Validate data source keys at config load instead of sending an absent key to Figma #706

Problem

A source with no key: value in the workspace settings is not caught anywhere. fetch builds the request URL from the missing value and sends the literal string undefined as the file key. Figma answers 404, and the CLI reports it as a key that is stale or out of reach — so the message names a cause that isn't the cause, and points at a key that was never there.

The same gap has a second consequence: a full Figma file URL pasted into a config key also 404s, while --source <url> accepts one and resolves it to a key.

Observed:

[CLI] GET file: https://api.figma.com/v1/files/undefined?geometry=paths
Error: File not found (404) while fetching organisms.file
  Figma returned 404 for the file key configured for "organisms".
  This usually means the key in your config is stale or out of reach:
    • The file was moved, deleted, or recreated (keys change on duplicate/recreate)
    • Your FIGMA_TOKEN account cannot open this file

Potential solution(s)

• Fail at config load, naming the source and the missing field, before any network call is made
• Accept a Figma file URL in a config key the same way --source does

Acceptance criteria

• A source with an empty or missing key fails before any request is sent, naming the source and the field
• The failure message never suggests the key is stale or out of reach
• A full Figma file URL in a config key resolves to the file key, as --source does
• No request is ever sent with undefined as the file key

Case data

• Workspace: fm — during a fetch
• Territory: cli
• Impacted file(s): packages/cli/src/commands/FetchCommand.ts (normalizeSources), packages/cli/src/Config/ConfigLoader.ts, packages/cli/src/utilities/figmaFileKey.ts
• Size: s

Notes

Found while diagnosing two unrelated specs fetch failures in one run. The other failure in that run was an intermittent transport drop on a large file payload, tracked separately.

Implementation details are tracked internally.