[gregoreesmaa]

Closes #388.

What changed:

• mmap: MAP_SHARED -> MAP_PRIVATE (read-only view); wired Goldilocks release — releaseColdPages after scan+metrics at open/reload, releaseSettledPages on the onTick settled edge + Reduce Motion snap path; new pure goldilocksScrollWindow + GoldilocksWindow with unit + wiring-audit tests; strict benchmarks untouched.
• ViewportConfig: block_scroll_x [128]f32 inline (512 B copy per call) -> borrowed []const f32 slice over the app live table; layout/render/measure entry points take *const ViewportConfig (UnitCx borrows); all call sites + tests updated. Behavior identical (same reads, clamped the same way).
• macos.m: CodeBlockRecord.text[8192] x64 (512 KiB + per-frame 8 KB memcpy) -> borrowed ptr+len over DrawCommand/mmap bytes; ~8-entry NSFont cache (style+quantized size keyed, ARC retained); runs >= 511 B chunked into cacheable 448 B pieces (bounded 8 links, ~4 KiB) instead of fresh CTLineCreate+CFRelease every frame.
• macos_zatex.m: ZATEX_INPUT_CAP 65536 -> 4096 (60 KiB BSS saved incl. NFC buf); zatex_pos/zatex_gbuf 4096 -> 1024 each with over-cap run guards.

Verification (Windows host — macOS UI binary cannot build here):

• zig build test -Doptimize=ReleaseFast: identical before/after — hot module 13/13 pass; full suite blocked by pre-existing Windows-host errors (std.c void-param, AT.FDCWD, os.windows.OpenFile, simd.zig:58), byte-identical count (17 errors) on stashed baseline vs patched tree. No new failures introduced.
• Strict benchmarks: never loosened (no threshold touched); full benchmark run is platform-blocked here, needs macOS CI.
• size_gate.sh + screenshot_suite.sh: macOS-only (need Cocoa link + headless renderer); NOT run here — needs CI/macOS runner. Twin-delta therefore unquoted; expected direction: core __TEXT down slightly (config-by-pointer, borrowed code text), plugin untouched.
• Screenshots: not regenerated (platform-blocked); no rendering math changed — layout outputs flow the same values through pointers instead of copies, code-block copy path only affects clipboard bytes source.

RSS expectation: 50 MB file no longer stays ~50 MB resident after open; steady-state keeps viewport +/-1 screen. Behavior for typical docs unchanged.