feat(agents): add dynaflow graph orchestration engine and control flow (#277, #278)

[Ashishds]

Summary

Implements the dynaflow graph orchestration engine runtime for the P1 — Orchestration engine milestone.

Changes

src/dynavec/agents/graph.py (new file)

• GraphState — typed shared-state dict with custom field reducers and isolated branch copies for concurrent execution
• BaseNode / FunctionNode — abstract node protocol + Python callable wrapping
• Edge — conditional transitions with safe AST expression parser (==, !=, <, <=, >, >=, in, and, or) — no eval() used
• add_conditional_edges() — state-driven router nodes
• add_parallel_branches() — concurrent fan-out with ThreadPoolExecutor + join barrier synchronization
• Bounded loops — iteration-capped with MaxIterationsExceededError runaway guards
• Cycle detection — DFS validator; permits guarded cycles, rejects malformed infinite cycles with GraphCycleError
• GraphResult / NodeTrace — per-node telemetry traces and timing

src/dynavec/agents/__init__.py (updated)

• Adds all new graph orchestration symbols; fully preserves all existing exports

tests/test_flow.py (new, 10 tests)

• Linear pipelines, state reducers, conditional branching (string + callable), parallel fan-out/join, bounded loops, max-iteration guard, cycle error validation, serialization

Test Results

[Kaap10]

LGTM. The graph orchestration runtime cleanly implements state reducers, safe expression routing without eval, parallel barrier execution, and bounded loop controls. Tested end-to-end with all unit tests and CI checks passing.