Read the timetable from WebUntis

Schulcloud holds the material for a lesson but not the lesson: this school's
course `times` are empty and it publishes the schedule in WebUntis. So "what
do I have today, and has anything been cancelled" was unanswerable, and the
timetable cannot be typed into a prompt either — it changes daily.

core/untis.ts talks to the API the Untis Mobile app uses, and three tools sit
on it: untis_timetable (a day or a range, Entfall, Vertretung, room changes,
the notes on each period, inline homework, the period id), untis_homework (the
class register's list, which is not Schulcloud's tasks) and
untis_lesson_topics (what earlier lessons of a series actually covered, which
is what says where a subject got to).

Read-only, but not by the Schulcloud client's rule: this API is JSON-RPC, so
every call is a POST, reads included. READ_METHODS is the guarantee instead,
enforced at the single choke point and asserted by a test. It matters because
the key can do what the app can — the live account holds W_OWN_ABSENCE, so
the same key could report the user absent.

What the live instance taught us, all recorded in docs/API.md:

- `startDateTime` ends in Z and is local time. The 08:00 lesson reports
  08:00Z, so new Date() would move every lesson by an hour or two.
- A substitution is two periods, the original CANCELLED and the replacement
  IRREGULAR beside it, not one period with a changed teacher.
- Announced tests live in the period's info text. The exam module is unused
  here, so getExams2017 is always empty and that field carries the tests.
- A day with no lessons is not a holiday: the weeks this account spends in the
  company simply have no periods.
- `?v=i3.2` is required, or the call fails with a Java NPE reported as -8998.
  Errors arrive with HTTP 200 and an error member. -8504 is a rejected key and
  -8524 a drifting clock; the tools name both, because no retry fixes either.

Configuration is all four UNTIS_* values or none — three are identifiers and
the fourth is a credential, so a half-filled block is a paste that went wrong.
Without them the tools are not registered at all, since a tool that can only
fail is worse than a missing one. whoami reports the WebUntis identity and
survives a dead Schulcloud session, so "is the server reachable" no longer
gets a misleadingly total no. mcp-env.sh switches WebUntis off for a fixture
run: that key belongs to the real school.

224 tests. All 10 WebUntis smoke checks pass, with a key and without one; the
Schulcloud checks in those runs answer 401 because this machine's session is
logged out.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/context.ts

@@ -2,6 +2,7 @@ import type { Config } from './config.ts';
 import { SchulcloudClient } from './core/client.ts';
 import { FileManager } from './core/legacy-files.ts';
 import type { LegacyUser, MeResponse } from './core/types.ts';
+import { UntisClient } from './core/untis.ts';
 import type { Indexer } from './indexer/indexer.ts';
 import type { Store } from './store/store.ts';
 
@@ -20,6 +21,8 @@ export class ServerContext {
 	/** Shared across sessions; undefined when running without an index. */
 	readonly store: Store | undefined;
 	readonly indexer: Indexer | undefined;
+	/** WebUntis — the timetable — or undefined when the server has no key for it. */
+	readonly untis: UntisClient | undefined;
 	private identity: Promise<MeResponse> | undefined;
 	/**
 	 * id -> display name, for the whole session.
@@ -35,13 +38,20 @@ export class ServerContext {
 
 	constructor(
 		config: Config,
-		shared?: { client?: SchulcloudClient; files?: FileManager; store?: Store; indexer?: Indexer },
+		shared?: {
+			client?: SchulcloudClient;
+			files?: FileManager;
+			store?: Store;
+			indexer?: Indexer;
+			untis?: UntisClient;
+		},
 	) {
 		this.config = config;
 		this.client = shared?.client ?? new SchulcloudClient(config);
 		this.files = shared?.files ?? new FileManager(this.client);
 		this.store = shared?.store;
 		this.indexer = shared?.indexer;
+		this.untis = shared?.untis ?? (config.untis ? new UntisClient(config.untis, config.requestTimeoutMs) : undefined);
 	}
 
 	/** Cached `/me`. Shared promise, so concurrent first calls make one request. */