[FEATURE] Advanced Decision Simulation and What-If Analysis

## Problem Semantica can trace historical decisions, but alternatives are not modeled as first-class decision branches. ## Goal Enable contributors to add branch simulation so teams can compare baseline vs alternative decision paths. ## In Scope - Decision branch creation and storage. - Baseline vs branch path comparison APIs. - Deterministic impact simulation on causal chains. - Provenance linkage for branch lineage. ## Out of Scope - Full probabilistic planning engine. - Rich visual UI for simulation in phase 1. ## Files and Folders to Contribute - `semantica/context/decision_models.py` - `semantica/context/decision_methods.py` - `semantica/context/causal_analyzer.py` - `semantica/context/decision_query.py` - `tests/context/` - `cookbook/integrations/` or `cookbook/introduction/` ## Proposed New Files - `semantica/context/decision_simulator.py` - `tests/context/test_decision_simulation.py` - `docs/reference/decision-simulation.md` ## Implementation Milestones 1. Schema milestone: add branch ids, parent links, branch metadata. 2. API milestone: add `branch_decision()` and `compare_decision_paths()`. 3. Simulation milestone: add impact scoring on branch paths. 4. Documentation milestone: cookbook example and reference docs. ## Contribution Tracks - Easy: schema fields + serialization tests. - Medium: baseline/branch comparison helper. - Advanced: impact propagation algorithm and tuning config. ## Test Plan - Unit tests for branch creation and validation. - Regression tests for deterministic path comparison. - Edge-case tests for missing parent branch or cycles. ## Docs to Update - `docs/reference/context.md` - `docs/feature-requests/FR-001-advanced-decision-simulation.md` - one cookbook notebook/example snippet. ## Acceptance Criteria - Branches are persisted with provenance continuity. - API can compare baseline and alternative chains. - Simulation output is deterministic for fixed inputs. - Tests and docs are included in the PR.