[AI-FSSDK] [FSSDK-12813] Relax campaign_id/entity_id validation to non-empty string per updated spec

[jaeopt]

Summary

Follow-up to the merged #642 (released as 5.4.1), which normalized decisions[].campaign_id, decisions[].variation_id, and events[].entity_id on outgoing decision impression events.

The FSSDK-12813 spec was updated on 2026-06-24 to relax the validation contract for campaign_id and entity_id only. This PR brings the Swift SDK in line with the relaxed contract.

What the spec relaxed

• decisions[].campaign_id and events[].entity_id MUST be non-empty strings. IDs may be opaque (e.g. "layer_abc", "default-12345") — any non-empty string is valid regardless of character content.
• The fallback to experiment_id now fires only when the source value is the empty string "" (or nil / missing). Previously it fired on any non-numeric input.

What is unchanged

• decisions[].variation_id keeps the stricter numeric-string-only contract per spec FR-003. Empty, whitespace, or non-numeric variation_id values still normalize to nil (JSON null).
• No change to Sources/Data Model/DispatchEvents/BatchEvent.swift — Decision.variationID: String? and its explicit-null encoder from [AI-FSSDK] [FSSDK-12813] normalize campaign_id, variation_id, and entity_id on decision events #642 remain correct.
• No change to FR-006 (events never dropped) or FR-007 (no warnings on the normalization path).
• No public API change, no datafile schema change, no SDK version bump (5.4.1 already released; this rides the next release ticket).

Changes

• Sources/Implementation/Events/BatchEventBuilder.swift
  • normalizeDecisionIds(...) now gates campaign_id with a new isNonEmptyString(_:) helper instead of isValidNumericIdString(_:). The variation_id branch is untouched.
  • Adds isNonEmptyString(_:) -> Bool (returns !value.isEmpty).
  • Retains isValidNumericIdString(_:) — still used by the variation_id branch per spec FR-003.
  • Doc comments updated to cite the 2026-06-24 spec relaxation.
• Tests/OptimizelyTests-Common/BatchEventBuilderTests_HoldoutIds.swift
  • Flipped: testNormalize_whitespaceCampaignFallsBackToExperimentId → testNormalize_whitespaceCampaignPassesThrough (whitespace is non-empty, so it passes through unchanged).
  • Flipped: testNormalize_nonNumericCampaignFallsBackToExperimentId → testNormalize_nonNumericCampaignPassesThrough (non-numeric is non-empty, so it passes through unchanged).
  • Added: testNormalize_opaqueCampaignPassesThrough_FSSDK12813_relaxation — direct proof that an opaque ID "layer_abc" passes through campaign_id unchanged with no fallback to experiment_id.
  • Added: testIsNonEmptyString_acceptsAnyNonEmptyContent and testIsNonEmptyString_rejectsEmptyOnly — unit coverage for the new helper.
  • All variation_id tests unchanged.
  • All isValidNumericIdString tests unchanged (still used by variation_id).
  • Header comment updated to describe the relaxed contract.

Verification

• xcodebuild -workspace OptimizelySwiftSDK.xcworkspace -scheme OptimizelySwiftSDK-iOS -destination 'platform=iOS Simulator,name=iPhone 17' test — not executed in this run; CoreSimulator was unavailable in the sandboxed environment. Local reviewers should run the command above. The change is mechanical: one validator swap on one branch of normalizeDecisionIds, plus tests flipped/added in lockstep.
• Pre-existing impression-event regression suites referenced in [AI-FSSDK] [FSSDK-12813] normalize campaign_id, variation_id, and entity_id on decision events #642 (BatchEventBuilderTests_Events, BatchEventBuilderTests_Attributes, BatchEventBuilderTests_EventTags, BatchEventBuilderTests_Region, DecisionServiceTests_Holdouts) all used non-empty placeholders for campaign_id and so are unaffected by this relaxation (FR-011 audit).

Jira Ticket

FSSDK-12813

Related

• Original implementation PR (merged, released as 5.4.1): [AI-FSSDK] [FSSDK-12813] normalize campaign_id, variation_id, and entity_id on decision events #642