xs text-base-content/60">Rule</span>
+        <select
+          class="select select-sm select-bordered mt-1 w-full"
+          :value="element.rule?.kind ?? ''"
+          @change="onKind"
+        >
+          <option value="" disabled>Choose a rule…</option>
+          <option value="constant">Constant</option>
+          <option value="proportional">Proportional</option>
+          <option value="gap">Gap</option>
+        </select>
+      </label>
+
+      <label v-if="element.rule" class="mt-2 block">
+        <span class="text-xs text-base-content/60">
+          {{ element.rule.kind === "constant" ? "Value" : "Factor" }}
+        </span>
+        <input
+          type="number"
+          step="any"
+          class="input input-sm input-bordered mt-1 w-full"
+          :value="ruleNumber(element.rule)"
+          @change="onParam"
+        />
+      </label>
+
+      <p v-if="element.rule" class="mt-2 text-xs leading-snug text-base-content/50">
+        {{ RULE_HINT[element.rule.kind] }}
+      </p>
+    </template>
+  </div>
+</template>

src/components/ResultsPanel.vue

@@ -0,0 +1,176 @@
+<script setup lang="ts">
+/**
+ * Results panel (phase 2, ADR-0004) — what makes the Model *alive*: it runs the
+ * simulation and traces each Stock's value over time. Stocks are the system's
+ * memory, so their trajectories are the behaviour worth watching (the savings
+ * balance snowballs; the coffee settles toward room temperature).
+ *
+ * It reads the source-of-truth Model straight from the store and recomputes
+ * reactively, so editing a rule and reopening re-runs. When the Model is not yet
+ * sim-ready, it shows what is missing instead of a plot — the gap list doubles as
+ * a checklist for bringing a diagram to life. No charting dependency: the plot is
+ * a hand-built SVG (the same lean-substrate choice as the rest of the editor).
+ */
+import { computed } from "vue"
+import { checkSimReady, simulate } from "@/model/simulation"
+import { DEFAULT_SIM_SPEC, type SimSpec, type StockNode } from "@/model/types"
+import { useModelStore } from "@/store/model"
+
+defineEmits<{ close: [] }>()
+
+const store = useModelStore()
+
+const problems = computed(() => checkSimReady(store.model))
+
+/** The current run window; falls back to the default until the Model carries one. */
+const spec = computed<SimSpec>(() => store.model.sim ?? DEFAULT_SIM_SPEC)
+
+function onSpec(key: keyof SimSpec, event: Event): void {
+  const n = Number((event.target as HTMLInputElement).value)
+  if (!Number.isFinite(n) || (key === "dt" && n <= 0)) return
+  store.setSimSpec({ ...spec.value, [key]: n })
+}
+
+/** Distinct, legible track colours; cycled if a Model has more Stocks than these. */
+const COLORS = ["#2563eb", "#dc2626", "#16a34a", "#d97706", "#7c3aed", "#0891b2"]
+
+// SVG canvas in its own coordinate space; it stretches to the panel width, and
+// non-scaling strokes keep lines crisp under that non-uniform scale.
+const W = 600
+const H = 200
+const PAD = 12
+
+const chart = computed(() => {
+  if (problems.value.length > 0) return null
+  const run = simulate(store.model)
+  const stocks = store.model.nodes.filter((n): n is StockNode => n.kind === "stock")
+  const all = stocks.flatMap((s) => run.series.get(s.id) ?? [])
+  if (all.length === 0 || run.times.length < 2) return null
+
+  let min = Math.min(...all)
+  let max = Math.max(...all)
+  if (min === max) {
+    // A flat trajectory: pad so the line lands mid-panel instead of on an edge.
+    min -= 1
+    max += 1
+  }
+  const n = run.times.length
+  const x = (i: number) => PAD + (i / (n - 1)) * (W - 2 * PAD)
+  const y = (v: number) => PAD + (1 - (v - min) / (max - min)) * (H - 2 * PAD)
+
+  const lines = stocks.map((s, i) => {
+    const values = run.series.get(s.id) ?? []
+    return {
+      id: s.id,
+      name: s.name,
+      color: COLORS[i % COLORS.length],
+      points: values.map((v, j) => `${x(j).toFixed(1)},${y(v).toFixed(1)}`).join(" "),
+      last: values[values.length - 1] ?? 0,
+    }
+  })
+
+  return { lines, min, max, t0: run.times[0], t1: run.times[n - 1], diverged: run.diverged }
+})
+
+/** Compact numbers for axis ticks and the legend (e.g. 7039.99 → "7040"). */
+function fmt(value: number): string {
+  return Math.abs(value) >= 100 ? value.toFixed(0) : value.toFixed(2)
+}
+</script>
+
+<template>
+  <div
+    class="absolute inset-x-3 bottom-3 z-30 rounded-box border border-base-300 bg-base-100/95 p-3 shadow-lg backdrop-blur"
+  >
+    <div class="flex items-center gap-2">
+      <span class="text-sm font-semibold">Behaviour over time</span>
+      <span class="truncate text-xs text-base-content/50">{{ store.model.name }}</span>
+      <div class="ml-auto flex items-center gap-2 text-xs text-base-content/60">
+        <label class="flex items-center gap-1">
+          from
+          <input
+            type="number"
+            class="input input-xs input-bordered w-16"
+            :value="spec.start"
+            @change="onSpec('start', $event)"
+          />
+        </label>
+        <label class="flex items-center gap-1">
+          to
+          <input
+            type="number"
+            class="input input-xs input-bordered w-16"
+            :value="spec.stop"
+            @change="onSpec('stop', $event)"
+          />
+        </label>
+        <label class="flex items-center gap-1">
+          step
+          <input
+            type="number"
+            step="any"
+            min="0"
+            class="input input-xs input-bordered w-16"
+            :value="spec.dt"
+            @change="onSpec('dt', $event)"
+          />
+        </label>
+        <button
+          type="button"
+          class="btn btn-circle btn-ghost btn-xs"
+          aria-label="Close"
+          @click="$emit('close')"
+        >
+          ✕
+        </button>
+      </div>
+    </div>
+
+    <!-- Stopped early because values ran past what a float can hold. -->
+    <p v-if="chart?.diverged" class="mt-2 text-xs text-warning">
+      ⚠ Values grew beyond what can be plotted and the run stopped early — try a smaller step, a
+      smaller factor, or a Balancing loop to rein it in.
+    </p>
+
+    <!-- Sim-ready: the plot, with a legend of final values. -->
+    <div v-if="chart" class="mt-2 flex items-stretch gap-3">
+      <svg
+        :viewBox="`0 0 ${W} ${H}`"
+        preserveAspectRatio="none"
+        class="h-40 flex-1 rounded-md bg-base-200/40"
+        role="img"
+        aria-label="Stock values over time"
+      >
+        <text :x="PAD" :y="PAD" class="fill-base-content/40 text-[10px]">{{ fmt(chart.max) }}</text>
+        <text :x="PAD" :y="H - PAD / 2" class="fill-base-content/40 text-[10px]">
+          {{ fmt(chart.min) }}
+        </text>
+        <polyline
+          v-for="line in chart.lines"
+          :key="line.id"
+          :points="line.points"
+          fill="none"
+          :stroke="line.color"
+          stroke-width="2"
+          stroke-linejoin="round"
+          vector-effect="non-scaling-stroke"
+        />
+      </svg>
+      <ul class="flex w-44 flex-col gap-1 self-center text-xs">
+        <li v-for="line in chart.lines" :key="line.id" class="flex items-center gap-2">
+          <span class="size-2.5 shrink-0 rounded-full" :style="{ backgroundColor: line.color }" />
+          <span class="truncate">{{ line.name }}</span>
+          <span class="ml-auto font-mono text-base-content/60">{{ fmt(line.last) }}</span>
+        </li>
+      </ul>
+    </div>
+
+    <!-- Not sim-ready: what to fill in to bring it to life. -->
+    <div v-else class="mt-2 text-sm">
+      <p class="text-base-content/70">To bring this model to life, set:</p>
+      <ul class="mt-1 list-inside list-disc text-base-content/60">
+        <li v-for="(problem, i) in problems" :key="i">{{ problem }}</li>
+      </ul>
+    </div>
+  </div>
+</template>

src/store/model.ts

@@ -24,7 +24,15 @@ import {
   nextName,
 } from "@/model/factory"
 import { detectLoops } from "@/model/loops"
-import type { ConverterNode, Model, ModelNode, Position, StockNode } from "@/model/types"
+import type {
+  ConverterNode,
+  Model,
+  ModelNode,
+  Position,
+  Rule,
+  SimSpec,
+  StockNode,
+} from "@/model/types"
 import { canConnect, intentFor } from "@/model/validation"
 
 /** Ring-buffer depth for undo (F9 target: ≥50 steps). */
@@ -96,6 +104,47 @@ export const useModelStore = defineStore("model", () => {
     node.name = name
   }
 
+  /**
+   * Set (or clear) a Stock's initial value — the quantity the simulator starts
+   * from (ADR-0004). `undefined` un-equips it, sending the Model back to "not yet
+   * simulatable". No-op when unchanged, so a blur with no edit doesn't burn undo.
+   */
+  function setInitialValue(id: string, value: number | undefined): void {
+    const node = findNode(id)
+    if (!node || node.kind !== "stock" || node.initialValue === value) return
+    record()
+    if (value === undefined) delete node.initialValue
+    else node.initialValue = value
+  }
+
+  /**
+   * Set (or clear) how a Flow's rate or a Converter's value is computed (ADR-0004:
+   * one of the fixed rules, never a formula). No-op when unchanged.
+   */
+  function setRule(id: string, rule: Rule | undefined): void {
+    const node = findNode(id)
+    if (!node || (node.kind !== "flow" && node.kind !== "converter")) return
+    if (JSON.stringify(node.rule) === JSON.stringify(rule)) return
+    record()
+    if (rule === undefined) delete node.rule
+    else node.rule = rule
+  }
+
+  /** Set the run parameters (start / stop / dt). No-op when unchanged. */
+  function setSimSpec(spec: SimSpec): void {
+    const current = model.value.sim
+    if (
+      current &&
+      current.start === spec.start &&
+      current.stop === spec.stop &&
+      current.dt === spec.dt
+    ) {
+      return
+    }
+    record()
+    model.value.sim = spec
+  }
+
   /**
    * Create whatever source→target means under the structure guard: an
    * Information Link (default `+` polarity, F6) onto a Flow/Converter, or a Flow
@@ -229,6 +278,9 @@ export const useModelStore = defineStore("model", () => {
     beginInteraction,
     moveNode,
     renameNode,
+    setInitialValue,
+    setRule,
+    setSimSpec,
     removeNode,
     removeInfoLink,
     toggleLinkPolarity,