📋 Implement Configurable Response Headers

[jongalloway]

Description

Add support for configurable response headers including license specifications, data retention policies, and custom metadata.

New Capabilities

• License Specification: MIT License headers with terms links
• Data Retention Policies: Configurable retention policy headers
• UI Component Specifications: Custom rendering hints for client applications
• Custom Metadata: Deployment-specific headers

Implementation

• Add ResponseHeadersOptions configuration
• Implement middleware for automatic header injection
• Update demo to showcase header customization
• Document header configuration patterns

Priority & Effort

• Priority: Medium
• Effort: Small
• Timeline: Phase 3 (Months 4-6) - 2-3 weeks
• Business Value: Medium - Compliance and customization

References

• NLWeb June 2025 Analysis - Section: "Configurable Response Headers"
• GitHub Issues Plan - Issue 6

[jongalloway]

Suggested implementation plan for configurable response headers:

• Add ResponseHeadersOptions (license, retention, ui-hints, custom metadata) with configuration binding.
• Implement a small middleware that injects configured headers at the start of each response stream.
• Wire up a minimal sample config in the demo to showcase behavior; disabled by default for backward compatibility.
• Document the JSON/YAML config pattern and the precedence rules.

Acceptance criteria:

• No change in behavior when options are not configured.
• Headers appear as the first messages for streaming endpoints and as regular headers for non-streaming responses.
• Sample + docs updated.

I can open a PR for this—let me know preferences on names and defaults (e.g., X-NLWeb-License, X-NLWeb-Retention).

[jongalloway]

Onboarding note: This is a nice, self-contained change touching a few files. Suggested steps:

• Add ResponseHeadersOptions to src/NLWebNet/NLWebOptions.cs (class with optional properties: LicenseUrl, RetentionPolicy, UiHints: Dictionary<string,string>, Custom: Dictionary<string,string>). Bind from config.
• Implement a small middleware (or extend NLWebMiddleware) to inject headers if options are set. Look at src/NLWebNet/Middleware/NLWebMiddleware.cs for pattern.
• Update samples/Demo/appsettings.json to show sample header config.
• Add a docs section in doc/configuration-format-updates.md showing the new keys and example.

Acceptance check: Running the demo sets the headers when values are configured.