feat: API Endpoint for Post HTML

[fboucher]

Parent PRD

#155

What to build

Create a new API endpoint GET /api/posts/{id}/html that fetches cleaned HTML from the cleanedposts blob container and returns it to the client. The endpoint should return the HTML content with Content-Type: text/html on success, or a 404 error with a clear message if the blob does not exist.

The endpoint follows the same auth and routing patterns as existing post endpoints in PostEndpoints.cs. The blob container name is cleanedposts and blob files are named {postId}.html.

Acceptance criteria

• New route GET /api/posts/{postId}/html is registered in the API
• Endpoint fetches the blob from the cleanedposts container using name {postId}.html
• Returns 200 with Content-Type: text/html and the HTML body when the blob exists
• Returns 404 with { "error": "Post HTML not found" } when the blob does not exist
• Uses the same auth/authorization as existing post endpoints
• Unit tests cover: blob exists, blob not found, blob service error

Blocked by

None - can start immediately

User stories addressed

• User story 15: As a developer, I want a new API endpoint GET /api/posts/{id}/html that fetches from the cleanedposts blob container
• User story 16: As a developer, I want the API endpoint to return a clear error when the HTML file doesn't exist

[fboucher]

This was generated by AI during triage.

Agent Brief

Category: enhancement
Summary: Add GET /api/posts/{id}/html endpoint to serve cleaned HTML from blob storage

Current behavior:
The API has endpoints for posts, notes, summaries, and settings, but no way to retrieve the cleaned HTML content stored in the cleanedposts blob container. The MAUI app has no access to post content for offline reading.

Desired behavior:
A new endpoint GET /api/posts/{postId}/html that:

• Fetches the blob named {postId}.html from the cleanedposts container
• Returns 200 with Content-Type: text/html and the HTML body when the blob exists
• Returns 404 with { "error": "Post HTML not found" } when the blob does not exist
• Uses the same auth/authorization as existing post endpoints

Key interfaces:

• New route registration in the API Minimal API endpoint configuration
• BlobServiceClient (or equivalent) to access the cleanedposts container
• Follow existing patterns in PostEndpoints.cs for route registration and auth

Acceptance criteria:

• New route GET /api/posts/{postId}/html is registered in the API
• Endpoint fetches the blob from the cleanedposts container using name {postId}.html
• Returns 200 with Content-Type: text/html and the HTML body when the blob exists
• Returns 404 with { "error": "Post HTML not found" } when the blob does not exist
• Uses the same auth/authorization as existing post endpoints
• Unit tests cover: blob exists, blob not found, blob service error

Out of scope:

• Modifying the blob container or its contents
• Caching or CDN configuration
• Other blob containers (readingnotes, final-markdown)