fix(core): fold loopback hosts to 127.0.0.1 in tenant host normalization

[tonbistudio]

Problem

On any deployment with a loopback BUZZ_DOMAIN (e.g. the compose stack with BUZZ_DOMAIN=localhost), the desktop app connects fine but every managed-agent harness gets 404 Not Found on the WebSocket upgrade and exits with code 1.

The two sides disagree about loopback equivalence:

• Clients canonicalize. buzz-core::relay::normalize_relay_url rewrites every loopback host (localhost, [::1], 127.0.0.0/8) to 127.0.0.1. The desktop runs the workspace relay URL through it for the managed-agent runtime key (ManagedAgentRuntimeKey::new) and passes the canonicalized URL to the spawned harness as BUZZ_RELAY_URL (managed_agents/runtime.rs). buzz-auth's NIP-42 verification applies the same equivalence (nip42.rs normalize_relay_url).
• The relay compares literally. Host-based community resolution (buzz-core::tenant::normalize_host) does no loopback folding, so a community stored under localhost:3000 never matches a connection whose Host is 127.0.0.1:3000.

The repo already half-knows about this footgun — desktop/tests/helpers/seed.ts warns: "localhost != 127.0.0.1 to normalize_host — … or every /query 404s."

Reproduction: deploy deploy/compose with BUZZ_DOMAIN=localhost, add the community in the desktop app as ws://localhost:3000, start any managed agent. The app works; the agent harness logs initial relay connect failed with terminal error: WebSocket error: HTTP error: 404 Not Found and dies.

Fix

Fold loopback hosts (localhost, [::1], any 127.0.0.0/8 address) to the canonical 127.0.0.1 in normalize_host — the single normalization rule shared by storage (communities.host) and lookup — preserving explicit non-default ports. This mirrors the equivalence clients already apply, and it lands at the one choke point, so relay_url_authority (startup seeding, bind_deployment_community, buzz-admin) inherits it automatically.

Non-loopback hosts are unchanged; near-misses (localhost.example, 128.0.0.1) stay distinct tenants (covered by tests).

Tests

• buzz-core: new normalize_host_folds_loopback_variants and normalize_host_does_not_fold_non_loopback; existing tests that pinned the unfolded behavior updated ([::1] cases now use non-loopback IPv6 literals to keep testing bracket preservation).
• buzz-relay: new deployment_loopback_spellings_bind_to_one_community regression test — a community seeded from any loopback RELAY_URL spelling binds for all loopback connection hosts.
• cargo test -p buzz-core and cargo test -p buzz-relay --lib tenant pass.

Compatibility note

An existing deployment whose community row is stored under a localhost host key will, after this change, be ensured/looked up under 127.0.0.1. That is the intended convergence, but operators of existing loopback deployments will see a fresh deployment community unless stored loopback host rows are rewritten. If preferred, I can add a migration that folds existing stored loopback hosts — happy to take guidance from maintainers on which shape you want.

An alternative fix (passing the un-normalized URL to spawned harnesses) was considered and rejected: it only fixes the desktop's own agents, while this fixes all clients that canonicalize, and keeps the NIP-42 equivalence consistent end to end.

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