docs(runtime): record world environment ownership

docs/research/2026-07-26-slice-j6-1-environment-ownership.md

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+# Slice J6.1 — canonical world-environment ownership
+
+**Date:** 2026-07-26
+**Production commit:** `902076c0a42079596a8a273e9be402776cabf4b0`
+**Exact rollback:** `git revert 902076c0a42079596a8a273e9be402776cabf4b0`
+
+## Outcome
+
+`AcDream.Runtime` now owns one world-environment lifetime per client session:
+
+- an instance-scoped `DerethCalendar`;
+- the server-synchronized world clock;
+- weather progression and active weather state;
+- retail day-group selection;
+- AdminEnvirons state;
+- typed debug time and weather overrides.
+
+`AcDream.App` remains the graphical host. It converts immutable DAT sky
+definitions into the Runtime definition and maps Runtime's selected day-group
+index, clock, and weather snapshot into sky rendering. It does not own a
+second clock or weather state.
+
+The production path no longer mutates a process-global Region calendar origin.
+Two Runtime instances may therefore use different Region origins and server
+times without contaminating each other. Startup environment variables enter
+once through `RuntimeOptions`.
+
+## Retail mechanism
+
+- `SkyDesc::CalcPresentDayGroup @ 0x00500E10`
+- `CPlayerSystem::Handle_Admin__Environs @ 0x0055DE20`
+
+`SkyDayGroupSelector` preserves the named-retail ordered selection algorithm
+and its `0x6A42FDB2` pseudo-random multiplier. `DerethCalendar` preserves the
+existing retail epoch conversion while moving the mutable Region origin into
+the owning Runtime instance.
+
+No new retail divergence was introduced.
+
+## Automated evidence
+
+- Runtime: 332 passed.
+- App: 3,718 passed / 3 skipped.
+- Complete solution: 8,611 passed / 5 skipped.
+- Release build: 0 errors, 0 warnings.
+- Runtime dependency/source guards: passed.
+- Two-instance calendar, TimeSync, rollover/day-group, AdminEnvirons, debug
+  override, reset, and projection fixtures: passed.
+
+## Connected evidence
+
+Report:
+`logs/connected-world-gate-20260726-164602/report.json`
+
+The report records source and embedded binary commit
+`902076c0a42079596a8a273e9be402776cabf4b0`.
+
+- Capped process: 244.907 seconds, six checkpoints, graceful code-zero exit.
+- Uncapped fresh-process reconnect: 61.46 seconds, one checkpoint, graceful
+  code-zero exit.
+- Route: fresh login, Aerlinthe, Rynthid world edge, Facility Hub dungeon,
+  Holtburg, Aerlinthe revisit, then fresh-process reconnect.
+- Failures: zero.
+- Expected warning: 25 instrumented world-edge landblock misses.
+- Reveal invariant failures: zero.
+
+This proves the new environment owner preserves connected login, outdoor,
+world-edge, dungeon, revisit, disconnect, and reconnect behavior before J6.2
+moves the independent portal/reveal lifetime.