docs(tt5): record macOS Tier-4 confirmation + Windows verification stance

- TT5: macOS is now fully covered — the full suite incl. Tier 4 ran green
  natively on macOS (4 flows + startup; Linux-only RSS test cfg-skipped).
- TT5 Windows wording: automated execution is the one open piece. A standing
  Windows CI runner is more involved than the Linux/macOS runners already in
  use; kept open with no timing promise. Interim: Windows builds ship every
  release and are verified by running the suite on Windows by hand periodically
  — the same builds, manually verified rather than per-push. TT5 stays [/] by
  deliberate scope. Framed in project terms, no host specifics.
- handoff-76 §6: macOS confirmation, the `pid` dead-code fix (1ffe11c), normal
  off-target crate downloads, and the Windows decision.

docs/handoff/20260622-handoff-76.md

@@ -96,3 +96,26 @@ managers + TT4 are post-tag → Unreleased.
   the two light-theme contrast bugs and the #39 schema-cache behaviour — both
   before finalizing).
 - Consider a `cargo sweep` at this milestone (release build added ~ a GB).
+
+## §6. Post-finalization (same session)
+
+- **macOS fully verified.** A native `cargo test` on macOS was fully green —
+  1813 lib + **5 `e2e_pty`** + 500 integration + 200 typing. This **confirms
+  Tier 4 on macOS** (the 4 flows + startup; the Linux-only RSS probe is
+  `#[cfg]`-skipped, hence 5 not 6). Closes the runda "Tier-4 unverified on macOS"
+  item.
+- **`fix(tt4)` `1ffe11c`** — the macOS run surfaced a `method `pid` is never
+  used` warning: `rss_kib` is Linux-only and was `pid`'s only caller, so off
+  Linux it was dead code. The Linux clippy gate can't catch this (pid *is* used
+  on Linux). Read `child.process_id()` inline; deleted the helper.
+- **Cross-platform crate downloads off-target are normal** — `cargo` fetches the
+  whole locked graph (Windows ConPTY bindings, Unix libc/nix from `portable-pty`)
+  but only compiles host-target crates; nothing off-target is actually built.
+- **TT5 / Windows decision (2026-06-22):** a permanent Windows CI runner stays
+  **open, no promises** — standing one up is more involved than the Linux/macOS
+  runners already in use. Interim: Windows builds ship every release (D1/D2) and
+  are **verified by running the suite on Windows by hand periodically** — the
+  same builds Windows users get, manually verified rather than per-push. The TT5
+  note was reworded to say this plainly and welcomingly; it stays `[/]` by
+  deliberate scope. (Virtualization options explored for a future runner are not
+  recorded here — they hinge on host specifics rather than project constraints.)