fix(security): remove silent gradlew RCE, stop leaking VCS token and JWT, validate ARTEMIS_URL

[Mtze]

Summary

Fixes four issues from the security audit of the feat/env-var-passthrough work. The audited code (auto-gradlew prewarm, token-in-clone-URL, Theia Bearer injection, StompJs frame logging) exists only on feat/env-var-passthrough, not on main, so this PR targets that branch. Basing it on main would not touch the vulnerable code.

Changes are minimal and preserve normal UX for legitimate exercises.

1. HIGH - silent RCE via auto-executed ./gradlew

warmupGradleDaemon no longer runs the cloned repo's ./gradlew wrapper automatically. The student must explicitly confirm (non-modal prompt) before any repository-controlled Gradle build runs, and confirmation defaults to no - if ignored, nothing executes.

Choice: I went with explicit confirmation rather than a "trusted pinned Gradle" because any Gradle invocation against the repo (wrapper jar and build.gradle/settings.gradle) evaluates repository-controlled code, so a pinned binary would not remove the RCE. Confirmation is the least-disruptive option that is actually safe; prewarm stays available as opt-in.

2. MEDIUM - token in clone URL .git/config and argv

• The VCS token is no longer embedded as user:token@host in the clone URL (Artemis path now uses an HTTP Basic header), so it is out of the clone URL and the stored remote.
• The auth header is injected into the git process via GIT_CONFIG_COUNT/GIT_CONFIG_KEY_0/GIT_CONFIG_VALUE_0 env vars (git >= 2.31) instead of -c on the command line, so the token never appears in process arguments (ps).
• Removed the now-unused addVcsTokenToUrl helper.
• Residual risk (documented): to keep in-IDE fetch/push working (submitCurrentWorkspace().push()), the auth header is still persisted into .git/config after clone. A full move to an on-demand credential helper / GIT_ASKPASS with no on-disk token is deferred (see below).

3. MEDIUM - JWT logged

StompJs debug is now a no-op, so the CONNECT frame (which carries the Authorization Bearer JWT) is never written to the debug console.

4. INFERRED - unvalidated ARTEMIS_URL env override

ARTEMIS_URL is validated against the configured Artemis origin (scheme + host + port) before it is used as the API base. A mismatching value is rejected with an error message, so the Bearer token cannot be redirected to an untrusted host.

Tests

Added unit tests: clone auth handling (no token in argv, header via env, persisted to .git/config), the gradle confirmation gate (no build without explicit confirm), and ARTEMIS_URL validation. npm run build, eslint src and tsc --noEmit are green.

Deferred / product decisions

• No-on-disk-token credential flow (item 2): fully removing the token from .git/config requires reworking push/fetch to re-inject credentials on demand (e.g. GIT_ASKPASS or a credential helper). Larger change, deferred; current PR removes the URL and argv exposure.
• ARTEMIS_URL allowlist source (item 4): the allowlist is the configured scorpio.artemis.apiBaseUrl origin (packaged default https://artemis.cit.tum.de). Self-hosted deployments that point ARTEMIS_URL at a different host must ship a matching apiBaseUrl default, otherwise the override is rejected. Flagging in case a broader allowlist is wanted.

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