test(ios): replay the round engine vectors through the round adapter

[sunnylqm]

Summary

• New scripts/tests/ios-purge-restore/round_replay_test.mm, built by scripts/test-ios-purge-restore.sh (so the existing Native purge-restore ordering CI job runs it, with ASan/UBSan). It compiles the unchanged RCTPushyOrchestrator round adapter — runOnce, perform:, download:, commit:, finishRound:, PushyWaitSeconds and their globals, extracted by extract.py into round*.inc — against a scripted flowcore::StepRound. No production code changes.
• For each trace in cpp/update_flow_core/tests/round-engine-vectors.json the engine returns the trace's commands and the IO (PushyHttpRequest, install check, RCTPushyInstaller fetch, commitRoundWithGeneration:, monotonic clock) is faked from the trace's next event. Checked: every answered event (type/text/installed/ok/code/timedOut/reason/error/activated/now, ok/code as the engine reads them), sticky crashHold/forceActivate, the arguments each command ran with, the start facts, the host result, the remembered unactivated hash, the breadcrumb.
• 30 traces replay — crash hold, forceActivate (activation dropped by the commit), round deadlines and timed-out downloads included; only the protocol-error traces are skipped. Same idea as Harmony's harmonySyncRound.test.ts and Android's SyncRoundReplayTest (test(android): replay the round engine vectors through the sync adapter #680).
• New negative control drop-config-changed (VERIFY_REGRESSIONS): a lost commit reported without reason: "config_changed" fails the config-change trace.

Test plan

• SANITIZE=1 VERIFY_REGRESSIONS=1 bash scripts/test-ios-purge-restore.sh: all orderings, round replay: 30 rounds, all seven negative controls detected
• CI

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Summary by CodeRabbit

• Tests
  • Expanded update-flow validation with iOS round replay scenarios, checking event results, state, timing, command arguments, and protocol errors.
  • Added Android round-replay coverage and a regression check for configuration changes during a round.
• Documentation
  • Documented how to run an individual iOS round replay and updated the negative-control check count.

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Reviewing files that changed from the base of the PR and between 3558280 and 339ea41.

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• docs/NATIVE_CHECKUPDATE_DESIGN.md

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• docs/NATIVE_CHECKUPDATE_DESIGN.md

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📝 Walkthrough

The iOS test harness now builds a round-adapter replay executable, checks round-engine vectors, and verifies a config-change mutation. The test script, extractor, test host, README, and design test list include the new replay checks.

Changes: iOS Round Adapter Replay

Layer / File(s)	Summary
Extract the round adapter scripts/tests/ios-purge-restore/extract.py, scripts/tests/ios-purge-restore/test_extract.py	The extractor generates round adapter sections and applies the drop-config-changed mutation to the round commit. The source-drift test checks that mutation target.
Run vector-backed adapter replays scripts/tests/ios-purge-restore/round_replay_test.mm	The Foundation-only host replays eligible vectors with scripted events and IO. It checks event values, state flags, command arguments, finish results, and cleanup.
Build and verify replay runs scripts/test-ios-purge-restore.sh, scripts/tests/ios-purge-restore/README.md, docs/NATIVE_CHECKUPDATE_DESIGN.md	The script builds and runs the replay test when no test-name arguments are supplied. Its regression check verifies the config-change mutation. The README and design test list describe the replay test.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to 339ea

This change adds an iOS test replay harness and updates documentation. It does not change production behavior, and no merge-blocking risk was identified.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files. (1 skipped: 1…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: adding iOS round-engine vector replay through the round adapter.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files. (1 skipped: 1 unsupported.)

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