docs(openspec): archive fpagent-installer-multiarch and sync specs

Bundle selection is now architecture-aware, not just codename-aware, and the
no-compatible-bundle failure names the host architecture. Merged into the
fpagent-installer spec and archived the change.

openspec/specs/fpagent-installer/spec.md

@@ -11,10 +11,13 @@ proxies the private release and serves the installer.
 ### Requirement: Public installer endpoint
 
 The app SHALL serve an installer script at `/fpagent/install.sh` that is
-reachable without authentication. When run, the script SHALL fetch the latest
-release metadata, choose a bundle for the host, verify the bundle's published
-sha256 checksum, extract it, and hand off to the extracted bundle's own
-installer. The script SHALL be served uncached.
+reachable without authentication. When run, the script SHALL determine the
+host's architecture, fetch the latest release metadata, choose the bundle for
+the host architecture, verify the bundle's published sha256 checksum, extract
+it, and hand off to the extracted bundle's own installer. It SHALL prefer a
+bundle built for the host's distro codename when one exists for that
+architecture, and otherwise use the generic bundle for that architecture. The
+script SHALL be served uncached.
 
 #### Scenario: Installer is fetched anonymously
 
@@ -33,6 +36,19 @@ installer. The script SHALL be served uncached.
   codename
 - **THEN** the installer uses the generic bundle
 
+#### Scenario: Bundle matches the host architecture
+
+- **WHEN** the latest release offers a bundle for the host architecture and a
+  bundle for another architecture
+- **THEN** the installer chooses the bundle for the host architecture
+- **AND** it never chooses a bundle for another architecture
+
+#### Scenario: 32-bit host uses the 32-bit bundle
+
+- **WHEN** the installer runs on an i386 host and the release offers only a
+  generic 32-bit bundle
+- **THEN** the installer uses that generic 32-bit bundle
+
 #### Scenario: Checksum is verified before extraction
 
 - **WHEN** the installer downloads a bundle and its published checksum
@@ -41,14 +57,21 @@ installer. The script SHALL be served uncached.
 
 #### Scenario: Options are forwarded to the bundled installer
 
-- **WHEN** the installer is invoked with options such as `--enable-service` or
+- **WHEN** the installer is invoked with options such as `--no-service` or
   `--check`
 - **THEN** it passes those options through to the extracted bundle's installer
 
 #### Scenario: No compatible bundle
 
 - **WHEN** the latest release contains no bundle for the host architecture
-- **THEN** the installer exits with a failure message and installs nothing
+- **THEN** the installer exits with a failure message that names the host
+  architecture and installs nothing
+
+#### Scenario: Unsupported architecture
+
+- **WHEN** the installer runs on a machine whose architecture is neither
+  x86_64 nor i386
+- **THEN** it exits with a failure message and installs nothing
 
 ### Requirement: Release metadata endpoint
 
@@ -175,16 +198,23 @@ tag that is not a valid release tag without contacting the forge.
 
 ### Requirement: Installed version is tracked and upgrades are reported
 
-The installer SHALL treat the git hash in the bundle's asset name as the version.
-It SHALL hand that version to the bundle installer, which SHALL record it beside
-the installed binary and SHALL report an upgrade with the previous and new
-versions on the next run. Uninstalling SHALL remove the recorded version.
+The installer SHALL treat the git hash in the bundle's asset name as the
+version, for every architecture it can install. It SHALL hand that version to
+the bundle installer, which SHALL record it beside the installed binary and
+SHALL report an upgrade with the previous and new versions on the next run.
+Uninstalling SHALL remove the recorded version.
 
 #### Scenario: Version is derived from the asset name
 
 - **WHEN** the installer selects a bundle named `fpagent-<hash>-<platform>.tar.gz`
 - **THEN** it uses `<hash>` as the version
 
+#### Scenario: Version is derived for a 32-bit bundle
+
+- **WHEN** the installer selects a generic bundle named
+  `fpagent-<hash>-linux-i386.tar.gz`
+- **THEN** it uses `<hash>` as the version
+
 #### Scenario: Upgrade is reported
 
 - **WHEN** the recorded version differs from the version being installed