docs(sdk): Migrate Feature Flags spec to Writing SDK Specs guidelines

[sentry-junior]

DESCRIBE YOUR PR

Migrates the Feature Flags spec to the Writing SDK Specs guidelines (#20081), using the writing-sdk-specs skill (#20083). This is the first trial run of that skill. The page is short, so the result is easy to check by hand.

What changed in the spec:

• Requirements now describe only externally observable behavior. "Stored on the scope" and "hook into a third-party SDK" are rewritten as what you can see in sent events, spans, and the scope API. The hook pattern moved to Implementation Guidance.
• Every requirement now uses an explicit bold keyword. Before, some obligations were lowercase "should" or plain statements ("we track the first 10…").
• Requirement levels follow RFC 2119 Section 6. Exposing add_feature_flag and accepting string/boolean arguments are now "SHOULD", and API names can follow platform conventions. "MUST" is kept only for the wire formats Sentry reads (Feature Flag Context, flag.evaluation.<name> span attributes), for never recording non-boolean results, and for what clear_feature_flags does when an SDK exposes it.
• The page follows the intro → Definitions → Requirements → Implementation Guidance → Changelog structure and declares spec_guidelines: writing-specs@0.1.

Because existing requirements changed, this is a major bump to 2.0.0, and every section's since is 2.0.0. Span attribute key and limits are taken from Span Data Conventions and the platform feature flag docs. SDK owners should confirm the new requirement levels before this leaves draft.

IS YOUR CHANGE URGENT?

• Urgent deadline (GA date, etc.): YYYY-MM-DD
• Other deadline: YYYY-MM-DD
• No deadline: Not urgent, can wait up to 1 week+

PRE-MERGE CHECKLIST

• Checked Vercel preview for correctness, including links
• PR was reviewed and approved by any necessary SMEs (subject matter experts)
• PR was reviewed and approved by a member of the Sentry docs team

via @szokeasaurusrex.

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Project	Deployment	Actions	Updated
develop-docs	Ready	Preview	Oct 20, 2026 8:57am UTC

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Project	Deployment	Actions	Updated
sentry-docs	Ignored	Preview	Oct 20, 2026 8:57am UTC

[szokeasaurusrex]

The spec writing guidelines were updated. Please check if this page needs any updates and apply them