fix(flows): route flows run through the DAG-honoring swarm code preset

[RNT56]

The bug

nilcore flows run consumed a portable agentic-flows workflow by composing every agent_task node into a single newline-joined goal string and handing it to the decompose preset. decompose runs its children independently off HEAD and merges them in declaration order.

That silently collapsed the flow's DAG. The adapter correctly decodes each produces→requires dataflow edge into a real spawn.Subtask.DependsOn — but flattening the subtasks into a goal list threw those edges away. A dependent agent_task was then coded against the original tree instead of its dependency's output, which is exactly the structure a flow exists to express.

The fix

Route flows run through the verified swarm path with the code preset instead:

• Lift the agent_task subtasks into a planner.Tree — id / goal / DependsOn carried verbatim, plus the flow title + id@version provenance on the run goal.
• Dispatch through swarm's code preset (Shape=DAG, FanIn=merge, Role=implementer, packs software+code). Swarm honors the tree's DependsOn: a dependent shard runs in a later pass on the integrated tip of its dependencies, not HEAD — so the flow's structure survives.
• Completion stays verifier-owned (I2): each shard is pack-verified and the merged tip re-verified; no self-report ships.

Mechanics

• swarm.TreeSharder (+ a shared treeToShards) maps a pre-built planner.Tree onto run-namespaced shards, re-namespacing DependsOn (plan-task ids) onto Shard.Deps (shard ids) — the same mapping PlanSharder uses, minus the model call.
• swarmMain's tail is refactored into a reusable swarmRun(swarmDeps); swarmDeps gains an optional tree *planner.Tree seam consumed by buildInitialShards (falls back to the flag/preset sharder when nil — unchanged).
• flowsRun builds default swarm flags, forces preset=code + the flow's dir, and calls swarmRun with the injected tree. No new dispatch loop.

Invariants

Pure additive seam. I1 backend contract untouched; I2 preserved (verifier still owns "done"); no I3/I4/I5/I6/I7 surface changed. flows/swarm/agenticflows/docs file sets are disjoint from the currently-open #93.

Tests

• TestTreeSharderReNamespacesDeps — a 2-dep diamond (wire depends on scaffold+impl) maps onto swarm-<run>-{0,1,2} with Deps re-namespaced, routing carried, state queued.
• TestFlowRunPreservesDAGThroughSwarm — the full flow→flowTree→TreeSharder path keeps implement-depends-on-plan as a real Shard.Dep, and stamps title + id@version provenance on the run goal.

Gate

make verify (119 pkgs) · go vet · golangci-lint (0 issues) — all green locally.

🤖 Generated with Claude Code