feat: compose authenticated stdio MCP with explicit runtime tool mapping

Assistant: codex
Assistant-Model: gpt-6-astra
Assistant-Session: 01a0e747-8f27-7242-8df8-8bc44f88c929

workplans/HUB-WP-0012-netkingdom-platform-root-access.md

@@ -347,6 +347,29 @@ sync and workflow YAML/shell syntax checks also pass.
 These are local source/release gates, not live platform or remote CI acceptance;
 T01–T04 remain `progress` and T06 remains open.
 
+## MCP caller continuation — 2026-09-28
+
+The standalone MCP runtime profile now advertises the four tools whose GET
+routes exist in the runtime. The other 27 remain explicit embedded-host tools;
+no legacy message/progress semantics are silently translated to native ports.
+
+Added rotating, bounded single-principal stdio credential-file composition.
+Enforced CLI network transports refuse startup pending an authenticated host;
+credential files cannot be attached to a shared network listener. SDK hosts
+retain per-invocation providers. Credential-bearing requests require HTTPS,
+disable redirects and ignore proxy environment variables. Facet arguments cannot
+inject paths or queries. Inventory rows record each tool's backend profiles.
+
+Actual tool-invocation tests cover concurrent caller isolation, credential
+rotation/removal, all four runtime route mappings and enforced backend denial.
+See the [MCP composition contract](../docs/owner-access-integration.md#mcp-caller-composition-and-backend-mapping).
+Validation: **350 tests pass** (one optional owner-source module skipped);
+inventory drift, distribution builds and isolated installed-wheel checks pass.
+The package gate caught reuse of an older same-version uv installation; it now
+forces a fresh environment and refreshes the Hub package, and the rerun passed.
+No credential was issued or retrieved and no consumer was switched. T04 remains
+`progress`; host authentication/exchange, real caller admission and T05 remain open.
+
 ## Acceptance checkpoints
 
 - [x] Architecture/source/runtime review captured; new implementation owner is hub-core