Why: RDM G1/G2 are blocked on four base capabilities - the member agent
cannot see published project knowledge inside a run, plugin commands are
unreachable as tools, members cannot see or open conversations in shared
projects, and the isolated exec tier needs a backend seam.
Evidence: SELF - code citations verified at Dev main (runmgr.go:726-736
owner-only Retrieve; hostcaps.go:64-66 owner-only search; server.go:438-441
owner-only listProjects; store/projects.go:124-130 owner-scoped conversation
creation); bwrap availability tested on this host (2026-10-09).
Impact: Docs only. New proposal docs/proposals/2026-10-09-ext-g1-b1-b3-exec-backend.md
registering EXT-13..EXT-16 per the compat-policy template; no code change.
Refs: RDM plan V1.1 sections 3.3/3.4/5.3; owner Q1-Q8 (Q4=option A, Q2)