Implement control flow routing: on_false and on_success

[jeremymanning]

Problem

Issue #307 specifies advanced control flow routing that is missing from YAML pipeline specification:

steps:
  - id: check_input
    condition: "len(topic) > 10"
    on_false: short_topic_handler
    on_failure: error_recovery  
    on_success: main_processing

Solution Required

Implement complete control flow routing system:

1. Conditional Execution

• condition field with Python expression evaluation
• Runtime condition evaluation with pipeline variables
• Skip step execution when condition is False

2. Control Flow Routing

• on_false - next step when condition is False
• on_failure - next step when step execution fails
• on_success - next step when step completes successfully
• Default behavior when routing not specified

3. StateGraph Integration

• Modify LangGraph StateGraph to support conditional edges
• Dynamic routing based on execution results
• State management for complex control flows

Implementation Details

• Extend YAML compiler to parse routing attributes
• Modify StateGraph construction for conditional edges
• Add condition evaluation engine with variable access
• Implement routing decision logic in execution engine
• Compile-time validation of routing targets

Acceptance Criteria

• All 4 routing attributes supported in YAML
• Python condition expressions work with pipeline variables
• StateGraph properly routes based on execution results
• Compilation validation prevents invalid routing
• Tests cover complex control flow scenarios

Files to Modify

• src/orchestrator/compiler/yaml_compiler.py - YAML parsing
• src/orchestrator/execution/engine.py - Routing logic
• src/orchestrator/core/pipeline.py - StateGraph construction

Priority: High - Core specification requirement from #307

[jeremymanning]

No longer relevant after Claude Skills refactor (issue #426)

[jeremymanning]

Re-verified: 2 of 3 still missing.

grep -rn "on_false\|on_success" src --include='*.py' finds no routing implementation. on_failure does exist, so the remaining scope is on_false and on_success only — reduced from the original.

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Reopened during a repository-wide issue audit. This issue was closed on 2025-10-18 with "No longer relevant after Claude Skills refactor (issue #426)", but that refactor never shipped a working replacement — its compilers are orphaned and unreachable from orchestrator run (see the audit comment on #426). The gap described here is in the canonical YAMLCompiler path, which that refactor never touched. Evidence above was re-verified against main today.