# Unit of Work Dependency — atheos-blog-lxc

**Stage**: INCEPTION — Units Generation (Part 2)

## Dependency matrix

Rows *depend on* columns.

| | U1 Guest | U2 Web stack | U3 Atheos | U4 Git+clone | U5 Docs |
|---|---|---|---|---|---|
| **U1 Guest** | — | — | — | — | — |
| **U2 Web stack** | ✔ | — | — | — | — |
| **U3 Atheos** | ✔ | ✔ | — | — | — |
| **U4 Git+clone** | ✔ (git) | — | ✔ (workspace) | — | — |
| **U5 Docs** | ✔ | ✔ | ✔ | ✔ | — |

## Build order

```
U1  ──►  U2  ──►  U3  ──►  U4  ──►  U5
 │                 ▲        │
 └─────────────────┴────────┘
      (U4 needs git from U1)
```

**Critical path**: U1 → U2 → U3 → U4 → U5. Strictly sequential — no parallelism worth the
coordination cost at this size. Each unit already includes a verification step, so a failure is
caught at unit granularity rather than at the end.

## Why these boundaries

| Boundary | Reason |
|---|---|
| U1 before everything | nothing can be installed without the guest |
| U2 (nginx+php) is one unit, not two | the **socket contract (I-1)** spans both — splitting them would create a boundary through a single interface, which is exactly where integration bugs live |
| U3 after U2 | Atheos has nothing to run on until PHP exists |
| U4 separate from U3 | **different failure class**: U3 is PHP-runtime risk (C-1); U4 is VCS/permissions risk. Separating them keeps a U3 failure from disguising itself as "git is broken" |
| U4 before U5 | the RUNBOOK must document the real remote command, which only exists after the clone |
| U5 last | docs describe what was actually built |

## Cross-unit risks

| Risk | Units | Note |
|---|---|---|
| FPM user identity | U2 → U3 → U4 | U2 resolves the run user; U3 sets ownership; U4 owns the key. **All three must agree on the same user** — a mismatch yields "dubious ownership" (I-3) |
| FPM socket path | U2 (internal) | must match across nginx + pool |
| Pinned Atheos SHA | U3 → U5 | U5's update script must re-pin the same mechanism |
| Remote URL | U4 → U5 | U5 documents it; U4 must not change it to SSH |