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/changes/archive/2026-10-06-fpagent-installer-multiarch/specs/fpagent-installer/spec.md

@@ -0,0 +1,103 @@
+# Spec Delta
+
+## MODIFIED Requirements
+
+### 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 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
+
+- **WHEN** a client requests `/fpagent/install.sh` without a session
+- **THEN** the app returns the installer script and does not redirect to login
+
+#### Scenario: Host-appropriate bundle is chosen
+
+- **WHEN** the latest release offers both a bundle for the host's Ubuntu
+  codename and a generic bundle
+- **THEN** the installer uses the codename bundle
+
+#### Scenario: Generic bundle is the fallback
+
+- **WHEN** the latest release offers no bundle matching the host's Ubuntu
+  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
+- **THEN** it verifies the checksum before extracting and refuses to install
+  when the checksum does not match
+
+#### Scenario: Options are forwarded to the bundled installer
+
+- **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 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: Installed version is tracked and upgrades are reported
+
+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
+- **THEN** the bundle installer reports the change from the old to the new
+  version
+
+#### Scenario: First install records the version
+
+- **WHEN** no version has been recorded yet
+- **THEN** the bundle installer records the new version and reports no upgrade
+
+#### Scenario: Uninstall removes the recorded version
+
+- **WHEN** the installer is asked to uninstall
+- **THEN** the recorded version is removed