feat(host): Keychain and Credential Manager token stores, a macOS/Windows CI job (P11a step 0)

The agent path was Linux-only because tokens had a keyring store only
there (every other OS hit NOT_YET, so `connect` and the bridge failed).
D-56's destination is one installation for macOS, Windows and Linux.
Both new stores sit behind the same Items trait as the Secret Service,
so INVARIANT 4 (one account, one item, locked is an error) is kept once
and tested once through the file keyring. Windows credentials have a
unique target name, so a probe stands in for a search.

New dependencies (ledger-host only, target-gated): apple-native-keyring-store
(feature keychain) and windows-native-keyring-store, the stores the
keyring-core 1 API we already use is published with. No ledger-core change.

The `portable` job builds and tests the workspace on macos-latest and
windows-latest. Windows is allowed to fail: the rest of the host is
Unix-only (inventory in docs/packaging.md). Not verified locally: no
macOS or Windows target is installed; CI is the evidence.

Also pins cargo-packager, cargo-packager-updater and cargo-generate-rpm
in mise.toml for the trial, and records that the trial is not yet run.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

docs/packaging.md

@@ -0,0 +1,42 @@
+# Packaging and updates: the trial (P11a step 1)
+
+Status 2026-10-29: **the trial has not been run.** It needs clean Linux,
+macOS and Windows machines for the six formats (`.deb`, `.rpm`, AUR,
+AppImage, `.dmg`, NSIS `.exe`), and the one machine that built step 0 is a
+Linux desktop with neither a macOS nor a Windows target, no container
+runtime and none of the packager tools installed. The tools are pinned in
+`mise.toml` now (`cargo-packager` 0.11.8, `cargo-packager-updater` 0.2.3,
+`cargo-generate-rpm` 0.21.1), so the trial is `mise install` and the VMs.
+Nothing below is a result; it is what is known before the trial, and the
+table is filled by the person who runs it.
+
+| format | built by | installs as | updated by | signed by |
+|---|---|---|---|---|
+| `.deb` | `cargo packager` | (trial) | apt repository (step 3) | (trial) |
+| `.rpm` | `cargo-generate-rpm` | (trial) | dnf repository (step 3) | (trial) |
+| AUR `PKGBUILD` | hand-written | (trial) | the package manager | n/a |
+| AppImage | `cargo packager` | (trial) | `cargo-packager-updater` | (trial) |
+| `.dmg` | `cargo packager` | (trial) | `cargo-packager-updater` | Developer ID (step 5) |
+| NSIS `.exe` | `cargo packager` | (trial) | `cargo-packager-updater` | Windows identity (step 5) |
+
+## What step 0 found about the platforms (read before the macOS and Windows rows)
+
+The agent path was Linux-only because of the keyring. Step 0 adds the
+macOS login Keychain and the Windows Credential Manager behind
+`ledger-host/src/tokens.rs::Keeper`; CI (`portable` job) is the evidence.
+Beyond the keyring, the Windows host is a port, not a `cfg` gap. Today
+Unix-only, found by grep (2026-10-29):
+
+- `ledger-host`: `bridge`, `host`, `start`, `opener` and others are
+  `#[cfg(unix)]` modules; `host.rs`/`start.rs` use `setsid`, `umask`,
+  `close_range`, `geteuid`, Unix sockets and `libc` unguarded;
+  `commands.rs` calls `isatty`/`tcgetpgrp`.
+- `ledger-mcp`: the owner-only socket check reads peer credentials
+  (`SO_PEERCRED`, `getpeereid`); `admin`/`local` listen on Unix sockets.
+  Windows needs named pipes with a peer SID check (plan 3.9).
+- `ledger-store`: `ops.rs` takes `flock` locks; `root.rs` has no owner-only
+  DACL (`set_mode` is a no-op off Unix) and the data root falls back to
+  `%USERPROFILE%`, not the known-folder `%LOCALAPPDATA%`; `refuse.rs`
+  (seccomp) and `renameat2` are Linux-only (macOS needs its own
+  equivalents or `cfg` fences).
+- The `portable` job runs Windows as allowed-to-fail until that port lands.