Detect NixOS host timezone automatically instead of defaulting to UTC

Enables services.automatic-timezoned so every host's clock/calendar
reflects its actual location with no manual timedatectl step or auth
prompt, since GNOME's own automatic-timezone toggle isn't wired to a
passwordless polkit rule on NixOS the way KDE's is.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/openspec/specs/automatic-timezone/spec.md b/openspec/specs/automatic-timezone/spec.md
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+# automatic-timezone Specification
+
+## Purpose
+
+Keeps every NixOS host's system timezone in sync with its actual physical location automatically, so the system clock, GNOME's clock/calendar, and log timestamps reflect local time without any manual `timedatectl` step.
+
+## Requirements
+
+### Requirement: NixOS hosts detect and apply their timezone automatically
+Every NixOS host built from this flake's shared system module SHALL determine its current timezone based on location and apply it to the system, without requiring the user to run a manual command or interactively authenticate the change.
+
+#### Scenario: Timezone is applied after boot with network access
+- **WHEN** a NixOS host built from this flake's shared system module boots with network connectivity available
+- **THEN** the system's active timezone is set to the timezone matching the host's current location, without any interactive prompt
+
+#### Scenario: No per-host opt-in required
+- **WHEN** a NixOS host is built from this flake's shared system module and its own `hosts/<name>/configuration.nix` does not configure timezone detection itself
+- **THEN** automatic timezone detection is still active, exactly as if it had been configured directly
+
+### Requirement: A host can still pin an explicit fixed timezone
+A NixOS host built from this flake SHALL be able to override automatic detection with a fixed, explicitly configured timezone when that host's own configuration requires one.
+
+#### Scenario: Host-level override takes effect
+- **WHEN** a host's own `hosts/<name>/configuration.nix` sets an explicit timezone at a priority higher than the shared default
+- **THEN** that host uses the explicitly configured timezone instead of an automatically detected one