docs: kalenderen den anden vej, og én registrering til begge Google-ting

`caldav.md` beskrev to måder at sende opgaver *ud*. Den tredje er den modsatte
retning og hører til samme sted, fordi det er dér, man ville lede.

`configuration.md` hed "Gmail" og handler nu om Google: samme klient, to
redirect-URI'er, to API'er, to scopes. Bemærkningen om en Internal-app står
begge steder, fordi den gælder begge veje — og for én privat konto er
kalenderens egen hemmelige ICS-adresse den kortere vej. Intet i verdande
abonnerer på sådan en endnu.

README.md

@@ -96,15 +96,16 @@ Apple Reminders, forward mail into it, and add it to Claude as a connector.
 | Mail-to-task | Done, tested |
 | AI layer (Anthropic/OpenAI/Google/local) | Built, degrades when unconfigured |
 | Gmail: OAuth2 with PKCE, polling, one-way to tasks | Done, tested |
+| Google Calendar: read-only, laid over the task calendar | Built, never run against Google |
 | Update notice for administrators | Done, tested |
 | Personal API tokens | Done, tested |
 | OpenAPI 3.1 spec, checked against the router | Done, tested |
 | End-to-end smoke tests (Playwright) | Done |
 | Documentation, landing page, licence | Done |
 
-**Not finished:** Web Push, the AI providers and the Gmail API calls are
+**Not finished:** Web Push, the AI providers, and the Gmail and Google Calendar
-implemented against their specifications and have only ever been exercised there,
+API calls are implemented against their specifications and have only ever been
-not against live services. Everything else has an interface: opening a task shows
+exercised there, not against live services. Everything else has an interface: opening a task shows
 its description, sub-tasks, comments, files and reminders, and the settings pages
 cover the account, notifications, integrations, AI, API tokens, import, export and
 templates.

docs/caldav.md

@@ -1,13 +1,14 @@
 # Calendar and CalDAV
 
-Two ways to get your tasks into a calendar, and they are not the same thing.
+Two ways to get your tasks into a calendar, one way to get a calendar into
+verdande, and none of the three is the same thing.
 
-| | [Feed](#subscribing-to-a-feed) | [CalDAV](#connecting-a-caldav-client) |
+| | [Feed](#subscribing-to-a-feed) | [CalDAV](#connecting-a-caldav-client) | [Google Calendar](#showing-a-google-calendar-in-verdande) |
-|---|---|---|
+|---|---|---|---|
-| Direction | Read only | Two-way |
+| Direction | Tasks out, read only | Tasks out, two-way | Events **in**, read only |
-| Works with | Anything that subscribes to a URL | Apple Reminders, Thunderbird, DAVx⁵ |
+| Works with | Anything that subscribes to a URL | Apple Reminders, Thunderbird, DAVx⁵ | A Google account |
-| You can tick things off | No | Yes |
+| You can tick things off | No | Yes | No — an event is not a task |
-| Setup | Paste a URL | Username and token |
+| Setup | Paste a URL | Username and token | Connect, then pick calendars |
 
 ## Subscribing to a feed
 
@@ -39,6 +40,42 @@ most people actually keep.
     **Settings → Calendar feed → Rotate** issues a new one and breaks the old
     immediately.
 
+## Showing a Google calendar in verdande
+
+The two sections above send your tasks *out*. This is the other direction: your
+Google calendar drawn underneath them, so one screen answers "what does this day
+already have in it".
+
+**Settings → Integrations → Google Calendar → Connect**, then tick the calendars
+you want and press Save. They appear in **Calendar** in the sidebar, in Google's
+own colour for each one, beside your own tasks with due dates.
+
+It needs the same OAuth client Gmail uses, with the Calendar API enabled and the
+second redirect URI registered — see [Configuration](configuration.md#google).
+
+!!! warning "Read only"
+    verdande never writes to your Google calendar. An event cannot be dragged,
+    edited or ticked off here; clicking one opens it in Google, which is where it
+    can be changed. Your own tasks in the same grid still drag to another day as
+    they always have.
+
+    Writing would need the `calendar.events` scope and an answer to what should
+    happen when both sides moved the same meeting — which is a synchronisation
+    model rather than a scope, and it is deliberately not built yet.
+
+!!! note "The Internal client applies here too"
+    An OAuth client registered as *Internal* in a Google Workspace can only be
+    used by accounts in that workspace, calendars included. A personal
+    `@gmail.com` address is refused with `org_internal`. For one personal account
+    the shorter road is the calendar's own secret address: in Google Calendar,
+    **Settings → the calendar → Integrate calendar → Secret address in iCal
+    format**. Nothing in verdande subscribes to one yet — it is the next piece of
+    this feature.
+
+Events are kept for ninety days back and a year forward, refreshed every fifteen
+minutes and whenever you press **Fetch now**. Paging the grid past that window
+says so rather than showing an empty month.
+
 ## Connecting a CalDAV client
 
 This is the one where ticking something off in Apple Reminders ticks it off here.

docs/configuration.md

@@ -39,12 +39,24 @@ Any Go duration: `720h`, `30m`, `45s`.
     yourself, password resets are written to the log, and reminders arrive in the
     app and as Web Push rather than by email.
 
-## Gmail
+## Google
 
-Only needed if anyone will connect a mailbox. Register an OAuth client in Google
+Only needed if anyone will connect a Gmail mailbox or a Google calendar. One
-Cloud (**APIs & Services → Credentials → OAuth client ID → Web application**) with
+registration covers both: register an OAuth client in Google Cloud
-the redirect URI `https://your-address/oauth/gmail/callback`, enable the Gmail API,
+(**APIs & Services → Credentials → OAuth client ID → Web application**) and add
-and add the `gmail.readonly` scope.
+**both** redirect URIs:
+
+```
+https://your-address/oauth/gmail/callback
+https://your-address/oauth/calendar/callback
+```
+
+Then enable the APIs and scopes for whichever you want:
+
+| For | Enable | Scope |
+|---|---|---|
+| Mailboxes | Gmail API | `gmail.readonly` |
+| Calendar | Google Calendar API | `calendar.readonly` |
 
 | Variable | What it does |
 |---|---|
@@ -52,8 +64,15 @@ and add the `gmail.readonly` scope.
 | `VERDANDE_GMAIL_CLIENT_SECRET` | The client secret. |
 
 One registration serves every user on the instance; each person authorises their
-own mailbox from **Settings → Gmail**. The redirect URI is derived from
+own mailbox from **Settings → Integrations → Gmail** and their own calendar from
-`VERDANDE_BASE_URL`, so it cannot drift out of step with what you registered.
+**Settings → Integrations → Google Calendar**. Both redirect URIs are derived from
+`VERDANDE_BASE_URL`, so they cannot drift out of step with what you registered.
+
+!!! note "Two connections, two grants"
+    Connecting a calendar does not disturb a working Gmail connection, and
+    disconnecting one does not take the other with it. Google issues a refresh
+    token per authorisation and keeps up to a hundred of them live per account,
+    each carrying only the scopes it was granted with.
 
 ## Secrets
 

docs/mailboxes.md

@@ -16,7 +16,7 @@ administrator who can read yours.
 **Settings → Integrations → Gmail → Connect.**
 
 Gmail needs an OAuth client, which is the instance's registration with Google
-rather than anybody's account — see [Configuration](configuration.md#gmail).
+rather than anybody's account — see [Configuration](configuration.md#google).
 Once it is set up, each person connects their own mailbox through it.
 
 Choose what makes a task: