feat: AI moderation feature

[Alam-2U]

Description

Adds provider-agnostic AI moderation to forum-v2.

New threads and comments are classified by a configured AI backend. Content classified as spam is flagged, optionally deleted, and recorded in an audit log.

Forum provides the moderation interface and workflow, but does not include a specific AI provider. AI_MODERATION_BACKEND has no default; deployments configure the backend they want to use, and each backend handles its own provider-specific credentials and model settings.

What's Included

Moderation Pipeline

Located under forum/ai_moderation/:

• backends/base.py — Adds BaseModerationBackend as the backend interface and HTTPModerationBackend as a reusable base for JSON-over-HTTP providers. classify() returns {classification, reasoning, confidence_score, full_api_response} or None. Classification failures never raise exceptions, allowing posting to continue if moderation is unavailable.
• service.py — Runs the moderation workflow: classify → flag → optionally delete → audit-log. Spam verdicts are cached using a content hash to avoid repeated API calls for identical content. Clean verdicts are not cached.
• defaults.py — Provides provider-independent defaults, including a ready-to-use spam classification prompt.

Hook Points

The following operations trigger moderation after successful content creation: create_thread, create_parent_comment, create_child_comment.

Moderation runs inside a broad try/except. Any moderation failure is logged and does not cause the original post/comment creation to fail.

Data Model

Migration 0006 adds:

• is_spam boolean field to CommentThread and Comment, with indexes on is_spam, (course_id, is_spam), and (author, course_id, is_spam).
• ModerationAuditLog containing content body, full classifier response, reasoning, classification, actions taken, confidence score, original author, moderator_override, and override_reason.
• flag_content_as_spam and unflag_content_as_spam backend methods.

Flagged content is attributed to the configured AI moderation user through abuse_flaggers, allowing it to surface through the existing report path.

Admin

Adds is_spam to thread and comment list displays and filters. Adds a read-only ModerationAuditLog admin with search across author, moderator, reasoning, and body.

Documentation

Adds docs/how-tos/configure_ai_moderation.rst, covering backend implementation, required and optional settings, and enabling the course-level waffle flags.

Configuration

Required

Setting	Purpose
AI_MODERATION_BACKEND	Dotted path to the backend class
AI_MODERATION_API_URL	Provider endpoint
AI_MODERATION_USER_ID	User ID used to attribute flagging/deletion; the user is not auto-created

Optional

AI_MODERATION_SYSTEM_MESSAGE, AI_MODERATION_CONNECTION_TIMEOUT (1.0s), AI_MODERATION_READ_TIMEOUT (30s), AI_MODERATION_FLAGGED_CACHE_TTL (24h), AI_MODERATION_FLAGGED_CACHE_PREFIX.

Course Waffle Flags

Both flags are off by default: discussions.enable_ai_moderation, discussions.enable_ai_auto_delete_spam.

Testing

Added and updated tests covering service behaviour, caching, flagging, deletion, audit logging, failure handling, backend interface, and HTTP backend.

• tests/test_ai_moderation.py
• tests/test_ai_moderation_backends.py
• test_utils/moderation.py
• Extended tests/test_backends/test_mysql/test_api.py and tests/test_backends/test_mysql/test_models.py

Rollout

The feature has zero impact when unconfigured. With no AI_MODERATION_BACKEND configured and both waffle flags disabled, no moderation calls are made and existing forum behaviour remains unchanged.

AI moderation can be enabled on a per-course basis.

Related PRs

• Frontend app discussions: feat: AI moderation feature frontend-app-discussions#878
• OpenedX platform: feat: AI moderation feature openedx-platform#39036