agentic-sx Phase 2: branch — one branch = one agent (TDD)

space handle (repo + relations Datalog db); spawn! = branch-from-briefing
with a genesis spawn commit at the fork point; commit! verb snapshots a full
worktree VALUE into a typed agent-commit and CAS-advances the branch (no
shared index — multi-agent safe). Topology: fork-point via merge-base,
agents from refs, typed edges sub-agent-of/reviews/merges. Session merges
always record a two-parent session-merge commit (no-ff); conflicts commit
nothing and conclude via merge-resolve!. 53/53 (118/118 total).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/agentic/scoreboard.md

@@ -5,4 +5,5 @@ _Generated by `lib/agentic/conformance.sh`_
 | Suite | Pass | Fail | Total |
 |-------|-----:|-----:|------:|
 | schema | 65 | 0 | 65 |
-| **Total** | **65** | **0** | **65** |
+| branch | 53 | 0 | 53 |
+| **Total** | **118** | **0** | **118** |