Verify random battle and capture routines against the original engine

docs/SESSION_HANDOFF.md

@@ -1,6 +1,6 @@
 # Recovered Claude session
 
-Latest continuation: see **Battle items, hBattleTurn and the stats screen: 2026-09-30**
+Latest continuation: see **Controlled capture comparisons: 2026-09-30**
 at the end of this file. Earlier sections are historical snapshots.
 
 Recovered on 2026-09-23 from the local Claude Code transcript
@@ -607,3 +607,83 @@ without it); 97 Chromium/WebKit browser tests passed, 19 skipped
 intentionally; native and reference builds; reference, release and
 vendor checks; `git diff --check`. Committed and pushed to `main` as
 `b13e09e`.
+
+## Controlled random battle comparisons: 2026-09-30
+
+Resumed from `be7575a` with a clean working tree. The user requested a bounded
+increment suitable for a limited session. Continued PLAN section 2 with
+accuracy, criticals and damage variation; capture stays as the next item.
+
+- `tests/reference-random.spec.ts` runs the original, unpatched
+  `BattleCommand_Critical`, `BattleCommand_CheckHit` and
+  `BattleCommand_DamageVariation` in the reference emulator. The native
+  commands receive the same ten-byte Link RNG stream. Results include the
+  final RNG stream/cursor, so extra or missing draws are detected too.
+- Per browser: 2,560 critical cases (all random bytes at all five reachable
+  stages and held-item exceptions), 2,914 accuracy cases (all stage pairs,
+  Foresight, BrightPowder, bypasses, Dream Eater/substitute and Jump Kick
+  miss damage), and 2,149 variation cases (0/1, rounding, 16-bit boundaries,
+  rejected draws and RNG stream regeneration).
+- Shared ROM input and symbol helpers moved from `reference-parity.spec.ts`
+  into `tests/reference-fixture.ts`. No ROM bytes or extracted assets added.
+- Deliberately changing critical `<` to `<=`, accuracy `>=` to `>`, and the
+  damage divisor from 255 to 256 each made its comparison fail. All three
+  mutations were reverted; no production gameplay change was needed.
+
+Boundary: these compare isolated commands with controlled random inputs.
+They do not compare a whole battle, the hardware-timed non-Link RNG, or the
+Protect text path. Lock-On/Fly/Dig remain refused. This does not enable Link
+battles or later maps.
+
+Checks: 337 unit tests passed with the local ROM; 131 passed and 206
+skipped with an absent ROM. All 103 Chromium/WebKit browser tests passed,
+with the existing 19 intentional WebKit skips. Native and reference builds,
+reference, vendor and release checks, and `git diff --check` passed. No CI
+or physical-device run. This increment was initially left uncommitted and
+is included in the subsequent capture-comparison delivery below.
+
+Next: controlled-input capture comparisons (`PokeBallEffect` and
+`GetPokeBallWobble`), then the party/bag menus outside battle, MOVE PKMN W/O
+MAIL and evolution. Keep section 2's capture checklist open until verified.
+
+
+## Controlled capture comparisons: 2026-09-30
+
+Continued PLAN section 2 from the existing uncommitted accuracy, critical and
+damage-variation comparisons. Preserved that work and completed its next
+capture-comparison item.
+
+- `tests/reference-capture.spec.ts` compares the native capture decision with
+  the calculation inside `PokeBallEffect`, then its shake loop with
+  `GetPokeBallWobble`. Per browser: 3,220 capture cases and 7,424 shake cases,
+  including supported ball multipliers, all catch-rate bytes, HP scaling and
+  overflow, status bonuses, equality boundaries, every random byte at each
+  wobble-table entry, every escape count and guaranteed catches. Final rate,
+  caught/escaped outcome, shake count and random-draw count agree.
+- Capture uses hardware `Random`, not `BattleRandom`. The private in-page ROM
+  copy replaces `Random` with a supplied-byte reader; the fixture enters
+  after the UI setup and inserts a return after `wWildMon` is written.
+  Catch arithmetic, multipliers and `GetPokeBallWobble` remain unmodified.
+- Extracted `rollCapture` and `ballWobbles` as private production helpers
+  called by `pokeBallEffect`, without changing gameplay behavior. Added
+  maximum HP 683 beside 342 in the synthetic divide-by-zero regression.
+- Deliberately changing success `<=` to `<`, formula floor to ceiling, and
+  shake `>=` to `>` each failed the comparisons. Mutations were reverted.
+
+Boundary: isolated capture decision/shakes with supplied random bytes, not
+hardware RNG timing, animation, caught-mon reloading, party/PC writes or a
+whole battle. No actual item has `HELD_CATCH_CHANCE`; that effect remains
+covered by pure vectors. Native division-by-zero refusal remains in place;
+the emulator fixture omits the hanging HP inputs. No additional balls or
+maps are enabled.
+
+Checks: 337 unit tests passed with the local ROM; 131 passed and 206 skipped
+with an absent ROM. All 107 Chromium/WebKit browser tests passed, with the
+existing 19 intentional WebKit skips. The four new capture tests skip cleanly
+without a ROM. Native and reference builds, reference, vendor and release
+checks, and `git diff --check` passed. No CI or physical-device run.
+The accuracy, critical, damage-variation and capture comparisons are delivered
+together, preserving the previously uncommitted work.
+
+Next: party and bag menus outside battle, MOVE PKMN W/O MAIL and evolution.
+PLAN section 2 is complete within its recorded acceptance boundaries.