Null phases render as active stations on assembly line

[williamthorsen]

Description

After CODY-34 relaxed the status-adapter validator to accept null phase entries (representing skipped phases), a type mismatch causes skipped phases to render as active stations on the Factory assembly line.

The Phases interface defines each phase as SomePhase | undefined, but JSON data uses null for skipped phases. Since the validator now passes null through without coercing it, client-side code that checks phases.architecture !== undefined treats null as present (because null !== undefined is true).

Affected code paths:

• run-to-scene.ts — isPhaseActive() uses !== undefined checks to determine station activation
• agent-state-resolver.ts — PHASE_STATUS_ACCESSORS use optional chaining (?.), which safely returns undefined for null (no crashes, but the station still lights up because isPhaseActive already flagged it as active)

Impact: Skipped phases appear as active stations in the visualization. No crashes — optional chaining protects against null dereferencing — but the visual state is incorrect.

Root cause: null (JSON's "absent") vs undefined (TypeScript's "absent") mismatch. The fix needs to either normalize at the boundary (coerce null → undefined in the adapter) or update the type + client checks to handle both.

Acceptance criteria

Must have

• Skipped phases (null in run-index.json) do not render as active stations on the assembly line
• Existing phases with valid data continue to render correctly
• Tests cover the null-phase rendering path

Should have

• The Phases type accurately reflects the runtime values (either by normalizing nulls to undefined in the adapter, or by updating the type to include | null)

Nice to have

• A consistent convention across the codebase for how "absent" values from JSON are handled at the adapter boundary

[williamthorsen]

Implementation note

This is a textbook case for boundary normalization. JSON has null but no undefined; TypeScript has both. The cleanest fix is to normalize at the adapter layer (the system boundary) so that downstream code only ever sees one representation of "absent." That keeps the null-vs-undefined concern confined to a single place rather than spread across every consumer.

Concretely: coerce null → undefined in isValidPhasesObject (or in normalizeV2) before the data leaves the adapter. Then the Phases type stays SomePhase | undefined and no client code needs to change.