Adds the `capture` MCP tool: the #55 relay for harnesses that cannot run
the use-case in-process (claude.ai Chat/Cowork/Design, Crush, Pi, LLM
Council). They reach it through the existing /mcp OAuth connector.
- Thin: forwards to the SAME CaptureService as POST /capture; holds no
state and retains nothing beyond the I5 audit record. The containment
properties accepted in infra security-baseline (I2 ledger) hold by
construction.
- Per-principal: ServeHTTP re-derives the caller's principal from the
Bearer header (the chassis middleware gates but discards it) and stashes
it in context; the tool resolves the trust-zone origin from it. A
caller-asserted harness/origin in the body is ignored — origin is
server-derived, so the I1 confidential refusal still fires for us-nexus
callers (claude.ai), and sovereign-allowlisted JWT principals pass.
- Registered only when WithCapture is wired (all three sites: tools(),
handleCall, package doc); main wires REST + MCP from the same service,
resolver, and credentials.
Tests: listed-only-when-wired, forwards-via-static-principal,
confidential-via-us-nexus-refused, confidential-via-sovereign-allowed,
unauthenticated-rejected, caller-cannot-forge-origin.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
