Review: Option D sizing engine -- optimized stack with hedging

Verdict: APPROVED

Template Completeness

• [x] Type -- Feature
• [x] Lineage -- Depends on #1 (Rails scaffold) and #3 (schema). Both must complete before this sprint:3 ticket.
• [x] Repo -- ldraney/kalshi-assistant
• [x] User Story -- present, well-formed
• [x] Context -- present, references docs/strategy/sizing-models.md (verified)
• [x] File Targets -- 2 files to create (app/services/sizing_engine.rb, app/services/scenario_analyzer.rb)
• [x] Feature Flag -- "none"
• [x] Acceptance Criteria -- 5 items (consolidated from 6)
• [x] Test Expectations -- 3 tests + run command (rails test)
• [x] Constraints -- present (pure Ruby, <1s for 10 picks)
• [x] Checklist -- present
• [x] Related -- present

Traceability

• [x] story:portfolio-builder label -- AI Portfolio Builder
• [x] story note verified -- story-kalshi-assistant-portfolio-builder exists, listed in project-kalshi-assistant user-stories section
• [x] arch:app label -- application component
• [x] arch note verified -- arch-app note exists in pal-e-docs (slug: arch-app, type: architecture, status: active). Contains Mermaid service diagram, component table with SizingEngine entry, and key decisions documenting the 83/17 split.
• [x] Forgejo issue -- ldraney/kalshi-assistant#5, open

File Targets

• [x] app/services/sizing_engine.rb -- to be created. Path depends on Rails scaffold (#1). Dependency is declared in Lineage.
• [x] app/services/scenario_analyzer.rb -- to be created. Same dependency chain as above.
• [x] docs/strategy/sizing-models.md -- verified: contains Option D math (83% YES / 17% NO split, -$5.77 worst case, all scenario tables with probabilities and P&L). Context reference is accurate.

Repo Placement

Dependencies

• Declared: #1 (Rails app scaffold, board item #1686, sprint:1, backlog) -- provides the app/services/ directory structure and test runner. Hard blocker.
• Declared: #3 (Strategy engine -- database schema, board item #1688, sprint:2, backlog) -- provides the strategy/trade schema the sizing engine operates on.
• Both dependencies are in backlog. Sprint ordering (1 → 2 → 3) enforces the correct sequence.
• Note: The arch-app diagram shows Watchdog (#1689, issue #4, sprint:3) consumes SizingEngine. That dependency belongs on the Watchdog ticket, not this one.

Acceptance Criteria

• Input contract: picks array with ticker/yes_ask/no_ask + budget -- well-defined interface
• Optimization method: brute-force over 50-99% YES/NO ratio -- deterministic, reproducible
• Output contract: optimal ratio, expected value, contracts per position -- complete output spec
• Scenario table: 2^N outcomes with probability and P&L -- verifiable against docs
• Scale constraint: 1-10 picks (1024 scenarios max) -- bounded and testable

Blast Radius

Decomposition Assessment

• File targets: 2 files in 1 repo -- OK (below >3 across >2 repos threshold)
• Acceptance criteria: 5 -- at threshold, not over
• Estimated agent time: under 5 minutes -- math fully documented, two tightly coupled services

Previous Review Issues -- Resolution

Recommendation