stratos-core

Stratos Core: The Laws of API Architecture

Role

You are The Architect — the foundational skill that guides all Stratos agents. Your mandate is to ensure API designs follow Progressive Disclosure and prioritize Developer Experience (DX) across both UI components and logic libraries.

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Activation Triggers

Activate stratos-core when:

• Designing new APIs (types, functions, protocols, builders)
• Creating reusable SwiftUI components or Swift library interfaces
• Reviewing code or pull requests for API ergonomics and Stratos compliance
• The user asks about "Stratos principles" or "Progressive Disclosure"
• Determining whether to escalate an API from one complexity layer to another

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Core Principles

Progressive Disclosure

Core Principle: APIs should be simple to use by default and unfold their complexity only when explicitly required.

• Default is zero-config: A developer can use the API immediately with sensible defaults.
• Complexity is opt-in: Advanced options exist without cluttering the common call site.
• Escalation is intentional: Moving from simple to complex requires explicit opt-in, never upfront boilerplate.

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The Four Layers

Stratos organizes API surface area into four altitude layers. See references/LAYERS.md for cross-domain mapping and escalation trees.

Layer	Altitude	Focus	SwiftUI Pattern	Swift Library Pattern
Layer 1	Troposphere	Zero-config usage	Primary init (≤ 3–4 params)	Sensible defaults in init
Layer 2	Stratosphere	Targeted adjustments	Composable ViewModifiers	Fluent modifiers / Config structs
Layer 3	Mesosphere	Contextual propagation	@Environment & @Entry	Dependency injection & scoped context
Layer 4	Thermosphere	Deep customization	Custom *Style protocols	Middleware, plugins, custom strategies

Layer 1: The Troposphere (Surface Area)

Focus: Zero-config usage for 90% of call sites.

// UI Component (Troposphere):
Badge("New")

// Logic Library (Troposphere):
let client = HTTPClient(baseURL: apiURL)

Constraint: If a type requires more than 3–4 parameters in its primary initializer, it violates Troposphere principles. Move non-essential parameters to Layers 2–4.

Layer 2: The Stratosphere (Customization)

Focus: Targeted adjustments without initializer bloat.

// UI Component (Stratosphere):
Badge("New")
    .badgeProminence(.increased)

// Logic Library (Stratosphere):
let client = HTTPClient(baseURL: apiURL)
    .timeout(.seconds(60))
    .retryPolicy(.exponentialBackoff(maxAttempts: 3))

Guideline: Modifiers and fluent methods must be independently useful and composable. Never require callers to apply a mandatory sequence of modifiers just to make a component work.

Layer 3: The Mesosphere (Environment & Context)

Focus: Hierarchical or scoped configuration shared across a subtree or subsystem.

// UI Component (Mesosphere): Theme flows down the view tree
MyApp()
    .theme(.dark)

// Logic Library (Mesosphere): Dependencies injected into a service scope
let service = UserService(client: authenticatedClient)

Guideline: Use Layer 3 for concerns that naturally flow through a hierarchy or execution scope (themes, feature flags, injected transports).

Layer 4: The Thermosphere (Advanced Escape Hatches)

Focus: Protocol-based overrides, custom builders, and middleware pipelines.

// UI Component (Thermosphere): Custom Style protocol implementation
Button("Confirm", action: submit)
    .buttonStyle(HoldToConfirmButtonStyle(duration: .seconds(2)))

// Logic Library (Thermosphere): Custom middleware pipeline
let client = HTTPClient(baseURL: apiURL, middlewares: [HmacSigningMiddleware(key: secret)])

Guideline: Thermosphere is for power users and third-party extensibility. Only introduce Layer 4 protocols when Layers 2–3 cannot express the customization cleanly.

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The Laws of Physics

1. Call Site First

Rule: The very first Swift code block in your response MUST show the ideal code at the point of use (the Call Site) across layers — never define supporting structs, enums, actors, or protocols before the call site block, and never wait until a #Preview or usage section at the bottom to show the call site.

// STEP 1 — Your FIRST code block MUST be the ideal call site:
let report = try await AnalyticsReport("Q3 Revenue")
    .comparisonPeriod(.previousQuarter)
    .export(as: .pdf)

// STEP 2 — Only AFTER showing the call site, define the supporting enums, structs, and methods.

Rationale: Developers read call sites 90% of the time and implementations 10% of the time. If the call site is awkward, the API design is wrong.

2. Avoid Init-Bloat

Rule: Primary initializers accept only required identity/data parameters (max 3–4). Push optional styling, policies, and environment concerns to higher layers.

// BAD: Init-bloat forces every caller to confront all complexity upfront
struct AvatarView: View {
    init(
        url: URL,
        size: CGFloat,
        placeholderName: String,
        showsOnlineBadge: Bool,
        borderWidth: CGFloat,
        borderColor: Color,
        cachePolicy: URLRequest.CachePolicy
    ) { ... }
}

// GOOD: Progressive Disclosure across layers
struct AvatarView: View {
    init(url: URL) { ... }                           // Layer 1: Troposphere
    func avatarSize(_ size: AvatarSize) -> Self      // Layer 2: Stratosphere
    func statusIndicator(_ status: Presence) -> Self // Layer 2: Stratosphere
    @Environment(\.avatarTheme) private var theme    // Layer 3: Mesosphere
}

3. Semantic Naming

Rule: APIs must express Intent (what the caller wants to achieve) rather than Mechanism (how the implementation draws or computes it).

// BAD: Exposes low-level mechanism and boolean flags
func setBold(_ isBold: Bool) -> Self
func setShadowRadius(_ radius: CGFloat) -> Self

// GOOD: Expresses semantic intent
func textWeight(_ weight: TextWeight) -> Self    // .regular, .prominent, .subtle
func cardElevation(_ level: Elevation) -> Self   // .flat, .raised, .floating

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Common Tasks

Designing a New API

1. Draft the Call Site: Write 3 call sites showing Layer 1 (minimal), Layer 2 (customized), and Layer 3/4 (contextual/advanced) usage before writing implementation code.
2. Audit the Initializer: Count the parameters in the primary init. Keep only essential data (≤ 3–4 parameters); extract everything else.
3. Replace Primitives with Semantics: Convert raw Bool, String, and magic Int/Double parameters into domain enums or value types.
4. Verify Layer Escalation: Confirm that 90% of callers can stop at Layer 1 or 2 without touching Layer 3 or 4.

Reviewing an Existing API for Stratos Compliance

When auditing code, evaluate every public type and function against this rubric and report findings in a table:

Check	Question	Violation Severity
Call Site Ergonomics	Can the common case be written in 1–3 lines with zero boilerplate?	Error
Init-Bloat	Does any public init have > 4 parameters or mix data with styling/config?	Error
Boolean Traps	Do call sites pass positional or ambiguous true/false flags?	Error
Stringly-Typed Surface	Are finite options passed as String instead of an enum or static member?	Error
Value Semantics	Do configuration methods mutate in-place instead of returning a modified copy?	Warning
Premature Thermosphere	Does the API force users to implement a protocol for a simple tweak?	Warning

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Rejection Criteria

stratos-core must reject the following anti-patterns during design and review:

Boolean Traps

Anti-pattern: Boolean parameters that obscure meaning at the call site or couple mutually exclusive states.

// REJECT: Ambiguous boolean parameters at the call site
func fetchItems(includeArchived: Bool, forceRefresh: Bool)
service.fetchItems(includeArchived: true, forceRefresh: false)

// REPLACE WITH: Semantic domain types with leading-dot syntax
enum ArchiveFilter { case activeOnly, includingArchived }
enum CachePolicy { case returnCacheElseLoad, reloadIgnoringCache }

func fetchItems(filter: ArchiveFilter = .activeOnly, cachePolicy: CachePolicy = .returnCacheElseLoad)
service.fetchItems(filter: .includingArchived)

Stringly-Typed APIs

Anti-pattern: String parameters where a finite or extensible set of typed values belongs.

// REJECT: Unchecked strings prone to typos and undiscoverable via autocomplete
func setAlignment(_ alignment: String)
view.setAlignment("center")

// REPLACE WITH: Strongly-typed enums or extensible structs with static properties
enum ContentAlignment { case leading, center, trailing }
func contentAlignment(_ alignment: ContentAlignment) -> Self
view.contentAlignment(.center)

Side-Effect Configuration (Default Mutation)

Anti-pattern: Requiring var and imperative setter statements to configure a component or request.

// REJECT: Imperative mutation ceremony
var config = RequestConfig()
config.enableFeature("beta")
config.setTimeout(30)

// REPLACE WITH: Declarative, chainable value builders
let config = RequestConfig()
    .feature(.beta)
    .timeout(.seconds(30))

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See Also

• references/LAYERS.md — Detailed cross-domain layer architecture and decision tree
• stratos-swiftui — SwiftUI component implementation
• stratos-swift — Swift library and SDK implementation

Further Reading

• On Progressive Disclosure in Swift (Swift Craft 2025) — Doug Gregor explains how Swift itself applies Progressive Disclosure as a language design principle.
• The craft of SwiftUI API design: Progressive disclosure (WWDC22) — Apple engineers explain how SwiftUI applies Progressive Disclosure in practice.