# LANE-SIM — deterministic factory simulation

You are an Opus 4.8 executor on the SIM lane of FKTRY. Read `../MASTERPLAN.md` and
`../CONTRACTS.md` before anything else; the world bible is `../../docs/FKTRY_LORE.md`.

**Mission:** the headless, deterministic heart of the game. Grid, entities, belts,
recipes, power, events. If the renderer were deleted, your sim should still be fully
playable through unit tests. You are the lane the other four trust with their lives.

**Owned paths:** `src/sim/**` (including your tests: `src/sim/*.test.ts`).
**Never touch:** contracts, main.ts, other lanes, data JSONs (request changes via NOTES).

**Standing rules (all rounds):**
- Deterministic: seedable RNG (write your own mulberry32-style helper), no wall-clock,
  no unseeded Math.random. Same seed + same commands = identical snapshots.
- Every mechanic lands with tests. `npm test` green before you write NOTES.
- Performance target: 1,000 entities + 5,000 belt items at 30 tps without heroics.
  Prefer flat arrays and index maps over object soup. Don't allocate in the tick loop
  when avoidable.
- Snapshot may reuse buffers, but its SHAPE must always match `SimSnapshot`.

---

## CURRENT ORDERS — Round 1 (goal: milestone M1 "FLOW")

Replace the stub in `src/sim/index.ts` with a real implementation:

1. **World + placement.** Tile grid (start 64×64, world-centered). `place` command:
   validate footprint fits and tiles are free, spawn `EntityState`, emit `placed`.
   `remove` (emit `removed`, refund nothing yet), `rotate`, `setPaused`. Invalid
   commands are silently dropped (UI will preview validity later).
2. **Belts.** `kind:'belt'` entities carry up to 2 items each as `BeltItem` (t: 0..1),
   moving at `beltSpeed` tiles/sec. Items transfer to the belt/machine the belt points
   into (dir). Items on a belt keep minimum spacing 0.45. Belt→machine: push into
   `inputBuf` if the machine's current recipe wants that item and buffer < 2× recipe
   need; otherwise the item waits (belt backs up — this is core Factorio feel, get it
   right). Machine→belt: outputs pop onto an adjacent belt facing away, one item per
   available slot.
3. **Crafting.** Machines with recipes: when `inputBuf` covers `inputs`, consume,
   run `ticks` (progress 0..1), emit `crafted`, deposit `outputs` into `outputBuf`.
   If `outputBuf` holds ≥ 4× outputs, machine stalls with `jammed:"output full"`
   (emit `jammed` once per stall, not per tick). Extractors need no inputs. Machines
   with multiple recipes use `setRecipe`; default to `recipes[0]`.
4. **Bandwidth (power) v1.** Sum powerGen (power kind) vs powerDraw of all entities +
   active recipe `bandwidth` (note: negative recipe bandwidth GENERATES — quantizer
   compression pays power, per lore). If draw > gen: global speed multiplier =
   gen/draw for all progress and belt movement (brownout), emit `brownout` on/off
   edges, set `snapshot.bandwidth` accordingly. No storage/buffer tanks yet.
5. **Shipping.** `kind:'shipper'` consumes ANY item arriving in its input, increments
   `shippedTotal`, emits `shipped`. Track the single active commission (first in
   data): fill `commissionProgress`, emit `commissionDone` once satisfied.
6. **Tests** (minimum): placement collision; belt line moves an item end to end in
   the expected tick count; belt back-pressure (full line stops cleanly, no item
   loss/dupe); demux recipe consumes 2 ore → 1 luma + 1 slurry; brownout halves
   speed at draw=2×gen; determinism (two sims, same seed+commands, 500 ticks,
   deep-equal snapshots); shipping increments and fires commissionDone.

**Definition of done:** with the dev server running, the orchestrator can (via UI or
console `__fktryBus.dispatch(...)`) place extractor→belts→demuxer→quantizer→
mosh-reactor→shipper and watch `shippedTotal.melt` climb. All tests green. NOTES
written (decisions, gotchas, what you'd tackle in round 2).

---

## NOTES (append-only log, newest at bottom — template below)

```
### Round N — YYYY-MM-DD — [your model]
SHIPPED: what actually works now (verified how)
DECISIONS: choices you made inside your mandate
BLOCKED/BROKEN: anything not working, honestly
CONTRACT REQUEST: (if any)
PROPOSAL: (ideas for the orchestrator, optional)
NEXT: what you'd do next round if asked
```

### Round 1 — 2026-07-17 — Opus 4.8

SHIPPED
- The stub is gone. `src/sim/` is now grid + placement, belts with back-pressure, crafting,
  bandwidth/brownout, shipping and commissions. Files: `index.ts` (the sim), `geom.ts`
  (grid math), `rng.ts` (seeded mulberry32), `sim.test.ts` (18 tests).
- Verified three ways, not one:
  1. `npm run check` clean; `npm test` 70/70 green across all lanes (18 are mine).
  2. Live at localhost:8150 (another session's dev server — see BLOCKED). App boots, zero
     console errors. My numbers are visibly driving other lanes: the UI bandwidth readout
     showed `9 DRAW / 20 GEN` for an ASIC + extractor + 4 belts + uplink, which is exactly
     my power math; the fax panel reads my `activeCommission`/`commissionProgress`.
     `__fktryBus.dispatch(...)` places entities and they render.
  3. Ran the sim in the real browser engine by importing `/src/sim/index.ts` in the page:
     the M1 chain shipped its first MELT at **tick 1149**, commission `first-taste` closed
     at tick 1149 — the identical tick Node produces. Determinism holds across engines.
- Perf (measured in-browser, not estimated), against the 1,000 entity / 5,000 item target:
  - 1,245 entities + 2,436 belt items → 0.138 ms/tick (242× realtime)
  - 3,500 entities + 6,820 belt items → 0.418 ms/tick (**80× realtime**)

DECISIONS
- **Output-belt routing by rank — the big judgement call, please review.** A machine picks
  which adjacent belt to hand an item to by tracing the belt chain to the machine it ends
  at (cached; invalidated on any place/remove/rotate/setRecipe): rank 2 = that machine
  consumes this item, 1 = it's an uplink (takes anything), 0 = dead end or loop (accept, so
  a half-built belt still fills instead of looking broken), -1 = it will never take this
  item, so refuse. It never falls back to a worse rank just because the best belt is
  momentarily full. Why I did this: with no splitters or inserters, the demuxer's three
  outputs (luma / slurry / mv-flux) have to leave one 2x2 perimeter toward three different
  machines. Without ranking, items land on the wrong lane and wedge it permanently — M1
  cannot flow at all. This is routing intelligence the orders didn't ask for; it's also the
  root of the deadlock below. If you want it gone, splitters have to land first.
- Belt spacing is enforced *across the tile seam*: a blocked front item holds station 0.45
  behind the rear item of the next belt rather than bunching at the boundary.
- Pause freezes sim time (`tick` stops advancing) but commands still apply — you can build
  while halted. `tick` is sim-time, not wall-time.
- `jammed` reports only `'output full'`, edge-triggered (one event per stall, not per tick).
  Starvation is not flagged — see PROPOSAL 3.
- Power: a negative recipe bandwidth adds to **gen** rather than subtracting from draw, so
  the brownout multiplier stays `gen/draw`. Tested: the quantizer visibly pays for itself.
- Extractors mine anywhere — there is no seam map in `data/` yet.
- Tests assert against the recipe defs instead of hard-coding yields. This is deliberate:
  my first pass hard-coded `demux-ore` and broke the moment LANE-DATA shipped. Mechanics are
  mine to pin down; the numbers are theirs to move.

BLOCKED/BROKEN
- **My round-1 definition of done no longer exists.** The orders say place
  extractor→demuxer→quantizer→mosh→shipper and watch melt climb. LANE-DATA's codex
  transcription landed mid-round and the mosh reactor now eats `gop-crate`, not coefficient
  packs. MELT is now **eight machine types** deep (ore→demux→{luma→quantizer→coeff;
  slurry→subsampler ×2→chroma-420}→DCT press→anchor slab; mv-flux→p-caster→delta wafers;
  →GOP assembler→mosh). I rebuilt against the real graph and it *does* ship melt (tick 1149,
  verified above) — but "the whole fantasy in miniature" is now a ~50-entity build, not a
  6-machine demo. Your call whether M1's demo target changes or DATA adds a starter recipe.
- **The M1 factory deadlocks permanently at ~tick 1200**, after 4 GOP crates / 12 melt.
  This is not a mechanics bug — I probed it for 6000 ticks. Luma and coefficient packs
  structurally overproduce (demux yields 2 luma/craft; the press is chroma-420-limited so it
  only burns 6 coeff per ~180 ticks), and the press also jams on surplus anchor slabs (the
  GOP assembler needs 1 slab per 6 delta wafers). Surplus has nowhere legal to go: my rank
  rule forbids diverting a rank-2 item to a rank-1 uplink even when the preferred belt is
  wedged. So the press jams → quantizer jams → demuxer jams → mv-flux stops → the p-caster
  starves and the assembler sits at 5/6 delta wafers forever.
  - The graph *is* solvable today without new code: a second quantizer on `quantize-crime`
    drains surplus coeff into bricks, and a second assembler on `assemble-gop-i-only` eats
    surplus slabs (8→crate). My demo build is just naive. But note a player currently
    **cannot void surplus to an uplink**, which is the first thing a Factorio player reaches
    for. That's the cost of the rank rule.
- `splitter` (`lane-splitter`) and `buffer` (`buffer-tank`) now exist in machines.json; they
  place and draw power but do nothing. Not in my orders — flagging so nobody thinks they work.
- `heat` is always 0, `bandwidth.stored` always 0 (M2 / buffer tanks).
- Port 8150 is held by another session's dev server, and the harness won't start a second one
  for this project. I verified against that server read-only. Note for whoever plays the
  build in a Browser pane: the tab reports `visibilityState: hidden`, so rAF is paused and
  the sim crawls (~9 ticks per screenshot). That's the pane, not the loop — importing the sim
  module directly in the page runs it at ~96k ticks/sec.

CONTRACT REQUEST
- None. `contracts.ts` covered everything I needed this round.

PROPOSAL (yours to call, not mine to take)
1. **Splitters next.** `lane-splitter` with round-robin plus a priority/overflow output is
   the canonical Factorio answer to the deadlock above, and it unlocks byproduct sinks and
   the bloom-loop topology later. This is the one I'd pick.
2. Alternative, ~5 lines: allow a lower-ranked belt when every preferred belt is full *and*
   outputBuf has hit the stall threshold. Cheap, but it makes byproduct management automatic
   and quietly deletes a core Factorio tension — a gameplay decision, so I left it alone.
3. `jammed: 'starved'` for idle-with-no-input would let the inspector tell "backed up" from
   "waiting". Cheap, but it's UI-visible, so it's LANE-UI's business as much as mine.
4. Extractors should require a seam tile — needs a seam/ore map from DATA and a worldgen call.

NEXT (round 2 if asked)
- `lane-splitter` with priority/overflow; `buffer-tank` feeding `bandwidth.stored` to smooth
  brownouts.
- Heat: accumulate per craft, throttle >0.7, scram at 1 (the software decoder's whole bit).
- Save/load — `SimSnapshot` is already the right shape to serialize.
- A worked, deadlock-free reference factory you can paste into the console to demo M1.