feat(run): devstack-native task-graph runner (spec 31)

[gustavobertoi]

Summary

Second half of spec 31 / D19: a non-container task graph — run project commands with dependency ordering and parallelism.

What's in

• tasks: block on a project (command, run: host|exec, service, deps, workdir, env, watch) — validated via validator dive.
• internal/task — a pure DAG planner: transitive closure + Kahn layering, with cycle and unknown-task/dep detection; deterministic sorted layers.
• devstack run <task...> — resolves the active project, plans the graph, and runs layers in order with independent tasks in parallel (--parallel), streaming each task's output live and name-prefixed (mutex-serialized, race-free). run: host runs on the host toolchain; run: exec runs inside a service via compose exec. --dry-run prints the plan; --json supported. No flock — touches no shared/ledger state.

Verified

$ devstack run ci --dry-run
run plan for "app" (3 layer(s)):
  1: build, lint
  2: test
  3: ci
$ devstack run ci        # build+lint in parallel → test → ci, streamed + prefixed

Monorepo / Turborepo

The turborepo template (PR #118) runs turbo run in-container; or map package scripts into tasks: so devstack run owns the graph.

Tests / gates

Planner (linear / diamond / closure / cycle / unknown) + executor order + failure propagation, race-clean. make ci (fmt/vet/build/test-race) + make determinism green.

This completes spec 31. Remaining RFC work: spec 30 Phase 3 (the authoring TUIs).

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