feat(testservice): support file-based flag overrides

[kinyoklion]

Reopens #413 (auto-marked merged for the same base-branch reason as #412; see #415). Rebuilt as a cherry-pick stacked on #415 so the diff shows only the test service changes. Review discussion lives on #413.

Wires the contract-test service up to the flag-overrides feature so the harness suite (launchdarkly/sdk-test-harness#374) can run against this SDK: advertises the flag-overrides capability, mirrors the harness's overrides config block in the test service's servicedef, and maps it onto ldoverrides.FileSource() on the data system builder; requesting overrides without a data system configuration is an error, since overrides are an FDv2 feature. The test service module pins the same override-aware pseudo-versions of go-sdk-common, go-sdk-events, and go-server-sdk-evaluation as the SDK.

Verified locally against the harness branch with the updated override tests (which expect the overrideAffected reason indicator and summary counter marker): the flag-overrides suite passes (32 tests ran, 0 failures, across static configuration, uninitialized client, summary events, transitive marking, multiple files, YAML, and watching and polling hot reload), and the full harness run is green (4961 tests total, 4949 ran, 12 skipped, 0 failures).

SDK-2657

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Note

Overview
Refactors file-based flag overrides to use a single ChangeDetection mode (Polling vs Watching) instead of independent Watch / Poll toggles, and defaults to polling (1s) rather than filesystem watches. Build now rejects unknown detection modes; PollInterval applies only in polling mode.

The contract test service advertises flag-overrides, accepts an overrides config block (paths, duplicate-key handling, change detection, poll interval), wires it to ldoverrides.FileSource() on the FDv2 data system, and errors if overrides are requested without a data system. The testservice module bumps Go and pins override-related dependencies.

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Watch/poll harness fields ignored

Medium Severity

The test service overrides block reads changeDetection, but the harness contract cited here (sdk-test-harness#374) sends watch and poll booleans. Those fields are dropped, so every client stays on the Polling default. Watching-mode harness tests still pass because polling also reloads on file changes, so the suite never actually runs Watching.

Additional Locations (1)

• testservice/sdk_client_entity.go#L658-L670

 

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