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openspec/specs/delivery-and-rendering-performance/spec.md

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+## Purpose
+
+Canonical specification for delivery-and-rendering-performance requirements synced from OpenSpec change deltas.
+
+## Requirements
+
+### Requirement: HTTP delivery applies compression and cache policy
+The system SHALL apply transport-level compression and explicit cache directives for static assets, API responses, and public HTML routes.
+
+#### Scenario: Compressed responses are available for eligible payloads
+- **WHEN** a client requests compressible content that exceeds the compression threshold
+- **THEN** the response is served with gzip compression
+- **AND** response headers advertise the selected content encoding
+
+#### Scenario: Route classes receive deterministic cache-control directives
+- **WHEN** clients request static assets, API responses, or HTML page routes
+- **THEN** each route class returns a cache policy aligned to its freshness requirements
+- **AND** cache directives are explicit and testable from response headers
+
+### Requirement: Media rendering optimizes perceived loading performance
+The system SHALL lazy-load non-critical images and render shimmer placeholders until image load completion or fallback resolution.
+
+#### Scenario: Feed and modal images lazy-load with placeholders
+- **WHEN** feed or modal images have not completed loading
+- **THEN** a shimmer placeholder is visible for the pending image region
+- **AND** the placeholder is removed after load or fallback error handling completes
+
+#### Scenario: Image rendering reduces layout shift risk
+- **WHEN** article images are rendered in hero, feed, or modal contexts
+- **THEN** image elements include explicit dimensions and async decoding hints
+- **AND** layout remains stable while content loads
+
+### Requirement: Smooth scrolling behavior is consistently enabled
+The system SHALL provide smooth scrolling behavior for in-page navigation and user-initiated scroll interactions.
+
+#### Scenario: In-page navigation uses smooth scrolling
+- **WHEN** users navigate to in-page anchors or equivalent interactions
+- **THEN** scrolling transitions occur smoothly rather than jumping abruptly
+- **AND** behavior is consistent across supported breakpoints