[JacobStephens2]

Adds https://thirdshift.app/architecture/: six diagrams of how thirdshift works, drawn as a reference architecture.

1. The factory: the Day shift, your machine and GitHub, with thirdshift's seven numbered stages around the agent's Worktree. The same stages are listed in words below the figure.
2. A Run: where Ready issues come from (you, or thirdshift's own Architect runs, Security runs and Base fixes), then Prepare, the agent session, Deliver, Watch CI, Repair (at most 5) and Failed run.
3. A Merge run: Foreign commits and the Self-merge on the watched head.
4. A Spec run: Tickets as Merge runs into the Spec branch, then the Spec review and the Spec PR.
5. The Passes: Pickup, Architect and Security runs started by the OS scheduler.
6. Containment: from the outside in, your machine (ideally a VM with nothing from production on it), your user account, the Worktree (not a boundary), and the OS sandbox for target code, marked as proposed (Ship a tested sandbox runner for Security review proof-of-concept execution #726, thirdshift setup: check that Security sessions can sandbox target code on this machine #608, A sandboxed mode for Codex sessions #398). Below it, each layer's status.

How it's built

• The figures are static inline SVG with hand-placed coordinates and no library. The page needs no JavaScript and requests nothing from outside thirdshift.app; it uses the self-hosted fonts.
• The figures are drawn in the site's press inks: cyan for thirdshift, magenta for agent sessions, paper for results, and dashed paper for your machine. A shared key at the top explains the colours.
• Each SVG has a <title> that describes the figure in words. Each figure also has a numbered caption.
• Below 760px, a figure keeps a 720px width and scrolls sideways inside its frame, so the page itself never scrolls sideways.
• The page is linked from the homepage (credit line and footer), from the guide (nav, footer and the closing "Next" line) and from the videos page (nav and footer). It is also listed in sitemap.xml.

Tests

site/tests/pages.test.cjs adds /architecture/ to the public pages, which covers canonical URL, share metadata and the sitemap. It also adds tests that check:

• the homepage, the guide and the videos page link to the new page;
• there are six captioned figures, each with a description and unique SVG ids;
• the index links reach each figure;
• every local link and stylesheet resolves;
• the page fits at 320, 390, 768 and 1280px without JavaScript.

npm test in site/: 36 passed, 0 failed.