fix(api): allow Tailscale CGNAT origins in dev CORS allow-list (#246)

[w7-mgfcode]

Closes #246.

Adds the Tailscale CGNAT range (100.64.0.0/10) to the dev-only allow_origin_regex in app/main.py, alongside the existing localhost + RFC 1918 ranges. Lets a tailnet-reachable dev backend pass CORS the same as a LAN host.

• Dev-only — the else None production branch (explicit empty allow-list, no regex) is unchanged.
• No new tests: the regex sits inside the existing dev CORS construction; behaviour is dev-network reachability, not unit-testable logic.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Extends the development-only CORS allow_origin_regex to include Tailscale’s CGNAT address space so dev backends reachable over a tailnet are treated like LAN hosts, without affecting production behaviour.

Flow diagram for updated dev CORS origin matching (Tailscale CGNAT support)

flowchart LR
    Browser["Browser with Origin header"] --> App["FastAPI_app (dev)"]
    App --> CORS["CORSMiddleware allow_origin_regex"]

    CORS -->|matches localhost| Allow["CORS allowed"]
    CORS -->|matches RFC1918 10.x 192.168.x 172.16-31.x| Allow
    CORS -->|matches Tailscale_CGNAT 100.64.0.0_10| Allow
    CORS -->|no match| Block["CORS blocked"]

    subgraph Dev_only_configuration
      CORS --- Regex["allow_origin_regex includes:<br/>localhost<br/>10.0.0.0_8<br/>192.168.0.0_16<br/>172.16.0.0_12<br/>100.64.0.0_10 (Tailscale)"]
    end

    subgraph Production_configuration
      ProdCORS["CORSMiddleware allow_origins empty"]
      ProdCORS --> ProdBlock["No regex; Tailscale not specially allowed"]
    end

Loading

File-Level Changes

Change	Details	Files
Extend the development CORS allow-origin regex to allow requests from Tailscale CGNAT addresses.	Append a new regex fragment that matches the 100.64.0.0/10 Tailscale CGNAT range to the existing dev allow_origin_regex pattern Keep existing localhost and RFC1918 private network patterns unchanged while adding the new range as an additional alternation Ensure the new Tailscale pattern is only applied when settings.is_development is true, preserving the empty allow-list behaviour in production	app/main.py

Possibly linked issues

• fix(api): allow Tailscale CGNAT origins in dev CORS allow-list #246: PR updates dev CORS regex in app/main.py to include the Tailscale CGNAT range, matching the issue request.

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[sourcery-ai]

Hey - I've left some high level feedback:

• The IP allow-list regex is getting fairly complex; consider extracting it into a named constant or helper (e.g., DEV_CORS_IP_REGEX) so it’s easier to maintain or reuse without cluttering create_app.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The IP allow-list regex is getting fairly complex; consider extracting it into a named constant or helper (e.g., `DEV_CORS_IP_REGEX`) so it’s easier to maintain or reuse without cluttering `create_app`.

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