feat(ctl): filter frontend list by cluster id

[KannarFr]

What

sozu frontend list could only be narrowed by protocol and by domain. Answering "which frontends belong to this cluster, and what access-log tags do they carry?" meant dumping every frontend and filtering client-side.

FrontendFilters gains an optional cluster_id (proto tag 5), wired to sozu frontend list -i/--cluster-id <id>:

$ sozu frontend list -i MyCluster
┌─────────────────┬─────────────────┬─────────────┬──────────────────────────────────────────┬────────┬──────────┬────────────────────────────────────┐
│ HTTP frontends  │                 │             │                                          │        │          │                                    │
├─────────────────┼─────────────────┼─────────────┼──────────────────────────────────────────┼────────┼──────────┼────────────────────────────────────┤
│ cluster_id      │ address         │ hostname    │ path                                     │ method │ position │ tags                               │
├─────────────────┼─────────────────┼─────────────┼──────────────────────────────────────────┼────────┼──────────┼────────────────────────────────────┤
│ MyCluster       │ 127.0.0.1:18080 │ lolcatho.st │ PathRule { kind: Prefix, value: "/api" } │ None   │ 0        │ key=value, owner_id=MyOrganisation │
└─────────────────┴─────────────────┴─────────────┴──────────────────────────────────────────┴────────┴──────────┴────────────────────────────────────┘

ConfigState::list_frontends applies the filter to HTTP, HTTPS, TCP and UDP frontends, ANDed with the existing protocol and --domain filters. TCP and UDP frontends are keyed by cluster id in the state, so the filter is applied to the map key; HTTP/HTTPS frontends carry an optional cluster id, and a frontend that denies traffic (no cluster id) therefore never matches.

Protocol / security impact

• Protocol: additive proto change only — a new optional field on FrontendFilters at an unused tag. An older client omits it and gets the previous (unfiltered) behaviour; an older main process ignores it. No worker-facing message changes.
• Security: none. Read-only control-plane query, no new state mutation, no new network-facing parsing.

Tests

Added list_frontends_filters_by_cluster_id (command/src/state.rs), asserting both the positive and the negative space: the wanted frontend of every protocol is listed, no other cluster's frontend leaks through, an unknown id matches nothing, a Deny frontend is never selected, and cluster_id composes with (rather than replaces) the protocol and domain filters.

Commands run

cargo build --locked
cargo +nightly fmt --all -- --check
cargo clippy --all-targets --locked -- -D warnings
cargo test --locked -p sozu-command-lib -p sozu     # 306 passed, 5 ignored

Also exercised against a running proxy: frontend list -i MyCluster narrows a two-cluster state to one cluster's frontends, and frontend list -i nope returns nothing.

Docs

CHANGELOG.md — [Unreleased] / ✨ Added.

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