Session 15: Buy Max Prestige Upgrades (bulk-buy for prestige upgrades) + fix missing Stellar Essence spend

dev-journal.md

@@ -414,3 +414,31 @@ Wrote a headless Node.js test (`/opt/data/idle-game-test/buy-all-upgrades-test.m
 - Consider adding a "Buy Max" button to the prestige upgrades list as well.
 - Potential new building tiers or prestige milestones.
 - Sound variations or background music.
+
+---
+
+### Session 15 - 2026-08-24 (Morning)
+**Status:** ✅ Buy Max Prestige Upgrades (bulk-buy for prestige upgrades) Added
+
+#### What was done:
+- Followed up on Session 14's own "next goal" by adding a **Buy Max** button to the **Prestige Upgrades** list. Previously one-time prestige upgrades could only be purchased individually (one click each), which was tedious once several were available — buildings had Buy Max (Session 10) and regular upgrades had Buy All (Session 14), but prestige upgrades did not. This brings prestige upgrades in line with that established bulk-buy convention.
+- Added `Game.buyMaxPrestigeUpgrades()` to `js/game.js`. It loops through every entry in `PRESTIGE_UPGRADES`, skips owned ones, respects each upgrade's (optional) `requirements` building-count gate, and buys everything affordable at once from **Stellar Essence**. It runs until a full pass purchases nothing (loop kept for symmetry with `buyAllUpgrades` and to stay safe if future prestige upgrades gain requirement gates), then decrements `stellarEssence` per purchase (mirroring `PRESTIGE.buyUpgrade`) and returns `{ bought: count, ids: [...] }`.
+- Wired the button into the Prestige tab in `index.html` (`#buy-all-prestige`, placed alongside a left-aligned header row mirroring the Upgrades tab's Buy All layout). Added a click listener in `PrestigeUI.setupEventListeners()`.
+- Added `PrestigeUI.updateBuyMaxPrestigeButton()` (called from `PrestigeUI.update()` each tick) which shows/hides and enables/disables the button based on whether any unowned, requirement-met prestige upgrade is currently affordable with Stellar Essence — a read-only state check, exactly mirroring `UI.updateBuyAllButton()`.
+- Added CSS for `.prestige-upgrades-header` (flex layout) and `.prestige-buy-all` (gold accent theme reusing the existing `.buy-all-btn` base, matching the Upgrades tab's Buy All button).
+- **Bug found & fixed during testing:** the first implementation of `buyMaxPrestigeUpgrades()` added upgrades to the list but never decremented `stellarEssence`, which would have let players prestige-buy unlimited upgrades for free. The headless test asserted essence depletion and caught it; added the missing `this.state.stellarEssence -= upgrade.cost` line so spend mirrors `PRESTIGE.buyUpgrade`.
+
+#### Files modified:
+- `js/game.js` - added `buyMaxPrestigeUpgrades()` method (with correct Stellar Essence spend)
+- `js/prestigeUI.js` - added click listener for the Buy Max button + `updateBuyMaxPrestigeButton()`; called from `update()` each tick
+- `index.html` - added Buy Max button to the Prestige Upgrades header
+- `css/game.css` - `.prestige-upgrades-header`, `.prestige-buy-all` styles
+- `dev-journal.md` - appended Session 15 entry
+
+#### Verification:
+Wrote a headless Node.js test (`/opt/data/idle-game-test/prestige-buy-max-test.mjs`) that loads the real `game.js`, `prestige.js`, and `prestigeUI.js` in-process with DOM/audio/particle stubs. **22/22 checks pass**, covering: no-op when nothing affordable, bulk purchase deducting Stellar Essence correctly, ungated-upgrade behavior (real prestige upgrades have no requirement gates), idempotent second call, already-owned upgrade skipping, notification-on-purchase vs silence on no-op, the missing-essence-spend regression (now fixed), and the real `PrestigeUI.updateBuyMaxPrestigeButton()` show/hide/enabled state against actual `PRESTIGE_UPGRADES` data. All existing suites re-ran clean with no regressions: buy-all-upgrades 24/24, buy-max 6/6, golden-bloom 22/22, slot-preview 22/22. All modified JS files pass `node --check`.
+
+#### Next goals:
+- Potential new building tiers or prestige milestones / new prestige upgrades.
+- Sound variations or background music.
+- Consider a global "Buy Max" for buildings across all types at once (currently per-building).