Phase 19 — Capstone — Maintainer & Startup

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Don't Panic
Why this phase matters
What you'll learn
The map: where this lives in the real code
Labs in this phase
How to work this phase
Where you are

Don't Panic

You now understand the engine. The capstone turns understanding into a track record: land a real upstream PR, pass the staff interview loop, and (optionally) sketch a startup that's actually defensible. Don't Panic — you've already done the hard part; this phase is about leverage and judgment.

Why this phase matters

Knowledge without a public artifact is invisible. A merged PR, a benchmark writeup, and the mini_vllm engine you built ARE your portfolio. This phase is how you convert the last 18 phases into a maintainer reputation, a job, or a company.

What you'll learn

The contribution workflow: finding good-first-issues, duplicate checks, RFCs
vLLM's actual rules for AI-assisted contributions (read upstream/AGENTS.md!)
Writing a PR that gets merged: scope, tests, benchmarks, description
Code review etiquette and how trust accrues to maintainers
The staff competency map and the mock interview loop (see CAREER.md)
The startup playbook: where cost/moats live; build vs buy vs upstream

The map: where this lives in the real code

Open these in upstream/ (pinned to v0.22.1 @ 0decac0, see UPSTREAM_PIN.md). The deep-dive (01-deep-dive.md) walks through the important ones line by line.

AGENTS.md — vLLM's literal contribution policy (read it before any PR). Note: no pure code-agent PRs; disclose AI use; include tests + results; check for duplicates.
docs/contributing/ — The contributing guides.
[.buildkite/ and tests/](../upstream/.buildkite/ and tests/) — How CI is structured and what your PR must pass.
docs/design/ — Design docs / the kind of thinking RFCs require.

Labs in this phase

lab-01-find-and-scope-a-pr [CPU-OK] — issue triage as engineering: the five-check disqualification gauntlet, then the one-page implementation plan (invariants named, regression test planned, blast radius bounded, out-of-scope explicit) for the survivor.
lab-02-mock-staff-loop [CPU-OK] — the exit exam: four timed sessions (rapid-fire, deep-dive, a design scenario with shown arithmetic, two debugging trees), graded in three layers against the model answers and CAREER.md's competency map — honestly.

See labs/README.md for the exit criteria these two labs define.

How to work this phase

Read this guide for intuition.
Read 01-deep-dive.md with the upstream/ files open.
Do 02-mini-build.md — build the mini_vllm piece yourself.
Run the labs, then attempt EXERCISES.md.
Self-test with INTERVIEW.md; keep CHEATSHEET.md handy.

Where you are

This is one of the scaffolded phases: the guide, anchors, labs, exercises, and interview prompts are real and ready to study. The fully-worked, line-by-line treatment (with starter/ solution/test code in every lab) follows the gold-standard set by the flagship phases — Phase 02 · PagedAttention and Phase 03 · Continuous Batching. Use those two as the template for the depth to bring here.