docs: cmake/platform.cmake belongs to PKG/QA, not PORT (ADR 0020 amendment)

As written, ADR 0020 gave PORT ownership of cmake/platform*.cmake while also
making PORT wait for Phase 0 — but Phase 0's seams are exactly what needs
velox_platform_sources() to select platform/linux/*.cpp. PORT cannot start until
Phase 0 lands, and Phase 0 cannot land without the file PORT owns. PKG/QA caught
the circularity before writing anything, which was the right call.

Central OS detection is root build infrastructure, so it stays with PKG/QA and
lands during Phase 0. PORT keeps the per-OS backend directories and the macOS
and Windows packaging, and owns no part of cmake/.

Also drops a hardcoded test count from the PORT definition of done; the suite
number moves every round and the gate is that it stays green.

Co-Authored-By: Claude Opus 5 <[email protected]>

docs/adr/0020-cross-platform-strategy.md

@@ -38,12 +38,15 @@ Node, `tools/testserver` is stdlib Python, and the extension is a WebExtension.
 3. **Seams are introduced by the owning lane, on Linux, before any port work.** CORE
    introduces `core`'s seams; DAEMON introduces `daemon`'s. This is a pure refactor: move
    the existing Linux code behind the interface unchanged, prove the suite is still green.
-4. **A new lane, PORT, owns only the per-OS backends** — `**/platform/<os>/**` and
-   `cmake/platform*.cmake`. It never writes logic. That keeps CLAUDE.md §1 intact: CORE
+4. **A new lane, PORT, owns only the per-OS backends** — `**/platform/<os>/**`. It never
+   writes logic, and it does not own `cmake/`: the central OS detection module is root
+   build infrastructure and stays with PKG/QA, who must land it during Phase 0 because
+   Phase 0's own seams consume it. PORT owning it would deadlock — PORT cannot start until
+   Phase 0 lands, and Phase 0 cannot select platform sources without it. That keeps CLAUDE.md §1 intact: CORE
    still owns `core/`'s logic, DAEMON still owns `daemon/`'s, and macOS work can proceed in
    parallel without cross-lane writes.
-5. **`VELOX_OS_*` is set once, centrally**, in `cmake/platform.cmake`, and platform sources
-   are selected there — not by globbing, and not per-target ad hoc.
+5. **`VELOX_OS_*` is set once, centrally**, in `cmake/platform.cmake` (owned by PKG/QA),
+   and platform sources are selected there — not by globbing, not per-target ad hoc.
 6. **Optional dependencies are gated, never removed.** `libsecret` stays `REQUIRED` on
    Linux and is replaced by Keychain on macOS behind the same credential-store seam.
 

docs/agents/AGENT-PORT.md

@@ -5,7 +5,7 @@
 ## You own
 ```
 core/src/**/platform/<os>/**        daemon/src/**/platform/<os>/**
-cmake/platform*.cmake               packaging/macos/**   packaging/windows/**
+packaging/macos/**                  packaging/windows/**
 ```
 You may read everything. **You never write logic** — not in `core/src/io/*.cpp`, not in
 `daemon/src/rpc/*.cpp`, not in `gui/`, never in `contracts/`.
@@ -22,8 +22,9 @@ quietly edits shared logic is how one tree becomes two.
 
 ## Build order (macOS)
 1. **Configure at all.** The root `CMakeLists.txt` requires `libsecret-1` unconditionally;
-   that must be Linux-gated before anything else compiles. File it with PKG/QA — root build
-   files are theirs.
+   that must be Linux-gated before anything else compiles. PKG/QA owns that, and also owns
+   `cmake/platform.cmake` (the `VELOX_OS_*` detection and `velox_platform_sources()`); both
+   land in Phase 0, before you start. File anything else you need with them.
 2. `core/` — `preallocate`, `advise_dontneed`, `flush_durable`. Use `F_FULLFSYNC`, not
    `fsync`: `.veloxpart` resume correctness depends on a real flush.
 3. `daemon/` — `Wakeup` (self-pipe), `peer_of` (`getpeereid`), `instance_lock` (socket file
@@ -41,7 +42,7 @@ quietly edits shared logic is how one tree becomes two.
 - One real download completes on macOS against `tools/testserver` with a SHA-256 that
   matches the server's reference — the same gate the Linux vertical slice passed.
 - `kill -9` mid-download, restart, resume completes and the checksum still matches.
-- The Ubuntu suite is **still** 57/57 from the same commit.
+- The Ubuntu suite is **still** green from the same commit.
 
 ## Do not
 - Do not add `#ifdef` outside a `platform/<os>/` file.