mara on #755: "e.g. /agent/name should show an error page stating
that the agent could not be found if missing in json or that it is
not reachable if we get a connection error. we dont want a fully
generic fallback, only for routes already special cased in the
nginx config."
Adds two static HTML pages built at deploy time via
`pkgs.runCommand "hyperhive-agent-error-pages"`:
- **not-found.html** — served when `/agent/<unknown>/...` hits the
bare `/agent/` catch-all. The catch-all `return 404`s, and
`error_page 404 = /__hive_agent_not_found` rewrites to the static
page.
- **unreachable.html** — served when `/agent/<known>/...` proxy_pass
to the harness returns 502 / 503 / 504. `proxy_intercept_errors
on` + `error_page 502 503 504 = /__hive_agent_unreachable` on each
per-agent location block rewrites to the static page.
Mechanics:
- `agentErrorPagesDir` (in the `let` block) is a `runCommand` that
emits two HTML files using a `<<EOF` heredoc — no template engine
needed.
- Two `internal` nginx locations (`= /__hive_agent_not_found`,
`= /__hive_agent_unreachable`) `alias` the exact files. `internal`
keeps the URIs unreachable from direct operator request — only
nginx's own error-handling can hit them.
- Per-agent location blocks pick up the `error_page` directive
through the existing `lib.mapAttrs'` over `agentPortsTable`. No
per-agent generated content; same static page for all.
- `/agent/` catch-all generates from a tiny optionalAttrs alongside
the per-agent block — both are no-op when the agent table is
empty (matches the pre-#15 shape).
Pages: minimal inline CSS, catppuccin palette matching the
dashboard (`#1e1e2e` bg, `#cdd6f4` text, `#cba6f7` not-found heading,
`#f9e2af` unreachable heading). No frontend-dist dependency — render
even when hive-c0re is down. Both link back to `/`.
Per mara's "only for routes already special cased" — scope stays
narrow. Forge / matrix / fluffychat keep nginx defaults; extending
the custom-error pattern to other vhosts is a separate follow-up
if/when needed.
Verified:
- nginx location attrset has `["/", "/agent/", "= /__hive_agent_not_found", "= /__hive_agent_unreachable"]`
- container toplevel builds clean (`nixos-system-hive-gateway-26.05pre-git`)
- `docs/gateway.md::Per-agent error pages` section captures the
design + rationale + intentional narrowness
Closes#755.
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