feat(whaleflow): add mock executor skeleton

Add a crate-local mock executor over WorkflowSpec that records leaf, branch, and control-node results for Sequence, BranchSet, Leaf, Reduce, TeacherReview, LoopUntil, Cond, and Expand. Add reducer scaffolding for BranchTournament and ParetoFrontier, plus #2669 acceptance-style tests, without exposing workflow_run, spawning agents, or applying worktrees.

Refs #2669.
Harvests narrow WhaleFlow executor intent from #2482/#2486.

Co-authored-by: AdityaVG13 <44177453+AdityaVG13@users.noreply.github.com>

Author: Hmbown

CHANGELOG.md

@@ -40,7 +40,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   release-safe. The foundation now includes explicit `WorkflowSpec`,
   `WorkflowNode`, branch/leaf/policy metadata structs, plus serializable branch,
   leaf, and control-node result records toward the #2668 TraceStore contract.
-  Thanks @AdityaVG13 for the WhaleFlow draft and cost-tracking direction.
+  It also adds a crate-local mock executor skeleton for Sequence, BranchSet,
+  Leaf, Reduce, LoopUntil, Cond, Expand, BranchTournament, and ParetoFrontier
+  control flow so #2669 can progress without spawning agents, applying
+  worktrees, or exposing a `workflow_run` runtime tool yet. Thanks @AdityaVG13
+  for the WhaleFlow draft and cost-tracking direction.
 - Added a state-store v2 schema migration for WhaleFlow trace tables covering
   workflow, branch, leaf, control-node, and teacher-candidate runs. The
   migration creates persistence shape only; workflow execution and replay

crates/tui/CHANGELOG.md

@@ -40,7 +40,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   release-safe. The foundation now includes explicit `WorkflowSpec`,
   `WorkflowNode`, branch/leaf/policy metadata structs, plus serializable branch,
   leaf, and control-node result records toward the #2668 TraceStore contract.
-  Thanks @AdityaVG13 for the WhaleFlow draft and cost-tracking direction.
+  It also adds a crate-local mock executor skeleton for Sequence, BranchSet,
+  Leaf, Reduce, LoopUntil, Cond, Expand, BranchTournament, and ParetoFrontier
+  control flow so #2669 can progress without spawning agents, applying
+  worktrees, or exposing a `workflow_run` runtime tool yet. Thanks @AdityaVG13
+  for the WhaleFlow draft and cost-tracking direction.
 - Added a state-store v2 schema migration for WhaleFlow trace tables covering
   workflow, branch, leaf, control-node, and teacher-candidate runs. The
   migration creates persistence shape only; workflow execution and replay