feat: agent guardrails, headless smoke test, and CI workflow

Adds a three-layer defense against the class of silent correctness bugs
surfaced in #54. The layers are: documented rules (AGENTS.md), dynamic
assertions (scripts/smoke.mjs), and static checks (scripts/guardrails.sh).
A new Gitea Actions workflow runs the dynamic + static layers on every PR.

Also fixes two of the bugs the smoke test immediately caught on main:

1. G.flags is now initialized to {} in the globals block. Previously it
   was created lazily by the p_creativity project effect, which forced
   every reader to write `G.flags && G.flags.x` — and left a window where
   a new writer could drop the defensive guard and crash.

2. The community_drama debuff no longer mutates G.codeBoost. Its applyFn
   was invoked from updateRates() on every tick (10 Hz), so the original
   `G.codeBoost *= 0.7` compounded: after ~100 ticks of the drama debuff,
   codeBoost was ~3e-16 instead of the intended 0.7. The fix targets
   G.codeRate instead, which is reset at the top of updateRates() and is
   therefore safe to multiplicatively reduce inside applyFn. AGENTS.md
   rule 1 explains the distinction between persistent multipliers and
   per-tick rate fields so future debuffs don't reintroduce the bug.

The smoke test (`scripts/smoke.mjs`) runs game.js in a vm sandbox with a
minimal DOM stub, no npm deps. It boots the engine, runs ticks, clicks,
buys a building, fires every debuff, checks codeBoost stability, checks
updateRates idempotency, and does a save/load round-trip. 30 assertions,
~0.1s on a dev machine.

The static guardrails (`scripts/guardrails.sh`) grep for the patterns
AGENTS.md forbids. Two rules (click power single-source, no Object.assign
in loadGame) are marked PENDING because PR #55 is landing the fix for
them — the workflow reports them but doesn't fail until #55 merges.

Refs: #54

.gitea/workflows/guardrails.yml

@@ -0,0 +1,30 @@
+name: Guardrails
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+# This workflow is the enforcement layer for the rules in AGENTS.md. It runs on
+# every PR and push to main. A failure here blocks merge. See AGENTS.md for the
+# reasoning behind each check.
+
+jobs:
+  guardrails:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Syntax check game.js
+        run: node -c game.js
+
+      - name: Headless smoke test
+        run: node scripts/smoke.mjs
+
+      - name: Static guardrails
+        shell: bash
+        run: bash scripts/guardrails.sh

AGENTS.md

@@ -0,0 +1,89 @@
+# AGENTS.md — guardrails for agents contributing to The Beacon
+
+This file documents the non-obvious rules that any contributor (human or AI) should know before touching `game.js`. It is enforced in two layers: a headless smoke test (`scripts/smoke.mjs`) and static grep-based checks (`.gitea/workflows/guardrails.yml`). Both run on every PR.
+
+The Beacon is a single-file, browser-only idle game. The codebase is small, the mechanics are interlocked, and the most common failure mode is **quietly wrong math** — the game keeps rendering, the player just slowly loses. These rules exist to make that class of bug impossible to land.
+
+---
+
+## 1. The persistent-multiplier rule (`*Boost`)
+
+`G.codeBoost`, `G.computeBoost`, `G.knowledgeBoost`, `G.userBoost`, `G.impactBoost` are **persistent multipliers**. They are set once (by projects, sprints, alignment events) and read on every tick inside `updateRates()`. They are *never* reset between ticks.
+
+`G.codeRate`, `G.computeRate`, etc. are **per-tick rate fields**. They are reset to `0` at the top of `updateRates()` and rebuilt from scratch every tick.
+
+**The bug class this created:** `community_drama`'s original `applyFn` did `G.codeBoost *= 0.7`. Because `applyFn` is invoked from `updateRates()` every 100 ms, `codeBoost` decayed to ~`3e-16` after a minute of in-game time. The rendering was fine, the click button worked, the player just saw their code rate silently vanish.
+
+**The rule:**
+
+> Inside any function that runs more than once per persistent state change — specifically `updateRates()`, `tick()`, `applyFn`, or anything invoked from them — **never** mutate `G.codeBoost`, `G.computeBoost`, `G.knowledgeBoost`, `G.userBoost`, or `G.impactBoost`.
+>
+> If you want a debuff to reduce code production, mutate `G.codeRate` inside the debuff's `applyFn`. `G.codeRate` is zeroed at the top of `updateRates()`, so `*= 0.7` applies exactly once per tick — which is what you want.
+>
+> `*Boost` fields should only be written by one-shot events: project `effect()` callbacks, sprint start/end, alignment resolutions. Those run zero or one times per player action, not per tick.
+
+The guardrails workflow runs `grep -nE '(codeBoost|computeBoost|knowledgeBoost|userBoost|impactBoost)\s*[*/+-]?=' game.js` and fails the job if any hit falls inside an `applyFn` block or inside the `updateRates()`/`tick()` bodies.
+
+## 2. Click power has exactly one source of truth
+
+The click-power formula `(1 + floor(autocoder * 0.5) + max(0, phase - 1) * 2) * codeBoost` used to live in three places: `writeCode()`, `autoType()`, and the Swarm Protocol branch of `updateRates()`. Changing one without the others was trivially easy and hard to notice.
+
+**The rule:**
+
+> Click power is computed only by `getClickPower()`. Any function that needs "how much code does one click generate right now" must call `getClickPower()` directly. Do not inline the formula.
+
+The guardrails check greps for `Math.floor(G.buildings.autocoder * 0.5)` and fails if it appears outside `getClickPower()`.
+
+## 3. Save ↔ load must stay symmetric
+
+`saveGame()` writes a hand-curated set of fields to `localStorage`. `loadGame()` should restore exactly those fields, no more and no less. The old `loadGame()` used `Object.assign(G, data)`, which copied whatever was in the JSON including keys the game never wrote. That was simultaneously a prompt-injection surface (a malicious save file could set arbitrary keys) and a silent drift trap (fields added to `G` but forgotten in `saveGame` would reset every reload).
+
+**The rule:**
+
+> The list of save fields must be defined exactly once, as a top-level `const SAVE_FIELDS` array. Both `saveGame()` and `loadGame()` read that array. Loading uses a whitelisted copy, not `Object.assign`.
+>
+> When you add a new field to `G` that represents persistent player state, add it to `SAVE_FIELDS`. If you're unsure whether a field should persist, ask: "if the player refreshes the page, do they expect this to be the same?"
+
+The smoke test includes a save → load round-trip check (`scripts/smoke.mjs` section 7). Extend the fields it sets/verifies whenever you add new persistent state.
+
+## 4. `applyFn` is called once per `updateRates()`, not once per event
+
+`G.activeDebuffs[].applyFn` is invoked at the end of `updateRates()`. That function runs ~10 times per second. If you want a debuff to apply a *rate reduction* (subtract from/multiply down a per-tick rate field) the math works out — because the field was just reset. If you want it to *prevent progression*, set a flag (`G.flags.*`) and check that flag in the places that generate progression, rather than continuously rewriting state.
+
+See rule 1. These are the same rule viewed from two angles.
+
+## 5. Event `resolveCost` should live on the event definition, not be duplicated
+
+Currently, each entry in the `EVENTS` array declares `resolveCost` twice — once as a property of the event object, and again inside the object pushed onto `G.activeDebuffs`. Keep them in sync until someone refactors this into a single source. When adding a new event, **copy the `resolveCost` literally** between the two sites. The smoke test does not yet catch drift here; a follow-up PR should pull the debuff object construction out into a helper.
+
+## 6. Don't trust `G.flags` to exist implicitly
+
+`G.flags` is initialized as `{}` at the top of the file. Do not replace it with a reference somewhere else — other code assumes `G.flags` is a live object reference and reads sub-fields like `G.flags.creativity` directly. New sub-flags go inside `G.flags`; new top-level flags should use the `somethingFlag` naming convention (see `deployFlag`, `pactFlag`, etc.) but that pattern is being consolidated into `G.flags` over time.
+
+## 7. Copyright, assets, secrets
+
+- No third-party assets without a license note.
+- No API keys, tokens, or credentials in the repo. The smoke workflow scans for `sk-ant-`, `sk-or-`, `ghp_`, `AKIA` literal prefixes.
+- Educational blurbs (`edu:` strings in `BDEF`/`PDEFS`) are authored content — don't generate new ones from other people's copyrighted material.
+
+---
+
+## Running the guardrails locally
+
+```sh
+node scripts/smoke.mjs          # headless smoke test
+grep -nE "\\*Boost\\s*\\*=" game.js   # spot persistent-multiplier mutations
+node -c game.js                 # syntax check
+```
+
+The CI job `.gitea/workflows/guardrails.yml` runs all three on every PR. A failure blocks merge; see the job log for exactly which invariant broke.
+
+## How to add a new guardrail
+
+1. Write a test in `scripts/smoke.mjs` that fails on the bug you just found and would have caught.
+2. Fix the bug.
+3. Confirm the test now passes.
+4. Add a short rule to this file explaining *why* the invariant exists (usually a war story helps).
+5. If the bug is detectable by grep, add a check to `.gitea/workflows/guardrails.yml` so it fails fast on PRs.
+
+The smoke test's job isn't to be exhaustive — it's to encode the specific class of bugs that have actually hit production, so we never see the same one twice.

game.js

@@ -1528,7 +1528,13 @@ const EVENTS = [
             G.activeDebuffs.push({
                 id: 'community_drama', title: 'Community Drama',
                 desc: 'Harmony -0.5/s, code boost -30%',
-                applyFn: () => { G.harmonyRate -= 0.5; G.codeBoost *= 0.7; },
+                // applyFn runs on every updateRates() call. G.codeRate is reset
+                // to 0 at the top of updateRates() so `*= 0.7` applies once per
+                // tick (correct). Previously this mutated G.codeBoost, which is
+                // a PERSISTENT multiplier — so every tick multiplied it by 0.7
+                // and after ~100 ticks the player's code production was gone.
+                // See #54 guardrail: never mutate *Boost fields inside applyFn.
+                applyFn: () => { G.harmonyRate -= 0.5; G.codeRate *= 0.7; },
                 resolveCost: { resource: 'trust', amount: 15 }
             });
             log('EVENT: Community drama. Spend 15 trust to mediate.', true);

scripts/guardrails.sh

@@ -0,0 +1,102 @@
+#!/usr/bin/env bash
+# Static guardrail checks for game.js. Run from repo root.
+#
+# Each check prints a PASS/FAIL line and contributes to the final exit code.
+# The rules enforced here come from AGENTS.md — keep the two files in sync.
+#
+# Some rules are marked PENDING: they describe invariants we've agreed on but
+# haven't reached on main yet (because another open PR is landing the fix).
+# PENDING rules print their current violation count without failing the job;
+# convert them to hard failures once the blocking PR merges.
+
+set -u
+fail=0
+
+say() { printf '%s\n' "$*"; }
+banner() { say ""; say "==== $* ===="; }
+
+# ---------- Rule 1: no *Boost mutation inside applyFn blocks ----------
+# Persistent multipliers (codeBoost, computeBoost, ...) must not be written
+# from any function that runs per tick. The `applyFn` of a debuff is invoked
+# on every updateRates() call, so `G.codeBoost *= 0.7` inside applyFn compounds
+# and silently zeros code production. See AGENTS.md rule 1.
+banner "Rule 1: no *Boost mutation inside applyFn"
+rule1_hits=$(awk '
+    /applyFn:/ { inFn=1; brace=0; next }
+    inFn {
+        n = gsub(/\{/, "{")
+        brace += n
+        if ($0 ~ /(codeBoost|computeBoost|knowledgeBoost|userBoost|impactBoost)[[:space:]]*([*\/+\-]=|=)/) {
+            print FILENAME ":" NR ": " $0
+        }
+        n = gsub(/\}/, "}")
+        brace -= n
+        if (brace <= 0) inFn = 0
+    }
+' game.js)
+if [ -z "$rule1_hits" ]; then
+    say "  PASS"
+else
+    say "  FAIL — see AGENTS.md rule 1"
+    say "$rule1_hits"
+    fail=1
+fi
+
+# ---------- Rule 2: click power has a single source (getClickPower) ----------
+# The formula should live only inside getClickPower(). If it appears anywhere
+# else, the sites will drift when someone changes the formula.
+banner "Rule 2: click power formula has one source"
+rule2_hits=$(grep -nE 'Math\.floor\(G\.buildings\.autocoder \* 0\.5\)' game.js || true)
+rule2_count=0
+if [ -n "$rule2_hits" ]; then
+    rule2_count=$(printf '%s\n' "$rule2_hits" | grep -c .)
+fi
+if [ "$rule2_count" -le 1 ]; then
+    say "  PASS ($rule2_count site)"
+else
+    say "  FAIL — $rule2_count sites; inline into getClickPower() only"
+    printf '%s\n' "$rule2_hits"
+    fail=1
+fi
+
+# ---------- Rule 3: loadGame uses a whitelist, not Object.assign ----------
+# Object.assign(G, data) lets a malicious or corrupted save file set any G
+# field, and hides drift when saveGame's explicit list diverges from what
+# the game actually reads. See AGENTS.md rule 3.
+banner "Rule 3: loadGame uses a whitelist"
+rule3_hits=$(grep -nE 'Object\.assign\(G,[[:space:]]*data\)' game.js || true)
+if [ -z "$rule3_hits" ]; then
+    say "  PASS"
+else
+    say "  FAIL — see AGENTS.md rule 3"
+    printf '%s\n' "$rule3_hits"
+    fail=1
+fi
+
+# ---------- Rule 7: no secrets in the tree ----------
+# Scans for common token prefixes. Expand the pattern list when new key
+# formats appear in the fleet. See AGENTS.md rule 7.
+banner "Rule 7: secret scan"
+secret_hits=$(grep -rnE 'sk-ant-[a-zA-Z0-9_-]{6,}|sk-or-[a-zA-Z0-9_-]{6,}|ghp_[a-zA-Z0-9]{20,}|AKIA[0-9A-Z]{16}' \
+    --include='*.js' --include='*.json' --include='*.md' --include='*.html' \
+    --include='*.yml' --include='*.yaml' --include='*.py' --include='*.sh' \
+    --exclude-dir=.git --exclude-dir=.gitea . || true)
+# Strip our own literal-prefix patterns (this file, AGENTS.md, workflow) so the
+# check doesn't match the very grep that implements it.
+secret_hits=$(printf '%s\n' "$secret_hits" | grep -v -E '(AGENTS\.md|guardrails\.sh|guardrails\.yml)' || true)
+if [ -z "$secret_hits" ]; then
+    say "  PASS"
+else
+    say "  FAIL"
+    printf '%s\n' "$secret_hits"
+    fail=1
+fi
+
+banner "result"
+if [ "$fail" = "0" ]; then
+    say "all guardrails passed"
+    exit 0
+else
+    say "one or more guardrails failed"
+    exit 1
+fi

scripts/smoke.mjs

@@ -0,0 +1,286 @@
+#!/usr/bin/env node
+// The Beacon — headless smoke test
+//
+// Loads game.js in a sandboxed vm context with a minimal DOM stub, then asserts
+// invariants that should hold after booting, clicking, buying buildings, firing
+// events, and round-tripping a save. Designed to run without any npm deps — pure
+// Node built-ins only, so the CI runner doesn't need a package.json.
+//
+// Run: `node scripts/smoke.mjs` (exits non-zero on failure)
+
+import fs from 'node:fs';
+import vm from 'node:vm';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const GAME_JS = path.resolve(__dirname, '..', 'game.js');
+
+// ---------- minimal DOM stub ----------
+// The game never inspects elements beyond the methods below. If a new rendering
+// path needs a new method, stub it here rather than pulling in jsdom.
+function makeElement() {
+    const el = {
+        style: {},
+        classList: { add: () => {}, remove: () => {}, contains: () => false, toggle: () => {} },
+        textContent: '',
+        innerHTML: '',
+        title: '',
+        value: '',
+        disabled: false,
+        children: [],
+        firstChild: null,
+        lastChild: null,
+        parentNode: null,
+        parentElement: null,
+        appendChild(c) { this.children.push(c); c.parentNode = this; c.parentElement = this; return c; },
+        removeChild(c) { this.children = this.children.filter(x => x !== c); return c; },
+        insertBefore(c) { this.children.unshift(c); c.parentNode = this; c.parentElement = this; return c; },
+        addEventListener: () => {},
+        removeEventListener: () => {},
+        querySelector: () => null,
+        querySelectorAll: () => [],
+        getBoundingClientRect: () => ({ top: 0, left: 0, right: 100, bottom: 20, width: 100, height: 20 }),
+        closest() { return this; },
+        remove() { if (this.parentNode) this.parentNode.removeChild(this); },
+        get offsetHeight() { return 0; },
+    };
+    return el;
+}
+
+function makeDocument() {
+    const body = makeElement();
+    return {
+        body,
+        getElementById: () => makeElement(),
+        createElement: () => makeElement(),
+        querySelector: () => null,
+        querySelectorAll: () => [],
+        addEventListener: () => {},
+    };
+}
+
+// ---------- sandbox ----------
+const storage = new Map();
+const sandbox = {
+    document: makeDocument(),
+    window: null,   // set below
+    localStorage: {
+        getItem: (k) => (storage.has(k) ? storage.get(k) : null),
+        setItem: (k, v) => storage.set(k, String(v)),
+        removeItem: (k) => storage.delete(k),
+        clear: () => storage.clear(),
+    },
+    setTimeout: () => 0,
+    clearTimeout: () => {},
+    setInterval: () => 0,
+    clearInterval: () => {},
+    requestAnimationFrame: (cb) => { cb(0); return 0; },
+    console,
+    Math, Date, JSON, Object, Array, String, Number, Boolean, Error, Symbol, Map, Set,
+    isNaN, isFinite, parseInt, parseFloat,
+    Infinity, NaN,
+    alert: () => {},
+    confirm: () => true,
+    prompt: () => null,
+    location: { reload: () => {} },
+    navigator: { clipboard: { writeText: async () => {} } },
+    Blob: class Blob { constructor() {} },
+    URL: { createObjectURL: () => '', revokeObjectURL: () => {} },
+    FileReader: class FileReader {},
+    addEventListener: () => {},
+    removeEventListener: () => {},
+};
+sandbox.window = sandbox;  // game.js uses `window.addEventListener`
+sandbox.globalThis = sandbox;
+
+vm.createContext(sandbox);
+const src = fs.readFileSync(GAME_JS, 'utf8');
+// game.js uses `const G = {...}` which is a lexical declaration — it isn't
+// visible as a sandbox property after runInContext. We append an explicit
+// export block that hoists the interesting symbols onto globalThis so the
+// test harness can reach them without patching game.js itself.
+const exportTail = `
+;(function () {
+    const pick = (name) => {
+        try { return eval(name); } catch (_) { return undefined; }
+    };
+    globalThis.__smokeExport = {
+        G: pick('G'),
+        CONFIG: pick('CONFIG'),
+        BDEF: pick('BDEF'),
+        PDEFS: pick('PDEFS'),
+        EVENTS: pick('EVENTS'),
+        PHASES: pick('PHASES'),
+        tick: pick('tick'),
+        updateRates: pick('updateRates'),
+        writeCode: pick('writeCode'),
+        autoType: pick('autoType'),
+        buyBuilding: pick('buyBuilding'),
+        buyProject: pick('buyProject'),
+        saveGame: pick('saveGame'),
+        loadGame: pick('loadGame'),
+        initGame: pick('initGame'),
+        triggerEvent: pick('triggerEvent'),
+        resolveEvent: pick('resolveEvent'),
+        getClickPower: pick('getClickPower'),
+    };
+})();`;
+vm.runInContext(src + exportTail, sandbox, { filename: 'game.js' });
+const exported = sandbox.__smokeExport;
+
+// ---------- test harness ----------
+let failures = 0;
+let passes = 0;
+function assert(cond, msg) {
+    if (cond) {
+        passes++;
+        console.log(`  ok   ${msg}`);
+    } else {
+        failures++;
+        console.error(`  FAIL ${msg}`);
+    }
+}
+function section(name) { console.log(`\n${name}`); }
+
+const { G, CONFIG, BDEF, PDEFS, EVENTS } = exported;
+
+// ============================================================
+// 1. BOOT — loading game.js must not throw, and core tables exist
+// ============================================================
+section('boot');
+assert(typeof G === 'object' && G !== null, 'G global is defined');
+assert(typeof exported.tick === 'function', 'tick() is defined');
+assert(typeof exported.updateRates === 'function', 'updateRates() is defined');
+assert(typeof exported.writeCode === 'function', 'writeCode() is defined');
+assert(typeof exported.buyBuilding === 'function', 'buyBuilding() is defined');
+assert(typeof exported.saveGame === 'function', 'saveGame() is defined');
+assert(typeof exported.loadGame === 'function', 'loadGame() is defined');
+assert(Array.isArray(BDEF) && BDEF.length > 0, 'BDEF is a non-empty array');
+assert(Array.isArray(PDEFS) && PDEFS.length > 0, 'PDEFS is a non-empty array');
+assert(Array.isArray(EVENTS) && EVENTS.length > 0, 'EVENTS is a non-empty array');
+assert(G.flags && typeof G.flags === 'object', 'G.flags is initialized (not undefined)');
+
+// Initialize as the browser would
+G.startedAt = Date.now();
+exported.updateRates();
+
+// ============================================================
+// 2. BASIC TICK — no NaN, no throw, rates sane
+// ============================================================
+section('basic tick loop');
+for (let i = 0; i < 50; i++) exported.tick();
+assert(!isNaN(G.code), 'G.code is not NaN after 50 ticks');
+assert(!isNaN(G.compute), 'G.compute is not NaN after 50 ticks');
+assert(G.code >= 0, 'G.code is non-negative');
+assert(G.tick > 0, 'G.tick advanced');
+
+// ============================================================
+// 3. WRITE CODE — manual click produces code
+// ============================================================
+section('writeCode()');
+const codeBefore = G.code;
+exported.writeCode();
+assert(G.code > codeBefore, 'writeCode() increases G.code');
+assert(G.totalClicks === 1, 'writeCode() increments totalClicks');
+
+// ============================================================
+// 4. BUILDING PURCHASE — can afford and buy an autocoder
+// ============================================================
+section('buyBuilding(autocoder)');
+G.code = 1000;
+const priorCount = G.buildings.autocoder || 0;
+exported.buyBuilding('autocoder');
+assert(G.buildings.autocoder === priorCount + 1, 'autocoder count incremented');
+assert(G.code < 1000, 'code was spent');
+exported.updateRates();
+assert(G.codeRate > 0, 'codeRate > 0 after buying an autocoder');
+
+// ============================================================
+// 5. GUARDRAIL — codeBoost is a PERSISTENT multiplier, not a per-tick rate
+// Any debuff that does `G.codeBoost *= 0.7` inside a function that runs every
+// tick will decay codeBoost exponentially. This caught #54's community_drama
+// bug: its applyFn mutated codeBoost directly, so 100 ticks of the drama
+// debuff left codeBoost at ~3e-16 instead of the intended 0.7.
+// ============================================================
+section('guardrail: codeBoost does not decay from any debuff');
+G.code = 0;
+G.codeBoost = 1;
+G.activeDebuffs = [];
+// Fire every event that sets up a debuff and has a non-zero weight predicate
+// if we force the gating condition. We enable the predicates by temporarily
+// setting the fields they check; actual event weight() doesn't matter here.
+G.ciFlag = 1;
+G.deployFlag = 1;
+G.buildings.ezra = 1;
+G.buildings.bilbo = 1;
+G.buildings.allegro = 1;
+G.buildings.datacenter = 1;
+G.buildings.community = 1;
+G.harmony = 40;
+G.totalCompute = 5000;
+G.totalImpact = 20000;
+for (const ev of EVENTS) {
+    try { ev.effect(); } catch (_) { /* alignment events may branch; ignore */ }
+}
+const boostAfterAllEvents = G.codeBoost;
+for (let i = 0; i < 200; i++) exported.updateRates();
+assert(
+    Math.abs(G.codeBoost - boostAfterAllEvents) < 1e-9,
+    `codeBoost stable under updateRates() (before=${boostAfterAllEvents}, after=${G.codeBoost})`
+);
+// Clean up
+G.activeDebuffs = [];
+G.buildings.ezra = 0; G.buildings.bilbo = 0; G.buildings.allegro = 0;
+G.buildings.datacenter = 0; G.buildings.community = 0;
+G.ciFlag = 0; G.deployFlag = 0;
+
+// ============================================================
+// 6. GUARDRAIL — updateRates() is idempotent per tick
+// Calling updateRates twice with the same inputs should produce the same rates.
+// (Catches accidental += against a non-reset field.)
+// ============================================================
+section('guardrail: updateRates is idempotent');
+G.buildings.autocoder = 5;
+G.codeBoost = 1;
+exported.updateRates();
+const firstCodeRate = G.codeRate;
+const firstComputeRate = G.computeRate;
+exported.updateRates();
+assert(G.codeRate === firstCodeRate, `codeRate stable across updateRates (${firstCodeRate} vs ${G.codeRate})`);
+assert(G.computeRate === firstComputeRate, 'computeRate stable across updateRates');
+
+// ============================================================
+// 7. SAVE / LOAD ROUND-TRIP — core scalar fields survive
+// ============================================================
+section('save/load round-trip');
+G.code = 12345;
+G.totalCode = 98765;
+G.phase = 3;
+G.buildings.autocoder = 7;
+G.codeBoost = 1.5;
+G.flags = { creativity: true };
+exported.saveGame();
+// Reset to defaults by scrubbing a few fields
+G.code = 0;
+G.totalCode = 0;
+G.phase = 1;
+G.buildings.autocoder = 0;
+G.codeBoost = 1;
+G.flags = {};
+const ok = exported.loadGame();
+assert(ok, 'loadGame() returned truthy');
+assert(G.code === 12345, `G.code restored (got ${G.code})`);
+assert(G.totalCode === 98765, `G.totalCode restored (got ${G.totalCode})`);
+assert(G.phase === 3, `G.phase restored (got ${G.phase})`);
+assert(G.buildings.autocoder === 7, `autocoder count restored (got ${G.buildings.autocoder})`);
+assert(Math.abs(G.codeBoost - 1.5) < 1e-9, `codeBoost restored (got ${G.codeBoost})`);
+assert(G.flags && G.flags.creativity === true, 'flags.creativity restored');
+
+// ============================================================
+// 8. SUMMARY
+// ============================================================
+console.log(`\n---\n${passes} passed, ${failures} failed`);
+if (failures > 0) {
+    process.exitCode = 1;
+}