fix(sync): accept legacy Codex account identity metadata

[robinebers]

TL;DR

Restore compatibility with older iCloud history files that include a Codex account ID. Valid history from another Mac no longer gets rejected merely because it contains this extra metadata.

What was happening

• Earlier v2 sync writers included both Claude and Codex account identities.
• The current reader only accepted Claude identities, so a valid Codex identity caused the entire device file to be skipped.
• Settings showed a generic unreadable-data warning, while the log misleadingly reported an invalid Claude account identity.

What this changes

• Accept the legacy bare codex identity in v2 documents, while still requiring its provider history and a valid identity value.
• Scope duplicate identity checks by provider family, so identical opaque IDs in Claude and Codex do not collide.
• Cover legacy document decoding, malformed and orphaned Codex identities, and aggregation with legacy Codex metadata.
• Document compatibility with these older files.

Heads-up

• Codex usage remains synced as before; this does not introduce Codex account-based matching or change the writer format.
• No synced files are deleted or rewritten by the compatibility fix. Claude account matching and its duplicate checks remain intact.
• This is a reader-only logic fix, with no UI layout or copy changes.

Tests

• Confirmed the new regression test failed before the fix with invalidIdentity("codex").
• swift test --filter 'UsageHistoryDocumentTests|UsageHistoryAggregatorTests|ICloudUsageSyncStoreTests': 23 tests passed. The local Xcode beta test runner needed a symlink to the existing Sparkle framework under its ignored build-output directory.
• CONFIG=debug ./script/build_and_run.sh verify: rebuilt, signed, and relaunched successfully.
• With sync enabled, confirmed this Mac wrote fresh history and no new iCloud read errors appeared after restart. Visual inspection was unavailable because the UI tool timed out.
• git diff --check passed.

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Note

Low Risk
Reader-only validation tweak for synced history documents; Claude account matching and duplicate rules within Claude are unchanged.

Overview
Restores iCloud compatibility for v2 history files that still carry a bare codex entry in identities from older writers. Those peers were failing UsageHistoryDocument.validate() and being dropped entirely in ICloudUsageSyncStore, even when Claude/Codex usage was otherwise valid.

validate() now treats codex identities as allowed metadata on openusage.history.v2 (still requiring matching providers["codex"] and the same identity format rules as Claude). Duplicate identity detection keys on providerFamily:identity instead of identity alone, so the same opaque string on Claude and Codex no longer counts as a duplicate.

Tests cover decode/validate edge cases (malformed or orphaned Codex identities) and aggregation with legacy Codex metadata; docs note that the extra Codex ID is readable but does not change Codex merge behavior.

^{Reviewed by Cursor Bugbot for commit 17e2745. Bugbot is set up for automated code reviews on this repo. Configure here.}