refactor: add host and collection runtime sdk seams

docs/plugins/sdk-migration.md

@@ -127,7 +127,9 @@ is a small, self-contained module with a clear purpose and documented contract.
   | `plugin-sdk/channel-runtime` | Runtime wiring helpers | Channel runtime utilities |
   | `plugin-sdk/channel-send-result` | Send result types | Reply result types |
   | `plugin-sdk/runtime-store` | Persistent plugin storage | `createPluginRuntimeStore` |
+  | `plugin-sdk/collection-runtime` | Bounded cache helpers | `pruneMapToMaxSize` |
   | `plugin-sdk/fetch-runtime` | Wrapped fetch/proxy helpers | `resolveFetch`, proxy helpers |
+  | `plugin-sdk/host-runtime` | Host normalization helpers | `normalizeHostname`, `normalizeScpRemoteHost` |
   | `plugin-sdk/retry-runtime` | Retry helpers | `RetryConfig`, `retryAsync`, policy runners |
   | `plugin-sdk/allow-from` | Allowlist formatting | `formatAllowFromLowercase` |
   | `plugin-sdk/allowlist-resolution` | Allowlist input mapping | `mapAllowlistResolutionInputs` |

docs/plugins/sdk-overview.md

@@ -94,7 +94,9 @@ subpaths is in `scripts/lib/plugin-sdk-entrypoints.json`.
     | `plugin-sdk/runtime-store` | `createPluginRuntimeStore` |
     | `plugin-sdk/config-runtime` | Config load/write helpers |
     | `plugin-sdk/infra-runtime` | System event/heartbeat helpers |
+    | `plugin-sdk/collection-runtime` | Small bounded cache helpers |
     | `plugin-sdk/fetch-runtime` | Wrapped fetch, proxy, and pinned lookup helpers |
+    | `plugin-sdk/host-runtime` | Hostname and SCP host normalization helpers |
     | `plugin-sdk/retry-runtime` | Retry config and retry runner helpers |
     | `plugin-sdk/agent-runtime` | Agent dir/identity/workspace helpers |
     | `plugin-sdk/directory-runtime` | Config-backed directory query/dedup |