Why: A member's agent cannot see published project knowledge inside a run
(runCtx.Retrieve and hostcaps.search are owner-only), and members can
neither see shared projects nor open conversations in them - both are P0
prerequisites for RDM G1 (EXT-13/EXT-15, proposal
2026-10-09-ext-g1-b1-b3-exec-backend).
Evidence: Red tests first - TestRunContextRetrieveShared (undefined
SetSharedKnowledgeAllow), TestInprocHostKnowledgeSearchShared (0 shared
hits), TestSharedProjectListAndConversation (empty list) all failed before
and pass after; go test ./... 32/32 packages ok.
Impact: runmgr gains SetSharedKnowledgeAllow and routes Retrieve through
RetrieveShared when the predicate is registered (nil = unchanged); hostcaps
search consults the same EXT-8 slot; GET /api/projects appends
adapter-authorized shared projects (projectView with shared flag, deduped);
POST /api/projects/{id}/conversations falls back to
CreateConversationInProject when the own-project path misses and the
adapter authorizes; store gains ListAllProjects (candidates only, callers
must filter through the adapter) and CreateConversationInProject.
Revocation takes effect immediately on both paths; absence of an adapter
is byte-for-byte the previous behavior. No pkg/extension surface change.
Refs: docs/proposals/2026-10-09-ext-g1-b1-b3-exec-backend.md (EXT-13, EXT-15)
