flow: combinator library — tap, recover, map-flow + 11 tests (Phase 5 complete)

tap: side-effecting pass-through (returns input). recover: fail-VALUE counterpart
of try-catch (run node; on (fail r) run handler on r). map-flow: run a node over
each item of a list, join results sequentially. 116/116 across 7 suites.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/flow/scoreboard.md

@@ -1,6 +1,6 @@
 # flow-on-sx Scoreboard
 
-**All tests pass: 105 / 105 across 6 suites. Phases 1-4 complete; Phase 5 in progress.**
+**All tests pass: 116 / 116 across 7 suites. Phases 1-5 complete.**
 
 `bash lib/flow/conformance.sh`
 
@@ -14,6 +14,7 @@
 | recovery |  8  | Phase 3: crash recovery — store export/import, resumable scan, restart-at-every-step, replay-log survival |
 | distributed | 19 | Phase 4: `remote-node` (7); `remote-failover` (6); replication + handoff across instances (6) |
 | api |  12  | Phase 5: introspection — `flow/status`, `flow/result`, `flow/list`, `flow/pending` |
+| combinators | 11 | Phase 5: `tap` side-effect, `recover` (fail-value), `map-flow` fan-over-list |
 
 ## Architecture
 
@@ -43,6 +44,6 @@ capture the flow continuation directly.
 - [x] Phase 2 — Control flow + error handling (branch, error model, try-catch, retry, timeout)
 - [x] Phase 3 — Suspend/resume (suspend/resume/cancel + crash recovery via deterministic replay)
 - [x] Phase 4 — Distributed nodes via fed-sx (remote-node, failover, replication + handoff)
-- [~] Phase 5 — Operational API + combinators (introspection done; tap/recover/map-flow next)
+- [x] Phase 5 — Operational API + combinators (introspection, tap, recover, map-flow)
 - [ ] Phase 3 — Suspend / resume (the showcase)
 - [ ] Phase 4 — Distributed nodes via fed-sx