## Summary
Pure performance optimizations to the attack/conquer/cluster hot paths
in `src/core`, driven by the full-game perf harness from #4228. **No
behavior change**: the final game-state hash is identical before/after
on every config tested — world quick run (2 different seeds),
giantworldmap, and the default 1800-tick run.
### Changes
- **Flat-arithmetic neighbor iteration**: `forEachNeighbor` /
`forEachNeighborWithDiag` / `isBorder` / `isOceanShore` are now
implemented inside `GameMapImpl` using raw `ref±1` / `ref±width` index
math, skipping the per-neighbor `ref()` coordinate validation
(`Number.isInteger` etc.). `GameImpl` and `GameView` delegate.
- **New `neighbors4(ref, out)`**: zero-allocation, callback-free
neighbor query for hot loops (W, E, N, S — same order as
`forEachNeighbor`).
- **`AttackExecution`**: the per-tile closures in `tick()` /
`addNeighbors()` are replaced with reusable neighbor buffers, a cached
`GameMap` reference, and integer `smallID()` owner comparisons instead
of owner-object lookups.
- **`GameImpl`**: the per-conquer `updateBorders` closure is hoisted to
a method with a reusable buffer; `removeInactiveExecutions` compacts the
executions array in place instead of allocating a new ~4200-element
array every tick.
- **`PlayerExecution`**: `surroundedBySamePlayer` / `isSurrounded` /
`getCapturingPlayer` de-closured (`neighbors4` + integer compares;
neighbor visit order preserved, so `getCapturingPlayer`'s
Map-insertion-order tie-breaking is unchanged); flood-fill visit closure
hoisted out of the while loop.
- **`FlatBinaryHeap.dequeue`**: returns the tile directly instead of
allocating a `[tile, priority]` tuple per dequeued tile (AttackExecution
is the only caller).
### Performance (`npm run perf:game`, same machine, before → after)
| run | mean tick | ticks/sec | max tick |
|---|---|---|---|
| default (world, 400 bots, 1800 ticks) | 9.04 → **7.98 ms** | 111 →
**125** | 31.7 → 35.7 ms |
| giantworldmap, 600 ticks | 22.5 → **17.4 ms** | 44 → **58** | 52.8 →
**36.2 ms** |
The giantworldmap tail improvement (max tick −31%) is the most relevant
for the 100 ms tick budget.
### Determinism verification
Identical `Final hash` before and after on all configs:
| config | hash |
|---|---|
| `--map world --ticks 200 --bots 100` | `5455008589403520` |
| same + `--seed second-seed-check` | `5580840142777488` |
| `--map giantworldmap --ticks 600` | `37373734953428430` |
| default run | `26773450321979388` |
### Tests
- New `tests/NeighborIteration.test.ts` pins the exact neighbor
iteration orders (W,E,N,S cardinal; dx-major diagonal — conquest order
and RNG consumption depend on them) and conquer/border-tile invariants
checked mid-battle.
- New `tests/FlatBinaryHeap.test.ts` covers heap ordering, clear, and
growth.
- Full suite passes (122 files / 1386 tests + server tests); lint and
prettier clean.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Evan