feat(openfeature): expose dynamic offline rules (FFL-2837 PR3)

[btthomas]

Pull request stack

1. Plan PR (#1345)
2. PR1: Rules engine boundary (#1346)
3. PR2: Dynamic offline evaluation (#1347)
4. PR3: Provider API and documentation (feat(openfeature): expose dynamic offline rules (FFL-2837 PR3) #1348) <- you are here

This description uses Simplified Technical English. Technical names and API names do not change.

Summary

This PR exposes dynamic offline rules through the existing offline provider.

• The provider passes every effective OpenFeature context to FlagsClient.
• The provider treats {} as a real context.
• clearContext() does not restore a context from the configuration.
• A missing targeting key stays missing.
• Rules configurations stay ready after context changes.
• Context changes do not fetch configurations.
• Configuration parse failures produce provider errors.
• Recovery emits Ready before ConfigurationChanged.
• The README explains precomputed, rules, and mixed configurations.
• Both example applications include a rules-context switch.

Protobuf integration

• Integration tests and examples use a version 1 rules.response envelope.
• The response contains one base64 encoding of UFC protobuf bytes.
• The integration test changes the context and evaluates locally.
• The integration test verifies targeting-key sharding and no configuration fetch.
• The integration test verifies an unsafe int64 PARSE_ERROR and no tracking for that error.
• No legacy rulesBased JSON fixture remains.

OpenFeature behavior

OpenFeature supplies {} for an unset or cleared global context. The provider cannot distinguish this state from an explicit {}. Therefore, it passes {} literally. For a context-specific precomputed configuration, the application explicitly sets the context returned by getPrecomputedContext(configuration).

Matching precomputed data has priority when both capabilities exist. Rules data is the fallback for a different context.

TODO status

This PR adds no new TODO(FFL-2837) marker. The complete stacked branch has the two PR1 follow-ups for regular-expression limits and the future peer-dependency minimum.

Checks

• Core and OpenFeature TypeScript checks
• Changed-file ESLint and formatting checks
• 160 focused flags and OpenFeature tests
• git diff --check

This PR remains a draft.

[sameerank]

This converts an empty effective OpenFeature context ({}) to undefined, causing FlagsClient to reuse its stored/embedded context, and this is being removed in #1359, right?

[datadog-prod-us1-5]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

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[greghuels]

Closing since we took a different implementation path