[PLT-3079] docs: add the unified eventing guide

[TheMostlyGreat]

Why

Developers need one accurate path through triggers, schedules, retained events, and signed outgoing webhooks before eventing can ship.

What

• adds one /build/eventing guide with the producer → event → subscription → delivery model
• includes scoped Dashboard and REST walkthroughs for Gmail and schedules
• documents signature verification, stable delivery IDs, retries, recovery/replay, retention, and cleanup
• adds executable guide and Python receiver contract tests

Verification

• focused eventing tests: 21/21 pass
• full docs suite: 873/873 pass
• lint and typecheck: clean
• production build: /en/build/eventing rendered successfully
• GitHub checks, including Vale and generated LLM text: green

Merge gate

Ready for review. Merge and publication remain intentionally gated on the corresponding Engine eventing release.

Linear: https://linear.app/arcadedev/issue/PLT-3079

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Note

Low Risk
Documentation, examples, and tests only; no runtime product code paths change.

Overview
Adds /en/build/eventing (“Events and webhooks”) to Build navigation with a new guide that walks from producers (triggers, schedules, provider ingress) through retained Arcade events to signed outgoing webhook delivery.

The page documents deployment origins, tenant scoping, HMAC webhook verification (with an embedded Python receiver.py sample), Dashboard/REST tutorials for schedules and Gmail filters, Slack/GitHub provider ingress, and operational topics (retries, recovery/replay, retention, stable webhook-id deduplication). The same receiver ships under examples/eventing/receiver.py, with Vitest checks that the MDX snippet matches the file and Python unittest coverage for signatures, rotation, idempotency, and handler rollback.

Also updates public/llms.txt for discoverability and ignores Python __pycache__/*.pyc in .gitignore.

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Project	Deployment	Actions	Updated
docs	Ready	Preview	Sep 1, 2026 8:36am UTC