docs: add build + runtime network egress requirements

Lists the egress the build assumes (Go module proxy, toolchain download,
raw.githubusercontent for golangci-lint, github for non-proxied modules) and the
runtime assumes (LiteLLM gateway, brain-mcp, YouTube/Vimeo APIs, per-user BYO-AI
hosts only on opt-in), so a locked-down koala act_runner or dev env knows what to
allow or which GOPROXY to set. Notes the claude.ai sandbox allowlist is separate
and unrelated.

docs/homelab-integration.md

@@ -68,6 +68,49 @@ This maps directly onto the copied `llm` package: `Client` is the OpenAI-compati
   LiteLLM relocating from piguard into k3s/ai-stack on koala — **confirm current location** if
   latency or endpoint matters.
 
+## Network egress the build and runtime assume
+
+If the koala act_runner (or a dev environment) has locked-down egress, these must be reachable
+or the build/run fails. Split into build-time and runtime because they're different lists and
+fail at different stages.
+
+### Build-time (CI `check`/`build`, and local `go`/`task` work)
+
+- `proxy.golang.org`, `sum.golang.org` — Go module proxy + checksum DB. The default `GOPROXY`.
+  If a homelab GOPROXY (e.g. Athens) exists, point `GOPROXY` at it and this pair is not needed
+  directly — **confirm** whether one is run.
+- `go.dev`, `dl.google.com` — Go toolchain download (the CI `setup-go` step / `go-version-file`).
+  Not needed if the runner already has the matching Go installed.
+- `raw.githubusercontent.com` — the CI installs golangci-lint via its install script from here
+  (`.gitea/workflows/ci.yml`).
+- `github.com`, `codeload.github.com` — any module not served by the proxy (incl. golangci-lint
+  and, later, `golang.org/x/oauth2` and its deps) is fetched from GitHub.
+- `objects.githubusercontent.com` — GitHub release asset downloads (some installers redirect here).
+
+A configured `GOPROXY` collapses most of the module-fetch entries into one host. Recording the
+homelab's actual `GOPROXY`/`GONOSUMCHECK` policy here once known would remove the **confirm**.
+
+### Runtime (the running service)
+
+- `koala:4000` (or the NodePort / post-relocation address) — LiteLLM gateway, the Primary.
+- brain-mcp host (`*-mcp.d-ma.be`, **confirm**) — only when the brain sink is enabled.
+- `www.googleapis.com` / YouTube Data API + `oauth2.googleapis.com` (token exchange/refresh) —
+  the YouTube provider adapter.
+- `api.vimeo.com` — the Vimeo provider adapter.
+- BYO-AI endpoints, per configured provider and **only when a user opts in**:
+  `api.anthropic.com`, `api.openai.com`, `generativelanguage.googleapis.com`.
+- 1Password / ESO reach for secret resolution follows the homelab's existing ESO egress, not
+  Tapir-specific — no new rule expected.
+
+Note: a user with **no** BYO configured means the service never needs the third-party AI hosts
+(the local-first guarantee, `docs/use-cases/ai_routing.feature`). Don't allow them by default;
+allow per-provider when a user connects one.
+
+> The claude.ai chat sandbox (where planning sessions run code) has its **own** separate egress
+> allowlist — unrelated to koala. It blocked `go.dev` during scaffolding, which is why the
+> scaffold was reviewed but not compile-verified in-chat; verification belongs on koala via
+> `task check` regardless.
+
 ## Deployment / GitOps (when Tapir reaches deploy)
 
 - The homelab is **Flux GitOps**: manifests in `mathias/infra` under `k3s/`, Flux watches `main`.