docs(1-getting-started): add opinionated MSSP walkthrough

[maximelb]

Summary

Comprehensive, opinionated walkthrough that a new MSSP can run their entire LimaCharlie POC off — docs/1-getting-started/mssp-walkthrough.md, 20 parts, ~2,660 lines, designed to be self-contained (the reader rarely needs to leave the page for the day-1 work).

Wired into the Getting Started nav (right after Core Concepts), linked from docs/1-getting-started/index.md, and cross-linked from the existing use-cases/mssp-msp-mdr.md overview as the practical companion.

Article structure

Uses a fictional MSSP (Northwind Security) with three sample customers (ACME, Globex, Initech) to keep examples concrete throughout.

1. Mental model — five primitives, four data streams (with sample event JSON, sample detect record), three access rules
2. Day 0 — regions, the internal control-org pattern, Unified Billing, billing math by source/size, Strict SSO from day zero
3. Control-org bootstrap — CLI, baseline Org API key (REST + permission grouping), JWT exchange, first Hive Secret, the standard MSSP extension kit (9 extensions)
4. Customer-org template anatomy — the 9 layers
5. What to connect in (telemetry) — sensor install commands for Windows EXE/MSI/PowerShell, Linux deb/binary, macOS; sleeper-mode end-to-end flow; full adapter YAML for M365/Okta/CloudTrail (S3+SQS); As-a-Service vs on-prem deployment options with systemd unit template; tag-based segmentation; Exfil Watch Rule examples; Day-1 telemetry smoke test per source
6. Detections in 30 minutes — Sigma → Soteria → Community Rules; top-10 EDR event types; 8 production-ready detection patterns (simple, nested boolean, stateful with-child, stateful with-events count/window, behavioral suppression-as-state, geo-lookup behavioral, threat-feed lookup, sensor-variable cross-rule state); FP rule layering; unit tests with full example; replay; common pitfalls
7. Queries and threat hunting (LCQL) — query shape, console/CLI/REST, cost estimation, 15 ready-to-use MSSP-baseline LCQL queries as a saved library, template-string reference, AI-agent integration
8. Alerting & Cases — full Cases config YAML (severity, SLA, auto-grouping, retention), case lifecycle CLI cookbook, tailored ingestion mode walkthrough, Slack/Teams/PagerDuty/Twilio fanout pattern, webhook with HMAC verification, real-time WebSocket
9. Outputs — four streams with sample event JSON; recommended pattern table; concrete output configs for S3 (with IAM policy), syslog/TLS, BigQuery (with custom_transform), webhook; allowlisting at the edge
10. Multi-tenant access — three rules, root-account pattern, five-OG model from mssp-demo (Administrators / Analysts / Viewers / Auditors / Break-Glass active-responders), permission groupings for automation use cases, full bash onboarding script, quarterly access verification script
11. NEW: Sensor commands and live response — top sensor commands by category, cross-fleet selectors, Reliable Tasking for offline sensors with full curl example, isolation as automated response action
12. NEW: Forensics and IR extensions — Artifact (WEL/MUL/PCAP), Dumper (memory), Velociraptor, Atomic Red Team for testing detections, YARA Manager, Payload Manager
13. NEW: Threat intelligence and lookups — Lookup Manager IaC with real public feeds (AlienVault, Tor, Talos), lookup-driven D&R, MSSP-managed soc-blocked-{ips,hashes,domains} pattern that turns one investigation into ongoing protection
14. AI: agentic SOC — D&R-driven vs user, lean-soc architecture mermaid + cost profile, full IaC YAML for triage and investigator agents with the production prompts from lc-ai, responder workflow snippets (isolation, IOC blocking, human-in-the-loop via Feedback ext), sample reporter daily report, mandatory cost guardrails, Bedrock/Vertex BYO-provider note
15. Infrastructure as Code — Infrastructure + Git Sync extensions, mssp-demo repo layout (concrete file tree with global/customers/templates), all.yaml, customer main.yaml with global+local includes, real installation_keys.yaml and outputs.yaml examples, secrets-as-references, bootstrap-from-existing-org, dry-run gating, Git Sync deploy-key setup commands, CI workflow example
16. Cost guardrails & operational hygiene — Usage Alerts IaC YAML, Sensor Cull rules, audit-review cadence, sleeper-when-idle, replay-before-prod, output billing per stream, FP-rate review loop
17. NEW: End-to-end 10-step smoke test — concrete validation with expected results for sensor connectivity, adapters, detections, cases, alert delivery, outputs, AI agents, IaC round-trip, audit forwarding, access verification
18. One-page onboarding playbook (target <60 min)
19. 12-month maturity ladder
20. Suggested next steps (10 reading priorities + 7 actions)

Stats

• 2,662 lines (was 813, +2,066 net insertions)
• 100+ internal cross-references, all verified to resolve
• Concrete bash, YAML, JSON, and config snippets throughout — no "see X" without showing X first when it matters

Test plan

• mkdocs builds cleanly
• Article renders correctly in the rendered site
• Nav entry "Starting an MSSP — Walkthrough" appears under Getting Started
• Link from use-cases/mssp-msp-mdr.md tip box works
• All ~100 internal cross-references resolve (verified locally)
• markdownlint-cli2 passes

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